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Re: A tuning fork sound effect....



It is even more interesting to slowly rotate the tuning fork near the
ear. One observes a total of four alternating loud and soft
intensities.

This comes from the quadrapole radiation pattern of the
tuning fork: a maximum parallel and perpendicular to the tines and nodes
at the 45 degree points.

When the student moves the tuning for past his ear, he is rotating the
fork relative to his ear, so he hears alternating loud and soft
intensity.

Regards, Eric Lane (split infinitives to go)

Prof. Eric T. Lane 423-755-4523 eric-lane@utc.edu
Physics Department, University of Tennessee at Chattanooga, TN 37403

On Thu, 1 May 1997, von Philp wrote:


A student of mine was messing around with my tuning forks and noticed the
following interesting effect:

From a distance of about 5 cm from the ear, a tuning fork is slowly moved
past the ear in a horizontal plane perpendicular to the ear canal. When
this is done, the sound appears to alternate loud and soft intensity every
few centimeters the tuning fork is moved.

First question: Have any of you ever noticed this effect? (If you haven't
tried this, do so at your first opportunity!)

Second question: Why does the sound get louder and softer? My first guess
is constructive and destructive interference (as in a resonance tube).
However, I want to be sure that it is not simply caused by a more direct
alignment of the sound down the ear canal.

Any thoughts?

-- Ralph von Philp

P.S. If this is a new effect, I shall call it the Newman effect, after the
student (P. Tyler Newman) that first pointed it out to me.