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
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