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May 1990

Volume 87, Issue S1, pp. S1-S164

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back to top Session CCC. Musical Acoustics IV: Physics of Musical Instruments II
Invited Paper
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On the excitation mechanism in reed wind instruments (A)

J. Agulló and A. Barjau

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S137-S137 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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The production of self‐sustained oscillations in reed woodwinds in based mainly on two physical mechanisms: the coupling mechanism—which makes use of the reflections coming from bore discontinuities—and the Bernoulli mechanism—which consists of a Venturi effect acting on the reed. As far as woodwinds with striking inward reeds are concerned, the only widely studied instrument has been the clarinet—a roundly cylindrical bore driven by a single reed—in which the coupling mechanism plays an essential role while the Bernoulli mechanism can be neglected in a first approach. However, little attention has been paid in the literature to the wider set of double‐reed conical woodwinds (oboe, bassoon, shawms, etc.), in which sound production is based on the cooperation between both coupling and Bernoulli mechanisms. In this paper, both mechanisms are assessed and a comparative analysis is made of cylindrical and conical bores' input impulse responses, whose shape and strength are related to the intensity of the coupling mechanism. Due to the low intensity of the impulse response reflections in conical bores, the coupling mechanism in this case behaves mainly as a trigger of the intense Bernoulli mechanism, which is the one that strongly acts on the reed. Experimental results are also presented showing the bore input pressure for several instruments when producing a note attack, and illustrating the collaboration between both mechanisms.
Contributed Papers
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On sound production in brass instruments (A)

Douglas H. Keefe

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S138-S138 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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The brass player's lips under playing conditions are displaced both longitudinally along the axis of the air column entryway, and laterally, or perpendicular, to the axis. Existing theories have modeled the valving action of the player's lips as a simple oscillator, or lip reed, but fall into two classes, depending upon whether the lip reed displacement is assumed to be purely longitudinal or lateral. An alternative model of sound production is proposed, retaining the single degree‐of‐freedom oscillator description, but including both longitudinal and lateral displacements. The lip reed is assumed to execute a circular, outwardly rolling motion. In the limit of small oscillations, this simplifies to linear displacement along an axis inclined relative to the air column entryway axis. The angle of inclination is a model parameter, but should depend upon mouthpiece geometry and player's embouchure. The lip reed is driven longitudinally by the pressure difference between the player's mouth (upstream) and the mouthpiece (downstream). It is driven laterally by the pressure within the lip orifice, which is related to the downstream pressure by momentum flux conservation. The time domain model incorporates reflection functions looking downstream into the air column, and upstream into the player's respiratory tract. The upstream reflection function can similarly be incorporated into player‐woodwind models.
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Computer simulation of a trumpet (A)

William J. Strong

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S138-S138 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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In an effort to generate realistic trumpet mouthpiece pressure waveforms, a player‐trumpet model was created that consisted of the player's lungs, the player's airway, the player's upper lip, and the trumpet. The player's lungs were modeled as a constant pressure source. The player's airway (from lungs to lips) was modeled as a resistance of 20 acoustic ω (cgs). The player's lip was modeled as a swinging‐sliding door having 1 deg of rotational freedom and one degree of translational freedom. The trumpet was modeled in terms of its pressure response to a volume‐flow impulse. Equations were solved iteratively to give (1) lip opening as a dynamic function of the forces and torques acting on the lip, (2) volume flow as a function of lip opening and the pressure difference across the lips, and (3) mouthpiece pressure as a convolution of volume flow with trumpet impulse response. Waveforms were calculated and displayed for the lip‐opening area, the volume flow through the lips, and the pressure in the mouthpiece. The lip‐opening area and mouthpiece pressure waveforms were realistic when compared to experimental waveforms in the literature. However, there are still too few experimental data to constrain the model in terms of lip closure time and total air flow on sustained notes. Simulation data will be presented and compared with experimental data. [The work to be reported was carried out while the author was on leave at IRCAM in Paris. René Caussé supplied player and trumpet data and Duanne Dudley supplied trumpet impulse data.]
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Vibrations of circular and noncircular cylindrical shells (A)

George J. Jelatis and Thomas D. Rossing

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S138-S138 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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In order to better understand the vibrational modes of Chinese two‐tone bells [Rossing et al., J. Acoust. Soc. Am. 83, 369–373 (1988)], the vibrational modes of capped and uncapped cylinders with circular and nearly elliptical cross sections have been studied. Mode doublets in the noncircular cylinders replace single modes in the circular cylinders. The higher frequency mode in each doublet, in both the capped and uncapped cylinders, generally belongs to the mode that has a node where the curvature is greatest. The frequency ratio of the doublet pair appears to decrease with increasing m (number of wavelengths around the circumference) but to increase with n (number of nodal circles). The splitting increases with eccentricity, as expected.
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Vibrational modes and damping in a snare drum shell (A)

Dell O. Fystrom and Thomas D. Rossing

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S138-S138 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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The lowest modes of a cylindrical snare drum shell, described by the number n of nodal circles and the number of m of nodal lines around the circumference, have been identified by means of holographic interferometry, scanning the nearfield sound with a microphone, and by attaching a small accelerometer to the shell. The modal decay rate in the free shell increases rapidly with modal frequency. In a complete snare drum, on the other hand, the normal modes of vibration are determined mainly by the motion of the drumheads. The modal decay rates are strongly dependent on the manner in which the drum is supported, being least when the drum is supposed on elastic cords. This indicates that a considerable amount of vibrational energy is transmitted to the shell of the drum as the heads vibrate.
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Demonstrating vibrations of musical instruments by use of modal analysis (A)

Uwe J. Hansen and Thomas D. Rossing

J. Acoust. Soc. Am. Volume 87, Issue S1, pp. S138-S138 (1990); (1 page)

Online Publication Date: 13 Aug 2005

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Modal analysis using impact excitation has been used to study the dynamical behavior of a wide variety of structures from B747 airplanes to handbells. Some modes of vibration of several musical instruments, including a guitar, a handbell, a Caribbean steel drum, a snare drum, and a piano soundboard, will be demonstrated on videotape.
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