[Arny Krueger]

"Dick Pierce" wrote in message
...
Arny Krueger wrote:

All of the strings are tightly mechanically coupled to the soundboard, a
piece of cast iron which is very rigid. Given the high speed of sound
and the rigidity of that piece of metal, my first order approximation
would be that it all vibrates as one piece. The strings have minimal
coupling to the air in comparison to the soundboard.

I've seen a LOT of pianos, and I must say I have NEVER seen one
with a cast iron sound board. All of them have cast iron frames,
put there primarily to keep the frame from collapsing in on
itself under the tremendous combined tension of the strings,
but that cast iron plays little or no role in the production
of sound.

The soundboard is, in fact, a larrge piece of joined, quarter-
sawn softwaood, like spruce, that, in a piano, is on the order
of 1/4" thick, that is genrally parallel to the string band
and maybe 1/2 behind it. One end of the strings is coupled
mechano-acoustically via the bridge, the other end of the
strings runs over the nut on the pin block, which is a very
thick piece of wood in which the tuning pins are screwed.

The soundboard in a piano serves the same role is constructed
in a way that would be very familiar to anyone knowing guitars
or violins.

The radiation pattern is dictated first by the complex
mechanical resonances of the soundboard, and also by the
fact that it is a very large, extremely non-uniform
radiating surface.

But, a cast iron soundboard? Not a chance.

Thanks for once again dispelling some of my erroneous ideas about pianos.

But the point is still taken that the sound board being a stiff board is
highly conductive of vibrations and is probably designed to not have a lot
of strong vibrational modes that are spatially or frequency dependent.

What I know for sure is that if you put two identical mics in most likely
places inside a piano, they sound very much alike. I therefore use a PZM
that is attached to the underside of the lid and keep the lid shut or on a
short stick. It takes a ton of eq to make the feed from the mic sound right,
but thats what eq is for.