Discussion: View Thread

A Refinement of Equilibrium for Maximum Soundboard Flexibility

  • 1.  A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-23-2016 23:11

    For optimum resonance the string scale and rib scale must be in equilibrium. If the string scale is altered, then so must the rib scale also be altered.  Of course, this also assumes that the original designer put it in equilibrium in the first place. If not, then that too must be fixed. Afterall, you wouldn’t want the new board to go flat like the original did.

    Due to the-

    1. Strings changing lengths, angles, and fanning.
    2. The curvature of the bridge.
    3. The angles and spacing of the ribs

    These combined factors create a downward force that is uneven across the soundboard. In fact, each soundboard has its own “signature”.

    Below is an example from a Heintzman Grand.

    s1Gxt7rgTFCUnvJHmTZH_Heintzman original rib scale.jpg

    The blue line is the downward force across the soundboard. The red line is the rib structure that is suppose to support it.

    Notice that they are not synchronized. They should be so that each rib can be efficient in its job. Not too weak, nor too stiff. The true state of equilibrium.

    Below is the corrected rib structure for the Heintzman that now correctly supports the downbearing force. This was achieved by changing the dimensions of the ribs accordingly. As shown by the parallel contours of the lines.

    QwFAMc7lTKawzNva5rd7_Heintzman Modified rib scale.jpg

    This refinement allowed the soundboards flexibility to increase by another 3% in the Heintzman beyond the 20% that I had obtained from the earlier modification. Thus reaching the maximum flexibility that the Heintzman board would allow.

    Maximum flexibility equals maximum resonance.

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


  • 2.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-23-2016 23:16
    Hi Chris,

    Heard you led a great technical at the Nashville chapter. Sorry I missed it!

    Chris





  • 3.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-24-2016 00:46

    Define "flexibility" and "resonance" please.

     

    David Love

    www.davidlovepianos.com

     






  • 4.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-24-2016 14:11

    Just to add to my previous post, how do you determine the load per rib?  One of the problems I see (if I understand your method) is that the load per rib is distributed some by the bridge.  When you put pressure on rib number 8, for example, some of that load is redistributed to rib #7 and #9 (and even farther afield than those two).  So it appears that you are making custom alterations to each rib based on a calculated load perhaps from the strings above each one???  I wouldn't approach it that way.  I would want a smoother MOI between ribs reflecting the actual load distributions that occur as a result of the bridge itself (and there are other criteria to consider as well).  

    I agree that the load and bearing capacity of the assembly must be in "balance" (whatever that is) or you will have an impedance problem--unwanted rate of energy transfer--but I'm not sure what that has to do with "resonance" or "flexibility" or how you define those terms exactly in this model.

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



  • 5.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-24-2016 15:45

    Hi David,

    I believe we have discussed load distribution before. But I believe my method is valid for two reasons.

    1. I am comparing to the original first. I want to stay true to the original design. I then simply look for any mistakes in calculations. Usually a common mistake is just not having enough overall mass and making up for that by inducing too much stiffness. Most often, the ribs go from narrow/tall to wide/short. (Stiff to flexible all while still having the strength/mass needed)
    2. It is a common engineering principle to isolate elements. And i follow that principle.  For example, ribs themselves are not treated as a single beam, but are treated as two levers that are attached in the middle.YtyYY03HTpi6zn438MPv_Moment 1.png

    1. Thats how you calculate Moment. (A*a).

         I treat each rib as an isolated structure. Looking something like this.              
    AwWfpGTaSaDq4aIBjKcf_Rib structure2.png

    I believe that isolating elements keeps things simple and doesn't complicate unnecessarily. So it's the method I prefer.

    Since all the ribs are calculated at the 20% of rupture. That leaves an 80% safety margin.

    Regarding MOI. I dont use it.  I prefer M/Z =S.  Section modulus(Z)  takes into account the rib profiles strength. MOI is an element of the deflection formula (which I keep an eye on) but it's not a critical element for me since I am working with new boards with a full crown.

    Thanks David

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



  • 6.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-25-2016 09:38

    Can you provide the actual rib dimensions before and after?

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



  • 7.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-26-2016 00:24

    These are interesting graphs. They look plausible, but I'm not sure of the extent to which they represent reality. In that regard, my first question (and the only one that really matters) is, "Can you hear the difference?"  And I realize this is a challenge for us in the the piano rebuilding or boutique building niche because of our general inability to do A/B comparisons.

    But, anyway, it looks like measurements are being calculated for the support for string load needed for each rib at the point the rib crosses under the bridge. (Please correct me if I'm just not fully grasping what is being shown). Anyway, if so, one element that is not being calculated (I believe) is the cantilever effect of the bridge functioning as a structural beam that connects the ribs.

    In a joist-supported floor where the joists are connected to their neighbors by bracing, pressure on any single joist is also shared by the neighboring joists through the bracing structure which results in a much more rigid structure and greater weight-carrying ability with less deflection than if the bracing were not in place. Calculations of deflection for individual joists would err without taking the bracing into consideration.

    Similarly, in a piano soundboard, the bridge will have the same kind of effect (how much depending on its dimensions and load-carrying ability) so as to "smooth over" erratic deviations in load-carrying ability that may exist in each single rib considered by itself.

    This is not to dissuade anyone from making these kinds of calculations. Certainly, better estimates of individual rib load-bearing capabilities and the actual load borne by each rib can't hurt. What I'm suggesting is that because of the bridge as an additional load-bearing factor, there will be some threshold below which individual rib mismatch to string load won't matter in terms of audible performance. It would be good to determine what that threshold is and to refine calculations accordingly. 

    ------------------------------
    Keith Akins
    Akins Pianocraft
    Menominee MI
    715-775-0022



  • 8.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-26-2016 01:08

    Hi Keith,

    Yes, you can hear the difference. For the presentation I give and offer to chapters, I made two exact sized soundboards. One was made with stiff ribs (every piano) and one was made according to my system of adding flexibility.  I invited the technicians to do a tap test on both. The first board (stiff)had a tone of F2 and had a standard sustain and sounded small. My board (flexible)had a tone of Bb1 (a fifth lower) and twice the sustain, and sounded like a much bigger board.

    I don't put much emphasis on the bridge as others do. i treat it as a constant. So i feel that whatever lateral effect the bridge has will be the same in the old board that i compared with, to the new board.

    I'm mostly concerned with equilibrium. Meaning if the downward force is 800lbs then the resistance should be 8 sq in of mass. If the downward force is 850 lbs, then 8.5 sq in of mass etc..  I believe that boards that fatigued over time were under massed. Boards that sound small are excessively stiff. The best board is one that is strong and flexible. So far i have only found two designers from the past (Jacob Goll, Albert Weber) who engineered their boards correctly. Once equilibrium is made then i make sure the stress level is at 20% and the rib profile is as close to 70%(H x 100/W=%) as possible. That in a nutshell is my method for a full resonating board. You can hear it for yourself if you ever want to visit or attend a future presentation.

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



  • 9.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-26-2016 01:11

    Good starting point. The premise seems to be that ribs should share the load fairly. Ideal for most teamwork like roofs and bridges but not necessarily relevant to music is it?




  • 10.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-27-2016 00:58

    That's correct (bridge distribution of the load).  See my posting.

     

    David Love

    www.davidlovepianos.com

     






  • 11.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-27-2016 01:29
    > It would be good to determine what that threshold is and to refine calculations accordingly.

    I agree, if it were only possible. I get around it by smoothing the
    individual rib loads with an order two polynomial trendline. This does
    about the same thing in redistribution of loading as the bridge does
    (except at the killer octave curve), so I can calculate rib dimensions
    for realistic loads. Though not quite as realistic as in the straighter
    sections, it's adequate through the curve. I stiffen the ribs through
    the killer octave(s) to compensate for the loss of beam support from the
    bridge through the curve, and I still voice the killer octave down some
    to blend with the rest of the piano.
    Ron N




  • 12.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-28-2016 00:33
    Edited by David Love 10-28-2016 02:19

    Sure, just for fun, you could take the actual per rib loads as described and create a trendline curve the smooths them out as one might expect the bridge to do and then calculate the rib dimensions accordingly.

    Graph of the original specified rib loads with the trendline calculations (in this case a third order polynomial)

    To be fair I did modify the original loads to reflect best estimate of the off center loading on the upper ribs and raised the upper end just slightly.

    Translate those to actual load numbers:

    Rib # Original Design Load Design Load Trendline
    1 22 41
    2 58 41
    3 51 45
    4 43 51
    5 48 59
    6 48 66
    7 60 73
    8 87 77
    9 90 77
    10 62 72
    11 52 60

    And then calculate rib dimensions based on targeted defections (I might not follow the w/h relationships exactly like this in actual practice)

    Rib # Working length mm Width mm Height mm
    1 540 22.0 18.0
    2 800 23.0 20.2
    3 1003 24.0 22.0
    4 1143 25.0 23.8
    5 1016 25.0 24.0
    6 838 24.0 23.8
    7 660 23.0 23.0
    8 514 22.0 22.0
    9 394 21.0 20.5
    10 305 20.0 18.5
    11 165 19.0 14.5

    And it looks something like this under load:

    With MOI like this:

    I think this design would probably work nicely (though I might push the rib heights up just slightly if I were doing it).

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



  • 13.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-28-2016 20:53

    David: These last 3 graphs are nice and starting to help thank you but I am still ignorant about the labels and abbreviations. The Y-axis on # 1 is foot pounds and on # 2 millimeters I think. What about graph #3?  Sorry to say I also do not understand the meaning, difference and importance of MOI and MOE. Are these terms interchangesable? Please explain if you would. I had no idea that ribs are planned to a mm or less. Very interesting.




  • 14.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-29-2016 02:24

    I'll put this in lay terms and let the engineers in the audience be more precise:

    Chart number one shows the lbs of force on each rib.  The y axis is in lbs.  The red line represents Chris's numbers that he provided (I don't now how he actually arrived at those numbers), the blue line represents my theoretical, trendline distribution of the load between the ribs as I projected due to the presence of the bridge. The total load on the assembly is generally calculated by the total string tension multiplied by the sine (in radians) of the downbearing angle.  The total load is then distributed between the 11 ribs, in this case, in the manner one sees fitting (which is what we're discussing in part).  

    Chart number two represents the total crown (blue line), the total deflection of each rib based on the loads given above (red line), the target safety margin of 90% of the crown (green line), and the residual crown--how much crown is left (purple line).  The crown and deflections are given in millimeters.

    Chart number three is a graphing of the Moment of Inertia (MOI) for each rib based on the rib dimensions.  The moment of inertia can be thought of as an object's resistance to movement (angular acceleration) based on the properties of the object itself.   For example, a beam that has larger cross section will have a higher MOI than one that has a smaller cross section (width and height are proportional--height has more of an influence than width).  It's important because it doesn't make much sense to have two ribs right next to each other whose resistance to acceleration (MOI) is vastly different.  That would mean one rib is working a lot harder than the one next to it to resist movement. A smoother transition between each rib makes more sense especially as the load likely distributes in a more uniform way due to the presence of the bridge.  

    MOE stands for modulus of elasticity and very basically represents the elastic properties or stiffness of that material (again, engineers will prefer a more precise definition) but think of it in simple terms, denser things are harder to bend.  In the case of ribs made of wood, certain species have a higher modulus than others (they are stiffer). When calculating rib deflections (how much a rib will bend) under load you need to know the MOE of that particular species.  Sitka spruce, for example, has a higher MOE than sugar pine.  Effectively, for the equivalent bending properties, a sugar pine rib will have to have a larger cross section than one made of sitka spruce.

    Hope that's helpful. 

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



  • 15.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-29-2016 10:44

    Paul:

    BTW, just to clarify one of your earlier questions, for one part of the analysis there was discussion about MOI versus Section Modulus.  For this part of the analysis Chris is using Elastic Section Modulus whereas I'm using 2nd moment of inertia.  They yield similar curves.  

    The formula for elastic section modulus is S = (w*h^2)/6 where w = width and h = height of a rectangular beam, in this case.   (you asked earlier where he derived this forumla of squaring and dividing by 6 came from).      

    The 2nd MOI formula is I = (w*h^3)/12. The curves are an indication of the continuity as you move from rib to rib. If you search "section modulus" or moment of inertia you will get a trove if information to help explain.

    When you graph the data you get this:

    This is the graph of the section modulus and MOI of Chris's suggested new ribset. You can see that the two curves are the same shape basically.

    This is the graph of the same data with my proposed ribset.  I prefer this.

    I doesn't answer every question about choosing the rib dimensions, it's just part of the overall equation.

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



  • 16.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-29-2016 10:56

    David: I need more study.Thanks but I’m still stuck on graph #3 and MOI. “ The moment” means to me that somehow it depicts a measure of time but the Y-axis seems  to show thousands of an inch which is a  distance.  Seems important.  I just do not get it yet but that’s my problem. You have already provided much. I think I understand MOE better. I had thought that boards were simply copied so it is interesting to know how they can be improved




  • 17.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-29-2016 11:07

    Don't confuse the term "moment" as having to do with time.  The "moment of inertia" is simply a quantity expressing an object's resistance to acceleration.  I presume the term "moment" derives from momentum.  

    Here's a link:  Second moment of area - Wikipedia

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



  • 18.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-29-2016 11:26

    Thanks again.




  • 19.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-29-2016 11:38

    Paul:

    BTW there are various approaches to building soundboards.  Some people do copy what's there, others take what's there analyze and try and refine it. It's important to consider that even though there may have been a design intention that the factory may not have hit the mark exactly so what you are seeing may not be what was intended--or it just may have been a bad idea to begin with.  Hard to know just how exact the instructions were on building any particular rib set and harder to know if they hit the mark.  Then there are others who prefer to totally redesign the rib array (layout), soundboard shaping with the use of cut-off bars, bass floats and treble "fish" (reductions in the working area behind the top of the treble bridge) and other features.  Ron Nossaman and Del Fandrich, to name two, have discussed this to a great extent in past dialogues and the archives are worth a search for this information if you are interested.  And then there are others who are pushing the envelope of redesign even more like Wayne Stuart or Ron Overs in Australia, for example (though what they do is quite different from each other) and there are others. 

    Most builders I know are at least doing some analysis on the existing rib scales to determine if what was there makes sense. If it didn't work very well the first time there's not much chance it will work the second time.  Changes in materials (say from sugar pine to sitka spruce) will also require a change in the dimensions even if you are after the same response. 

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



  • 20.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-29-2016 13:26
    Take a moment for this.

    https://en.wikipedia.org/wiki/Moment_%28physics%29

    Ron N




  • 21.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-24-2016 23:49

    Chris: Rib graphs are interesting. Why 2 Ys (axes)? Axes are unlabeled. The #s mean what? On graph #2 is the red line usually just under the blue line showing the bridge effect mentioned by David? Why the big exception for rib #11?  I missed your solution for the previous rib length riddle of 9” when I found 27”.  Share math details please. Maybe I cubed what you squared. Paul




  • 22.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-25-2016 12:23

    Hi Paul,

    The #s mean what?

    The blue line is the moment in inch pounds (Force). The red line is the size and strength of the rib(Resistance).

    On graph #2 is the red line usually just under the blue line showing the bridge effect mentioned by David?

    No. Since each line is expressing different values (force, mass), above, below or on top doesn't matter. I just look at the contours, and try to get them to have a similar shape.

    Why the big exception for rib #11?

    Because there is no moment. 

     I missed your solution for the previous rib length riddle of 9” when I found 27”.  Share math details please. Maybe I cubed what you squared. Paul

    Not sure what you mean. Did I forget something?

    Thanks Paul

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



  • 23.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-25-2016 18:32

    Chris: Awhile back you challenged us to find a ribs length by giving other variables. I do not recall seeing the details of your solution or if any sent the right answer. Mine was wrong but I would have liked to see how you did it. But that’s ok. Thanks anyways. Paul




  • 24.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-25-2016 19:16

    Well gosh Paul, that was awhile ago. But..........after searching through 200 old posts, I found what you were referring to.

    The problem was to find the length of the rib using the following details. Which as you mentioned, nobody solved it.

    Here was the details

    Heighth- .43

    Width- .82

    Stress- 1.854 lbf

    Force in Center- 60lbs

    soundboard thickness- .30

    So to solve it you use the Stress formula M/Z=S in reverse. Z x S = M

    Lets solve for Z

    Z= .73^2 x .82/ 6 = .07282   (by the way .73 is .43 + .30)

    So now Z x S =M  is  .07282 x 1,854 = 135 in-pounds (Moment)

    So half the Moment(bearing) is 30Lbs

    so 135 / 30 = 4.5 inches( half the lever length)

    so 4.5 x 2 = 9

    The rib length is 9"

    Hope that makes us friends again Paul

    -chris

     

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



  • 25.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-25-2016 20:52

    Correction: half of the force is 30lbs.






  • 26.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-25-2016 21:19

    Ok, Thanks.




  • 27.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-25-2016 22:52

    Total downbearing is 753LbsrzAqxlQQCJxxifUVBWzw_Heintzmanbeforeafter.png

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



  • 28.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-26-2016 01:02

    What's the force on each rib?  I assume you're using center  loading (even though the upper ribs are not center loaded exactly)

     

    David Love

    www.davidlovepianos.com

     






  • 29.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-26-2016 01:19

    Ok David here is a full spread. I'm not going to share my MOE values tho. Thats still a work in progress.AsiVTBCSL2EcxSnEcX4B_Heintzmanspead.png

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



  • 30.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-26-2016 01:31

    David,

    Oops, some cells were hidden. here's the bridge locations. Start from the curve side.WtQj17kERIOD7QGHQTff_Heintzmanspeadbridge.png

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



  • 31.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-26-2016 14:37

    Ok using your load values and a modulus corresponding to sugar pine of 1190000 this is the deflection response I get from the ribs (not including the presence of the soundboard panel.  I would like the red line to be at or slightly below the green line.  This is your modified design.  Even if the MOE were higher, say if you were using white spruce or sitka for ribs, and assuming those load values actually held up in real life you would still have a rib array that was not balanced and under engineered in certain areas.  I've used 18M radius for crown which gives 9 mm of crown on the longest rib. YMMV.

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



  • 32.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-26-2016 14:54

    Now I see your error David. Using Youngs modulus of a species as the MOE for a soundboard will give a false reading. This is the problem with most engineering books. The Moe's are representative of unfixed beams. That's the standard. The moe changes drastically with a fixed beam. Even more so  with an arched beam, and even more so with a structure like a soundboard.
    That's why I use the stress level as a more accurate marker.






  • 33.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-26-2016 15:58

    No.  The MOE is species specific in this case.  The load bearing or deflection formula takes into account that it is a beam with simple or fixed ends.  In my case I use a fixed ends formula.

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



  • 34.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-26-2016 16:25

    Here is some species data, various measures from Hoadley. You can find this easily from different sources.  Has nothing to do with how the beam is attached to anything or not.

    MOE FSPL Specific Gravity
    Sitka  1570000 6700 0.40
    White 1340000 6500 0.36
    Engelman 1300000 6300 0.35
    Sugar pine 1190000 5700 0.36
    Western Pine 1460000 6400 0.38
    Eastern Pine 1240000 8600 0.34
    ------------------------------
    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320



  • 35.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-26-2016 15:56

    btw I've reversed the rib order so your original #11 is now my #1 rib (lowest bass rib).  Just how my spread sheet is set up.

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



  • 36.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-26-2016 01:47

    First I think you should adopt the normal protocol that #1 rib is the lowest bass rib, that's the reverse order of what you have. 

     

    Second I've run your numbers through my spread sheet and all I can say is that neither the original nor the modification is anything that I would build-then again it is a Heintzman.  The lower ribs are particularly under engineered pretty much no matter how you distribute the 753 lbs of downbearing load.  The modification I find to be worse since you've reduced the height of the ribs (the height contributing more than the width to the load bearing capacity). 

     

    The distribution of load bearing capacity from rib to rib is also not what I would like to see.  You have some adjacent ribs where one is doing more work (or less) than the one right next to it even though the loads will be distributed to adjacent ribs via the bridge fairly, or at least somewhat, uniformly. 

     

    You're going to have to give me some more data for me to make any sense of this. 

     

    David Love

    www.davidlovepianos.com

     






  • 37.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-26-2016 19:45

    And your Heintzman rescale is?

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



  • 38.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-26-2016 20:40

    First tell me how you determined your load values and distribution.

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



  • 39.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-26-2016 20:50

    Its in the full spread above.

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



  • 40.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-26-2016 21:57

    I mean how did you come to those numbers?

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



  • 41.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-27-2016 00:51
    Edited by David Love 10-27-2016 09:36

    Here is an example of how I might approach this project.  There are some questions to answer in terms of what the design load is and how we determine that which will impact our rib calculations but for illustration and consideration this will suffice. (Note: #1 is the bass rib and #11 is the highest treble rib for all diagrams and I'm basing my calculations on sugar pine ribs--I generally use white spruce which is a bit stiffer and will affect the rib dimensions somewhat)

    Whereas your load response looks like this (this is with your load numbers and modified ribs):

    I'd want it to look more like this (see below for my load numbers and rib dimensions):

    Where rib deflection remains less than predicted crown and where residual crown is always positive.  There are some variables here in terms of the amount of crown and the amount of deflection you want. These are decisions that the designer has to make.  But certainly you don't want the rib deflection to ever exceed the amount of crown, at least in terms of design.  

    Your MOI for each rib plotted looks like this:

    I would prefer it look something more like this:

    The ribs are working together in a more unified way here.

    The design load distribution for me would probably look more like this.  The actual range might be somewhat different but this will suffice for this illustration.  This has to do with bridge distribution of the load and the fact that the upper ribs are not center loaded (a beam will support a lot more weight as you move away from the center as is the case with the top three ribs certainly):

    1 64 lbs
    2 65
    3 66
    4 67
    5 68
    6 69
    7 70
    8 71
    9 72
    10 73
    11 74

    Total load 759 lbs (yours was 757 lbs)

    Here are the proposed rib dimensions using your lengths and modified widths but with my proposed heights: (I usually work in mm btw but have converted to inches for this illustration).  Generally I favor something that is slightly taller than it is wide or about the same (I do cut a radius into the ribs).  Since the height contributes to the stiffness of a beam by a factor of ^3 as compared to the width, a rib that is taller than it is wide will have less volume and less mass than a rib that is wider than it is tall.  That's a design choice that you may consider as well.

    Rib # L (in) W (in) H (in)
    1 21.3 0.90 0.81
    2 31.5 1.05 0.87
    3 39.5 1.05 0.94
    4 45 1.05 0.98
    5 40 1.01 0.98
    6 33 1.01 0.93
    7 26 1.01 0.87
    8 20.3 1.01 0.79
    9 15.5 1.01 0.73
    10 12 0.95 0.69
    11 6.5 0.75 0.61

    That's the basic idea anyway.  I don't have all the necessary information from you so I can't say for sure that I would build it exactly like this. The actual load distribution might vary somewhat from what I've outlined and I may not use your actual widths but this would be the basic approach and goal.  If I wanted something with higher impedance for reasons of personal taste I may opt to make it somewhat stiffer, though it's not likely I would make it any less stiff than this.  Some differences in impedance will be accounted for by treatment of the panel itself, for example, by thinning the area below the bass bridge.  But this represents the basic minimum design requirements for a project such as this.  

    I have built many soundboards using this basic approach and it's not a unique approach and does work but there are always other things to consider and each piano will have its own particular design issues.  

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



  • 42.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-28-2016 20:51

    Z= .73^2 x .82/ 6 = .07282   (by the way .73 is .43 + .30)

    Chris: Thank you for your help. Okay .43 + .30 = .73 but why square this and divide by 6. I understood  another post to explain you treat components separately but here the board adds significantly to the rib height and seems combined with it. How does this equate?




  • 43.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-29-2016 23:36

    David,

    Here is a little chart I did of the downward forces on the Heintzman, and the sections they are located along the bridge. Now I know you were only going by my previous numbers, which were based on point loading. But your response of  trying to even up the forces 

    1

    64 lbs

    2

    65

    3

    66

    4

    67

    5

    68

    6

    69

    7

    70

    8

    71

    9

    72

    10

    73

    11

    74

    was intriguing. But that it too could be counter-intuitive to the original design.

    afEsyzDzSLSzFKTHmAvm_Heintzmanbridgechart.png

    Notice that most of the load is at the ends  400+ plus lbs on the treble end and 220+ on the bass end with a mere 96 lbs in the center.

    I'm curious on how you would find the centroid of the long bridge?  And how you would compensate for any lateral forces due to the curvature of the bridge? Or maybe what formula you use to calculate the load distribution.

    Ron N. Are you using a predetermined load curve of some kind?

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



  • 44.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-30-2016 00:00
    > Ron N. Are you using a predetermined load curve of some kind?

    No. I do a load analysis. I assign unisons to ribs as they fall, assign
    loads as the string scale dictates with tension and downbearing, and
    smooth the result with a second order polynomial to simulate what the
    bridge does in real life. No smoke, no mirrors. It's as close to reality
    as I can come with the methods at my disposal with as little arbitrary
    guessing as I can manage. I rib boards at 6% MC, which means that there
    is very little stiffness supplied from panel expansion, so I scale the
    machine crowned ribs as load supporting beams as if the panel wasn't
    even there.

    Last I heard, David ribs at 5%, which means his boards are largely panel
    supported, so he can use a lighter rib scale than I can for a similar
    stiffness. I have asked you what you use as an MC when you rib, and the
    crowns you machine into your ribs, but you have so far not said. This is
    a fundamental part of designing and building soundboards, which can't be
    shrugged off as unimportant.
    Ron N




  • 45.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-30-2016 00:39


    Thanks Ron,

    I prefer the straight rib low mc method.  I Glue ribs on at 4% then install hot as soon as it crowns to 60. Sand off the ridges after it's done growing.

    I believe stiffness and strength are two different things. So I go for a strong and flexible board. I think boards in the past went flat primarily due to being under massed. And secondarily because of flat rims and poor installation. As demonstrated by my tone boards, a stiff board sounds small.

    Ron N

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



  • 46.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-30-2016 00:58
    Compression crowned boards go flat because the panel compression must
    both bend the ribs, which resist crown, and support downbearing, which
    is typically set at the absolute compression limit of the panel.
    Cumulative compression set in the panel, particularly in areas where
    there are real seasons and cyclic humidity swings, crushes the wood. It
    has nothing to do with mass. It's pure compression stress. Making ribs
    shallower in compression crowned (CC) boards will increase the crown.
    What else it will do, I can't say because I don't build CC boards.

    Ron N




  • 47.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 12-27-2016 13:08

    Ron: Compression crowned boards go flat because the panel compression must
    both bend the ribs, which resist crown, and support downbearing, which
    is typically set at the absolute compression limit of the panel.

    Me: I disagree. Crowning is done before its glued in. Once glued in, it can only go flat if the sides

    expand out, Or...


    Ron: Cumulative compression set in the panel, particularly in areas where
    there are real seasons and cyclic humidity swings, crushes the wood. It
    has nothing to do with mass.

    Me: It has everything to do with mass. If the wood is being crushed, it's because of the insuffcient mass. If the mass and force are not in equilibrium, then the force is continually accelerating (board flattening). 

    Isaac Newton: Newton's first law of motion predicts the behavior of objects for which all existing forces are balanced. The first law - sometimes referred to as the law of inertia - states that if the forces acting upon an object are balanced, then the acceleration of that object will be 0 m/s/s. Objects at equilibrium (the condition in which all forces balance) will not accelerate. According to Newton, an object will only accelerate if there is a net or unbalanced force acting upon it. The presence of an unbalanced force will accelerate an object - changing its speed, its direction, or both its speed and direction.

    Ron: It's pure compression stress. Making ribs
    shallower in compression crowned (CC) boards will increase the crown.
    What else it will do, I can't say because I don't build CC boards.


    Me: Even if you make ribs pre-crowned, with a shortage of mass, the result will be the same. The force will over come.

     

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



  • 48.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 12-28-2016 11:13
    --

    >
    > Please do not forward this message due to Auto Login.
    > CAUT
    > Post New Message
    > Re: A Refinement of Equilibrium for Maximum Soundboard Flexibility
    > Reply to Group Reply to Sender
    > Chris Chernobieff
    > Dec 27, 2016 1:08 PM
    > Chris Chernobieff
    >
    > Ron: Compression crowned boards go flat because the panel compression must
    > both bend the ribs, which resist crown, and support downbearing, which
    > is typically set at the absolute compression limit of the panel.
    >
    > Me: I disagree. Crowning is done before its glued in.Once glued in, it can only go flat if the sides
    >
    > expand out, Or...

    No. Crown is not an end buttressed arch. If it were, crown could not
    form out of the piano without the rim. Read my PTJ article on Crown as
    Arch, do for yourself the suggested test, and learn why.
    >
    >
    > Ron: Cumulative compression set in the panel, particularly in areas where
    > there are real seasons and cyclic humidity swings, crushes the wood. It
    > has nothing to do with mass.
    >
    > Me: It has everything to do with mass. If the wood is being crushed, it's because of the insuffcient mass. If the mass and force are not in equilibrium, then the force is continually accelerating (board flattening).

    Two ribs of identical mass and length can be made considerably different
    in stiffness by chosen dimensions of depth and width, This is simple
    beam flexure formula, also easily demonstrated by anyone willing to learn.

    >
    > Isaac Newton: Newton's first law of motion predicts the behavior of objects for which all existing forces are balanced. The first law - sometimes referred to as the law of inertia - states that if the forces acting upon an object are balanced, then the acceleration of that object will be 0 m/s/s. Objects at equilibrium (the condition in which all forces balance) will not accelerate. According to Newton, an object will only accelerate if there is a net or unbalanced force acting upon it. The presence of an unbalanced force will accelerate an object - changing its speed, its direction, or both its speed and direction.

    Newton wasn't talking about load supporting beams.

    >
    > Ron: It's pure compression stress. Making ribs
    > shallower in compression crowned (CC) boards will increase the crown.
    > What else it will do, I can't say because I don't build CC boards.
    >
    >
    > Me: Even if you make ribs pre-crowned, with a shortage of mass, the result will be the same. The force will over come.

    Pre-crowning has nothing to do with it. The beam works the same in
    either case. Crowned ribs just let the rib positively support the
    bearing load without high panel compression levels.
    Ron N




  • 49.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 12-28-2016 14:14

    Read my PTJ article on Crown as
    Arch, do for yourself the suggested test, and learn why.

    I find this just a tad cryptic. Would care to share a link or date or both?

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



  • 50.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 12-28-2016 14:38
    I don't know what issue it appeared in. Anyone?
    Ron N




  • 51.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 12-30-2016 00:19

    No. Crown is not an end buttressed arch.If it were, crown could not form out of the piano without the rim. Read my PTJ article on Crown as
    Arch, do for yourself the suggested test, and learn why.

    I'm going to take a guess here.(Haven't seen article yet) This sounds like the "it's above the centroid, therefore the ends go inward" argument. That may be true when you isolate a rib with feathered ends. But it's not the case in the real world, because the soundboard as a whole is a very unique structure. Next time you have a soundboard made, put it on the bench(or floor) push down on the middle. The ends go outward. 

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



  • 52.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 12-30-2016 04:01
    > Next time you have a soundboard made, put it on the bench(or floor)
    > push down on the middle. The ends go outward.

    No they don't. You clearly haven't tried it, or you would know this.
    Michael Ravenscroft, days after reading the article and most definitely
    being interested in learning wrote me that he and Andrew had set their
    latest soundboard up on blocks on the floor and stood on it. The rib
    ends pull in for a soundboard assembly just like testing an individual
    rib. I did the same thing with the same result, as can anyone more
    interested in learning how something actually works than in trying to
    kite some theory that can't be demonstrated. Nothing otherworldly or
    magic and contrary to high school geometry happens when ribs are glued
    to a panel.

    Find and read the article, do some actual bench testing, and try to
    learn something of what you're talking about.

    But as long as techs can't be bothered to run a few simple bench tests,
    they'll believe any sort of Voodoo nonsense anyone pitches their
    direction. As many techs as there are building and installing
    soundboards these days (shop built, or board in a box),it's inexcusable
    that this hasn't been verified on these lists a dozen times.
    Ron N




  • 53.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 12-30-2016 10:38

    Rib Crown as End - Buttressed Arch.

    April 2006

    You'll need the Journal CD or someone will have to post the PDF.

    ( Won't be me I gotta work )

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



  • 54.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 01-01-2017 21:52

    I just spoke with Loui Nossaman. Ron died on Friday, the same day he posted this last message.

    One of our great voices has gone silent.

    ------------------------------
    Kent Swafford
    Lenexa KS
    913-631-8227



  • 55.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 01-01-2017 21:56
    Sad news.  Another great loss of an experienced, albeit blunt and sometimes caustic, voice for our industry. RIP Ron. Thank you for sharing your wit, wisdom and wealth of experience with us.
    Gary Bruce
    Registered Piano Technician





  • 56.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 01-01-2017 22:05

    I never met Ron, but I did appreciate  his many challenges. My best wishes to his family.
    R.I.P.






  • 57.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 01-01-2017 22:51

    Oh my....such sad news. He will be incredibly missed. Prayers for his family...🙏🏽

    ------------------------------
    [Kevin] [Fortenberry] [RPT]
    [Staff Techician]
    [Texas Tech Univ]
    [Lubbock] [TX]
    [8067783962]



  • 58.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 01-01-2017 22:52
    Not sure why the subject line was about soundboards when the subject is about the passing of Ron Nossaman, but I want to say that IMO Ron was the single greatest contributor to this forum since the passing of Newton Hunt. Maybe you considered him abrasive, or a curmudgeon, but I considered him an unrelenting source of verifiable information. A low threshold for BS, is, IMO, a great thing. I greatly appreciated his relentless quest for separating myth from truth, wheat from chaff, and his ability to do so thru real world testing and subsequent observations put him in a class of his own.

    Ron was a treasure that will be sorely missed.

    Mark Potter
    West Jefferson, OH 






  • 59.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 01-01-2017 22:57
    Well put, Mark, couldn't agree more. I also appreciate your mention of Newton Hunt, another one we miss very much. Two very independent souls, who contributed with extraordinary generosity.
    Regards,
    Fred Sturm
    "Since everything is in our heads, we had better not lose them." Coco Chanel






  • 60.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 01-02-2017 08:14

    Ron continued to participate and share his knowledge through years of illness and pain. The realization of his relentless generousity is overwhelming. I can't imagine who I would be, or what our field of active knowledge would be, without Ron's gift.

    ------------------------------
    Ed Sutton
    ed440@me.com
    (980) 254-7413



  • 61.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 01-03-2017 11:28

    Very sad to hear this news.  Ron's was a unique voice and whatever his style he was dedicated to moving the industry forward.  I'm not surprised that his contributions continued until the end.  We sometimes disagreed but he always made me think.  

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



  • 62.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 12-28-2016 15:47

    I don't agree with that Chris.  You can make a rib that is stiffer, will support more load, that has less mass by altering the width:height relationship. 

     

    David Love

    www.davidlovepianos.com

     






  • 63.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 12-28-2016 16:04

    Stiffness and strength are two different things. It can be small and stiff, as well as big and stiff. I'm finding in several pianos I have measured, that ribs are small and stiff. And because they are too small, the board fatigues. You cant cheat gravity by making them stiff to reduce the mass. It dont work that way. What I'm suggesting is make them the right size (bigger) and reduce the stiffness (more flexible). A win win.






  • 64.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 12-29-2016 10:37

    I would reiterate Ron's points. 

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



  • 65.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 12-29-2016 10:42

    Status quo.






  • 66.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 12-29-2016 12:50

    Re: Status quo. Right, wrong or indifferent I can imagine an empirical way. With a few cheese type presses for loading and dial indicators to measure deflection, trim oversize ribs down till the deflection was the desired percent of the overall crown.




  • 67.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 12-29-2016 13:28

    Paul,

    And if you go to far in the trimming? How much to trim? Wouldn't want to figure that out after a new soundboard is in.

    Anyways, all that experimenting has already been done. 

    I made a simple chart to illustrate the importance of Mass. (Oh, but I was told by experts mass not important,. Oh well)

    In the chart there are 13 ribs.

    The lengths are the same 

    The load is the same. 

    The STRENGTH in all is the same(Z).

    But look, they deflect different.

    All i did was change the mass(area).

    The rib on the far right is stiff (106%), but it lacks the mass for the load. ( =fatigue)

    Mass is important.

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



  • 68.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 12-29-2016 14:25

    Chris: I don’t know. Start over altogether. Replace just bad rib. If crown is not a buttressed arch size board to pop in and out to suit. Does it have to be glued in to test deflection?  Numbers on paper fatigue prompts questioning the premise.




  • 69.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 12-30-2016 13:27

    An increase in mass is likely to increase load bearing characteristics but it doesn't necessarily nor is it necessary (whether it's desirable for other reasons is a different discussion).  It depends on how the mass is distributed. You're making a mistake of correlation = causation.  

    Not sure what you mean by status quo (mine or others) but the load bearing characteristics of beams are not something made up by me or anyone else.  One can easily make an example of lower mass with higher load bearing characteristics and better FSPL numbers simply by distributing the rib dimensions with more height and less width.   Since the height of the rib contributes to its strength by factor of ^3, the width can be reduced by a greater amount than the increase in height to yield a stronger rib with less mass.  

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



  • 70.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 12-30-2016 13:55

    That assumes of course less mass is desireable. I'm thinking I like the extra mass and the sound it gives. But at least I've got you talking about mass.

    I'm not sure where all this silly talk of arch buttresses leads anyways. Sounds like theoretical stuff that makes for an interesting artictle topic. But I'll stick with making great sounding boards that I and others can hear the amazing depth of resonance up close.
    Have a great and prosperous new year guys.
    See you on the other side.






  • 71.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 12-31-2016 00:43

    ???

    You're changing the topic. It's fine if you like extra mass, but we're talking about the ability of the assembly to support crown. I don't think anyone in this discussion is trying to achieve adequate support at the expense of tone.

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



  • 72.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 10-30-2016 13:57
    Edited by David Love 10-30-2016 20:51

    (note:  I've gone back and edited the original posting to trim the old posts from bottom of this--it was getting a bit unwieldy)

    Chris:

    It does seem that the three of us are doing a bit of apples to oranges comparison.  Ron is correct that I rib at 5%, he ribs at 6%, as he mentioned, and you rib at 4%.  At 70 degrees that means you rib at 18% RH, me at 23% and Ron at 29%.  So if we keep the pianos at 70 degrees and 42% RH as it would be with the Dampp-Chaser installed, each panel has some compression but there is clearly a lot more in the 4% model than in the 6% model. Presumably rib sets will be stiffer in the assemblies that have less compression and rely less on stiffness from panel compression.  From the data I've seen so far that is the case.  I believe the tonal response in a board that has more compression and a lighter (less stiff) ribset is somewhat different than a board that has less compression with a stiffer ribset, probably for a variety of reasons.  That's another discussion but I say that from having built both types and the choice depends ultimately on what you're after.  For me, I prefer an assembly with some compression and a somewhat lighter ribset.  Tighter rib radii also make a difference, IMO. The differences are subtle but present.  

    There are different ways of determining the load per rib and (Chris) I'm still not clear on how you arrived at your numbers.  I've used Ron's method of determining by unison location over each rib and then created a trendline and my string scaling chart does that for me.  One still has to determine which rib is assigned to which unisons and what the downbearing setting is in each section.  At this point I don't really do that anymore because mostly I'm doing the same pianos (Steinway MLOB) and have a default rib design in place for those.  Generally I find that the factory rib dimensions show slightly less stiffness than the ribs I am making.  Of course, they use more compression than I do as well.

    How loads are distributed varies from designer to designer.  I have altered my designs slightly over the years with little tweaks along these lines which I'll illustrate with your piano.  But there are disagreements in this area.  Some designers that I know set the loading equal across the panel for their calculations.  Others distribute the loads in a straight but sloped line. Whichever way you choose it will ultimately impact the rib dimensions if you are using this approach.  There are other considerations as well.  For example, how much deflection do you want to calculate for: 90%, 50%, 25%?  All those will influence the outcome.  What I have below would be the minimum load bearing requirements under this given load with this crown radius.   They may not reflect the final outcome when all other criteria are considered or if your design parameters are different. 

    The procedure here was that the note unisons were assigned to each rib, as Ron pointed out, a trendline was created and then the actual design load determined.  I've shown a backing off of the loading on the upper ribs because the bridge moves away from center loading in that section and so the rib doesn't need to be built as strong as if it were center loaded.  I don't like it to be stiffer than necessary at the very top of the piano because it can prevent energy transfer from the strings to the board and the piano can jangle.  You can get around that by mass loading the bridge there but I don't prefer to do that.  Anyway, normally I would calculate the actual movement off center loading and make a determination about the load after running those actual numbers.  I've not done that here but just given an idea as to the approach.  Typically my loading of the upper end of the bridge would not go this high on a piano with this string scale

    The load outputs here are based on ~37000 lbs of total load and downbearing settings of .5 degrees for the bass monochords, .75 degrees for the bass bichords (through note 26) and then 1.5 degrees for everything else.  Your load requirements may be different. I've just roughed in the rib assignments not having this actual piano to work from.  Final downbearing settings can be tweaked after the fact based on actual tonal response but I usually only do that in the treble section.  I use WNG adjustable perimeter bolts which allow for small plate height alterations after the fact. Often I make no changes but sometimes I do make some.  It's just based on listening and aesthetic judgement.  

    I agree that the inner rim should be slightly canted and not flat and I make that change in the case where it is flat. I don't use flat ribs but cut crown into them with about an 18M radius (slightly less actually) and then press them into cauls with slightly tighter radius.  With some compression I usually end up with a crown radius around 15M.  I don't like to see a lot of compression ridges because I think that indicates some cellular damage to the panel and on a panel that relies much more on compression for crowning (as yours do) I think that can be a long term (and sometimes a short term) problem.  Sitka spruce panels seem less prone to compression ridges than white spruce in my experience. Sitka panels also will require more aggressive thinning behind the bass bridge and around the perimeter (in my opinion) but that's another topic--I do thin the panels.

    I've quickly plugged in some rib dimensions that I might use.  This is based on sugar pine ribs so the MOE is factored into that.  I typically use white spruce for ribstock.   I might tweak the w/h relationships but this would be ok.  I've included a graph of your section modulus as well.  Remember that these calculations are based only on the ribs without consideration of the panel.  The calculations are also based on a beam, or rib, in which there is no scalloping of the rib ends.  So the rib will be structurally slightly weaker than these rib calculations indicate but the assembly will be somewhat stronger with the presence of the panel itself. 

    So here's an illustration of that approach to your rib set.  The chart and graphs are below.  Just a disclaimer, again, I can't say this is exactly what I would do on this piano without some other data and considerations but it illustrates the basic approach.

    Probably given more than I intended here but there it is.  Have at it.  I've used your rib lengths as the working length (assumed to be measured from the inside of the inner rim).

    Rib # String Scale/Rib Load (lbs) Trend line calculation Design Load (lbs) Working length (mm) Width (mm) Target Height (mm)
    1 48 64 64 540 22.0 20.0
    2 87 67 67 800 23.0 23.0
    3 97 70 70 1003 24.0 24.5
    4 47 73 73 1143 24.0 26.0
    5 61 76 76 1016 24.0 25.5
    6 73 79 78 838 24.0 24.3
    7 77 81 80 660 23.0 23.0
    8 97 84 81 514 22.0 21.5
    9 96 87 82 394 21.0 19.8
    10 75 90 83 305 20.0 18.5
    11 87 93 84 229 19.0 17.0

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



  • 73.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 10-30-2016 17:48

    Thank for the thoughtful post David. I'll enjoy going over your analysis and notes. Enjoy the rest of the weekend.






  • 74.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 11-06-2016 00:47

    Hi David,

    After showing you this chart,

    afEsyzDzSLSzFKTHmAvm_Heintzmanbridgechart.png

    You came up with a trend line distribution that looked like this:

    2S3ndwJSR2IGCd3JYQnh_loveline.jpg

    These look like reasonable rib loads. I decided to have some fun this weekend and did an experiment that you may or may not find interesting. I made several spring scales and placed them under each rib location of the long bridge. Then i placed gram weights on top that simulates the load distribution of the strings on the bridge and the reaction was not what I expected on the spring scales.

    sLK1sr6ERQqRax1hRzi9_square 3 051.jpg

    The numbers came out like this.

    Z6MtADHaT6S2XhZcJMDY_long bridge.jpg

    This is just the long bridge. But what was interesting, was that due to the curvature of the bridge the load went heavy(added weight in the treble) and had a lifting effect on the low end (the weight on top of the low end was 32). I believe the lifting was because the Heintzman bridge is strongly an S shape bridge( as seen in the photo).

    Next experiment of course will be to add the bass bridge and see how that effects the long bridge.

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



  • 75.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 11-07-2016 10:38

    Chris:

     

    That's very interesting, I'll look at it more closely later-running out the door to engage my ETD (just joking).  Now you should factor in the rib loading point where it deviates from center loading, as it does in the upper treble.  That would flatten out the curve some at the top.  You could simply take those output numbers you have and plug it into a spreadsheet that factored that in.  The formula for that change is very straightforward. 

     

    Thanks for doing that!

     

    David Love

    www.davidlovepianos.com

     






  • 76.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 11-07-2016 21:04

    Well, I was able to do the second half of this experiment by adding on the bass bridge and measure the whole "Unit" on the spring scales.

    After I put the measurements in excel and created a spreadsheet, it became obvious that a little "smoothing" is called for as it is easy to see what the pattern is.

    I ended up with thisGI1vjNDvRz6KaBarZtI1_Heintzman experiment 1.jpg

    This is the chart with the long bridge alone.

    tPDfYwdYQPz5HuXShgVe_Heintzman experiment 2.jpg

    And with the bass bridge added.5emJ5ZuNTaG1URjmiQSJ_Heintzman experiment 3.jpg

    When I have time, I will also do a 7' since the bridge is longer and see what the distribution will be in that case.

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



  • 77.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 11-08-2016 14:38

    The next thing that needs to happen is to account for non center loading on the affected ribs. The low tenor and bass bridge will not be over the center of the rib so the load on the rib will be diminished proportionally. The same is true at the top of the long bridge where the bridge moves toward the belly rail. That formula is straight forward if you have the center load beam formula.

    Then you also need to be sure to have factored in the actual down bearing settings that you used for different sections of the scale in your original loads.

    Once that is done you will have a more complete snapshot from which you can calculate a trendline distribution.

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



  • 78.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Posted 11-08-2016 14:54

    That's already accounted for with the appropriate moment formulas. I use 3 different variants.

    I use a somewhat similar downbearing plan you do.

    I think at this point the only thing we do differently is the MOE. Which I believe your use of 1.2- 1.5M is too low and thus makes you over engineer a bit. I use MOE'S in the 5M -8M range which is based on measuring the old board before removal. Each board has its own value it seems. And it's variable within itself at times.

    But, variety is the spice of life.






  • 79.  RE: A Refinement of Equilibrium for Maximum Soundboard Flexibility

    Registered Piano Technician
    Posted 11-09-2016 09:49

    I use the MOE of the wood species, not of the anticipated stiffness of the whole assembly, and take into consideration only that I am calculating for the rib deflections.  I expect that the panel will stiffen things and plan accordingly.

     

    David Love

    www.davidlovepianos.com