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Re: [Phys-l] Plastics for soundboards



I disagree! material for sound boards is very much a teaching subject -- acoustics, modulus, density, hysteric dissipation, etc. all physical subjects. If not directly in the class room, then as projects.

I found your second link fascinating. My only experience w/ sound boards is building a coupala Zuckerman kit harpsichords and would, therefore, think a thin plywood would be suitable, what I suppose is already used. From your reference, I think CFRPs are too dense, and too stiff; would require very thin sheet, perhaps just what desired?

"... high enough Q to resonate, but not so high that no sound can be audible; ..."

I think you have this backwards -- Resonance not wanted, but also not so heavily damped there is no vibration and, therefore, no sound radiated. i.e. a single digit Q.

In searching I found this fascinating article:

http://www.speech.kth.se/prod/publications/files/qpsr/ 1992/1992_33_4_087-096.pdf

bc


On 2009, Mar 17, , at 10:05, curtis osterhoudt wrote:

Dear List,

I have a side-project going in which I am a consultant to a maker of music boxes. I have considerable experience in acoustics, and some in materials, but would appreciate any help which might be given here (and I know that this forum, despite its wonderful tangents, really isn't meant for such questions; I'd appreciate any off-list messages or pointers to more appropriate forums).

One of the questions a particular manufacturer has is about appropriate materials for sounding boards in their boxes (the bottom of music boxes usually acts as a sounding board). Though various woods give good results (high enough Q to resonate, but not so high that no sound can be audible; good looks; long lifetimes; ease of machining), a question has been raised as to certain plastics. Now, I know that plastics, almost by definition, are not going to be entirely suitable for such a use (they're _plastic_, can become brittle with age, light exposure, and ozone, warp under pressure, etc.). However, CFRPs seem almost ideal from my viewpoint (except for, perhaps, looks and sunlight resistance) http:// en.wikipedia.org/wiki/Carbon_fiber_reinforced_plastic has a few details, as does this article: http:// chambermusictoday.blogspot.com/2009/01/bow-kinematics-carbon-fiber- vs.html .
Does anyone here have experience with materials who could upload their brain to mine?

Best wishes,
Curtis O.