alternatives for soundboard

[Peter Kestens]

Stephen,

What's the parameter of the stiffnes/mass ratio, 1/x?   I understand very
well you can change it but there has to be something beyond the instrument
doesn't sound anymore: too much volume and no  sustain or to long sustain
and "no"volume.
Peter
-----Oorspronkelijk bericht-----
Van: Stephen Birkett <birketts@wright.aps.uoguelph.ca>
Aan: pianotech@ptg.org <pianotech@ptg.org>
Datum: donderdag 3 december 1998 17:48
Onderwerp: Re: alternatives for soundboard


>If the "crystal" soundboard was not deflected at all by the vertical
>component of the stringband loading it can only be explained if the board
>was much *stiffer* than an oridinary spruce board. So the thing is both too
>stiff and too heavy. Agreed, as Ron points out, it is an impedance
>question. I don't agree, though, that the stiffness parameter is affected
>by the loading. It is not functioning as a "hardening spring" such as a
>car suspension or the hammer coverings, in both of which the stiffness
>parameter changes with applied force. A soundboard stiffness is constant
>and pre-designed before any loading.
>
>Soundboard design determines a controlled impedance mismatch between wire
>and bridge/board that determines the relationship between sustain and
>volume. The stiffness to mass ratio of spruce is ideal for this purpose
>and determines well the parallel-to-the-grain parameter. Across-the-grain,
>of course, wood is much less stiff, so ribs are used to adjust the
>stiffness to mass ratio to an appropriate value. Within this basic plan
>many designs are possible. Graf (1830) used very wide and flat ribs,
>producing a board with comparatively less stiffness and more mass, giving
>sustain but a slower speech, more like the modern piano. Streicher (1820)
>is the antithesis, with very tall thin ribs, hence much higher
>stiffness:mass ratio, and a comparatively more explosive sound with less
>sustain. Other builders were in between these two. The overall objective
>with board design is to produce a panel that behaves all together as a
>single unit, a stiff membrane, with the appropriate stiffness:mass ratio.
>
>By the way, harpsichords *do* have ribs, often very complex ribbing, and
>the design is very variable between different builders and regional
schools.
>
>Stephen
>
>Stephen Birkett Fortepianos
>Authentic Reproductions of 18th and 19th Century Pianos
>464 Winchester Drive
>Waterloo, Ontario
>Canada N2T 1K5
>tel: 519-885-2228
>email: birketts@wright.aps.uoguelph.ca