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Correcting Steinway B SoundBoard Stresses

  • 1.  Correcting Steinway B SoundBoard Stresses

    Posted 05-22-2017 14:36
    Chart Legend:
    Dark area at the bottom is the load on each rib
    Vertical Bars are the size of the ribs
    The Line at the top is the stress levels of each rib

    Board 1:

    Analysis: Uneven stresses and incorrect dimensions for ribs. Both stress levels and rib dimensions not in sync with load distribution.  Profile: 82%  Stress: 2,099 Psi  Load 975 lbs 10.8 sq in.

    Board 2:

    Analysis:
    Not quite identical to the first board. Some ribs vary in stress up to 200 psi more than in the first board. The stress levels and rib sizes are again not in sync with the loads. Profile: 83% Stress: 2,044 Psi  Load 975 Lbs 11.0 sq. in.

    Why copy those obvious mistakes when they can be fixed and improved?

    Board 3:

    Analysis:
    Now the load, stress levels and rib sizes are in sync. As they should be. Profile: 74%  Stress: 2,208 psi  Load: 975  10.6 sq.in

    Amazing results.  Live demonstration at my shop June 6.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------


  • 2.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-23-2017 09:15
    How about analyzing a Hamburg Steinway B, just
    to throw in some controversy?

    Richard





  • 3.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-23-2017 09:57
    As soon as one comes to my shop, I will. I would really be interested to see if they are more precise in their engineering. Speaking of engineer, examining a Fazioli would be very interesting too. The David Rubinstein book is fantastic btw. Many CAD drawings, I'll be able to report on those scales in the near future. I do see a few errors tho upon first glance. A .78 x .78 rib in high treble wouldn't have been the best choice. His website is up for sale, so is he out of business? Very sad if so, he displayed a lot of ingenuity. Wonder what happened to the 12 footer?





  • 4.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-24-2017 10:07
    The "load on each rib"? Why would there be any load on any rib on a Steinway?

    Are you referring to the loading of the soundboard related to string downbearing?

    Again, I don't why/how there would be any load on the ribs.

    ------------------------------
    Terry Farrell
    President
    Farrell Piano Service, Inc.
    Brandon, Florida
    813-684-3505
    ------------------------------



  • 5.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-24-2017 14:37
    Thanks for the question.
    This may be quibbling over semantics, but I am not particularly fond of the word "downbearing". Slightly esoteric. First, it's really from the term "bearing stress" which is concerned with contact between two bodies.  Second, it tends to focus attention on a small facet of the "system". And third, it can confuse when discussing the system overall because the other bearings are the rib/soundboard to rim joint. Stress is the condition of the wood fibers under a load.  A good description of a piano soundboard is that it's a loaded spring. I like the term load better because then instead of focusing on a small part of the system, it makes you ask questions that think of the whole system. What happens to the load? What reactions are there? etc.
    Its all about force, which has different names along its path.
    So a force is created by stretching a string. Called tension.
    When a string is deflected by the bridge, a downward force is exerted on the soundboard. The board is loaded.
    Force applied at a distance on a lever is called moment.
    The woods internal reaction to a force is called bending stress. Stress for short.
    The rim holds up the soundboard loads called Bearings.
    BTW  "Bearing" X "Length of lever" is the formula for Moment  ( a x A)

    In the Steinway B, the tension is 39,000 lbs  the load roughly created is 975 Lbs  (1/40th rule) ( Wolfenden)
    The strings are spread out, so the load is distributed. The ribs are distributed to hold a distributed load. 
    I contend that there is a symbiotic relationship between the load and the size of the ribs that is not fully appreciated. 
    I have demonstrated that when that relationship is wrong, the tone suffers. When in balance, the board opens up and really sings.  
    The difference can really be heard when my board is placed next to another. At my next presentation we will be putting a Steinway soundboard ( in good condition) next to my soundboard. Should be fun!

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 6.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-24-2017 15:16
    I think Terry's point is that, the way Steinway boards are built at the factory -- i.e., with straight ribs and compressed panel, the ribs do not support any load. The panel compression working against the stress interface between the bottom of the panel and the tops of the ribs both forms the crown and supports, or resists, any downforce from the strings. The ribs actually resist the formation of crown.

    ddf 

    --
    Delwin D Fandrich
    Piano Design & Manufacturing Consultant
    6939 Foothill Court SW, Olympia, Washington 98512 USA
    Email  ddfandrich@gmail.com
    Tel  360 515 0119  --  Cell  360 388 6525





  • 7.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-24-2017 15:54
    "the ribs don't support any load"?? As in none?
    then remove them, they're just in the way. 
    If it's just to create a stress interface, then you wouldn't  need ribs 1" tall. 
    They could all be the same size too.
    The 2 Steinway boards I analyzed clearly show carefully chosen dimensions in sync with the load placed on them.
    Plus, a simple dial test proves the amount of load they take. Measure the deflection, use a weight to simulate the deflection, etc.
    It occurs to me just now, that maybe we're talking both sides of the same coin. Afterall, I am measuring the bending stresses. 
    What I'm pointing out, is that it doesn't make sense to have one rib heavily stressed that is between 2 ribs that are lightly stressed for example.





  • 8.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-24-2017 16:19
    I didn't say they don't add stiffness to the assembly. I said they do not support load. The ribs -- again, in the original Steinway fabrication -- start out flat. When the assembly is crowned they are forced into an upward curve. Their natural tendency is to want to return to their flat condition. Unless the string downforce is sufficient to force the soundboard assembly into a "reverse-crown" condition the ribs do not support any load. 

    Any load support has to come from the compressed panel working against those flat ribs. 

    There are, of course, other ways of building soundboards in which ribs can be treated as load-supporting members.

    ddf

    --
    Delwin D Fandrich
    Piano Design & Manufacturing Consultant
    6939 Foothill Court SW, Olympia, Washington 98512 USA
    Email  ddfandrich@gmail.com
    Tel  360 515 0119  --  Cell  360 388 6525





  • 9.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-24-2017 16:51
    I don't believe in the idea that when a rib is made straight on a saw or planer that that becomes it's natural tendency. Quite the opposite, wood wants to bow. Ask any carpenter laying a joist. "Make sure it's bowing up"! 
    If made incorrectly and glued in flat and dry, if it crowns up then it will want to go back. But not true if crowned first, then glued in as a crowned unit. Especially with the bow up.
    One could argue that routing a curve onto a rib is still a straight rib. Looking at the grain.
    Regardless, method doesn't negate that a load is applied to the structure.






  • 10.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-24-2017 17:14
    As is common in these discussions, apples and pomegranates get mixed up. 

    Floor joists that are milled wet or are cut from unstable (improperly "dried") wood may well bow up as a result of further drying. However, if clear, straight grain wood is milled after it is properly dried and stabilized at its working moisture content it will remain straight. Hence our spruce key leveling straight edges that have remained straight and true for decades. 

    The problem, as I see it, is that you are assuming the ribs, as originally sized and installed by Steinway, are load supporting beams. They are not. To be sure, they do add perpendicular-to-grain stiffness to the assembly and the assembly would not be crowned without them but in fact, as beams, they actually resist the formation of crown. Their natural state is to be flat. 

    When a load is applied to one of these soundboard assemblies sufficient to deflect it from its naturally curved state, that load is supported by an increase in the amount of compression within the panel and a subsequent increase in the stress-interface between the soundboard panel and the ribs.

    Once a crown is machined into the surface of the rib that is glued to the soundboard then it does, indeed become a load supporting beam. But that is a whole other system.

    Even if the musical results end up being similar, the two systems are not structurally, or mechanically, comparable and should not be analyzed as if they were. 

    ddf

    --
    Delwin D Fandrich
    Piano Design & Manufacturing Consultant
    6939 Foothill Court SW, Olympia, Washington 98512 USA
    Email  ddfandrich@gmail.com
    Tel  360 515 0119  --  Cell  360 388 6525





  • 11.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-24-2017 20:32
    Del,

    In trying to assimilate this information, correct me if I am wrong, but it sounds like the compression-crowned soundboard is actually more likely to "cave in" under excessive load (bearing) conditions, vs. a machined-crown board.

    Is this a sound (forgive the pun please) conclusion?

    Pwg

    ------------------------------
    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------



  • 12.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-24-2017 21:07
    Yes. But keep in mind that crown is not, in and of itself, the determining factor in how a piano soundboard performs its function of converting string vibrations into (hopefully) musical sounds.

    ddf

    --
    Delwin D Fandrich
    Piano Design & Manufacturing Consultant
    6939 Foothill Court SW, Olympia, Washington 98512 USA
    Email  ddfandrich@gmail.com
    Tel  360 515 0119  --  Cell  360 388 6525





  • 13.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-09-2017 18:11
    As to Fandrich's argument,
    When I describe to clients the loading of the board, I less have the level of compression in the board in mind and more string tension in mind. 

    If what is meant by loading of the board is string tension it is necessary to find another explanation when loading the board with pitch raising and unloading the board when pitch lowering for the fact that we need to calculate how much to overcompensate for the change of pitch that results by augmenting and attenuating string tension. 

    If there is no loading and unloading of the board by raising and lowering pitch, then the pitch should stay precisely the same as where we first set it, whether changing the pitch 1 cent or 100. But as tuners we understand that we estimate the pitch will drop half the amount it was flat when bringing to pitch. This would not happen if the board was not being loaded with string tension would it? If we cannot attribute this to loading of the board, we need to find another explanation.

    Isn't this why we are entirely correct in recommending frequent tuning of the instrument as that it will stress the belly without it? 100 cent pitch raises can easily add a ton of string tension, and it seems like semantics to me that we would not use the word load to help the client understand this is not good for the board, the soul of the instrument, and that to extend the life of the board, the piano must be tuned more frequently.

    I've seen bridges move half an inch when stringing from the plate when the bracket is almost touching the bridge before starting stringing. Is it not loading of the board that causes this? If the board is not being loaded why is learning to pitch raise so challenging?

    ------------------------------
    Benjamin Sloane
    Cincinnati OH
    513-257-8480
    ------------------------------



  • 14.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-09-2017 20:01

    Saying a rib is not necessarily a load supporting beam tells not about board load support as a whole.




  • 15.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-10-2017 01:21
    Benjamin, please go back and read what I actually wrote. I did not say the soundboard system was not supporting a load -- i.e., string downforce -- I said the ribs in a compression-crowned soundboard system were not supporting that load. 

    It is a complex visualization -- the soundboard panel, by itself (no ribs) will not support much of any load. It will simply bend. But when the ribs are attached and the soundboard panel is placed under compression and crowned then the system is stiffer (perpendicular-to-grain) as a system than it is by its constituent parts and it will support the string bearing load. At least for a time. But during this time the ribs are bent toward the load and are not functioning as load-carrying beams. Loading the soundboard system increases the internal compression within the soundboard pane and reduces some of the strain on the ribs.

    During pitch raises string frame strain is also a factor.

    ddf

    --
    Delwin D Fandrich
    Piano Design & Manufacturing Consultant
    6939 Foothill Court SW, Olympia, Washington 98512 USA
    Email  ddfandrich@gmail.com
    Tel  360 515 0119  --  Cell  360 388 6525





  • 16.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-10-2017 02:20
    As I said, it is a complex issue and it cannot be reduced to simplified one-liners. Brighter minds than mine have explored this before I came along and I expect that brighter minds than mine will still be exploring it after I'm long gone. 

    Personally, I'm off in a whole other direction.

    ddf

    ------------------------------
    [Delwin D] Fandrich] [RPT]
    [Piano Design & Manufacturing Consultant]
    [Fandrich Piano Co., Inc.]
    [Olympia] [WA]
    [360-515-0119]
    ------------------------------



  • 17.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-22-2017 20:50
    As for plate flex in not only soundboard stress, but the effect of torque on the rim and struts,

    For the most part metals respond to temperature change, which demonstrates the flexibility of metals regardless of temperature change. It is possible to create a shape out of iron with heat. Wood only burns at high temperature. It does not melt like metals. We add heat to metals and wood for different purposes, to wood, to remove humidity, to metals, to change shape. 

    Metal is no question flexible, on this I am in perfect agreement.

    Metal expansion and contraction experiment
    YouTube remove preview
    Metal expansion and contraction experiment
    An experiment to demonstrate that metal expands when heated and contracts when cooled. The metal bar in the video expands when it is heated by a bunsen burner and contracts after that when tap water is poured on it. The rotation of the white straw amplifies the expansion of the metal bar.
    View this on YouTube >
    So is the string frame.

    My argument that compression exists still holds whether the board is engineered to be stiff or not, more so if we argue metal is flexible. I never denied the string frame is flexible. The changes we see between single wound and double wound strings in a climate with fluctuating humidity, which affects wood more than steel, demonstrates that compression happens not with changing the string torque by alterating pitch, but the absortion and abstention of moisture in the wood of a piano. It goes beyond the soundboard and ribs to the rim and struts. The metal is almost a neutral factor in the process of augmenting and attenuating compression on a soundboard.

    Perhaps the best demonstration of the flexibility of metals is trying to tune a piano to an organ in a cold Sanctuary. 



    ------------------------------
    Benjamin Sloane
    Cincinnati OH
    513-257-8480
    ------------------------------



  • 18.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-23-2017 05:18
    Expansion of heated metal. One point not to be overlooked is that different metals expand differently - a fact put to good use in the bi-metal strip operated cut-off switch.      Michael    UK





  • 19.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-25-2017 10:41
    No that is not true. Its another matter when someone grabs an apple and tells you it's a pomegranate.
    Both compression crowned and machine crowned boards can be in a state of ( for lack of better terms) "under engineered" or "over engineered" or with any luck, engineered correctly.  Any soundboard that has a load (downbearing) placed upon it, will have a reaction (deflection) to that load. That reaction can be measured. It doesn't matter if it's a straight rib, pre-crowned rib, laminated rib, I-beam rib, etc.  If it's deflecting under a load, then those forces can be measured, and then manipulated for optimum performance. As shown in my charts.
    Let's say for a moment that what Del said is correct. That a straight rib will want to go back to being straight. Here's where he's mixing up fruit because many factors can contribute to early fatigue. Not necessarily the compression crowning method in itself.  Improper installation for example, I just pulled out a flat board the other day. As soon as it was removed from the rim, it crowned right back up. Clearly it was installed incorrectly in 1929. I say that because fatigued boards have lost their plasticity and dont crown back up.
    All style of ribs under a constant load will fatigue over time. Maybe one style will fatigue sooner than the other. 50 years? 75 years? 100 years?  Who's to say exactly?  I don't agree with the theory that a straight rib wants to go back to being straight because if its made and installed correctly the crown becomes its natural state of being. The rest is it succumbing to the load placed upon it.  For me fatigue makes much more sense than wood memory.
    You can agree or disagree with me on theories, but the results speak for themselves. That's what matters to me.
    Y'all are welcome to come by and give a listen.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 20.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-25-2017 18:33
    Chris - is your view that the ribs on an original Steinway board are structural arches - and perform as such?

    ------------------------------
    Terry Farrell
    President
    Farrell Piano Service, Inc.
    Brandon, Florida
    813-684-3505
    ------------------------------



  • 21.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-25-2017 19:04
    I think of them as Loaded springs.Kinda like leaf springs.
    So nice try Terrance, but I'm well aware of the Nossman Buttress Arch article.
    In fact, I encourage you to read spring design in the machinery handbook. Pg 238. The terminology, description, and formulas are eerily similar to soundboards.






  • 22.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-26-2017 06:38
    Yes, but a leaf spring has its shape (curved) in its structure all by itself - i.e., it will deflect from its original shape as one applied a force to it, and then when that force is removed will revert back to its original shape. A rib in a compression-crowned board (at least in a Steinway) has a flat shape originally - the only reason it is curved in a soundboard (if indeed it is curved at all), is because the swelling panel has caused it to attain a curved shape - but that shape is only there because there is a force being applied to it. As Del pointed out, the rib wants to go back to its natural state of being flat - it is the panel that is providing the spring.

    ------------------------------
    Terry Farrell
    President
    Farrell Piano Service, Inc.
    Brandon, Florida
    813-684-3505
    ------------------------------



  • 23.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-26-2017 09:10
    Terrance, your not applying the same logic to both materials. The very nature of a spring is that it has a different characteristic than that of the raw material through design. Take a straight piece of music wire, turn it around a rod. Congratulations, you just made a coil spring. Take a straight piece of wood, glue another piece of wood at opposing grain direction to it, let it bow up, glue it to a frame. Congratulations, you just made a wooden spring.
    Both will deflect under a load. Both have to be the appropriate size for that load. Both will fatigue over time.
    But to argue that the coil will unwind itself, or that the wooden spring has a different characteristic than its designed to have. That's the pomegranate in an apple barrel.
    I have in my shop a soundboard widget. I use it to measure and track humidity. It is 2 pieces of wood glued together with grain opposed and attached at one end. Its 10 years old. Its natural tendency is to stay curved.





  • 24.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-26-2017 09:23
    Terrence, looks like we were thinking of this the same time this morning. lol. can you draw a picture of your analogy?





  • 25.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-26-2017 10:39
    Mr. Farrell said:

    "the only reason it is curved in a soundboard (if indeed it is curved at all), is because the swelling panel has caused it to attain a curved shape"

    I must disagree. I don't know anyone (Steinway included) who glues a flat rib to a flat panel on a flat table. The use of a crown table will impart a curve to the rib and compression to the panel independent of any panel expansion. Hence my assertion that it's the glue joint that's really doing the work and my puzzlement regarding the scantlings (what a cool new word Mr. Fandrich has introduced to me.Thanks for that.).  Got to mind your elbows on those Gulbransens.

    ------------------------------
    Karl Roeder
    Pompano Beach FL
    ------------------------------



  • 26.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-26-2017 10:49
      |   view attached
    Okay, everyone keep your comments about my lack of artistic ability to yourselves. I flunked art class in junior high - okay!?!?!?!?

    Pull up on 2x4 that has the coil springs attached to it and the thin flat bar of spring steel. Seems to me that is more-or-less what is happening to a rib on a compression-crowned soundboard. Then apply a downward force (something like, perhaps, strings!) to the flat (curved) spring steel and coil springs assembly. The reason you would have a springy reaction to the downward force would be due to the coil springs, not the flat spring steel.

    ------------------------------
    Terry Farrell
    President
    Farrell Piano Service, Inc.
    Brandon, Florida
    813-684-3505
    ------------------------------

    Attachment(s)

    pdf
    spring.pdf   324 KB 1 version


  • 27.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-26-2017 08:46
    "I think of them as Loaded springs. Kinda like leaf springs."

    I had a thought this morning regarding your leaf spring analogy while walking my dog. So consider a length of straight spring steel (more or less what a compression-crowned soundboard rib is). Attach a coil spring to the center of the spring steel "leaf spring" and attach the ends of the spring steel to some reasonably solid foundation. Now pull upwards on the coil spring a small distance (perhaps ten millimeters). The length of spring steel will follow the coil spring some distance upward - a couple/few millimeters, depending on the stiffness of the spring steel length and the stiffness of the coil spring - but let's just say it does follow the coil spring a small distance. This is much the same case as a rib on a compression-crowned soundboard. Now if you apply a force downward on the spring steel length, how does the spring steel length work as a spring? Any resistance to the new downward force being applied comes from the coil spring - i.e. the soundboard panel.

    Yes?

    "So nice try Terrance, but I'm well aware of the Nossman Buttress Arch article."

    Ummm, the only thing I'm trying to understand is your reasoning. BTW, who is Terrance?

    ------------------------------
    Terry Farrell
    President
    Farrell Piano Service, Inc.
    Brandon, Florida
    813-684-3505
    ------------------------------



  • 28.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-25-2017 11:05
    If the ribs add stiffness and the assembly is a spring, why wouldn't they contribute to the load bearing properties?  Isn't that what a stiffer spring does--deflects less under load?  If not, then the implication is that no matter how large the ribs are (or small) the load bearing properties of the assembly will not change in a compression crowned system or that the that a larger rib will mean less load bearing properties since the bent larger rib will want to straighten with more force.  I'm not convinced of that.  We're also neglecting the fact that the assembly (and the ribs) are secured into the rim.  

    I can imagine that the internal dynamics of different types of assemblies will produce different types of responses when set into motion by, in this case, a vibrating string.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 29.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-25-2017 11:25
    Have you guys had the opportunity to see what is underneath a new Estonia piano? It is artistic as what is above...

    ------------------------------
    Benjamin Sloane
    Cincinnati OH
    513-257-8480
    ------------------------------



  • 30.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-27-2017 11:46
    Hi Ben

    The company I work for sells Estonias. They are lovely pianos. Would you like photos of the soundboard from underneath?

    Elizabeth




  • 31.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-27-2017 19:04
    Elizabeth,

    I think that would be of interest to most of us for more than just displaying good cabinetry. Not typically a part of the piano that much effort is put into visually, which is reflected in verticals to a fault by most manufacturers. Recently I have put effort and time into attempting to get my clients to get the vertical off the wall when there is room and stop making the child taking lessons feel like he or she is being punished. Particularly with extroverted children. I used to say I wasn't an interior decorator while goading clients to get pianos away from ductwork, outside walls, radiators, etc. Now I go further and talk about fung shui problems facing walls and such. But the cabinet behind the vertical is frequently so unappealing, it is refreshing to see something done there even on a grand. It would be nice to not hear that excuse from the client.

    I've found myself defending the preceding technician over where the piano is. E.g., a Russian piano teacher had the vertical flat against the wall positioning the pianist back to the only entrance/exit to the room. These things will incline many not to stay seated for the time it takes to learn anything. Moreover, the position of the piano should force the pianist to at least imagine the presence of an audience within view under light, or to be presented with distractions while playing.

    ------------------------------
    Benjamin Sloane
    Cincinnati OH
    513-257-8480
    ------------------------------



  • 32.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-28-2017 10:10
    Terrence, I read through your analogy again this morning, and I just couldn't visualize it. A drawing or a model would be great.One thing I was wondering though, are you taking into account that the shortest distance between 2 points is a straight line? A curved rib is "longer".
    So in your example, you would have to bow it up a little then secure it to a solid foundation. I'm not sure the attached coil spring analogy works either. It takes energy to squeeze the ends of a coil towards each other. Totally the opposite of what's happening in the panel. Its taking the moisture from the air as energy and pushing out. And a series of these pushing out springs along the top of the arch would find equilibrium to maintain the arch. Once that arch structure is secured to a foundation. Then it's load bearing capabilities come into play.





  • 33.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-25-2017 19:27
    I'm a firm believer that it's better to remain silent and be thought a fool than to speak up and remove all doubt. However............. I've been wondering for some time now what purpose is served by the increasing height and width of the ribs in relation to their length. While Mr Chernobieff correctly points out the discrepancies in execution one finds when measuring old boards, I was taught that the general idea was to have the longest rib be tallest and widest decreasing by a 16th inch or so in both dimensions as one moved toward either end of the bridge. The 16th inch figure is just an arbitrary number for the purposes of this discussion. Since, as Mr Fandrich and others point out, in a C.C. board the compression of the panel is responsible for the maintenance of the crown and the glue joint between the rib and panel is responsible for maintaining the compression; why then aren't the ribs uniform in dimension? For that matter, why are they so few in number and so widely spaced? I would like to thank Mr. Fandrich for his excellent series of articles in the Journal touching on these matters and giving us all cool thoughts to turn over in our minds while tuning yet another Whitney spinet.

    ------------------------------
    Karl Roeder
    Pompano Beach FL
    ------------------------------



  • 34.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-25-2017 20:55
    "..........................Since, as Mr Fandrich and others point out, in a C.C. board the compression of the panel is responsible for the maintenance of the crown and the glue joint between the rib and panel is responsible for maintaining the compression; why then aren't the ribs uniform in dimension?"

    An excellent question Karl. 

    Ribs 6 and 7 on the S&S B are nearly the same length, yet they are 4 cubic inches in volume different (HxWxL).
    That would make no sense for the purpose of just maintaining compression.


    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 35.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-25-2017 21:34
    At no point am I suggesting that the scantlings used by Steinway made any sense. Nor am I questioning whether or not the modifications made result in an improvement (or, at least, a change) in tone performance. I am, however, suggesting that the methods of analysis could use some refinement.

    ddf

    --
    Delwin D Fandrich
    Piano Design & Manufacturing Consultant
    6939 Foothill Court SW, Olympia, Washington 98512 USA
    Email  ddfandrich@gmail.com
    Tel  360 515 0119  --  Cell  360 388 6525





  • 36.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-25-2017 22:19
    Simplicity is the ultimate refinement. I kept it that way on purpose so it would be beneficial, and a practical tool for those wanting more out of their next rebuild.





  • 37.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-26-2017 06:40
    Thank you so much Karl for painting such a funny picture. Next Whitney spinet I tune - or maybe even a Gulbransen spinet - I'll think of your post!  :-)

    ------------------------------
    Terry Farrell
    President
    Farrell Piano Service, Inc.
    Brandon, Florida
    813-684-3505
    ------------------------------



  • 38.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-27-2017 10:06
    I highly doubt that, when the Steinway B was designed, they "calculated" much of anything. I believe it was 'seat of the pants' good piano building from the 19th century. It happened to turn out pretty darn good, so they simply didn't change it.

    That's just an educated guess, also based on the standard Steinway response to a technical question: "That's the way we've always done it, and we know how to build pianos..."

    So it should not really surprise us to find some less than perfect stuff in there when we start ANALYZING things with the kind of equipment and knowledge available to us today (just a dream back then).

    It's like an MRI or CT scan...they ALWAYS find something "wrong" in there. This is not a criticism, just an observation.

    Pwg

    ------------------------------
    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------



  • 39.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-27-2017 11:36
    Peter, I agree with you. Its actually quite amazing how that seat of the pants method got so darn close. They got next to the bullseye and we're happy with that. I just went one step further from were they left off and put all the darts dead on. 

    To try to give you an idea of how small these changes are, if you look at the charts, for every 35lbs of stress is 1/1000th of an inch change in height. When I put the heights, and thereby the stresses, in sequential order is when resonance was greatly improved.  Its like comparing a person who "thinks" they can sing, to a veteran opera star.

    Small changes, but big results!





  • 40.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 05-31-2017 12:43
    I would be surprised if Steinway had no design targets for the rib dimensions.  Actual rib dimensions do vary but it's more likely one of execution rather than complete randomness.  Rib scales within models do vary somewhat but there's a general pattern.  Using something like "tallest rib in the middle and decreasing by 1/16" inch as you progress outward' (paraphrase) is probably not that useful since it will depend a lot on what your starting point is and there are other considerations.  Using beam formulas to determine load bearing properties is not that new an idea.

    Rib calculations are meant as a reference point, not as an absolute reflection of what will happen once the ribs are tapered, the panel is glued on and the assembly glued into the rim with some amount of compression (even RC&S boards assembled and glued in at 6% EMC have some compression under normal RH conditions).   Obviously, those other factors contribute to the reactivity of the assembly.   

    Soundboard designers and manufacturers have slightly different methods and targets for calculating rib scales.  My method is somewhat different than Chris's or Del's or Nick G's but they all use similar means--as opposed to just copying what is there.  Methods for determining and measuring load distributions, what smooth load distributions look like, choices about downbearing settings, panel treatments including grain angles, thickness, thinning, panel drying targets, all vary to some degree and will impact the outcomes of a particular rib scale.  While there is some forgiveness in most assemblies, the targets, ultimately, are not as wide as you might think and if you venture too far afield you'll produce something unexpected and quite possibly unwanted.  

    It's not clear to me whether or not a company like Steinway had general targets but didn't mind if the executions varied somewhat as a way to discover empirically whether something different might be preferable.   Even under the  most well thought out formulaic approaches, there is an aesthetic choice that must be made and a decision as to whether or not the most beautiful looking formula actually produces something that you like.  And even then, tweaking the assemblies with slight downbearing modifications is pretty common even among the most current and state of the art manufacturers, at least the custom ones.   I have taken apart assemblies where the rib scales did vary by more than one usually finds (typically erring on the side of too light) and most of those ended up as structural failures.  That suggests that the ribs do play a role in the panel's ability to maintain compression in a CC system.

    Whatever your belief in the infallibility of your own formula(s), there's no substitute for actually building it and seeing what it produces and seeing what happens to that assembly over time.  Unfortunately most of us don't really get to see the later.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 41.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 05-31-2017 16:48

    This picture shows a model I made of 2 Steinway B rib scales side by side. The one in the back is original, and the one in front is my rescale.  Both have the same general plan as mentioned by Karl.  But the original SSB is very crudely done, as represented in the charts showing the uneven stress levels. My rescale features a smooth transition from rib to rib, with a  reduction in height in a few ribs, increasing their flexibility. Nothing drastic. All ribs are still in the elastic zone. Strength is controlled not sacrificed.  Resonance was much improved. BTW, last year I rebuilt an L that had a depth and sustain unlike other L's I heard. When I measured the ribs they too had a smoother transition in sizes like my rescaled B. Coincidence?  The Original scale is an 82% profile, 10.8 sq.in. area, stress = 2, 088 lbf;  Rescale is 70% Profile, 10.6 sq.in. area, stress= 2,228 lbf. The "L" I mentioned was also a 70% profile(H*100/W then divide by 13), so some Steinway's do go there, but not often.  Maybe somebody just went crazy with the hand plane that day.  Still had crown too.
    When you hear a 70% board, next to an 82% board, the difference is quite obvious. Maybe you can hear it too in 18'.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 42.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-01-2017 11:55
    Can you explain the math of your 70% versus 82% profile?  What exactly are you comparing?  H/W?  Are you targeting a 70% relationship between H/W for each rib or for the cumulative Hs versus Ws?

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 43.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-01-2017 14:02
    Good Morning David,
    Thanks for the decent question.

    Adding up the heights of the original 13 ribs is 10.68"
    Adding up all the widths is 13.04"
    So 10.68 / 13.04 *100  is the ratio of H to W  equals 82%

    My rescale was
    10.11 / 13.61 *100 = 74% 
    As you can tell, just a subtle difference. (Basically, as i look at it, transferring a collective 1/2" from the height to the width).

    The final stress number i use is cumulative as well. All the stress levels of each rib added up ( x 13). The original was 2,099 lbf, and my modification was 2,208 lbf.  Roughly a mere 100 lbf difference. The deflection will roughly be the same as the original, but just a tad more.

    I aim for a sweet spot of 70%  with 2,000 lbf  being a limiting factor for the system. I focus on smooth transitions from rib to rib. I like the deep resonance, and longer sustain this provides. And yes a little trade off, accepting 2,208 lbf getting down to 74%. 

    Going under a 70% profile usually means an individual rib somewhere in the system is stressed in the 3,000 lbf range. I try not to go over 2,600 lbf for the longer ribs. Why hover in the upper elastic zone with an imperfect material?

    2,000 lbf seems to be a great compromise as it is smack in the middle of the elastic zone for spruce and pine.  Somewhere around 4,000 lbf begins plasticity. 10,000 lbf is rupture. Going below 2,000 lbf just seems to add stiffness that is not needed. If we are talking respectable board lifespans, the  2,000 lbf is more than acceptable for slow fatigue.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 44.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-01-2017 23:57
    Ok got that.  But that doesn't tell you how they are distributed.  For example, you could distribute the rib load bearing dimensions so that they respond uniformly to an equal load across each rib or you could have the center ribs as the most load bearing and the outer ribs the least (as Steinway tends to do it).  Of course load bearing characteristics will be not just a matter H/W relationships but must factor in the length of the rib as well. So, for example, a short rib, #13, might have the smallest cross section but in fact have the most load bearing capacity owing to its short length. How do you distribute the loads and the bearing capacity?

    Here's an example of an original Steinway O board (#1 bass rib is at the top). You can see that the total percentage is 70.9, pretty much ideal by your standards but as you can see the H/W percentage for each rib varies quite a bit.  BTW this board was not successful and I altered the rib dimensions when I redid it.  

    Width mm  Target Height mm  H/W %
    25 13.5 54.0
    25 18.0 72.0
    25 19.0 76.0
    26 19.5 75.0
    26 22.0 84.6
    26 20.0 76.9
    26 18.0 69.2
    25 17.5 71.4
    24 16.5 68.8
    23 16.0 69.6
    23 13.5 60.0
         
    273 193.5 70.9%


    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 45.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-02-2017 00:12
    David,
    You're correct on all those points. As you mentioned in some of our earlier correspondence, this is kind of the art part of it. My approach is to work with a design and smooth out what I perceive as imperfections, while at the same time aiming for my targets. The lengths often dictate the limits of change. 





  • 46.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-02-2017 00:28
    Hey David,
    Can you send the lengths of the ribs as well? And if possible the bridge locations, and the total tension of that string scale.  I'd like to run through it and add it to my library. Thanks in advance.

    Chernobieff Piano and Harpsichord Mfg.

    Chris Chernobieff 
    Associate Member of the Piano Technicians Guild
    Facebook:  https://www.facebook.com/ChernobieffPianoandHarpsichordMFG/
    email: chrisppff@gmail.com
    phone: 865-986-7720








  • 47.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-13-2017 18:09
    Chris, as requested (mm)  Steinway Model O c1909 original rib dimensions

    Rib # length  Width  Height 
    1 730 25 13.5
    2 905 25 18.0
    3 1030 25 19.0
    4 1115 26 19.5
    5 1050 26 22.0
    6 845 26 20.0
    7 655 26 18.0
    8 520 24.5 17.5
    9 403 24 16.5
    10 343 23 16.0
    11 270 22.5 13.5


    Total tension is about 34,500 lbs.   Don't have the exact bridge locations.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 48.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-01-2017 10:23
    < While there is some forgiveness in most assemblies, the targets, ultimately, are not as wide as you might think and if you venture too far afield you'll produce something unexpected and quite possibly unwanted.  

    David, this is a value judgement. It may reflect your aesthetic and it may reflect that of some of your clients. It does not reflect my aesthetic or that of any of my clients, with the possible exception or one.

    Here is my experience...

    1-Pitch clarity, textural and tonal differentiation, volume at tonal break-up, and voice-like sustain require that the board's structure pass a base threshold of stiffness in order to support these attributes. Once the a new board structure achieves this base threshold, the bandwidth of stiffness a board can possess and still be tone regulated to a fine degree is huge. Boards of varying stiffness will present slightly different tone palettes, but, given serious tone regulation chops, these different tone palettes will lend personality to a piano that is, right out of the gate, pretty damn good, highly musical, and in demand from excellent players.

    2-Board design is at least 40% tone regulation(probably more)…ie, not board design at all. This part of the board "design" puzzle is never discussed in board talk, but it is so central to the success of a new board it needs to be explicitly discussed. Getting any new board to perform at or near its potential, requires high level tone regulation chops...and, it requires Time. Time meaning time to mess around with those regulating chops on that particular board, to learn what that board's unique requirements are. The chops include Choosing an appropriate set of hammers, hammers that match that particular board's impedance, Shaping those hammers in a way that supports register specific tone, on that particular board, Regulating and phasing the actual impact event with anal precision, and Regulating felt density to a very fine degree. A real biggy in this tone regulation process is that it may include some backtracking to correct tone regulation parameters, which we may have initially misjudged in the as-built board. This ability to backtrack and revise when necessary, may be one of the most important missed opportunities which prevent a new board with potential, from achieving that potential.

    This tone regulating aspect is so central to the "success" of any new board, I actually shy away from providing "board only" services, since the success of the "board" is partially non-board related, and out of my control. Interestingly, the only new board of mine that supposedly "didn't work" was my first board. It was not until I tore it out, redesigned it again, that I realized the "board failure" was in fact a failure in my newbie tone regulating chops, not of the board design…lesson learned...eyes wide open and observing, and has positively effected all my subsequent board work.

    Even on high profile instruments, given the essential pre-contract "what to expect" discussion any project should entail,  I am so comfortable, at this point, in the generously huge functional bandwidth of boards, that I have been comfortable and highly successful utilizing experimental rib parameters on high profile re-manufactures...why? Because knowing how to "tune the board", ie mass load if necessary, not by default, but if necessary, knowing how to read that new board, in order to direct tone regulating choices, and fully pre-loading and proving actual deflection-to-load parameter pre-gluedown, takes the statistical poker out of the mix. 

    These discussions tend to lean towards the sales department, and in Chris's case, this is clearly a thread in search of sales. Setting up a scaffold of fear, by implying as he has done, that rib changes in thousandths of an inch can are heard is demoralizing, and is simply not justified by the reality I experience.  Keep in mind, also, that there major brands whose structural profiles are considerably stiffer than the limited bandwidth presented by Chris, and Steinway, and to some degree agreed to by you with the way you voiced your caution. Perhaps I am reading into your caution, and that is not what you meant. If that is the case, please accept these comments simply as clarification.  

    Pre-contract frank, possibly sales-killing communication with clients is essential...and that wisdom is valuable. But the tenor of the statement, to me, implies a negative view towards any approach which exceeds the structural bandwidth that satisfies a certain manufacturer's aesthetic goals.

    Said another way, my experience is… that its not rocket science…and, as a rocket scientist has reputedly been quoted… rocket science isn't rocket science either.                

     








    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 49.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-01-2017 11:46
    I thought I was just making a small contribution to the trade, and talking about a REFINEMENT that I find ENJOYABLE. 
    But somewhere along the way,  I had become an EVIL soundboard maker that created a CAMPAIGN OF FEAR for the purpose of SALES.
    I'm so ashamed.





  • 50.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-01-2017 23:20
    vBz1Og2fSWqWqAounA8g_demos 012.jpg
    Now this demo is quite effective. Easy to see the rib scale and the related stress levels. Wow, the original is just all over the place.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 51.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-02-2017 12:35
    What are the values on the Y-axis derived from?

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 52.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-02-2017 05:03
    Jim, 

    Honestly I think you're being a bit presumptuous with your comments about my  value judgements and Chris's motivations. Of course I do make value judgments on tone for my own preferences but I'm open minded about differences at least to a point.  The piano literature dictates that the piano respond in a certain way, however, and when it doesn't then many pianists will have a problem. Yes you can always find that idiosyncratic pianist who will like the sound of kicking the side of a garbage can but I wouldn't  build something hoping that the customer I was working for was that man (or woman) or that I could talk them into it.  And no, I'm not calling your designs garbage cans, just an illustration). As for your points:

    1. The function of the soundboard (or one of them anyway) is to control impedance, the energy flow from the string.  Too low and the energy tranfers too quickly and the attack is too strong and the sustain too weak.  Too high and the board may sustain for a long time but will be lacking in power.  A balance between those two is necessary. There is some leeway (obviously boards change over time and we still think they're ok), and boards can be tweaked to some degree using different methods or selections but those modifications are limited in effectiveness.  Having built a variety of designs my conclusion is that there is leeway and forgiveness but not that much.  Of course most anything will "work" on some level but I'm not really after that. Nor am I interested in turning a Steinway into a Kawai. I stand by that value judgement and don't think it's a particularly narrow one.

    Of course the string scale dictates to a great degree what the board design needs to be. A higher tension scale will require a stiffer or heavier (or both) assembly.  The "pallettes" will be as much a function of the string scale as the board.  And I presume we agree that the hammer plays a role as well. A high tension scale, heavy board with a lightweight soft hammer won't sound like much and a low tension scale with a lightweight assembly and a massive hard hammer that might serve the previous iteration will likely sound like hell on that light design.  Let's just say that Claire de Lune will be tiptoeing in with combat boots.  Hammers do affect the pallette or color by their influence on partial development and filtering, but that's another discussion.

    2.  We disagree here, and strongly. If you have to correct what you've designed by 40% you haven't designed it very well, in my opinion.  That's not to say that you can't or that some refinement isn't necessary as I mentioned with slightly modified bearing settings after the fact, as some very high end manufacturers routinely do, or a slightly modified hammer choice. But let's be honest, a mass loaded design to correct jangles, for example, is and sounds different than a board that wasn't designed too stiff to begin with.  Not to mention the hammer requirement will change things as well.  Similarly, mass loading the end of a bridge to compensate for the end of the bridge effect is not the same as a proper bridge extension.  A board that is too stiff or has too much mass and lacks power cannot be adequately compensated for by a reduction in downbearing or a heavy rock of a hammer, even if that might make it better, and in that case there may be practical limitations with respect to touchweight dynamics or regulation. Nothing happens in isolation.  You can try and fix poor designs or poor executions or approach it from a 'just make sure you build it stiff enough and then try and compensate after the fact' perspective but that will not be the same as a more targeted design that requires no or fewer modifications or a more accurate execution to begin with and, in my experience and opinion, not better.  There's something to the adage, "stiff but not too stiff, light but not too light".

    I'm not sure what you mean exactly by being comfortable with a "huge functional bandwidth" but I would certainly not characterize the range of what I'm comfortable with as huge. I don't want to be jumping through hoops to fix something.  Been there, done that and let's just say "redone" that as well. Variability is fine, some differences are fine, but the test is simple, it should basically have the capacity to capture the range of the requirements of the piano literature, from Rachmaninov to Satie That's a different thing, btw, than someone's voicing preference.  That someone chooses to voice a piano to a certain level does not mean that the instrument has inherent limitations. Those are different things.

    I can't really speak for Chris but I appreciate his enthusiastic and open contributions even if we have disagreements or lack clarification of the differences in our methods.  He and I do seem to agree that a very precise and targeted approach is a good one and that there is a relationship between the design and outcome that is different than what one can achieve by correcting after the fact.  We're not alone in that. Much of this is quantifiable and predictable. In that sense it is rocket science, or at the very least it benefits from some level of engineering.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 53.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-10-2017 06:51
    Jim I wrote: "Because knowing how to "tune the board", ie mass load if necessary, not by default, but if necessary, knowing how to read that new board, in order to direct tone regulating choices, and fully pre-loading and proving actual deflection-to-load parameter pre-gluedown, takes the statistical poker out of the mix."

    I've pe-loaded a board pre-gluedown also. I'm just curious how you physically went about it. I used go-bars placed along the long bridge. Prior to placement, I measured the pressure of the go-bar with a scale. It was a bit cumbersome - just wondering if there is an easier method.

    ------------------------------
    Terry Farrell
    President
    Farrell Piano Service, Inc.
    Brandon, Florida
    813-684-3505
    ------------------------------



  • 54.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-10-2017 21:19

    Terry,

     I spent some time working this pre-load procedure out, as my interest is, starting with a very stiff structure, incrementally back off that stiffness, to see what the tonal limits are. So, I've been working out a pre-gluedown, pre-load procedure, that allows me to target actual as-designed deflection/load in the complete composite system…ie panel, ribs, diaphraming, scallop design, thickness and length of the scallop and proximity to the rim, number of ribs, complete full rim clampdown (as if gluing in the board-without the darn plate in the way!), and (importantly I think) as-built compression of the panel. Though I triangulate on the emc of the board pre-ribbing, experimental error is such that knowing exactly where the emc was at ribbing is only accurate to  +/- 1 or 2 %. So this sidesteps that experimental error and reads the total as-built deflection/load/length of the composite system, at whatever emc it was actually ribbed at.

     It also lets me plane down the ribs, which I install too tall as a starting point, planing as necessary to hit my deflection/length/load, with load applied where the actual string load will in real life be applied.

    It consists of a set of 20 calibrated, spring-loaded go-bars. The go-bars have a window and scale which can be set between 20-40lbs each including the weight of the go-bar. given internal friction of the go-bar device the calibration is within 15%-ish I think.


    You can see in the above pic a dial indicator beam, and yellow tape on the case top edge. Though this beam deflects when spanning the  case, measurements are taken at rib locations along the bridges, and the placement of the beam and indicator precisely triangulated so the beam is always in the same place when taking a reading at a given rib. Pre-and post-loading readings are taken.  



    readings are repeatable to .002.

    At this point after adjusting the rib heights, which along with the deflection reading includes a tap test, I use these numbers to set bridge height. Best downbearing setting I've had, but that's a side benefit. I want to know what the limits of the system are, and belly by belly I'm working away at the stiffness parameter. Also working other parameters, because I don't think its all about impedance...but that's beyond the scope of this post.    



    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 55.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-11-2017 18:46
    Mr. laleggio,
    Your method of procedure is interesting, but i'm sorry to say i believe that it's technically and strategically flawed.

    The first flaw is the idea of using deflection (or as you call it "Bandwith of Stiffness") as a means of determining rib dimensions. Since ribs have a symbiotic relationship with one another, it will be all too easy to remove material from the wrong rib, and end up with ribs of uneven stresses and false readings.
    Second flaw is changing only the heights of the ribs, and leaving the widths to a predetermined size. This strategy is very limited, and will most likely take the overall rib design back to the original at best,  will leave the rib scale more uneven, and most likely result in a high rib profile. My guess would be an over 90% profile which is seen in most horrible designs. In other words compounding any original mistakes.

    I suspect this is why you have repeatedly failed to submit for peer review any rib data frequently requested by me and other techs.

    BTW, your false accusation that I'm using fear, Is based on you misquoting me.
    You said:

    "These discussions tend to lean towards the sales department, and in Chris's case, this is clearly a thread in search of sales. Setting up a scaffold of fear, by implying as he has done, that rib changes in thousandths of an inch can are heard is demoralizing, and is simply not justified by the reality I experience.  Keep in mind, also, that there major brands whose structural profiles are considerably stiffer than the limited bandwidth presented by Chris, and Steinway….."


    I never said you can hear a thousandth of an inch change.  What I said was a thousandth of an inch change can cause a 35-60 lbf difference in bending stress. And uneven stresses cause problems.

    I'm not using fear tactics or trying to demoralize people. That's simply just ridiculous.

    Just show us the data, leave the personal attacks out of it, and maybe we can have a productive conversation.



    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 56.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-15-2017 23:40
    Hi Dave,
    Well that S&S O scale you shared was actually pretty good!  A 71% profile too. The lowest i have seen from Steinway was a 73%.  I would pretty much leave the way it is if it were me. I was able to get the bridge location measurements off of a photo of an O Board I found online. Not exact, but close enough. Also, the rib scale is pretty darn the same as an L with slight differences in lengths.
    Here's a screen shot. Thanks again.


    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 57.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-16-2017 17:55
    Clearly we have different approaches and methods for analyzing performance.  Were I using the original widths (which I didn't but just for comparison) and species on the ribs (pine in this case) I would have done something more like this.  By your method 78%.  The load is based on a 3rd degree polynomial.  

    Rib # Calculated rib load Working length  Width  Target Height  H/W
    1 60 730 23 21.3 92.6
    2 61 905 24 22.8 95.0
    3 63 1030 25 23.7 94.8
    4 66 1115 26 24.3 93.5
    5 68 1050 26 24.2 93.1
    6 70 845 26 22.6 86.9
    7 72 655 26 21.0 80.8
    8 73 520 24.5 20.0 81.6
    9 72 403 24 18.5 77.1
    10 71 343 23 17.5 76.1
    11 67 270 22.5 16.0 71.1
               
    299 231.9 78%


    Here's how those ribs would perform under load (panel contribution not included in this). Based on 15M radius.


    Under the same load the original rib scale performed more like this--not so good.  The tonally weaker areas of the original somewhat corresponded to what you see below.  I did not want to duplicate this rib scale and did not.  



    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 58.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-16-2017 21:22
    Thank you for sharing that David. Quick question: Is that pounds? If so, it looks a little on the light side at 743Lbs. I calculated that the board load should be about 860lbs. Plus my research has shown that the top rib is usually in the range of 90lbs to 120lbs.  Your is at 60. Im wondering if that is giving you a false deflection.
    Thanks again.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 59.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-17-2017 00:56
    Well, if the load were more, then my percentage would be pushed even higher than 78% and the original rib scale would perform more poorly even than shown.

    The load is derived based on bearing settings that are lower in the bass and 1.5 degrees everywhere else.  You are correct that sin(radians)1.5 * 34,500 lbs would yield a higher number than what I have shown.

    In addition (to the above) the actual load on the ribs in the high treble is higher but the bridge is also moving quite close to the belly rail and therefore not centered on the rib which increases the load bearing capacity of the rib or, for purposes of calculating, reduces the load if you are usuing center loading for these calculations, which I am.  I used to go through the exercise of figuring out the actual load and then the bridge position but this method (derived from that) works for me.

    With respect to the discussion with Jim, you can see that I've pushed up the rib scales somewhat but many of the RC&S scales that I've seen have been much heavier--though not all of them. The ones I prefer are definitely the ones on the lighter side of what I've seen.  (FWIW I rib and install at about 5% emc with precrowned ribs so mine is a hybrid system by our current definition). 

    And then there's the issue of compression crowning versus RC&S (no or little compression) with respect to tonal response. I do think that it is likely that the opposing forces (as Del pointed out) of ribs pulling down and panel pushing up in a compression system creates some internal dynamics and bi-directional (up and down) potential energy within the structure that will produce a different spring response when excited by a vibrating string than when the forces are more unidirectional, as in the case of an RC&S system with no or little compression. Working on 'splainin' that to myself but that is another discussion.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 60.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-16-2017 21:38
    Following this thread has certainly suggested more questions for me that it has answered. I am grateful to all who have posted for sharing their hard won knowledge and well considered speculation. In reading some of the posts from Mr. Chernobieff,Mr. Love and Mr.Ialeggio I find Mr. Fandrichs' earlier (implied) admonition that RC&S boards RC&C boards and CC boards all behave quite differently and are thus impossible to compare apples to apples.
     Mr. Ialeggio however brought up  a few things that resonated (get it?) with me.
      First the idea that some of the assertions in this discussion could create a scaffold of fear. I'm a big fan of fear. It's kept me at various times from being shot,stabbed beaten and attacked by wild animals. Sadly it hasn't kept me from doing belly work.
      Then there's the idea of some of these discussion leading to sales. I love sales. They let me pay for the daughter's piano lessons and pretty much everything else. I only wish that Mr. Love or Mr. Chernobieff (or Mr. Ialeggio for that matter) would offer to sell me a well set up spreadsheet program for rib and panel design. I've been very happy that Nick Gravagne sold me one for action geometry. Likewise the program Tremaine Parsons sold me for scale design. I never would have known they existed if not for their being mentioned on this forum. I haven't got the time or the engineering chops to develop one myself so buying one would seem to be the solution. Kind of like the way I bought a duplicating router rather than fabricating one from scratch.
      The thing that really spoke to me however was the idea that tone regulating chops might be more important than which belly system one employs.
      I couldn't agree more. I approach all of this work as a tone regulator. I tune and voice pianos for a living. I do belly work because I just can't help myself. The idea that I could get away with telling an artist or a client that the soundboard on their new $100k + piano or their $40k rebuild just isn't properly configured to give them the tone they're looking for is one I abandoned long ago. Never mind the client's immediate distrust of my assessment of the situation. Throwing the manufacturer or the re-builder under the bus is guaranteed to have long term consequences that I'm not going to like. Mr. Love is quite correct about the need to select the right hammers but even there one can go amazingly far towards great tone with the "wrong" hammers. It just takes a lot longer and is a lot more frustrating.
      Again my thanks to all of you for your contributions. They are the sorts of things that make an organization great.

    ------------------------------
    Karl Roeder
    Pompano Beach FL
    ------------------------------



  • 61.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-16-2017 22:34
    Thank you for that enjoyable read Karl.  There are difficulties when it comes to software sharing. First, its somewhat personalized. Second, it's only a small part of the analysis in my system.
    My procedure goes something like this: (BTW it doesn't matter what kind of board)
    I tune the original piano to 440 and I measure the string scale.
    Then I put "dials" on as many ribs as i can.
    Then I remove the strings and record the movement. 
    I then use weights on each rib to duplicate that recorded movement. This tells me the load per rib ( Hookes law) and the Youngs modulus per rib ( deflection values).
    The software at this point just records the loads and dimensions of the ribs and how they are reacting to the loads.
    Usually the adjustments from the original are small ones and focus on evenness to create more flexibility. Usually I am adding mass and "tighening up" the deflection. The computer allows a little more refinement than possible a hundred years ago. 
    I agree that voicing is the most valued skill for the tradesman.  My approach regarding rib design is not to scare customers, but to give my existing rebuilds an edge that i didn't have before. What I mean by this is I like having a 6 foot grand sound like a 6 foot grand, not a five foot grand.  Yesterday, I worked on a 6 foot Knabe that sounded almost like a 7 foot grand. That's what good rib scaling does in my opinion. 
    My software is still developing thanks to the welcome challenges from David and others. Maybe in the future, after i have developed a substantial database,  could i have something of value to put on the market for others.


    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 62.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-17-2017 13:39
    Karl:

    I'm afraid at this point the spread sheets are not available for sale.  They may be one day or I may just give them away at some point but not yet. Keep in mind that the spread sheets are just a guide and the data and analytics I use are at best incomplete. They are a guide and reference point but decisions still need to be made about how to build things. Over time you are still tweaking this area or that area and hopefully once you build enough you get a sense of what produces what but it's not a straight line from spread sheet to outcome.  There is some method to the madness but information can both clarify and confuse.  There are also other factors: grain angle, panel thickness, species, panel thinning, grain density not to mention what we've already mentioned, string scale, downbearing, crown choices, rib tapering, rib construction (laminate versus solid).  The list could go on.  

    With respect to tone regulating, I certainly agree that tone regulating is important.  I think what Jim was referring to was tweaking elements of the design after the fact, to some degree.  He can correct me.  He mentioned things like mass loading which is a method often talked about for dealing with things that are too stiff or where the stiffness/mass ratio is off. Even though tone regulating is important we should assume that any and all assemblies can be manipulated to get the result that we want.  We can (to use one of Del's favorite phrases) make things less bad but that doesn't mean the outcome is anything close to ideal.  We see that with old tired sound boards.  We can choose a lighter, softer hammer to reduce that aggressive attack and get the hammer rebounding off the string faster to improve sustain, we might even alter the scale design some to lower tensions, we can epoxy coat the board, add riblets, etc. etc.  But though we may be successful in extracting everything the assembly has to offer we wouldn't necessarily want to be building one that way.  

    In my experience (let me emphasize that) this is no less true with assemblies that are too stiff.  We can do certain things after the fact to improve the areas or responses we don't like but it will not be the same as the result we would have gotten had we built something that didn't require all that.  Who knows, maybe we might like it better but so far I have not.  For the record I'm not arguing that Jim's assemblies are too stiff, I don't what they are since I haven't seen the designs.  I can see from my exchanges with Chris that he may well build them lighter (less stiff) than I would. My original comments were only directed at the notion that there is, as some have put it, a sweet spot in the design--that assemblies can be made too stiff or not stiff enough. I don't believe that the spot is so narrow as to be impossible or unlikely to hit or that we don't have some wiggle room, but neither do I believe that it is so wide that we can count on tone regulating to completely salvage a less than optimum design.  

    Del gave me some good advice early on.  At some point you have to shoot the designer and just build the damn thing (paraphrased).  But hopefully when you do you learn something from it and take that with you to the next one.

    BTW I'm hardly the last word on this.  There are people who have built way more boards than I have and have established formulas for themselves based on what works for them rather than taking the spread sheet approach.  I think what's important to take away from this discussion is that just copying what you find when you take a board out of a piano is not always the best approach.  Factory executions, as we have seen, can vary considerably and so do outcomes.  You might get lucky but, in my experience, luck eventually runs out.



    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 63.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-17-2017 14:01
    We can make some easy a priori assumptions here

    1. if we ramp up tension and augment compression, higher partials will be more prominent. 

    2. It we lower tension and attenuate compression, lower partials will be more prominent.

    Creating a dialogue with the client about what the client wants is next to impossible. That is why I think the test to be an RPT should include a portion devoted to actually being able to play the piano. I don't fight for it because I know it is a battle I will never win. But we still have to deal with our inability to communicate with clients about these things.

    ------------------------------
    Benjamin Sloane
    Cincinnati OH
    513-257-8480
    ------------------------------



  • 64.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-16-2017 23:51
    Thanks for sharing that info david. One more point I am not sure on is what your deflection value is based on ( I think we have discussed this before). If it's based on the species M.O.E. (1,560,000) then I think that will give you a false read. This is the reason I test an original board before removal, in order to get a more realistic value and accurate prediction of movement in the deflection formula. I'm seeing values between 5,600,000 to 19,000,000 for soundboards ( I call it S.M.O.E). This makes sense to me because its a laminated structure that is glued to a border. The species value is ok in simple beam structures.  
    I'll look through your spreadsheet and charts  and get back to ya.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 65.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-17-2017 12:11
    The tolerances must be huge. 

    Chernobieff started a thread about scaling deficiencies in the Steinway L I took him to task for some time ago. I admit the Steinway B is a different animal. 

    I don't know if it was dumb luck or what. Arguably the most flexible piano scale with a plate ever invented. Reputable techs claim better than a D. Is there a piano more emulated by other manufacturers?

    The thing will tune 2:1 accross the board or 8:4 up to C5 C6 octave. Sure this translates into a wide range of possibilites for rib dimensions...

    ------------------------------
    Benjamin Sloane
    Cincinnati OH
    513-257-8480
    ------------------------------



  • 66.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-17-2017 13:02

    <… if the load were more, then my percentage would be pushed even higher than 78% and the original rib scale would perform more poorly even than shown.

    This comment illustrates one of my frustrations with the use of spread sheets (mine included). Spread sheets have to rely on information that is assumed, not proven. I have my own sheets, and have spent many hours on them, as Chris and David have. The difference between Chris' and David's load assumptions illustrates one of the problematic issues in spread sheet belly calcs.

    We can accurately calculate tension per string, calculate tension per unison, and calculate overall tension. Then we can calculate how much load those tensions will impose of the board, given a defined downbearing scheme. However, the actual fashion in which those loads are distributed on the spread sheet is a guess. This "guess" is an unproved assumption, and defines all the down stream calculations. Change the load and load distribution assumption and it changes all the down stream calculated results.

     Why is this assumption a guess?

     Among other things, the bridge is a beam which curves far away from a straight line draw between its end points. This means that beam cannot support weight in a linear fashion. Actually it can't even support its own weight. It will instead want to rotate around its end support points. It wants to rotate into the portion of the beam which is farthest away from that straight line drawn between 88 and 21. These rotational and leveraged forces will be greatest in the first capo section, where the out-of-axis condition is greatest. This means loads applied to the bridge will be distributed and smoothed, to some degree, by the bridge, but the distribution of loads will concentrate in the portion of the bridge that has the greatest rotational tendency...ie the 1st capo section. Not only that, as my own measurements continue to counter-intuitively show, the non-linear distribution of loads, actually seems to deflect up in the very high treble. From a pivot area under the top strut, and the end of the high treble bridge, despite being densely populated by significant loads...from my own measured observations…the bridge tends to deflect up against the loads, not down as if deflected down by the loads.  (That is why the very high treble can often tend to show more downbearing than intended.)  

    So, as David's comment illustrates we are making a central assumption as one of the first steps of the design. The assumed load and the distribution of that load is different from designer to designer. This assumption, among others, is what take this calculated process out of one-to-one calculation territory. Instead, the calculations become devices which help draw statistical trends. In the spread sheet, the act of quantifying parameters such as deflection/length, rib section, etc, allows one to visualize and draw statistical trends, given the fact that there are many unknowns in the system….they do not present a 1+1 scenario.

    One work around statistically here is for a sheet designer to define their assumptions in such a way that they remain consistent from belly to belly. Statistically, if you keep your load assumptions constant, it can have the effect of reducing the value of the assumption to "1". Multiplying anything by one, does not alter the thing you are multiplying.

    Karl has expressed an interest in a belly spreadsheet. When folks look to purchase a belly spreadsheet, they are often under the impression that because there are beam, tension and load calculations, the spread sheet presents a one-to-one calculated result. This impression, as I have described above, is incorrect. The reason you will probably never see a rib design spreadsheet sold, is that the sheet is a statistical tool which is only as useful as the user's assumptions, load assumptions, observed correlations in actual rebuilds and pre-rebuild conditions, and correlations with other factors of the complex composite system which are not even included in the sheet. These other factors include number of ribs, board thickness, diaphraming patterns, scallop designs, length of scallops, thickness of thinned part of the scallop, emc @ ribbing, string tensions if deviating from "normal" tension, bridge height x thickness, end-of-bridge phenomena as related to location of ribs, etc, etc.

    The complexity of the system forces us to make assumptions, and to exclude parameters which cannot be included on our sheets. The users eye and experience is paramount in the use of the sheets. This is one reason why, though I still consult my sheets, I have jumped ship, and am using an empirical method to test the as-built conditions of the entire as-built system, before its glued down for good. Rather than working from the spread sheet as I used to, I am currently using the sheets after the fact, to help draw trends. I described, previously in this thread, the pre-load procedure I am using as my way to analyze the system pre-gluedown.

    Actually, for someone wanting to get their feet wet in this area, the simplicity of the empirical method outlined can serve as a pedagogical device for beginning belly rebuilders. It will get you in the generous "damn-good piano" ballpark without having to negotiate the statistical difficulties presented by the spread sheet. Statistical and empirical both work…but pedagogically, for me, the empirical method is easier in the "how do you do this stuff" department, and easier on the brain.



    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 67.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-18-2017 00:41
    Jim:

    Well articulated. I agree, to do a meaningful comparison of, in this case, rib scales as a theoretical exercise, we would need to leave all other variables constant.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 68.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-18-2017 01:27
    Thank you, Jim. Finally we have an articulate comment on the complexities of soundboard and rib design. 

    If anyone has a demonstrably predictive spreadsheet of exactly how to design the perfect set of rib for any given soundboard panel (including how the moisture content of the panel affects this design) I'm all ears. I'd love to see it. 

    My own methods -- at least those I was using 10 or 20 years ago -- are out there. But, as I look back, they are woefully inadequate. 

    ddf

    --
    Delwin D Fandrich
    Piano Design & Manufacturing Consultant
    6939 Foothill Court SW, Olympia, Washington 98512 USA
    Email  ddfandrich@gmail.com
    Tel  360 515 0119  --  Cell  360 388 6525





  • 69.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-18-2017 11:24
    Well articulated? Sure.
    If you want to practice the " art of over-complication", then articulation is important.  
    Stating that the calculation of the distribution of the load(s) is a guess and assumption, i find incredibly fascinating!
    It's simply not true. It can be precisely calculated. The principle law was first written in 1678  "Ut Tensio Sic Vis" by Hooke, and here we are in 2017 calling it an assumption.
    I've shown how to do it with modern and easy to get equipment in past posts. (ad infinitum)

    Another principle overlooked when building a structure is the minimal safety factor. If you design something to hold up a 1,000lbs and it ends up only holding 900lbs, then so what.  That's good.

    The whole purpose of a speadsheet is to insure the opposite ain't true. Which is the case with so many old boards that just get copied. Why copy a mistake? That's not fear, that's just asking a logical question.

    The real assumption here is the one that says a speadsheet is isolated from the real life board. Yes, if you make it so. It's not isolated to me, but an integrated element.
    Dimensions taken from soundboard 
    Load values placed on soundboard 
    Deflection values taken from soundboard 
    How in the world is that isolated?
    It's a tool. And like all tools, the human has to learn how to use it.

    The beginner fears the sharp chisel, the craftsman treasures it.
    Yet, the competitor criticizes the choice of color of the handle.
    And when asked to see his chisel............disappears.

    Happy Fathers Day!

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 70.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-18-2017 18:05

    Chris: As I understand it a CC straight rib board has no load bearing beams so such calculations may/probably lack meaning.




  • 71.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-18-2017 23:15
    They certainly don't lack meaning if by that you mean that any random rib scale will perform like any other. Rib scales clearly matter, though other factors *may* add to the complexity.

    I do think that Jim articulated the complexities well. But I also agree with Chris that the complexities needn't paralyze us nor do they mean that spread sheets that take into account load, beam deflection, MOI, etc, are useless or misleading. They are indeed tools. 

    In my own designs many things do remain relatively constant: emc at glue up, rib radii, panel thickness, panel thinning, grain angle, etc. so that it is easier to discern how changes in the rib scales impact performance. If you are changing every element of the design for each execution then certainly you will have a more difficult time figuring out what's what. 

    It should be noted that many, if not most, current manufacturing protocols call far a hybrid design of modestly crowned ribs and some compression, emc of 5% is not atypical. Steinway NY may be one exception but I cant speak with authority about what their current system is. Most soundboard makers target specific rib scales that are either calculated on spreadsheets or derived empirically which they utilize repeatedly with predictable results. In my view a combination of calculation with empirical testing certainly makes the most sense. But it's not a crapshoot.

    I have posted the following question several times and never recieved an adequate answer. RC&S boards are typically ribbed at 6% emc (at 70 degrees about 28% RH). If those pianos are kept at 45% RH (dampp-chaser equilibrium) then they will have some compression.  A bit less than one ribbed at 5% (23% RH) but not that much less.  The difference between a panel ribbed at 4% (18% RH--a typical compression crowned board) and one ribbed at 6% (a typical RC&S board) is only 10% RH. Steinway suggests that their pianos be kept in a range of 40-60% RH. At 60% RH an RC&S board will have just as much compression as a compression crowned board at 50% RH. So it seems to me that all current soundboard making processes have some degree of compression and differences are only a matter of degree.

    My question is: if calculating rib scales is important for determining load support for an RC&S board ribbed at 6% emc, why is it not important for one ribbed at 5% or 4% and what real difference would that make in the actual ribscales that are calculated or used?  In my view the differences in rib scale requirements have been exaggerated and quite possibly led to my experiences with overly stiff assemblies in those cases.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 72.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-19-2017 11:12

    That was by far your most powerful post David. Great question! I'm waiting in eager anticipation to see if Del or Jim will tackle that one. 
    I too, question the idea that the systems are really that different. If that were true, I believe the physical differences would be great as well. As it is, the average person looking at a soundboard couldn't tell you if it was a CC board or the other. The first question would be "what brand is it"? And then make that determination based on knowledge of the history of the company. 

    It seems to me that if one was a load bearing system and the other was a "stiffness/strain bearing system, their physical structure would be quite different. 
    For example (and this is speculation), if it was about stiffness and a glue joint to obtain that stiffness in a lateral plane. Wouldn't we see thick(er) panels and numerous small(er) ribs closely spaced? That certainly would create more gluing surface area. And the stiffness would be controlled by the panel thickness and to a small degree the size of the little ribs. But that's not what we see. Both look like load bearing designs to me. Instead of numerous little ribs with a thick panel , there are a few big ribs spaced far apart with a thin panel.  As you see in other load bearing structures.

    Paul's statement highlights the perpetuated fallacy.
    Paul stated:
    Chris: As I understand it a CC straight rib board has no load bearing beams so such calculations may/probably lack meaning.

    First "straight rib":  It's not a straight rib anymore! It's a laminated hygroscopically made arch before it's glued onto the rim if done correctly.  This means its new natural tendency is to be arched not straight. I think that makes it stronger, not weaker. Granted, the opposite may be true if it was glued onto the rim straight and dry, and hoping the hygroscopic forces crowns it up after glue in. Then in that situation, would it want to be straight?  I have actually seen that problem with some boards i have removed.
    Flat as a pancake loaded
    Flat as a pancake with strings removed
    But once removed from the rim. Crowned up immediately. So how does the theory of a "straight rib wanting to be straight" fit in that scenario?  Obviously, a  sabotage of improper installation a 100 years in the making. If any board wanted to be straight, that one would.
    Second "beams". I have come to dislike this term, because it confuses and falsely associates with architecture.
    Although not 100% analogous, the study of leaf spring design stirs up many similarities.  Thin on the outer extremities, and thicker in the middle. Arched.  The more load there is the thicker it's made(more leafs added). 
    It's a spring that is obviously made to move carrying a load.

    Soundboards are wooden springs meant to move carrying a load.

    You wouldn't want an overloaded spring, nor would you want an overly stiff spring. Both have unpleasant effects in your car and piano. 
    Thankfully, there is a nice range of "personal choices" in the middle between overload and overbuilt as demonstrated by David and I in the choices of design. I'm still leaning towards the direction that David is overbuilding slightly due to the dependance on species M.O.E. 
    But that will be left for the future ongoing fun conversation.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 73.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-19-2017 11:36

    David and Chris: Thanks for help learning. I used to think the ribs need a tight fit against the case because the board acts as a buttressed arch. Now I don't know and wonder if ribs can/should therefore feather down to zero. I also wonder if the board is thinned from the bottom, top, or both and why?




  • 74.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-19-2017 21:16
    Paul wrote: "...wonder if ribs can/should therefore feather down to zero."

    One certainly can do that. In fact, I have built soundboards with ribs that taper to zero without intersecting the rim. Whether a rib does or does not intersect the rim is a product of desired soundboard flexibility at the edge and what the grain angle of the panel is in that edge area. When the panel grain angle is roughly parallel with the rim, a thin rib end extending into the rim can go a long way in minimizing the tendency for the panel to crack compared to not having any rib in that edge area.

    ------------------------------
    Terry Farrell
    President
    Farrell Piano Service, Inc.
    Brandon, Florida
    813-684-3505
    ------------------------------



  • 75.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-20-2017 01:05

    Terrence: Thanks for info.  I am a nearly retired tuner afraid of asking foolish belly questions. Volume and duration are 2 of the 3 main elements of music so I initially thought the before/after board numbers to compare are decibels and ring time as increasing one or both would appear to be the objective. I am surprised/dismayed to find detailed numerical data on previous unknowns such as MOE and MOI, confusing graphs with more than 1 y-axis but no basic comparisons obtained with a decibel meter or stopwatch. Thanks for your help but I increasingly think this is not for me.




  • 76.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-20-2017 23:11
    Paul:

    In an indirect way that is what we're talking about. Volume and "ring time", or sustain, are at opposite ends of the continuum. Volume is a function, in this respect, of the speed in which the assembly reacts to energy inputs from the strings. More reactive, more volume (at attack). But the more reactive it is, by definition, the faster energy is transferred from the string and also, then dissipated, i.e. the shorter the sustain.(Readers Digest version).

    One of the challenges for soundboard builders is to figure out where on the continuum they want to be and how to get there. In addition there are certain structural requirements for the assembly to not come apart or collapse under a load for which it's not  adequately designed.

    When we're discussing safety margins, one of the considerations is that the greater the safety margin, i.e the more substantial in terms of load bearing properties, the less reactive the assembly will be which will result in lower volume and greater sustain.  Finding the sweet spot where we build an assembly that adequately supports the designed load while remaining reactive enough to produce adequate volume but not so reactive as to dissipate energy too quickly and compromise sustain is the great challenge. There are obviously other considerations but that is a fundamental one and at the heart of the discussion.

    Thanks for participating.

    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 77.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-19-2017 22:24
    I don't have an answer to that question.  I always extend the rib ends into the inner rim notches and typically the thickness of the end of the rib coincides with the depth of the notch which is about 5-6 mm (slightly less on the belly rail side of the top three ribs). In addition I use a traditional scalloping rather than a straight taper as some RC&S people do.  


    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 78.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-19-2017 12:20
    Regarding M.O.E. (Modulus of Elasticity) the measurement of a load placed on an object and how much that object deforms to that load.
    In species dependant structures like a beam, MOE is a reliable constant to predict the deflection. However, published M.O.E's are based on open beams (the ends pivot up). For closed beams (the ends are secured) the constant would need to be adjusted to give that same reliability of predicting the deformation. 

    The arch is not strictly species based, but by its very nature a design element is introduced that adds to the structure. Further, a soundboard is glued around its perimeter (unlike a closed beam) and has even more design advantages. 

    This is why i have what i call S.M.O.E. (Soundboard Modulus of Elasticity). I measure each original soundboard before removal. This gives an actual reading of how that particular soundboard deforms to the load placed on it in the deflection formula.   A species M.O.E looks like this 1,560,000.
    But S.M.O.E is a series of numbers.
    One particular board looked like this:
    12  2,000,000
    11  2,000,000
    10  2,500,000
    9    3,500,000
    8    5,000,000
    7    5,000,000
    6    7,000,000
    5     9,000,000
    4    10,000,000
    3    11,000,000
    2    14,000,000
    1    12,000,000

    Every soundboard is unique, and has it's own sequential pattern. These are adjustments to the constant in the deflection formula that give reliable predictions of that soundboards reaction as is or to any modifications made.

    If the species M.O.E (1,560,000) were used throughout the sequence, that would give a false reading and look like the board was overloaded. And hence lead one to think the ribs are too small and increase their size. Thus adding undo stiffness.
    Reading that David has been questioning the overbuilt structures, makes me think a wrong M.O.E is the reason why.



    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 79.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-19-2017 21:58
    <...So it seems to me that all current soundboard making processes have some degree of compression and differences are only a matter of degree.

    I see a couple of points to consider...

    1- Its is entirely reasonable to ask what the relatively small difference between a tiny 2 point range of EMC.s might have on a structure's as-built impedance....stated in the way you stated it, it does seem rather negligible.  However stating the question the way you have, misses the central point of using compression as a structural tool.

    The point of a true compression board is to bring the board right to the point where the wood fibres can no longer compress further. Compression belly-folks cite that in setting DB,  they smack the board and wedge it under the plate until it stops deflecting. "Until it stops deflecting" means it hits the limit beyond which the panel cannot deflect further without experiencing compression failure. As in any threshold, the amount of energy needed to deflect the further through that threshold is considerably greater than at any point previous to arriving at the threshold.  At this "threshold of compression failure" the stiffness of the system is significantly higher than its deflected but shy of the compression threshold condition. Actually held at the threshold, its a qualitatively different board and different structure, than 1 point shy of the threshold. 

    So I don't think your question can be asked without making clear how close this 2 point range is to the compression limit of the panel. If we are talking the difference between 10 and 12%...the difference will be negligible...agreed. Between 6 and 4%, the 4% is very close to a threshold which redefines the whole ball game. This close to the compression limit, an ambiguity zone is created, because where that compression limit actually is, cannot entirely be known. (see #2)

    Between 5 and 6% ...ehhh...negligible I think...The rib scale, and the glue joint interface between rib and panel is producing the structure with small amounts of stiffness contributed by the 1% differential...assumng the board is actually at 5-6%, or higher.  Between 5-4%, again one is approaching the redefinition and ambiguity threshold.  

    The true compression board, ie the board at the threshold of compression failure does not just have some compression, similar to, if not negligibly more than a board ribbed 2 points higher. It is a qualitatively different structure. Once it passes the limit of compression failure, its all ribs. If the ribs were designed with the expectation that the compression threshold would add significantly to the structure, there will be a problem. Living in New England we experience how unforgiving this threshold is to a belly...maybe not that unforgiving in Seattle or SF, but in Boston, the evidence is plentiful and unforgiving.  

    2-When we bring this 2 point spread this close to the compression limit, the limits of what can be known about the board's actual emc at ribbing, is at or beyond the limits imposed by experimental error. Experimental error is real and it is inescapable. When attempting to hit a target that small, where the measurement devices are already at or beyond their lower limits of effectiveness, where the tolerances of the devices are also exceeded, where piece-to-piece differences of the wood panel are unknown,  the limit of what we can know about ribbed board's actual emc, as relates to its proximity to the fiber compression threshold, are unknown. We don't know for sure whether we are; much too close to fiber failure, close to design intent, or too far from the compression limit, given the rib sizing. One cannot know which of these apply to a particular board until its too late, this unknowing imposed by the limits of experimental error. 

    So I think the question is not what is the difference between 5 -6%...its probably very little...but rather how close is this target range to the threshold of compression failure...how close it it to the point where the structural capabilities of the panel become something to plan on.
      
    -----------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 80.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-20-2017 00:09
    See comments interspersed. 


    I see a couple of points to consider...

    1- Its is entirely reasonable to ask what the relatively small difference between a tiny 2 point range of EMC.s might have on a structure's as-built impedance....stated in the way you stated it, it does seem rather negligible.  However stating the question the way you have, misses the central point of using compression as a structural tool.

    The point of a true compression board is to bring the board right to the point where the wood fibres can no longer compress further.

    Is that true?  I think I would argue with that.  

    Compression belly-folks cite that in setting DB,  they smack the board and wedge it under the plate until it stops deflecting.

    I do compress the board before setting bearing (in the process of planing the cap to the proper height) but I don't compress until the board stops deflecting, just enough to take the "slack" out of the board.  That's pretty typical.  It's also unclear whether you could compress the board to the threshold of its elastic limit by pounding on it with the palm of your hand.

    "Until it stops deflecting" means it hits the limit beyond which the panel cannot deflect further without experiencing compression failure. As in any threshold, the amount of energy needed to deflect the further through that threshold is considerably greater than at any point previous to arriving at the threshold.  At this "threshold of compression failure" the stiffness of the system is significantly higher than its deflected but shy of the compression threshold condition. Actually held at the threshold, its a qualitatively different board and different structure, than 1 point shy of the threshold. 

    I agree if that were the case, but I don't think the board being held at the threshold is an accurate assessment.  The soundboard assembly is non-linear whether it's a compression crowned, hybrid or RC&S board.  The more you compress it the stiffer it gets.  The RC&S board may start out earlier in the compression cycle and therefore appear to be a more linear construction but it's not linear, it just starts a bit farther left on the curve. 


    It is worth considering whether stiffness achieved through compression (whether it's panel or downbearing) is the same as stiffness achieved through construction, say using a stiffer rib scale with less downbearing.  From my experience I believe that acoustically they perform very differently.  With respect to your previous comments, boards that are held at the threshold, as you describe, will typically sound "choked". When you compress the board down to where it can't move (to hold the board down to its threshold requires that the board can't move up either) then you will hear that and it won't be a good thing. So I don't believe that compression crowned systems are either designed to perform that way or sound best when they are set up that way.  The spring is certainly compressed but there is still (and must be!) latitude for the board to move both up and down when set in motion by a vibrating string.  The internal dynamics and opposing forces that exist in a compression system versus and "non-compression" system are worth exploring (as I mentioned previously) and it's a question I'm trying to answer that would explain a lot about the differences that I hear.
     

    So I don't think your question can be asked without making clear how close this 2 point range is to the compression limit of the panel. If we are talking the difference between 10 and 12%...the difference will be negligible...agreed. Between 6 and 4%, the 4% is very close to a threshold which redefines the whole ball game. This close to the compression limit, an ambiguity zone is created, because where that compression limit actually is, cannot entirely be known. (see #2)

    Between 5 and 6% ...ehhh...negligible I think...The rib scale, and the glue joint interface between rib and panel is producing the structure with small amounts of stiffness contributed by the 1% differential...assumng the board is actually at 5-6%, or higher.  Between 5-4%, again one is approaching the redefinition and ambiguity threshold.  

    The true compression board, ie the board at the threshold of compression failure does not just have some compression, similar to, if not negligibly more than a board ribbed 2 points higher. It is a qualitatively different structure. Once it passes the limit of compression failure, its all ribs. If the ribs were designed with the expectation that the compression threshold would add significantly to the structure, there will be a problem. Living in New England we experience how unforgiving this threshold is to a belly...maybe not that unforgiving in Seattle or SF, but in Boston, the evidence is plentiful and unforgiving.  

    We can experience that here on the west coast as well if the board is exposed to lots of periods of very high humidity where compression damage to the panel is done.  On the other hand I've also seen panels that have lived their life on the west coast in fairly benign conditions (no real periods of excessive humidity) where compression crowned systems survive very well and for a long period of time.  I think it's reasonable to assume most wooden musical instruments will suffer when exposed to large swings in humidity whether they are pianos, cellos or oboes. Perhaps RC&S boards are less prone to over compression by a small factor (10% RH) but then we need to ask the question why are we building the panel the way we are?  Is it because we think it will last longer under some conditions or because we think it sounds better (perfectly willing to accept that it might be both--but not yet convinced)?  And then what does that say about hybrid systems?    


    2-When we bring this 2 point spread this close to the compression limit, the limits of what can be known about the board's actual emc at ribbing, is at or beyond the limits imposed by experimental error. Experimental error is real and it is inescapable. When attempting to hit a target that small, where the measurement devices are already at or beyond their lower limits of effectiveness, where the tolerances of the devices are also exceeded, where piece-to-piece differences of the wood panel are unknown,  the limit of what we can know about ribbed board's actual emc, as relates to its proximity to the fiber compression threshold, are unknown. We don't know for sure whether we are; much too close to fiber failure, close to design intent, or too far from the compression limit, given the rib sizing. One cannot know which of these apply to a particular board until its too late, this unknowing imposed by the limits of experimental error. 

    So I think the question is not what is the difference between 5 -6%...its probably very little...but rather how close is this target range to the threshold of compression failure...how close it it to the point where the structural capabilities of the panel become something to plan on.

    Granted ribbing at 5% rather than 6% puts you theoretically closer to compression failure. I also agree that we are not able to determine with absolute certainty where that point is given the inherent variations in different species, different grain configurations, and variations in specific gravity that might occur within the same species.  Does it put us closer enough to worry about it? I don't think so.  Can we use spread sheets and engineering formulas to determine a close enough approximation of where that point is and whether we are in danger of crossing it?  I think we can.  

    The further question to ask is this: we can certainly build a board that will be less likely to experience compression damage by, say, limiting the amount of panel compression, increasing rib scales and reducing deflection characteristics, reducing downbearing loads, using alternative materials or just abandoning the current paradigm altogether and going off in a new direction, something I think Wayne Stuart tried to do with his unique rib structure (among other things--see picture below).  If we can do that and get the sound we want then why not.  But it begs the question.  With the current paradigm can we get the sound we want by designing something with a guaranteed safety factor under all conditions or do we need to get a bit closer to the edge to really appreciate the view?  So far I think we need to get a bit closer to the edge and I don't think we need to worry about falling off the cliff.  

    Stuart and Sons Piano Soundboard

    David Love


    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 81.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-22-2017 11:34
    BTW, I was thinking about the statement " the rib wants to go back to being straight" thing this morning.
    I think that is a false statement.
    So I went to my current pre cut "straight" rib stock(about 50 pieces). And guess what, not a single piece was straight. Every piece had a natural bow to it. At least half way, but some were a full 60' radius. So a simple observation says wood naturally wants to bow (crown) not be straight. Certainly, if the bow wasnt taken advantage during the construction of the soundboard, that could lead to early fatigue.

    Here's a true side story:
    I'm offering free consultation a local tech who can't afford me (hey, I don't do soundboards on the cheap, too much work) Every once in a while he asks for my advice. The other day, he asks "what species to use?" I told him that Jeffries in Knoxville has some beatiful Eastern White pine at the moment.
    I cautioned him (this is me playing a prank) to taste the wood first! I told him that if it's bitter then don't buy it, only buy it when it's sweet. This assures the resin is low.
    He texts me back " oh, that's amazing, I didn't know that! Thank you so much!"
    I know the owner of Jeffries very well. He'll tell me if he sees anyone licking the Eastern White Pine!
    Could be my best prank ever. I'll let you know.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 82.  RE: Correcting Steinway B SoundBoard Stresses

    Registered Piano Technician
    Posted 06-22-2017 15:30
    I don't agree with that.  If a panel bends a rib in the process of panel compression the rib will want to straighten back to its original condition, whatever that was.  The question for me is what happens when you glue the entire dome shaped assembly with compression bent ribs into the rim.  What happens to those forces.   

    I believe the answer has something to do with the location of the neutral axis once you glue the beam to the 8-10mm thick soundboard panel in addition to how forces are distributed once that entire assembly is buttressed into the rim.  

    http://courses.washington.edu/me354a/Curved%20Beams.pdfhttp://courses.washington.edu/me354a/Curved%20Beams.pdf



    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 83.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-22-2017 18:43
    No problem David. My understanding is that whatever crown that comes to be before glue-in becomes the neutral. Then after glue-in the further on going compression adds hygroscopic strength. I believe the past pianomakers took advantage of that phenomenon by making the boards slightly undermassed  (I consistently see roughly a 1/2 sq.in. shy). Then as time went on the hygroscopic force dissipated away and the load became solely dependent on the ribs, which alone are not of quite enough mass and fatigue sets in. I don't believe that "rib wants to be straight thing" because fiber fatigue has to happen first.

    Overall its an interesting concept to use a phenomenon to accomplish a lighter structure that can last decades.







  • 84.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-25-2017 16:57
    Hi David,
    I read that PDF you linked to.  Did you realize it's based on three "Assumptions"? That's the problem, most of the time, with articles like that.  Assumptions by their very nature are not necessarily based in fact. I think #3 Modulus of Elasticity might not apply as stated to hygroscopic soundboards. As you know, there is a big chasm between writing about theory vs building the thing.  Safe to say the soundboard is a unique structure, so I would put more credence into your statements than theirs.
    -Chris

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 85.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-23-2017 05:08
    Chris - I didn't know it was 1st April today!!? And not to forget a tin of striped paint . . .     Michael   UK





  • 86.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-25-2017 11:49
    Chris - I'm trying to understand what you are doing with your soundboard/rib analysis.

    Profile: 74%  -  What is this? 74% of what? How is this calculated? What does it mean?


    Stress: 2,208 psi  -  Is your "stress" downbearing pressure measured somehow? Maybe total string tension?


    Load: 975 -  Is your "load" downbearing pressure on the bridges? Measured in pounds?


    10.6 sq.in  -  What is this? Bridge area? Rib total cross-sectional area?

    Thanks.

    ------------------------------
    Terry Farrell
    President
    Farrell Piano Service, Inc.
    Brandon, Florida
    813-684-3505
    ------------------------------



  • 87.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-25-2017 15:06
    Welcome aboard Terrence,

    I'll explain my system for you.

    I look at seven elements to evaluate a soundboard

    1)Force (lbs)
    2)Area (sq. in)
    3)Panel Sq. ft.
    4)Rib Count
    5)Profile%
    6)Stress (Lbf)
    7)Deflection (inches)

    I avoid using the word "downbearing" because it adds confusion with " bearings" in the stress formula. Downbearing is from the strings perspective, we want to be thinking  from the soundboards perspective. The "bearings" is the rim support on either end of the rib.   To determine the load (force) i simply get the string tension and divide by 40.   For example  39,000lbs / 40 = 975 Lbs.  Obviously, the load is distributed across the soundboard. This is actually turning out to be the most complicated part and is a work in progress. What I am currently playing with to determine the distribution is:
    1) Tune to the strings A-440
    2) Place dials under each rib
    3) Remove the strings and record the range of movement of each rib. With this info I can calculate a fair approximation of the load distribution. 
    Here's an example on a chart. The top Orange Line is a 60' Radius reference. The Red line is the actual measured crown. The dotted line is the range of movement when loaded. The largest range of movement was .060


    "Square Inch" is the aggregate area of all the ribs. 

    H x W = area of each rib. Then add up all the areas to get the aggregate square area.  In the photo its 10.8.

    Notice also that together it's the F/A formula used in physics. It averages 100 lbs for every square inch in soundboards.

    The profile is the ratio of the aggregate Height to Width relationship. H x 100 / W. In the photo its 10.68 x 100 / 13.04 = 82%.   I like to get the profile down into the low 70's. I increase the mass a little for strength, and accept a slight wider range of deflection. This increases the sustain and gives a board a lower tone on a tap test.

    Panel square feet and rib count help with categorizing when comparing boards to each other and between different makers.  For example, an interesting study would be to compare a "12 sq. ft. board w/ 12 ribs" to one with "12 sq. ft. board  and 13 ribs".  What advantage is the extra rib?

    The formula for calculating stress is M/Z =Stress (Moment / Section Modulus). It's the F/A formula again but in disguise.
    Moment is Force applied at a distance. The formula to calculate Moment is A x a. There are 3 types of ribs 1) force in the center  2) Force off center 3) Two forces.  I'll just explain force in the middle.  Lets say a 24"rib is loaded with 50 lbs in the center. That means the bearings (a and b) are both 25 lbs and the rib is divided into 2 parts (A and B).  So Moment is 12" x 25 lbs = 300 inch pounds.

    Section Modulus is H^2 x W/ 6.  So if we have a rib that is .87 in height and 1.01 in width we would have .127
    That would equal 2,362 Force pounds (Lbf).  300 / .127 = 2,362
    Again that was one rib. The stress number I give a board is the aggregate stress of all ribs / rib count.
    Hope that helps TF.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 88.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-25-2017 16:26
    A quick note on why Force, Area, Profile and Stress are important numbers.

    Force and Area:
    I like at least 1 square inch per 100 lbs of force.   Not uncommon to see a board loaded with and holding up 1,000 lbs., with only 8 square inches of mass. Usually a designer will design the ribs to be tall. But tall ribs add stiffness, not necessarily add strength.  A Depression Era  Heintzman I once rebuilt had a profile of 94%, and had 8.0 Square inches of mass to hold up 880 lbs. It was flat.
    Now I think its an amazing act of engineering to take that, and lower the profile and make the rib structure stronger.
    I was able to reduce the profile to 78% by adding mass to the widths and reducing the heights. The final numbers were 8.8 square inches holding up that 880 lbs. F/A = 100 to 1.  Boards that are under-massed succumb to fatigue. A 78% profile is a heck of a lot more flexible than a 94% profile.

    Stress is important to know because of wood behaviour. Roughly, wood ruptures at 10,000 lbf, it remains elastic between 0 to 4,000 lbf, and it becomes "plastic" beyond 4,000 lbs. A tradition safety factor puts the bending stress in a comfortable middle of the elastic zone. Usually between 2,000 - 3,000 lbf.  For example if I designed the Heintzman with the proper mass and a 94% profile it would be stressed around the 1,200 lbf range. Why do that unnecessary stiffness? 

    My system is simple ( no ego elite-ism here), its effective ( offers data you can actually manipulate), and it works on all styles of soundboards;  Hygroscopic, RC&S, Laminated  and Carbon fiber boards whatever, Even Stuart and Sons, but that would be a pain (actually, I could improve their pianos greatly).

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 89.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-25-2017 17:18
    A quick question for the " Rib wants to be straight again" guys.
    Here's a picture of wooden coil springs.Does it want to be straight again?
    Or does the design make it behave differently?
    As I see it, a straight rib behaves differently that a laminated rib ( the cross grained rib/panel combo).



    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 90.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-26-2017 09:30
    Does it want to be straight again?

    A straight rib is straight, not coiled. A straight rib with a force acting on it to make it bent slightly will want to go straight again.

    Or does the design make it behave differently?

    Does what want to make it behave differently? Steam bending it into a coil? Sure. You do something to the strip of wood (rib) to effect a permanent shape/bend of some sort and it will tend to stay that way. I have steam bent 1"x1" white oak ribs in my Folkboat - steam bent into an "S" shape. I can guarantee that if I removed one, it would more-or-less stay in that steam-bent "S" shape. However, if I took the unbent rib, applied a force to the center of it to put a small bend in it and then let go, it would go back to straight.

    As I see it, a straight rib behaves differently that a laminated rib ( the cross grained rib/panel comb

    Why? A straight piece of spruce should perform similarly to an otherwise similar laminated piece of spruce. The laminated rib would tend to be a bit more consistent in properties, but otherwise similar. Some say it will be a bit stiffer - I'm not sure of that - haven't read of any research on that topic. I've done some crude testing in my shop and they seem to bend about the same under the same load. AND they straighten back up after the load is removed!

    ------------------------------
    Terry Farrell
    President
    Farrell Piano Service, Inc.
    Brandon, Florida
    813-684-3505
    ------------------------------



  • 91.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 06-29-2017 14:48
    Mr. Farrell said:
     "A straight rib with a force acting on it to make it bent slightly will want to go straight again".  
    First of all Mr. Farrell, Hygroscopic ribs are not straight ribs. They are Laminated Hygroscopically Arched ribs. If a builder uses them correctly they will even be naturally bowed as well. Secondly, the whole point of your sentence is not true. It depends on how much force is applied. Read my post above above wood behaviour and the elastic and plastic zones. Or google it.


    Mr. Farrell said:
    "You do something to the strip of wood (rib) to effect a permanent shape/bend of some sort and it will tend to stay that way.
    That's why I've been saying its not a straight rib anymore.
    See, I said this:

    As I see it, a straight rib behaves differently that a laminated rib ( the cross grained rib/panel comb

    And then to disagree with me  Mr Farrell says:
    Why?  A straight piece of spruce should perform similarly to an otherwise similar laminated piece of spruce. removed!

    I was trying to follow your line of thinking Mr Farrell, but the contradiction kept hindering me from doing so.

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------



  • 92.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 07-01-2017 09:23
      |   view attached
    Attached is a pdf of a simple bending stress experiment to determine youngs modulus of different materials.

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    ChrisChernobieff
    Chernobieff Piano and Harpsichord Mfg.
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com
    www.facebook.com/ChernobieffPianoandHarpsichordMFG
    ------------------------------

    Attachment(s)

    pdf
    Bend Test of wood.pdf   1.45 MB 1 version


  • 93.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 07-05-2017 03:43
    I wonder if Jim would be so kind and fill in the remaining #8-14 H, W and L, so I could study the altered Knabe's tonal palette?


    ------------------------------
    ChrisChernobieff
    Chernobieff Piano Restorations
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com chrisppff@gmail.com
    http://chernobieffpiano.com/
    The Declaration states, "We hold these Truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty, and the Pursuit of Happiness…."
    ------------------------------



  • 94.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 07-12-2017 09:32
    Ok Jim, I'll just take that as a refusal to share. Thanks

    ------------------------------
    ChrisChernobieff
    Chernobieff Piano Restorations
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com chrisppff@gmail.com
    http://chernobieffpiano.com/
    The Declaration states, "We hold these Truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty, and the Pursuit of Happiness…."
    ------------------------------



  • 95.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 07-17-2017 23:40
    So Steinway gets the parabolas wrong, scalloping randomly done, and everybody just copies it.
    Not Me.


    ------------------------------
    ChrisChernobieff
    Chernobieff Piano Restorations
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com chrisppff@gmail.com
    http://chernobieffpiano.com/
    The Declaration states, "We hold these Truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty, and the Pursuit of Happiness…."
    ------------------------------



  • 96.  RE: Correcting Steinway B SoundBoard Stresses

    Posted 07-17-2017 23:55


    ------------------------------
    ChrisChernobieff
    Chernobieff Piano Restorations
    Lenoir City TN
    865-986-7720
    chrisppff@gmail.com chrisppff@gmail.com
    http://chernobieffpiano.com/
    The Declaration states, "We hold these Truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty, and the Pursuit of Happiness…."
    ------------------------------