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Rib height or width?

  • 1.  Rib height or width?

    Posted 04-09-2018 20:14
    In another thread Mr Chernobieff wrote:

    "On width, usually the top 5 treble ribs are too narrow, you can mic them yourself, anything less than 1.00" is a problem rib. "

    First off, I use a caliper for this measurement  and not even a good one as anything under a 64th of an inch is beyond my woodworking skills to duplicate. Why not leave the width the same and change the height? That way one doesn't have to change the notch in the inner rim. Mr. Chernobieff doesn't strike me as someone that does things haphazardly so I'm guessing he has a reason. Perhaps others will venture an opinion.

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


  • 2.  RE: Rib height or width?

    Posted 04-09-2018 21:41
    Edited by Jim Ialeggio 04-09-2018 21:48
    We all have rather incomplete models we use to tease out what makes a board function...all of us. Chris is speaking a language that is not consistent with my model. Though I can build a real nice sounding instrument, I don't by a long shot have all the answers, and have  reasonable doubts about how I view my own model. That means I continually challenge my own assumptions.

    Chris's model appears not to be primarily an impedance model. What would be very helpful, in describing his model, would be a good un-messed with recording showing how the flexible systems he favors behaves in the problem areas of the scale...that being A4-A5.  Low bass really is not a defining area, as it can function well with a flexible system.

    Dead bellies often retain an acceptable bass, so low bass response really is not helpful, in my view, in evaluating the success of a design. The test of a design is A4-A5. It is unforgiving, even in a new board. The tendency in this area is for there to be local dead zones. I have observed this in pianos of all the major brands, as well as the extremely expensive brands. The dead zones can be located higher of lower in pitch depending on either the overall stiffness of the entire system, or localized inconsistencies, but they are mostly either extant or threatening to rear their ugly heads. Fine unison tuning in these areas, even in new instruments, is paramount, as there is no forgiveness either in our ears at these frequencies, or in the piano's  system.

    So, a question for Chris:  A new Steinway piano heads to a showroom, sounding quite nice in the problem areas. As it ages the problem areas become first noticeable, then worse and worse. Eventually they are tonally non-responsive and the utmost care in voicing is required to have these areas behave in a remotely musical fashion. Even with fine regulating, changing out worn hammers, etc, the challenged areas don't respond, and require constant attention. Since your model does not recognize diminishing structure as an issue (I think, if I am understanding what you have written) what has changed?  This is a question Chris, not a challenge, in order to try and understand what you may or may not be discussing in your model. (samples of the sound are essential, now that you have reasonable
    recording capabilities.)

    In contrast with the A4-A5 alto capo, what about the high treble, as per Carl's question. For me, as my high trebles start to take off, my own model shifts from an impedance model to termination conditions/hammer mass/string pivot model, AKA Ed Mcmorrow's work. These days, I'm not even sure, how important the ribs are at all, in the top capo...its really a termination game. Perhaps that's what Chris is getting at, and why he feels wider ribs with less height, which are significantly less stiff than a skinnier-taller rib, make more sense there.  I should also add here, that as I have challenged my understanding of this top capo, I have noticed that the top capo does not "die" as the A4-A5 area does. The bridge falls apart and the terminations cease to function well, but fix those issues, including the use of low mass hammers, and a board that is not functioning in other areas, still functions adequately(top capo).




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



  • 3.  RE: Rib height or width?

    Posted 04-10-2018 01:40
    Why is <1" a problem?  Doesn't it matter the height, number of ribs in the section, width of the soumboard, rib material, to name just a few other factors?  There's nothing magic about 1".

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



  • 4.  RE: Rib height or width?

    Posted 04-10-2018 10:52
    **Long Post**

    Ah, my favorite topic!

    Installing a soundboard is very labor intensive. For too long, my normal procedure was to merely copy the original. Then came the Heintzman grand. After installation I did a standard tap test and was sorely disappointed. It just didn't have the liveliness that a new board should have. Thank goodness I recorded the info. The board had a 3/8"+ thick panel, and the ribs had what I now call a high profile (7/8" x 7/8") throughout. The result is an uneven section modulus and an uneven proportioning.

    (Blue line is section modulus curve, red line is rib transition smoothness, treble on the left)

    Thus, and so far, a three year research project began. I have been collecting soundboard data, listening to pianos, and observing rib scales and related problems etc etc. At first, one would naturally think that all ribs are the same and don't do much, therefore dimensions don't matter.  But, just like string scales, there are many decisions to be made when it comes to a rib scale. Many different rib scale plans.

    Steinway uses the plan of an 80%+ rib profile,  7 belly rail ribs ( the rest are spine ribs), with the top belly rail ribs getting smaller and narrower in an inconsistent fashion ( why widen the fields in the treble?). On the rare occasion when I come across a Steinway that sounds fuller and more alive than most others, the rib scale profile (so far) has been between 71% -76%.  But they always have poor rib scale transitions.

    Here's my latest rebuild a Steinway A pre 1900 original scale.

    Now, when you have a rib scale this horrible, you need riblets, you'll have dead spots, etc etc. To answer Jim, my belief is that some ribs are worker harder than others, when they all should be working as a team.

    For comparison, here is the Steinway A rib scale modified.

    Silky Smooth.

    This Steinway A went back to the Nashville technician, who has sworn to give me an honest feedback. Good or Bad. I am eagerly waiting.

    Yes Jim (LOL) I will be producing recordings. I already have two professional pianists that will gladly perform, lined up.

     

    Here are some fundamentals that I have settled on that give good and consistent results and deliver a sound quality that I like.

    The rib count should equal the panel square feet. The sum of the width of the ribs should also equal the panel square feet.

    Example:

    12 square feet panel

    12 ribs

    Rib widths equal 12" ( Thus 1" wide ribs)

    This does a few things. Creates evenness across the scale, provides smooth transitions, smooth section modulus curves. Allows for a 70% rib profile by adjusting heights and maintaining the section modulus TARGET. Allows for even and smooth Volume to length curves. Plus, it's simpler to deal with one parameter than juggle two.

    A characteristic that I have noticed in the last few boards since adapting this method is a surprising carrying power. The piano seems to be more powerful the farther away you get from the piano.  The Mason and Hamlin BB I recently did seemed to ROAR when I stepped across the room. I've heard many different pianos, never heard one do that, like that before. Certainly was motivating for me.

    The ultimate goal of course was to come up with a product that impresses the clients, so the business will grow. Time will tell.

    -chris



    ------------------------------
    A hunter's drumbeat steers the stampeding herd,
    His belly growls in hunger to what he sees.
    The mammoth aware blows his mighty trumpet,
    But alas, the caveman tickles the ivories.

    chernobieffpiano.com
    865-986-7720
    ------------------------------



  • 5.  RE: Rib height or width?

    Posted 04-11-2018 10:56

    OK I understand the derivation of section modulus but what do mean by "rib transition" and how are you calculating that. BTW here's a graph of a 17 rib board, section modulus, the widths, as you can see below, are not equal. (bass on the left)

    Width 
    22.0
    23.0
    24.0
    24.0
    24.0
    24.0
    24.0
    23.0
    23.0
    23.0
    22.0
    22.0
    21.0
    20.0
    19.5
    19.0
    18.5


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



  • 6.  RE: Rib height or width?

    Posted 04-11-2018 17:19
    David,
    Looks like you have improved some. That Modulus curve looks smoother than the last scale you shared.

    If you give me the height and length to that scale, i'll run it through my software. BTW, because of the collective strength i have gained, i am able to keep my Z curve below .045 in most cases. I've checked a couple boards that have a target z modulus under .040 that have survived time quite well, so i don't know why the extra material, .060 seems like a lot of muscle not needed.
    -chris
    #caveman




    ------------------------------
    A hunter's drumbeat steers the stampeding herd,
    His belly growls in hunger to what he sees.
    The mammoth aware blows his mighty trumpet,
    But alas, the caveman tickles the ivories.

    chernobieffpiano.com
    865-986-7720
    ------------------------------



  • 7.  RE: Rib height or width?

    Posted 04-12-2018 01:41
    This isn't a board I built it's just an example of a smooth modulus that has variable rib widths.  I've always aimed for a smooth modulus though there are other considerations that might impact how precisely smooth the curve is.  I'd be happy to run a scale by you.  Always interested in input.  I'll get something together in the next few days.

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



  • 8.  RE: Rib height or width?

    Posted 04-12-2018 13:35

    ***Long Post***

    Well I  did say "allows", not "only" LOL.

    Comments are regularly made by many regarding problems exhibited by old boards. In this case the problem octaves in Steinways.

    The cause, it seems to me, is blamed incorrectly on a method of construction, namely the hygroscopic compression crown. Thus the proposed solution is to replace that method with something else. That usually results in laminating ribs, adding more ribs, i-beam ribs, narrow and tall ribs, and uneven rib layouts. I think all of these plans just introduce other types of problems. Namely, and especially in Steinways, a different un-steinway sound. I like the description that it creates a thin sound (too much stiffness).

    Players use to describe some Steinways and other by-gone pianos as having a fat sound.

    My belief is that the root cause of the problems in compression crown boards has never been addressed. I am simply making an observation, based on analysis of numerous boards and constitutes as an opinion. I have seen some common traits such as: uneven rib transitions, incorrectly sized ribs for that location, poor rib volume distribution, wrong rib count, and as mentioned before, making the ribs narrow in the treble.

    I am also collecting data that supports my case, for example:

    I played and studied a REED and Sons Upright that was a 100 years old with a rib structure similar to what I am talking about.

    It had a nice fat sound, was in fantastic condition with no cracks and good downbearing. I did not notice any problems in the treble such as dead spots. There were some false beats.

    There were minor design flaws, but nothing horrible. Here's the data.
    Clearly suppose to be all 1" widths, but human imperfection as it is.

    Length and Volume a bit out of proportion.
    Height and widths uneven.

    Section modulus and Delta curves uneven and rough.

    For a fun exercise, here's how i would clean it up and make it more precise and efficient.



    Section Modulus and delta curves silky smooth.

    Length and volume curves in proportion
    Height and width smooth and even.


    -chris





    ------------------------------
    A hunter's drumbeat steers the stampeding herd,
    His belly growls in hunger to what he sees.
    The mammoth aware blows his mighty trumpet,
    But alas, the caveman tickles the ivories.

    chernobieffpiano.com
    865-986-7720
    ------------------------------



  • 9.  RE: Rib height or width?

    Posted 04-12-2018 17:07
    Edited by Jim Ialeggio 04-12-2018 17:08

    This is where we have to wait for a decent recording to see what various sounds you are valuing in your aesthetic actually sound like. For instance, in my book, the "roaring" of your BB, could possibly be, in my take on it, a "booming" sound...which I find highly objectionable. I remember a recording of a Marc Allen piano a couple of years ago, that had that booming bass. The description in the journal of how he achieved it was interesting. But...that booming bass was large and ungainly, and somewhat out of control...big, but out of control.  I'm not saying this is the case, and perhaps for you "booming" means high fundamental which pulses one's solar plexus. Words are not helpful past a certain point, and I think we have progressed past this point.

    Same with the "fat" sound. "fat" is what I refer to as an old Steinway structural inability to create a pitch focus, particularly in the tenor. Thick textures are indistinct and registration undifferentiated. I absolutely hate that sound, and take measures to make sure that my pianos never make this sound...hence my tendency to create a more controlled sound. Decisions are aesthetically driven. But once again, these are just words, and "fat" may mean something entirely different to the two of us...so I look forward to a sound sample, because I think you are making some interesting points.

    Re the pretty graph lines, I have lost my affinity for these graphs, as I have seen wonderful sounding string scales that look like a saw-tooth that had ADD...all over the place.  The lack of prettiness in the lines did not translate to experience of the sound, which was quite nice. That's not to say the lines are useless. But, I have gone through great trouble to create designs that looked smooth on paper, only to find that yeah...yadayada...it sounded like a piano, like all the other less beautifully smoothed designs.

    I know you are working on the sound aspect, so I look forward to that bit of data.
    .



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



  • 10.  RE: Rib height or width?

    Posted 04-12-2018 18:41
    The only piano recordings I could find of marc allen sounded thin and glassy. I suspect poor recording equipment because of the room acoustics sounded bad. 
    I totally agree words only go so far when it comes to describing sound. I'm not advocating a muddy sound, nor an overpowering bass. 
    I also agree about charts with regard to string scales, but with rib scales they are more appropriate because of their structural nature. 
    I am looking forward to recording in the future. 
    Should be fun.
    -chris





  • 11.  RE: Rib height or width?

    Posted 04-13-2018 11:02
    Just finished a Steinway A.  I took a lot of pictures during the process of rebuilding it. I think the before and after pictures are striking, since the original board was in such bad condition. The original graph shows, i think, a typical case of a Steinway Dead spot. The second graph shows that by making small changes to the scale and creating evenness, the dead spot is engineered out of it.








    Shows a problem at 4 and 5. Length and volume curves dont match.


    Silky Smooth. The dead spot is gone and the length and volume curves are parallel.  Because these changes are subtle, visually there is not much change in appearance.
    All Steinways that I have looked at exhibit this same problem area characteristic, Constriction.
    Believe it or not!
    -chris






    ------------------------------
    A hunter's drumbeat steers the stampeding herd,
    His belly growls in hunger to what he sees.
    The mammoth aware blows his mighty trumpet,
    But alas, the caveman tickles the ivories.

    chernobieffpiano.com
    865-986-7720
    ------------------------------



  • 12.  RE: Rib height or width?

    Posted 04-13-2018 16:20
    The killer octave in the steinways may be related to the mistake in strike point. Dale Erwin discovered this. I hung maybe 20 sets of hammers in his shop and I had seen his horseshoe shape strike line. When I had to do it, he showed me how to put a piece of tape so when I pulled out the action and found the best strike point, i put a mark. The line goes out almost 3mm in the first 3 notes and then goes back in 3 notes. I forget whether it was C#5 to C#6 of F#





  • 13.  RE: Rib height or width?

    Posted 04-25-2018 08:01
    Hi Chris,

    Although I agree with Jim Ialeggio about pretty looking graphs, I am intrigued by your use of section modulus and would like to delve deeper. I believe you're calculating the elastiic modulus as opposed to plastic, but the units in your graph do not correspond to what you state in text by one decimal place. Are you using bh%^2/6? If not, perhaps you can help sort me out?

    Thanks,



    ------------------------------
    Jude Reveley, RPT
    President
    Absolute Piano Restoration, Inc.
    Lowell, Massachusetts
    978-323-4545
    www.absolute-piano.com
    ------------------------------



  • 14.  RE: Rib height or width?

    Posted 04-25-2018 09:16
    Beautiful looking board. I'm curious why you used screws/buttons between the ribs. Do you feel that the bridge to panel glue joint isn't strong enough or are you employing them as micro-mini riblets?

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



  • 15.  RE: Rib height or width?

    Posted 04-25-2018 13:39
    Jude,
    They are not just pretty graphs, they are tools i use that actually help me achieve my goals.
    Very observant on the numbers!!  I like seeing others trod down the same path. I use the standard Moment Z formula (bh^2/6) regarding rectangles now. I used a different version of Z modulus ( that helped when comparing the value to another parameter) back when that chart was made that i no longer use.  The result of ongoing study and experimentation.
    Regardless, The important thing about my charts is not so much the individual rib, but the relationship each has to the others. My thinking is, If the lengths produce a smooth transitional curve, and a bridge smooths out the downward forces,  then it makes no sense to me that the rib dimensions be haphazardly all over the place. And that can be corrected with minor changes.
    Also important to mention, is that the "chart tool" is not a stand alone tool, but a small part of a process.

    Karl,
    1)Thanks, i'll take what compliments i can get on these brutal forums.
    2)Tradition I suppose, i stay as close to the original as possible unless the customer says otherwise.
    -chris

    ------------------------------
    A hunter's drumbeat steers the stampeding herd,
    His belly growls in hunger to what he sees.
    The mammoth aware blows his mighty trumpet,
    But alas, the caveman tickles the ivories.

    chernobieffpiano.com
    865-986-7720
    ------------------------------



  • 16.  RE: Rib height or width?

    Posted 04-26-2018 10:54
    I'd like to follow up specifically on the point of bridge dowels/screws;
    although it may stray slightly from the original rib dimension question,
    there is still some relevance.

    I have read several posts about use screws/don't use screws. Some
    manufacturers use them copiously, some not, and some have changed
    their methods and do so among different models. While I don't think there
    will be a definitive answer here, I would like to get input pro and con.
    This relates to the rib question, as in addition to material, I also see some
    pianos that have bridges screwed/doweled to the board through the
    ribs themselves.

    I am working on a 1918 M right now and have the ribs attached, and am
    preparing to place the board in for loading and was planning to screw the
    bridges in place for setting bearing. This poses the problem of getting the
    cantilevered bass bridge in place with accurate enough contact using only
    the two original screws between the ribs without gluing so that I can do the
    notch angles and then notch the bridge on the bench, which is part of an
    evolution from doing everything in the piano with all it's inherent problems.

    Thanks in advance for your many opinions.

    Dave

    ------------------------------
    Dave Conte
    Owner
    North Richland Hills TX
    817-581-7321
    ------------------------------



  • 17.  RE: Rib height or width?

    Posted 04-26-2018 20:34
    Related to Karls question ( that no one has attempted to answer) is rib count. How do you know when to add or subtract a rib?
    -chris

    ------------------------------
    A hunter's drumbeat steers the stampeding herd,
    His belly growls in hunger to what he sees.
    The mammoth aware blows his mighty trumpet,
    But alas, the caveman tickles the ivories.

    chernobieffpiano.com
    865-986-7720
    ------------------------------



  • 18.  RE: Rib height or width?

    Posted 04-26-2018 21:24
    Edited by Jim Ialeggio 04-26-2018 21:25
    Many different scenarios seem to function well. This puts us in the low stress position of knowing that no structural decision is the optimal decision...I like that.

    How one attaches the bridge to the panel is probably defined more by the bridge-to-panel clamping setup you have in your shop, rather than any real big make or break difference. There will probably be less weight in the doweled bridges. Whether that is a benefit or not I think is one of those hard to quantify areas, where quantifying is very difficult. This can lead one to be over-subjective.

    I would say, make the decision based on the shop process you are trying to refine. Notching the bridge on the bench has benefits besides comfort, ie improved pinning/notching  precision. If there's anything to be lost in the extra weight (not saying there is, but if...) you will probably make it up in the precision you can build into the terminations, working in the comfortable and controllable bench top scenario. Working in the piano, the last parts of the bridge notching and pinning often degrade somewhat, as one's back gets sore, so that's a down side for the in-the-piano process.

    I notch with a machine, outside the piano, bridge temporarily installed for DB measurements, screwed. One the one hand, the drilling ( a machine operation), notching, and pinning are really clean and precise (no bent pins, and no sore back). On the other hand, I find a measured/calculated DB to be quite time consuming, and requires my poor brain to work overtime, in order to avoid blowing the calculation.So, since the in-the-belly setting of DB is easier on the brain, and much less prone to calc errors, that's a plus for the that preference. But...for me working on the bench has enough going for it to make the on-the-bench tradeoffs attractive for me.



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



  • 19.  RE: Rib height or width?

    Posted 04-27-2018 10:15
    Thanks for the clarification, Chris, and I meant no disrespect by quoting Jim's comment about "pretty graphs." You will not find a more enthusiastic advocate for graphically representing and visualizing piano design data than myself. I do, however, wholeheartedly agree with Jim Iallegio in essence that as piano technicians/artisans, we live somewhere in the membrane that divides subjective from objective. And while I have also come to terms with this, I say let the good work continue into a greater understanding of what makes the piano tick.

    Regarding, rib widths: the first published recommendation for 1" widths that I recall is in Wolfendon's book. The reason given is that anything less would not provide sufficient surface area for an acceptable glue joint. This is certainly not true for a myriad of adhesives presently available.

    In my own designs, I am trying to explore the ratio and balance of mass and stiffness to a given design load. Admittedly, I have failed miserably to qualify and quantify these components with proper controls; however, I feel I have made progress. And yes, at the end of the day, I ask myself, how does it sound? Am I hearing my own personalized Holy Grail of Tone? The answer is generally no; but sometimes I think I'm very close and sometimes I learn more when I'm way off. And to echo Jim's sentiments once again, my Tonal Holy Grail is likely to be quite different from each and every person reading this. If my work is to be judged, I would hope that there would at least be a quorum of agreement that some evolution has occurred in both quality and consistency.

    In my own experiments with rib designs, I sometimes feel I have come full circle, several times (I only hope that it is more of a spiral than a circle). Specifically, in the last decade, I have backed off on stiffness and increased mass only to reverse direction with subtle modifications. In the last couple of years, I have come to the conclusion that I should be reducing mass while maintaining a requisite amount of stiffness, albeit less than I employed around 2010. This involves specific choices regarding rib dimension and crowning (relatively thinner, taller ribs with aggressive radii), lighter bridgepins and eliminating buttons as needed and rib count (balanced but not overdone). Without presenting data and graphs, I know this is more philosophical than scientific. Presently, I am working on 4 Steinway Ms, which will allow for about as good of a control as it gets in my small world.

    Anyway, I don't get to unbury myself from work often enough to visit the forums; but this thread caught my attention, and every once in a while I have to chime in and mention how much I appreciate you all.

    Have a great weekend,


    ------------------------------
    Jude Reveley, RPT
    President
    Absolute Piano Restoration, Inc.
    Lowell, Massachusetts
    978-323-4545
    www.absolute-piano.com
    ------------------------------



  • 20.  RE: Rib height or width?

    Posted 04-27-2018 12:19
    Edited by David Love 04-27-2018 12:23
    One thing to consider (if you are quantifying rib performance) is that with that kind of "aggressive" radii you will need to compensate for the large reduction in volume (erspecially on the longer ribs) and the distribution of mass in the rib to the center.  I don't cut nearly that much of a radius in the ribs (typically about 20M radius) and even then, since I am using a rectangular beam formula for calculating load bearing properties, I compensate for the loss of volume by recalculating the required height in the center of a radiussed beam for volume parity.  It's not an exact performance parallel because the bearing loads have to be intergrated over the entire length but it at least compensates for the loss of material.  If you calculate your beam strength with a uniform rectangular length and don't compensate for the radius then you will be underperforming.

    It might be worth noting that while we think of soundboards as crowned in a smooth radius, with traditional scalloping the board may well take on a more plateau like shape, especially under load.

    Re this discussion, I still don't see anything magic about 1" widths.  If the strength of the glue joint was an issue when that standard came about I don't think that's an issue now.  The distribution of load bearing between the ribs should aim (among other things) to have the load distributed smoothly across the rib scale such that no one rib is doing more or less work than it's neighbor, or at least minimize those transitional (from rib to rib) differences.  That needs to be calculated to get that right.  It can't really be done by seat of the pants flying.

    While different designers will come up with different amounts of load bearing capacity as their target given equal string scale loads, there is a practical limit to the variation that can take place without the soundboard assembly starting to sound strange or failing to perform as it needs to structurally.  That limit is also audible, unfortunately, not until after the fact.

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



  • 21.  RE: Rib height or width?

    Posted 05-02-2018 10:13
    Jude,
    You said:
    "In my own designs, I am trying to explore the ratio and balance of mass and stiffness to a given design load. "

    And you asked if I use elastic or plastic Section Modulus.
    These are related.

    Here is a basic stress/strain chart.


    There are two zones, the elastic zone and plastic zone. When a structural element ( in our case a rib) is under stress, it should be designed to stay in the elastic zone. Once the rib is stressed to the plastic zone, elasticity is forever lost. In my research of many makers, they generally followed traditional engineering principles of building in a 20% safety factor from plasticity. Over time, when a structural element is subject to a continuous load, it will fatigue, creeping closer to the plastic zone. In our trade, a 20% safety factor translates to more or less a 100 year lifespan of elasticity. Other factors as craftsmanship and proper care play in the equation. Many redesigns i see today have a much greater safety factor- 40%, 50%, etc.  There is a give and take in everything, so to gain that much safety in my opinion has to be at the sacrifice of...( well i'll let you fill in the blank).

    Elastic section modulus is a geometric property of the compression/tension couple ( in our case) of a rectangle.

    Moment is force applied at a distance, which is a rotational torque.

    Stress is Moment divided by section modulus.
    Here is a recommended video that is also helpful.
    Properties of Wood
    YouTube remove preview
    Properties of Wood
    THIS VIDEO IS PRESENTED BY TECHTRAINING LLC. IT DISCUSSES THE PROPERTIES OF WOOD BY CALCULATING THE BENDING STRESS, MOMENT OF INERTIA, MODULUS OF ELASTICITY AND COMPAING THESE NUMBERS TO THE PUBLISHED VALUES FOR THAT WOOD.
    View this on YouTube >


    -chris










    ------------------------------
    A hunter's drumbeat steers the stampeding herd,
    His belly growls in hunger to what he sees.
    The mammoth aware blows his mighty trumpet,
    But alas, the caveman tickles the ivories.

    chernobieffpiano.com
    865-986-7720
    ------------------------------



  • 22.  RE: Rib height or width?

    Posted 05-03-2018 11:20
    Graphically that might look like this



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



  • 23.  RE: Rib height or width?

    Posted 05-03-2018 18:06
    Jim,

    Thanks for your reply. Cutting down the edge of the treble rim to get the correct bridge pin angle is always a bummer for me...
    kidding, of course none of us do that, but it gets pretty frustrating, and one of the reasons I like to do it on the bench, as well,
    as you so aptly state it, results are better and fatigue is mitigated, thus helping to get better results.

    I have witnessed real arguments about putting in screws, but it seems like either way they are mechanical fasteners and I don't think the wood knows or cares. Also, weight difference is probably negligible from an overall mass standpoint. I often see boards with double the amount of fasteners, all metal screws, that sound good. One I just saw was a 1918 BB.

    Best,

    Dave

    ------------------------------
    Dave Conte
    Owner
    North Richland Hills TX
    817-581-7321
    ------------------------------



  • 24.  RE: Rib height or width?

    Posted 04-28-2018 15:06
    Chris

    What is "Z Delta"

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



  • 25.  RE: Rib height or width?

    Posted 04-29-2018 03:29

    Narrow/tall ribs is dependant on stiffness with the idea of reducing weight.  That's great for ceiling joists, but is counterintuitive to spring design. The stiffer a board is the quicker it burns up energy and dissipates it. A flexible board will take that same input of energy and slowly use it and release it. Thats increased efficiency and is easily demonstrated.
    1" wide ribs assures that the proper mass is attained while engineering the most flexibility that a board can accept.
    Keeping the same amount of mass, while lowering the section modulus is a different twist. David Love in his rescale of my Weber did this. I'm still contemplating whether this is an advantage or a disadvantage. Maybe it just offers a different tonal palette.  I like to compare boards to one another. Especially the same make and model. One parameter I use is what I call "The sum of Z".  This is just adding up all the section modulus values. The original Weber was 1.72 (in3) with a mass of .76 in3 per inch.  My approach is to stay fairly close to the original design with reputable makes. So my modification was to increase the Z (flexibility)slightly to 1.80 (in3) and lower the mass a little to .75 in3 per inch.  The .75 in3 per inch is a reliable amount of mass based on study and observation of old boards and how they survived time. Love went the other way and stiffened the Z to 1.50 in3 and also lowering the  mass to .75 in3 per inch.  Since I heard the old board, saw how the old board did over time, i don't understand the justification for changing the Z to such an extreme.  I recall now that I was criticized for under designing the Weber, but i actually increased its strength slightly over the original.  It was ironic though, that Love and I both had changed the mass to .75 in3. But that is what makes this fun when other ideas come into the mix, because it gets you thinking in ways you wouldn't think before.
    The Z Delta is my favorite parameter. Delta measures the rate of increase or decrease in size from rib to rib.
    I find it very useful.



    ------------------------------
    A hunter's drumbeat steers the stampeding herd,
    His belly growls in hunger to what he sees.
    The mammoth aware blows his mighty trumpet,
    But alas, the caveman tickles the ivories.

    chernobieffpiano.com
    865-986-7720
    ------------------------------



  • 26.  RE: Rib height or width?

    Posted 04-29-2018 10:52
    Edited by Jim Ialeggio 04-29-2018 13:17
    <A flexible board will take that same input of energy and slowly use it and release it.

    Chris,  this statement illustrates my major hesitation in buying your argument. This is not to say I think you are "wrong", but rather that the words may not be adequately describing the situation.

    There are several points here...

    1- you are speaking about the board as flexible in the singular, as if the entire compass has the same requirement to achieve adequate sustain.  Flexible, as a quantity in the singular, may exhibit excellent tonal characteristics in the bass, and horrible characteristics in the 4-6th octave. Perhaps you are thinking flexibility per unit length will be reduced automatically as the spans decrease up the scale, and its all a "singular" flexibility relative to span.

    2-contrary to your statement above, my understanding of the concept of impedance is that, the frequency of the driver, must not match natural frequency of the structure (board in this case). The reason being, as is illustrated by the famous Tacoma Narrows Bridge failure, the closer the driver frequency is to the structure's natural frequency, the more energy the structure accepts instantaneously. At worst this scenario results in catastrophic failure, as in the Tacoma Narrows bridge, and at best the classic 4th-6th octave failure of harsh attack with no sustain...read...the board accepts all the driven energy instantly...no metering...no slow release of energy.

    This is where speaking of flexibility in the singular, will mean that, since the frequency compass of the piano scale is so large, some frequency(s) in the driven compass must match a natural frequency in the board. Where there is a match, there will be an explosive zone, and needles will be invoked to mask it (to a very small degree). The physical problem is that, wherever the above "flexible"  board's natural frequency matches the driven frequency (ie the frequency of the note at  that location), there will be no metering of energy. There will be an instantaneous explosion at impact. Reducing the natural frequency(ies) doesn't eliminate this impedance match, it only shifts it lower in the scale. Increasing the natural frequency doesn't eliminate the match, it only shifts it higher in the scale.

    Though you have stated in the past that you are not working according to the impedance model, the quote above, and the whole discussion of modulus relates to the impedance model.  In the impedance model of soundboard design, the goal has been, at least this is my understanding, which I don't particularly grasp well on this point,  make sure the localized driver is lower than the localized natural frequency. This assumes, that there are local natural frequencies in the plural, not singular. Harder said than done, even with mass loading which has its own drawbacks tonally.

    Though I have learned what I do based on the impedance model, I do not accept it as the singular all powerful parameter in such a complex system as a piano. My empirical observations challenge this singularity, especially given how attention to termination conditions, play such an important role in the system's trebles. Pivot terminations, and certain permutations of Duplex scaling which try to incorporate transverse and maybe longitudinal wave behavior, in the high treble, seem to minimize the impedance aspects of the system. Impedance is but one aspect of the system, and the quote above, can be interpreted to go counter to the existence of natural frequencies and their overwhelming effect on systems.





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



  • 27.  RE: Rib height or width?

    Posted 04-29-2018 13:22
    <The stiffer a board is the quicker it burns up energy and dissipates it.


    This is incorrect. The stiffer the board, the less energy it accepts from the driver (string/bridge). This is why really stiff boards have long but weak sustain. The energy is being metered into the board extremely slowly.

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



  • 28.  RE: Rib height or width?

    Posted 04-29-2018 14:50
    What's your proof? 
    If you have no proof, then I don't know how you can challenge my statement. 
    I on the other hand have proof that my statement is true. I created a variable vibrating rib demonstration for when I give presentations. So far 200 technicians have seen it, and not one has questioned it's validity. Actually, I've heard more wows than anything else. Maybe I'll make a video of it, but then that would spoil the presentations. We'll see. 
    I'll respond to your impedance post later, it was too in depth for me to respond now, since I'm currently planting more grapes in the vineyard. Back to work I go.
    -chris





  • 29.  RE: Rib height or width?

    Posted 04-29-2018 17:37
      |   view attached
    Not pretending to know everything that Chris has presented over time, but in this single instance of understanding impedance Jim is correct.

    "The stiffer the board, the less energy it accepts from the driver (string/bridge). This is why really stiff boards have long but weak sustain. The energy is being metered into the board extremely slowly."

    See attached paper. The proof is mathematical and the concepts of impedance, compliance and power output saturate the larger world of physics. The paper hopes to shed light on the concepts, so all should be able to appreciate it.

    nick


    ------------------------------
    Nick Gravagne, RPT
    Mechanical Engineering
    Nick Gravagne Products
    Strawberry, AZ 85544
    gravagnegang@att.net
    928-476-4143
    ------------------------------

    Attachment(s)

    docx
    Impedance to List.docx   23K 1 version


  • 30.  RE: Rib height or width?

    Posted 04-29-2018 21:12
    <A flexible board will take that same input of energy and slowly use it and release it. Thats increased efficiency and is easily demonstrated.

    This is backwards as well.  The word "efficiency" in regards to the physics we are discussing, is generally referred to as a rate or perhaps a relative resistance or non-resistance to energy transfer between systems. The most "efficient" scenario is a frequency match between the driving frequency and a structure's Natural Frequency. "Efficient" in the literature means the energy transfers from one system to another very quickly, or instantaneously, or without resistance.

    In a piano soundboard system, we are actually looking for a relatively inefficient transfer of energy between strings and board. "Relatively inefficient" describes the behavior we are trying to encourage.  Impedance mismatch is another way of describing the goal. How much mismatch is another question.

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



  • 31.  RE: Rib height or width?

    Posted 04-30-2018 10:03
    Honestly, The word "impedance" has always bothered me a little, I think, because of its non-pragmatic nature.
    Approaching instrument making from a science and physics point of view, historically has not proven its case. One just has to observe some of the best instrument makers that ever lived, to see they learned their craft in a shop setting.
    I read Gravagnes article, but i don't think it meets the burden of proof. The math is ok, but the interpretation i question.  Also, there is a little comparing of apples to oranges thing going on.  Comparing an imaginary cast iron soundboard to an imaginary drum head with a thin membrane?  Or should i say imaginary apples and oranges?
    How about an apples to apples comparison. I think the result is different.

    Timpani:
    Ludwig Universal Timpani Drums
    YouTube remove preview
    Ludwig Universal Timpani Drums
    These 3 timpani have been modded to take heads that are 3 inches larger than the bowl. So the 23" has a 26''head. The 25 has a 28" head. The 28 has a 31" head. Great for projection but all the extra vibration is creating some rattling issues that will be fixed for future vids.
    View this on YouTube >


    Small drum:
    The Smallest Drumkit in the World - maybe!

    YouTube remove preview
    The Smallest Drumkit in the World - maybe!
    View this on YouTube >


    You can hear it yourself. The more flexible drum head (the timpani) sustains longer than the small drums (stiffness).
    This confirms my variable rib demo also, the stiffer the rib is, the faster it vibrates and shorter the sustain is. To move the rib fast takes up the input of energy quickly. When i make the rib flexible, it vibrates slower and longer with the same input of energy.
    It's the same rib.
    Now to be fair, my varible rib demo adjusts the flexibility/ stiffness by adding and removing weight.  I think this is a fair representation of the 2 different rib profiles in action. A narrow tall rib will treat a downbearing weight lightly, and a short wide rib will treat that same weight heavily.
    If i'm missing something in the reasoning, i'm open to hearing why.
    I do think in the plurality, since there is a plurality of ribs.  But for purposes of comparing one board to another, i have various parameters that i have reduced to a