alternatives for soundboard

[Delwin D Fandrich]

Stephen Birkett wrote:

> . . .  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.

Yes, it does.  And it is fairly easy to test.  Try it.  A freshly built
soundboard just installed in a piano rim can easily be deflected.  When it is
loaded (by weights) to approximately its final height it is MUCH stiffer.  The
stiffness parameter has changed considerably with applied force.  That is the
whole purpose of soundboard crown and string loading (downbearing).  It provides
a way of greatly increasing the stiffness of the soundboard assembly without
adding to its mass.


> A soundboard stiffness is constant and pre-designed before any loading.

No, it isn't.  In the case of the compression-crowned soundboard it is pretty
hard to predict either the exact amount of soundboard crown or stiffness.  So
much depends on the specific characteristics of the wood used in the panel and
on the specific moisture content of the wood used in the panel both at the time
of ribbing and then at the moment in question.  With a rib-crowned board, this
is a bit easier to design and predict.  It is certainly more reliable.  But the
stiffness parameter still increases dramatically when the strings load it.


> 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.

Yes.  And no.  In the compression-crowned soundboard assembly the ribs resist
the formation of crown.  The crown comes from the internal compression of the
soundboard panel working against the rib.


> 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.

Would you please define 'very wide and flat' (the Graf) and 'very tall, thin'
(the Streicher)?  I'm also curious about the thickness of the soundboard panels
that these builders used.


> By the way, harpsichords *do* have ribs, often very complex ribbing, and
> the design is very variable between different builders and regional schools.

Certainly, every harpsichord that I've ever seen had ribs.

Regards,

Del