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TUESDAY AFTERNOON, 8 NOVEMBER 1983 ß
DEL MAR/HELIX/SANTA FE ROOMS, 3:35 TO 4:55 P.M.
Session P. Musical Acoustics III: Wind Instruments
R. Dean Ayers, Chairman
Department of Physics-Astronomy, California State University, Long Beach, California 90840
Chairman's Introductions3:35
Contributed Papers
3:40
P1. The effects of the flaring bell on the normal frequencies of a
trombone. J. Duane Dudley and William J. Strong (Department of
Physics and Astronomy, Brigham Young University, Provo, UT 84602)
As sinusoidal waves encounter the bell of a brass wind instrument,
they are effectively reflected by the flaring part of the bore. A given fre-
quency is effectively reflected from that part of the bell where a significant
change in bore radius occurs within a wavelength. Hence the longer wave-
lengths reflect from points closer to the inlet end of the bell than do the
shorter wavelengths. A computer calculation of the equivalent lengths
corresponding to the normal frequencies shows this effect, and shows how
the frequency shifts depend on the shape of the bore. Through this effect,
the bell makes an important contribution towards making the normal
frequencies harmonic.
3:55
P2. Effect of the player's vocal tract on the tone quality of reed woodwind
instruments. John Backus (Physics Department, University of Southern
California, Los Angeles, CA 90089-134 l)
It has been argued by woodwind instrument players that the configu-
ration of the player's vocal tract has an effect on the tone quality of the
instrument when played. This matter is being investigated. The following
arrangement has been set up: A "clarinet" is simulated by mounting a
clarinet mouthpiece and reed on a piece of brass tubing of such length as to
sound the note D3 when blown, using a foam neoprene "lip" with the
reed. A microphone is attached to the mouthpiece to monitor its internal
pressure. The open end of the brass tube is sealed onto the end of a 4-in.-
diam tube l0 ft long filled with sound absorbing material. By attaching a
vacuum cleaner to the other end of the 4-in. tube, the "clarinet" can be
"blown," as it were, in reverse, with the reed end out in the open. Various
systems can now be attached to the mouthpiece and their effect on the
internal waveform of the mouthpiece determined. Results so far indicate
that the effect of the player's vocal tract on the instrument's tone quality
should be negligible. [Work supported by the NSF.]
4:10
P3. Edgetone spectra. A. W. Nolle (Department of Physics, The
University of Texas at Austin, Austin, TX 78712}
It is well known that as the velocity of an air jet impinging on an edge is
increased, various regimes of periodic oscillation are found in which the
frequency increases with jet velocity. It will be shown that also there are
narrow ranges in which the signal consists of two or more components,
not harmonically related, and various intermodulation products. Ultima-
tely, as the jet velocity increases, the signal becomes a noise band. Exten-
sive data on these phenomena will be shown. In the present work the jet-
to-edge distance is 4-12 mm, and the jet velocity lies between 5 and 30 m/
s. In resemblance to a common practice in organ pipe construction, the
piece whose edge is struck by the jet is unsymmetrical, consisting of a 45 ø
wedge mounted so that one side is parallel to the center line of the jet.
4:25
P4. The conical bore in musical acoustics. R. Dean Ayers, Lowell
J. Eliason, and Daniel Mahgerefteh (Department of Physics-
Astronomy, California State University, Long Beach, CA 90840}
A review of textbooks and research literature reveals that there is
room for improvement in the treatment of this simple but important bore
shape. We use plots of acoustic pressure standing waves to show students
in a descriptive course that a complete cone and an open pipe of the same
length have the same natural frequencies. These plots also predict the
qualitative behavior for the frequencies of a frustum closed at the small
end and suggest a rigorous approach to their calculation. Incorporating
the open end correction for a straight pipe plus a correction for viscosity
and thermal conductivity in the calculation results in agreement with
experimental values to within 0.5%. In order to understand the inhar-
monicity of the frustum's frequencies from a different approach, we have
calculated the pressure impulse response for reflection from its closed end.
We find that this consists of a delta function plus an inverted, exponential-
ly decaying wake. Experimental observations confirm both that shape for
the impulse response and its contribution to the evolution of the waveform
through several reflections.
4:40
P5. Recorder multiphonics. R. Dean Ayers, Lowell J. Eliason, and
David Forel (Department of Phys;,cs-Astronomy, California State
University, Long Beach, CA 90840)
A systematic study has been undertaken to identify and analyze all
possible multiphonics on a popular brand of plastic recorder (Aulos, alto
voice). The absence of a bell at the end of the recorder combines with the
open-hole cutoff effect to guarantee strong, nonharmonic bore reson-
ances, and many of the forked fingerings produce stable multiphonics
when blown somewhat hard. The more stable and aurally interesting mul-
tiphonics have two strong spectral components, one supported by the
fundamental bore resonance and the other by the fourth or fifth reso-
nance. Heterodyne descendants of these components are also found, but
rarely with comparable strength. The less interesting multiphonics have
just one strong component, often at the third resonance, with noticeably
weaker components beating against it. Some fingerings will produce more
than one multiphonic, depending on the breath pressure and/or attack
used. One factor that may be significant for stability is the fact that the
edge tone itself goes multiphonic at the blowing pressures used, without
any feedback from the bore.
S29 J. Acoust. Soc. Am. Suppl. 1, Vol. 74, Fall 1983 106th Meeting: Acoustical Society of America S29
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