Pianotech

Topic: Correcting Steinway B SoundBoard Stresses

1.  Correcting Steinway B SoundBoard Stresses

Posted 05-22-2017 14:36
Edited by Chris Chernobieff 05-22-2017 14:38
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.

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ChrisChernobieff
Chernobieff Piano and Harpsichord Mfg.
Lenoir City TN
865-986-7720
chrisppff@gmail.com
www.facebook.com/ChernobieffPianoandHarpsichordMFG
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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
Edited by Chris Chernobieff 05-23-2017 10:32
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.

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Terry Farrell
President
Farrell Piano Service, Inc.
Brandon, Florida
813-684-3505
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5.  RE: Correcting Steinway B SoundBoard Stresses

Posted 05-24-2017 14:37
Edited by Chris Chernobieff 05-24-2017 14:40
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

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

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

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

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

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Peter Grey
Stratham NH
603-686-2395
pianodoctor57@gmail.com
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12.  RE: Correcting Steinway B SoundBoard Stresses

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 15 days ago
Edited by Benjamin Sloane 15 days ago
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?

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Benjamin Sloane
Cincinnati OH
513-257-8480
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14.  RE: Correcting Steinway B SoundBoard Stresses

Posted 15 days ago

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

Posted 14 days ago
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

Posted 14 days ago
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 2 days ago
Edited by Benjamin Sloane 2 days ago
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.



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Benjamin Sloane
Cincinnati OH
513-257-8480
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18.  RE: Correcting Steinway B SoundBoard Stresses

Posted yesterday
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 30 days ago
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 30 days ago
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 30 days ago
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 29 days ago
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 29 days ago
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 29 days ago
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

Posted 29 days ago
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.

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Karl Roeder
Pompano Beach FL
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26.  RE: Correcting Steinway B SoundBoard Stresses

Posted 29 days ago
  |   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   324K 1 version


27.  RE: Correcting Steinway B SoundBoard Stresses

Posted 29 days ago
"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

Posted 30 days ago
Edited by David Love 22 days ago