Casters and Tone

[James Ellis]

Hi Folks:

I have not done any experiments with regard to grand piano casters and
tone, but I have noticed profound differences in the tone of a big grand
piano on a wooden floor, and the same piano on a concrete floor.  I will
venture a guess that it has more to do with the floor than it does the
casters, per se.  

Several things happen.  Some of the very low-frequency components are
carried right down the piano legs to the floor, and the floor acts as a
secondary low-frequency soundboard.  It's all in the coupling of the piano
to the floor.  Those hard brass casters do it.  Solid blocks will do it
too.  A stage truck will not do it.  In fact, it will isolate the
vibrations of the piano's structure from the floor.  I'll be willing to bet
that if you try the same experiment over a poured concrete floor on a bed
of rock, you won't get the same results at all.  A wooden floor over a
concrete base won't give you the same results as either of these.  Then
there is the sonic coupling of the piano's soundboard to the floor by the
air itself that contributes yet another factor.

There will be still another factor.  Solid coupling of the piano legs to a
concrete floor should make a slight difference in the tone, but in a
different direction from that of the wooden floor.  The reason is that the
solid concrete will make the piano's frame, rim, etc., slighty more rigid
to the vibrations than it already is.

I'll bet if we put some sensitive accelerometers on the floor under the
piano, it would be interesting to see what's going on there. 

In short, folks, I'll bet it's the floor, not the casters.  The casters are
only providing the coupling, while the stage truck provides isolation.

Jim Ellis