Sound Propagation

[Richard Brekne]

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Ok gang,

Arthur Benades book "Fundamentals of Musical Acoustics" at the end of Chapter six
he make a short dip into the natural vibrations of extended objects and his
example for this is very similar to our pond example. Instead he is using a
Trough of Water in which the water is caused to slosh back and forth. This is on
page 88 - 90 for anyone who has the book. The point is that he ties the vertical
component of the waves directly to the horizontal component.  Looking from the
side we are still in a 2 dimensional system, but we clearly can see both the
transverse and longitudinal components in action at the same time. And the neat
part is that, and I quote


     "in every case (for each successive mode) the largest horizontal
     oscillation of the water takes place precisely at those points where
     the vertical motion is zero. Conversely we find that the nodes of the
     horizontal motion are located at the exact spots where the water's
     vertical oscillation is the largest. We have discovered that every mode
     of watery oscillation in a trough has two interlaced aspects: a
     vertical motion and a horizontal motion...."


This is still in the opening chapters of his book and I still don't have anything
to couple this kind of wave propagation directly to the sound board. But if
vibration energy has to propagate in similar fashion for all elastic
medium...then ...well I am still pointed in that direction. In any case it was
neat to see that my thinking along the pond / ripple tangent wasn't completely
out in left field. :)


Ricb




--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no


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