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From: "Sir Charles W. Shults III"
References: <96dU9.21919$jM5.firstname.lastname@example.org> <email@example.com> <1pvIMwAJ$rI+EwVe@jmwa.demon.co.uk> <firstname.lastname@example.org>
Subject: Re: Acoustic Feedback reduction
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Mon, 13 Jan 2003 23:01:27 GMT
NNTP-Posting-Date: Mon, 13 Jan 2003 18:01:27 EST
Organization: RoadRunner - Central Florida
Now here is an interesting audio phenomenon that occurs with sounds
reflecting off surfaces that have a regular pattern- such as corrugated metal.
The sound of a sharp pop turns into a rising squeak. This is due to the
many "facets" each reflecting the pop at a slightly different time- the sum of
all those individual events are heard as a squeak because the ear is receiving
numerous closely spaced pops and interprets this as frequency.
I first observed this near an old farm building as a child when gunshots
from nearby hunters were reflected from the corrugated metal. My left ear could
hear the gunshots more clearly as they were to my left, but the echo from the
metal building made a rising squeak in my right ear.
At the time, it was just another mystery of life. Later, when I worked at
Universal Studios, I was behind a large building during a fireworks display and
the same effect occurred again, but this time, it was strong and repeated many
With each shell that burst, the angled roof of the building (which had
hundreds of identical parallel metal rectangles on it) shot back a delayed
squeaking echo of the boom. Upon looking at the roof, the cause of the mystery
sound was immediately obvious. Each facet contributed a single "tick", but my
angle caused the ticks to occur at a different rate- the shock wave was hitting
them at different times!
If I (and the booms) had been perpendicular to the surface, I would have
heard only a boom. But since we were at angles, the reflection had been broken
up in time and space hundreds of times.
So it would seem that in some cases, even sound can illustrate a principle
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
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