<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html> <head> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=us-ascii"> <meta name=Generator content="Microsoft Word 10 (filtered)"> <style>  </style> </head> <body lang=EN-US link=blue vlink=purple> <div class=Section1> I’m not sure that trying to figure out “compression” isn’t chasing the untamed ornothoid (i.e. the wild goose).  The question is more one of stiffness, or as has been mentioned by various people, the relationship between stiffness and mass—at least in certain parts of the scale.  As I see it, compression is used to achieve stiffness, or resistance to deflection, and therefore is a means to an end, not the end in itself.  Understanding deflection in absolute terms (not as a function of residual percentages which really tell you nothing without first knowing what your starting point was) will tell you more about the load resistant properties of the assembly and eventually (one hopes) how effective that section will capture and transduce specific frequencies or sets of frequencies.  If that’s a goal (which I think it is) then one of the biggest arguments for RC&S assemblies is being able to duplicate with some degree of predictability and regularity, degrees of stiffness without having to rely nearly as much on compression.  Even then, you don’t escape dealing with compression altogether but it is modulated through downbearing adjustments rather than wondering what the panel delivered during the CC process, what it still has after a month and what it might have after several years.  Without that, you have little hope of teasing out the variables that give you a better opportunity for reliable repeatability.       <div> David Love davidlovepianos@comcast.net www.davidlovepianos.com </div> <div>   </div> <div> Symantecs aside, it seems like a fair and interesting question to ask to me. </div> <div>   </div> <div> I've built my rib data spreadsheet to calculate the sag by entering the pressure of the string bearing force, rib dimensions, modulus of elasticity of rib material, bending and resisting moments & moment of inertia. Many of these factors come from static tables in old industrial standard texts for the given material (ie sitka spruce, sugar pine etc.) and are based upon some sampling once upon a time. I know it's been brought up that the modulus of elasticity, for example, will vary from rib to rib even with the same species and dimensions (this by the way is definitely one of the advantages of the laminated ribs in that the elasticity coefficient is averaged out). </div> <div>   </div> <div> Here are some potential drawbacks: </div> <div>   </div> 1.      Even with all this data, some of the static values and constants are averages or aproximations.  2.      Everyone I know, including myself, uses the formula for center loaded beams, which isn't exactly the case in the piano, where there may be two to three different loads on a given rib and even when there is only one load it is not necessarily in the center. This does make a good case for the symetrical design though, if for no other reason than to make the math easier. 3.      A judgement still has to be made as to how stiff you want your assembly to be. <div> Nevertheless, it's still a pretty good tool, a point of departure shall we say. I don't know how much compression this translates into but I would sure like to know. And I would like to experience how this affects the sound. All in due time I hope, unless this is my Moby Dick. </div> <div>   </div> <div> Ron N. makes some very good points about staying out of the "swamp of details" and staying aware of the diameter of the hair we are trying to split (definitely goes in the Ron N. Greatest Hits of List Quotes), but there's no harm in asking questions. </div> <div>   </div> <div> Cheers, </div> <div>   </div> <div> Jude Reveley, RPT Absolute Piano Restoration, LLC Lowell, Massachusetts (978) 323-4545 </div> </div> </body> </html>