[CAUT] Lack of low-frequency response

[Ron Overs]

Richard and all,

This is the line I was waiting for someone to contribute, and uncle 
Jim was the one who did it. Thanks Jim.

>. . . We try to make the board stiffer in the middle and more
>flexible around the edges so it will vibrate as a unit at low frequencies
>instead of breaking up into standing waves. . . .
>Jim Ellis

Several commentators have said that they believe the board is too 
stiff. But the further qualification which we need to answer is, ". . 
. too stiff where", which may lead us to conclude that the soundboard 
might not be stiff enough. I've looked at images of the piano around 
which this topic is focused, and to me it looks like the board very 
likely has insufficient stiffness in the middle area of the panel to 
act as an effective low frequency driver.

Now some might say, why then did the original maker build the 
soundboard with these dimensions? Well this design probably was 
originally built as a compression crowned panel. So it would have 
somewhat-worked for a time. I say somewhat worked, because I believe 
that almost everything I've seen which was built between 1860 and 
1880 had grossly insufficient panel stiffness when compared to some 
of the more effective later designs (its always easy to be wise in 
hindsight). Again, some will claim that these older boards have lost 
their stiffness with time. Yes they will have. But if you build a 
replacement panel for instruments of this period, using the same 
physical dimensions, they will exhibit a quite similar tonal quality, 
in spite of the fact that the soundboard is new. I believe it comes 
down to insufficient belly stiffness. Sure the rim weight/stiffness 
will play a part also, but the soundboard design along with the 
choice of hammer will be, above all else, the two principle factors 
which determine the overall tonal outcome.

When thinking about the desired physical characteristics of a sound 
board assembly, remember that while the very best low frequency 
speakers have a flexible perimeter region, the cone itself is 
reinforced to increase stiffness and reduce standing waves. Watching 
standing wave patterns form on a driven panel might look very 
interesting, but the propensity of the panel in itself to form 
standing waves is not helpful. We really should be trying to reduce 
them. I believe an effective design can help to minimise their 
influence over the tonal outcome. Considering where to make a board 
stiff and where to make it flexible, would seem to be a major 
priority.

Much of the sound board tone building equation comes down to a 
relationship between area/stiffness/mass per unit area. I don't know 
of anyone who has a magic formula for determining how much of what is 
desirable, but there are answers out there in waiting as the 'circle 
gets smaller'.

Ron O.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
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Web http://overspianos.com.au
mailto:ron at overspianos.com.au
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