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Klarinet Archive - Posting 000260.txt from 1997/09

From: Mark Charette <charette@-----.com>
Subj: Re: ending the GreenLine plastic/composite thread
Date: Sat, 6 Sep 1997 14:11:23 -0400

Excerpted from an excellent article at
http://www.windworld.com/wq/12/dessy-12.htm

Response to Readers Questions on
Wood, Oil and Water
by Raymond and Lee Dessy

(C) Copyright 1996 | ISSN 1070-2512 | The Woodwind Quarterly -- for
author.

...

It is worth outlining just some of Backus' and Coltman's work on
pipes, clarinets, and flutes, and include more recent work on
fipple flutes. Backus' basic premise is that people feel some type
of vibration at the outer bore wall, and then conclude that this
affects the vibrating air column. His data clearly contradict this
belief. Backus comments: "...these arguments probably started in
early Stone-Age musical circles with assertions that a flute made
of a human thigh bone had a better tone than one fashioned from
the rib of a saber-tooth tiger."

Wooden vs. plastic clarinets, silver vs. gold transverse flutes,
and a large variety of metal, wood, and even paper organ pipes
have been examined for evidence of an affect of wall composition
on sound timbre. The construction materials studied span a range
in Young's modulus of 10**5 (a measure of stress vs. strain
response). Backus reports, "In no case is there a body vibration
large enough to give a sound level that could be a perceptible
component of the normal sound." The air column vibration sound
pressure levels (SPL) for either silver or gold flutes with wall
thicknesses of 300 micron (12.5 mil) are 60 dB above any from
wall vibrations. (The dB scale is not linear, but logarithmic.
For reference, the threshold of hearing is 0 dB; the threshold
of hearing pain is 120 dB; an office ~60 dB. The dB scale is the
log of the ratio of two sound measurements, matches how our ear
hears, and allows many different measurements to be easily
compared. 60 dB SPL is a ratio of 1000/1.)

What would the instrument body have to be doing to affect sound?
Backus concludes that "In order for the body sound to be a
prominent component it would be necessary to have body
acceleration levels on the surface of the order of 120 dB*."
Nominal coin silver or gold flute body acceleration levels are
only 60 dB. The body acceleration levels in the fipple flutes
studied lie at or below those of metal transverse flutes, and far
below that required to affect tonal quality. (*Note the switch from
measurement of acoustic pressure to body acceleration levels.)

Organ pipes experiments have been performed in which the sounding
tube was surrounded by a water jacket that was filled and emptied
of water during performance. "No changes ... could be observed for
any harmonic when the water was allowed to run out, nor could any
change in the sound be heard." If significant wall vibrations were
present they would have been damped out, affecting the perceived
tone.

...

"Effect of Wall Material on the Steady-State Tone Quality of
Woodwind Instruments", J. Backus, J. Acoust. Soc. Amer., 36,
1881 (1964)

"Wall Vibrations in Flue Organ Pipes and Their Effect on Tone",
J. Backus, and T. Hundley, J. Acoust. Soc. Amer., 39, 936 (1966)

"Effect of Material on Flute Tone Quality", J.W. Coltman, J.
Acoust. Soc. Amer., 49, 520 (1971)

--
Mark Charette "How can you be in two places at once
charette@-----.com when you're not anywhere at all?"
http://sneezy.mika.com/clarinet - Firesign Theater

   
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