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A tuning fork sound effect....




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.