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Journal of the Acoustical Society of America

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Jun 2009

Volume 125, Issue 6, pp. EL221-4109

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Hidden Markov and Gaussian mixture models for automatic call classification

Judith C. Brown and Paris Smaragdis

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. EL221-EL224 (2009); (4 pages) | Cited 2 times

Online Publication Date: 11 May 2009

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Automatic methods of classification of animal sounds offer many advantages including speed and consistency in processing massive quantities of data. Calculations have been carried out on a set of 75 calls of Northern Resident killer whales, previously classified perceptually (human classification) into seven call types, using, hidden Markov models (HMMs) and Gaussian mixture models (GMMs). Neither of these methods has been used previously for classification of marine mammal call types. With cepstral coefficients as features both HMMs and GMMs give over 90% agreement with the perceptual classification, with the HMM over 95% for some cases.
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43.80.Ka Sound production by animals: mechanisms, characteristics, populations, biosonar
43.80.Ev Acoustical measurement methods in biological systems and media
43.60.Uv Model-based signal processing
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Rhythmic structure in humpback whale (Megaptera novaeangliae) songs: Preliminary implications for song production and perception

Stephen Handel, Sean K. Todd, and Ann M. Zoidis

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. EL225-EL230 (2009); (6 pages) | Cited 1 time

Online Publication Date: 11 May 2009

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The hierarchical organization of the male humpback whale song has been well documented. However, it is unknown how singers keep these intricate songs intact over multiple repetitions or how they learn variations that occur sequentially during each mating season. Rather than focus on the sequence of sounds within a song, results presented here demonstrate that the individual sounds are organized into rhythmic groups that make the production and perception of the lengthy songs tractable by yielding a set of simple groups that, although arranged in rigid order, can be repeated multiple times to generate the entire song.
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43.80.Ka Sound production by animals: mechanisms, characteristics, populations, biosonar
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing
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A note on the effects of roughness on acoustic propagation past curved rough surfaces

Andrew Whelan and James P. Chambers

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. EL231-EL235 (2009); (5 pages)

Online Publication Date: 14 May 2009

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Previous work on sound propagation past curved rough rigid surfaces demonstrated substantial changes in the insertion loss in the shadow zone due to the roughness ranging from +6 to −20 dB from their smooth counterparts. These previous data also lead to new propagation modeling efforts to incorporate the effects of roughness via an impedance model but the data and modeling efforts were limited to a narrow range of roughness and hill sizes. The current effort was designed to expand the range of roughness and hill sizes in order to explore the range of influence of the roughness. The work presented here confirms the effects of surface roughness as observed in previous work and indicates where the effects of roughness begin to emerge as well as where they transition between decreasing the insertion loss to increasing the insertion loss.
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43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.20.Fn Scattering of acoustic waves
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The use of fundamental frequency for lexical segmentation in listeners with cochlear implants

Stephanie Spitzer, Julie Liss, Tony Spahr, Michael Dorman, and Kaitlin Lansford

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. EL236-EL241 (2009); (6 pages) | Cited 10 times

Online Publication Date: 14 May 2009

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Fundamental frequency (F0) variation is one of a number of acoustic cues normal hearing listeners use for guiding lexical segmentation of degraded speech. This study examined whether F0 contour facilitates lexical segmentation by listeners fitted with cochlear implants (CIs). Lexical boundary error patterns elicited under unaltered and flattened F0 conditions were compared across three groups: listeners with conventional CI, listeners with CI and preserved low-frequency acoustic hearing, and normal hearing listeners subjected to CI simulations. Results indicate that all groups attended to syllabic stress cues to guide lexical segmentation, and that F0 contours facilitated performance for listeners with low-frequency hearing.
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43.71.Ky Speech perception by the hearing impaired
43.71.An Models and theories of speech perception
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Rough surface scattering in a Born approximation from a two-way coupled-mode formalism

Steven A. Stotts and Robert A. Koch

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. EL242-EL248 (2009); (7 pages) | Cited 2 times

Online Publication Date: 14 May 2009

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Scattering from a rough surface in an ocean waveguide is described in a new derivation from a two-way coupled-mode representation. The general formalism, which contains scattering effects to all orders, is truncated to the first-order terms of an iterative (Born) expansion. Both two- and three-dimensional ocean waveguide geometries are discussed. By reducing the mode functions in terms of plane wave reflection coefficients, the off-diagonal components of the scattering kernel that is derived are shown to be consistent with a standard solution, but the diagonal components are different from the standard solution.
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43.30.Bp Normal mode propagation of sound in water
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Hw Rough interface scattering
43.20.Mv Waveguides, wave propagation in tubes and ducts
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Anomalous signed passive fathometer impulse response when using adaptive beam forming

Chris H. Harrison

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3511-3513 (2009); (3 pages) | Cited 4 times

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The impulse response of the seabed can be extracted from sea surface ambient noise by cross-correlating the time series from an upward and a downward steered beam. When the steering for each beam is standard minimum variance adaptive beam forming it has been found that the impulse response for significant echoes appears to have the same amplitude but opposite sign. A mathematical explanation is offered for this strange phenomenon. Crucial contributing factors are that the cross-spectral density matrix for the vertical array typically consists of the sum of a Toeplitz matrix and a much weaker Hankel matrix and that it is ill-conditioned.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.30.Nb Noise in water; generation mechanisms and characteristics of the field

Effect of a stack on Rayleigh streaming cells investigated by laser Doppler velocimetry for application to thermoacoustic devices

Solenn Moreau, Hélène Bailliet, and Jean-Christophe Valière

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3514-3517 (2009); (4 pages)

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A preliminary study was conducted to observe the influence of a stack on the Rayleigh streaming pattern for application to thermoacoustic devices. The velocity field was estimated from laser Doppler velocimetry measurements in a resonator first without a stack; then a stack was placed at various positions along the resonator axis for various acoustic levels. It was observed that adding a stack locally modifies the streaming pattern and that new streaming vortices appear. When the stack position approaches the location of the streaming velocity maximum or when the acoustic velocity amplitude is increased, the amplitude of additional acoustic streaming vortices at the ends of the stack increases.
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43.25.Nm Acoustic streaming

A sound field separation technique based on measurements with pressure-velocity probes

Yong-Bin Zhang, Xin-Zhao Chen, and Finn Jacobsen

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3518-3521 (2009); (4 pages) | Cited 3 times

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It has recently been shown that statistically optimized near field acoustic holography based on measurement with an array of pressure-velocity transducers makes it possible to distinguish between sources on the two sides of the array and thus suppress the influence of a disturbing source [ F. Jacobsen and V. Jaud, J. Acoust. Soc. Am. 121, 1550–1558 (2007) ]. However, the suggested technique uses a transfer matrix optimized for the source under test and may be expected to perform less well when the disturbing source is not placed symmetrically on the other side of the array, and this will usually be the case. In this letter, a modified method is presented.
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43.60.Sx Acoustic holography
43.60.Pt Signal processing techniques for acoustic inverse problems
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods

Greater sensitivity to prosodic goodness in non-native than in native listeners

Anne Cutler

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3522-3525 (2009); (4 pages) | Cited 1 time

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English listeners largely disregard suprasegmental cues to stress in recognizing words. Evidence for this includes the demonstration of Fear et al. [J. Acoust. Soc. Am. 97, 1893–1904 (1995)] that cross-splicings are tolerated between stressed and unstressed full vowels (e.g., au- of autumn, automata). Dutch listeners, however, do exploit suprasegmental stress cues in recognizing native-language words. In this study, Dutch listeners were presented with English materials from the study of Fear et al. Acceptability ratings by these listeners revealed sensitivity to suprasegmental mismatch, in particular, in replacements of unstressed full vowels by higher-stressed vowels, thus evincing greater sensitivity to prosodic goodness than had been shown by the original native listener group.
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43.71.Hw Cross-language perception of speech
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
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A model for sound absorption by spheroidal particles

Alexander K. Hipp

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3526-3538 (2009); (13 pages)

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This paper describes a mathematical model for the scattering of acoustic waves in dispersions of prolate or oblate non-spherical particles. Based on fundamental equations of change for mass, momentum, and energy, wave equations are derived and solved in spheroidal coordinates. The examination of the boundary-value problem of an aligned spheroidal particle in a continuous medium, excited by a plane wave, leads to a description of the viscoinertial, thermal, and diffractive phenomena. The model is analogous to the Epstein–Carhart–Allegra–Hawley theory for spherical particles, and suggests itself for studying non-sphericity in the acoustic analysis of industrial dispersions.
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43.20.Hq Velocity and attenuation of acoustic waves
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
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Radiation force of a helicoidal Bessel beam on a sphere

Philip L. Marston

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3539-3547 (2009); (9 pages) | Cited 10 times

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The partial-wave series for the scattering of an acoustic helicoidal Bessel beam by a sphere centered on the axis of the beam is applied to the calculation of the acoustic radiation force by the beam on the sphere in an inviscid fluid. The term “helicoidal” refers to a type of beam having an axial amplitude null and an azimuthal phase gradient. Such a beam is known as an acoustic vortex and only the case of a vortex having a unit magnitude topological charge is considered. There is no monopole contribution to the radiation force. Radiation force examples are computed for a soft sphere, a fixed rigid sphere, a movable rigid sphere, an aluminum sphere in water, and an acrylic sphere in water. Beam parameters are found for the rigid sphere and the aluminum and acrylic cases in which the radiation force is directed opposite the propagation direction of the beam. Negative radiation forces appear to be associated with relatively weak scattering into the backward hemisphere. Some aspects of the low frequency scattering of plane waves and helicoidal Bessel beams are examined for movable rigid spheres.
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43.25.Qp Radiation pressure
43.25.Uv Acoustic levitation
43.80.Ev Acoustical measurement methods in biological systems and media
43.40.Fz Acoustic scattering by elastic structures

Stirring and mixing of liquids using acoustic radiation force

Armen Sarvazyan and Lev Ostrovsky

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3548-3554 (2009); (7 pages) | Cited 1 time

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The possibility of using acoustic radiation force in standing waves for stirring and mixing small volumes of liquids is theoretically analyzed. The principle of stirring considered in this paper is based on moving the microparticles suspended in a standing acoustic wave by changing the frequency so that one standing wave mode is replaced by the other, with differently positioned minima of potential energy. The period-average transient dynamics of solid microparticles and gas microbubbles is considered, and simple analytical solutions are obtained for the case of standing waves of variable amplitude. It is shown that bubbles can be moved from one equilibrium position to another two to three orders of magnitude faster than solid particles. For example, radiation force in a standing acoustic wave field may induce movement of microbubbles with a speed of the order of a few m/s at a frequency of 1 MHz and ultrasound pressure amplitude of 100 kPa, whereas the speed of rigid particles does not exceed 1 cm/s under the same conditions. The stirring effect can be additionally enhanced due to the fact that the bubbles that are larger and smaller than the resonant bubbles move in opposite directions. Possible applications of the analyzed stirring mechanism, such as in microarrays, are discussed.
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43.25.Qp Radiation pressure
43.35.Mr Acoustics of viscoelastic materials
43.80.Qf Medical diagnosis with acoustics

Bistable and dynamic states of parametrically excited ultrasound in a fluid-filled interferometer

Isabel Pérez-Arjona, Víctor J. Sánchez-Morcillo, and Víctor Espinosa

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3555-3560 (2009); (6 pages) | Cited 1 time

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In this paper the problem of parametric sound generation in an acoustic resonator filled with a fluid is considered, taking explicitly into account the influence of the nonlinearly generated second harmonic. A simple model is presented, and its stationary solutions were obtained. The main feature of these solutions is the appearance of bistable states of the fundamental field resulting from the coupling to the second harmonic. An experimental setup was designed to check the predictions of the theory. The results are consistent with the predicted values for the mode amplitudes and parametric thresholds. At higher driving values a self-modulation of the amplitudes is observed. This phenomenon is identified with a secondary instability previously reported in the frame of the theoretical model.
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43.25.Ts Nonlinear acoustical and dynamical systems
43.25.Rq Solitons, chaos
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The rumble sound generated by a tidal bore event in the Baie du Mont Saint Michel

Hubert Chanson

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3561-3568 (2009); (8 pages) | Cited 2 times

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A tidal bore is a sharp rise in free-surface elevation propagating upstream in an estuarine system at the leading edge of the flood tide. It generates a powerful noise that was sometimes compared to the sounds of a horse cavalcade. Herein the sounds generated by a tidal bore event in the Baie du Mont Saint Michel were carefully recorded. The data showed three distinct periods. These were the incoming tidal bore when the sound amplitude increased with the approaching bore front, the passage of the tidal bore in front of the microphone where the impacts of the bore on the bank, rocks, or jetty generated powerful noises, and the upstream propagation of the bore when the flood flow motion caused additional loud noises. During the arrival of the tidal bore, the sound levels were less energetic and a lower-pitch sound was noted than during the subsequent record. For the breaking bore process, the analysis of the sound record indicated a dominant frequency around 76–77 Hz. The low-pitch rumble had a frequency comparable to the collective bubble oscillations, suggesting that air entrapment in the bore roller might play a major role in the acoustic signature.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.28.Tc Sound-in-air measurements, methods and instrumentation for location, navigation, altimetry, and sound ranging
43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
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The vertical structure of shadow-zone arrivals at long range in the ocean

Lora J. Van Uffelen, Peter F. Worcester, Matthew A. Dzieciuch, and Daniel L. Rudnick

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3569-3588 (2009); (20 pages) | Cited 6 times

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Multimegameter-range acoustic data obtained by bottom-mounted receivers show significant acoustic energy penetrating several hundred meters into geometric shadow zones below cusps (caustics) of timefronts computed using climatological databases [ B. D. Dushaw et al., IEEE J. Ocean. Eng. 24, 202–214 (1999) ]. This penetration is much larger than predicted by diffraction theory. Because these receivers are horizontal arrays, they do not provide information on the vertical structure of the shadow-zone arrivals. Acoustic data from two vertical line array receivers deployed in close proximity in the North Pacific Ocean, together virtually spanning the water column, show the vertical structure of the shadow-zone arrivals for transmissions from broadband 250-Hz sources moored at the sound-channel axis (750 m) and slightly above the surface conjugate depth (3000 m) at ranges of 500 and 1000 km. Comparisons to parabolic equation simulations for sound-speed fields that do not include significant internal-wave variability show that early branches of the measured timefronts consistently penetrate as much as 500–800 m deeper into the water column than predicted. Subsequent parabolic equation simulations incorporating sound-speed fluctuations consistent with the Garrett–Munk internal-wave spectrum at full strength accurately predict the observed energy level to within 3–4-dB rms over the depth range of the shadow-zone arrivals.
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43.30.Ft Volume scattering
43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
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Attenuation and dispersion of antiplane shear waves due to scattering by many two-dimensional cavities

Jun Kawahara, Taichi Ohno, and Kiyoshi Yomogida

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3589-3596 (2009); (8 pages) | Cited 1 time

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Propagation and scattering of antiplane shear waves within media with two-dimensional cavities are numerically simulated, and the attenuation and phase velocities are experimentally determined. The results are compared with the predictions by the Foldy theory and its three corrected versions. If the cavity concentrations are small such as 0.02, the differences among the theoretical predictions are insignificant, and every theory is consistent with the experimental results. For higher concentrations such as 0.1, the differences become significant, but there are no objective grounds to say that any of the corrected versions of the Foldy theory works better than the original. If the error tolerance is as high as 10%, the simple Foldy formula may remain useful for concentrations up to about 0.1.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Bi Mathematical theory of wave propagation

Resolving the shape of a sonoluminescence pulse in sulfuric acid by the use of streak camera

Wei Huang, Weizhong Chen, and Weicheng Cui

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3597-3600 (2009); (4 pages) | Cited 1 time

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A streak camera is used to measure the shape of sonoluminescence pulses from a cavitation bubble levitated stably in a sulfuric acid solution. The shape and response to an acoustic pressure field of the sonoluminescence pulse in 85% by weight sulfuric acid are qualitatively similar to those in water. However, the pulse width in sulfuric acid is wider than that in water by over one order of magnitude. The width of the sonoluminescence pulse is strongly dependent on the concentration of the sulfuric acid solution, while the skewed distribution of the shape remains unchanged.
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43.35.Hl Sonoluminescence
43.35.Ei Acoustic cavitation in liquids

A new safety parameter for diagnostic ultrasound thermal bioeffects: Safe use time

Irfan Karagoz and Mustafa K. Kartal

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3601-3610 (2009); (10 pages) | Cited 2 times

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It is widely accepted that diagnostic ultrasound has the potential to elevate the temperature of tissue being scanned. Because both the maximum value of the temperature rise and the temporal profile of that rise are necessary to estimate the risk correctly, the temperature rise [ΔT(t)] at an observation point for an exposure condition is presumed to have two components, that is, ΔT(t) = ΔTmaxX(t). The amplitude component ΔTmax is the maximum value of ΔT(t), and the exposure time component X(t) represents the time dependency of that ΔT(t). Ninety-six cases were investigated to obtain the proposed ΔT(t) model at six frequencies, four source diameters, and four f-numbers. Then, using the relative change in the rate of induction of a thermal effect due to ultrasound exposure that produces ΔT(t) different from a threshold exposure, the safe use time (SUT) model was constructed. SUT informs the user of the maximum duration of exposure in a region at a particular output level that would be no more hazardous than scanning at the threshold exposure. Using the SUT model, high power ultrasound can be applied for a short time so that the user can improve imaging performance while staying within safe limits.
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43.35.Wa Biological effects of ultrasound, ultrasonic tomography
43.80.Gx Mechanisms of action of acoustic energy on biological systems: physical processes, sites of action

A Fabry–Pérot fiber-optic ultrasonic hydrophone for the simultaneous measurement of temperature and acoustic pressure

Paul Morris, Andrew Hurrell, Adam Shaw, Edward Zhang, and Paul Beard

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3611-3622 (2009); (12 pages) | Cited 7 times

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A dual sensing fiber-optic hydrophone that can make simultaneous measurements of acoustic pressure and temperature at the same location has been developed for characterizing ultrasound fields and ultrasound-induced heating. The transduction mechanism is based on the detection of acoustically- and thermally-induced thickness changes in a polymer film Fabry–Pérot interferometer deposited at the tip of a single mode optical fiber. The sensor provides a peak noise-equivalent pressure of 15 kPa (at 5 MHz, over a 20 MHz measurement bandwidth), an acoustic bandwidth of 50 MHz, and an optically defined element size of 10 μm. As well as measuring acoustic pressure, temperature changes up to 70 °C can be measured, with a resolution of 0.34 °C. To evaluate the thermal measurement capability of the sensor, measurements were made at the focus of a high-intensity focused ultrasound (HIFU) field in a tissue mimicking phantom. These showed that the sensor is not susceptible to viscous heating, is able to withstand high intensity fields, and can simultaneously acquire acoustic waveforms while monitoring induced temperature rises. These attributes, along with flexibility, small physical size (OD ∼ 150 μm), immunity to Electro-Magnetic Interference (EMI), and low sensor cost, suggest that this type of hydrophone may provide a practical alternative to piezoelectric based hydrophones.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
43.35.Wa Biological effects of ultrasound, ultrasonic tomography
43.30.Xm Underwater measurement and calibration instrumentation and procedures

Excitation and scattering of guided waves: Relationships between solutions for plates and pipes

Alexander Velichko and Paul D. Wilcox

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3623-3631 (2009); (9 pages) | Cited 6 times

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The detection of localized defects such as cracks and corrosion in pipes using guided elastic waves is now an established non-destructive testing procedure. However, the prediction of guided wave excitation and scattering in pipes is a complex three-dimensional (3D) problem with many parameters that can generally only be solved using numerical methods. In many important industrial applications, the diameter of a pipe is much larger than wall thickness. In this case an approximate theory is applicable, when a pipe is considered as an unwrapped isotropic plate. In this paper, a technique for obtaining pipe mode amplitudes in terms of the solution to the forced 3D problem on a plate is presented. The same principle is extended to relate guided wave scattering from defects in plates to scattered circumferential modal amplitudes from defects in pipe. This is of practical benefit as the scattering of guided waves by defects in a plate is a much simpler problem than that in a pipe, and one that, in some cases, can be solved using analytical methods. Results are shown that illustrate the application of the method to reflection from through-thickness circumferential cracks in pipes.
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43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
43.20.Bi Mathematical theory of wave propagation
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
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Electroacoustic analysis of an electret loudspeaker using combined finite-element and lumped-parameter models

Mingsian R. Bai, Rong-Liang Chen, and Chun-Jen Wang

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3632-3640 (2009); (9 pages) | Cited 3 times

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An unconventional type of electrostatic loudspeaker is presented in this paper. The loudspeaker made of thin, light, and flexible electret material lends itself well to the space-concerned applications. Electrical impedance measurement reveals that the coupling between the electrical system and the mechanical system is weak, which renders conventional parameter identification based on electrical impedance measurement impractical. A different approach is thus employed to model the electret loudspeaker. To predict the loudspeaker’s dynamic response, finite-element analysis (FEA) is conducted on the basis of a simple model and a full model. In the simple model, FEA is applied to model the electret membrane, leaving the rest of system as rigid parts. In the full model, FEA is applied to model the entire membrane-spacer-back plate assembly. Velocity response of the membrane subject to a uniformly distributed force is calculated using FEA harmonic analysis. Mechanical impedance is then calculated with the velocity response. The acoustical impedance due to the back cavity, pores, and the radiation loading at the front side is calculated by theoretical formulas. The volume velocity of the membrane and the resulting on-axis sound pressure level are predicted with electrical-mechanical-acoustical analogous circuits. The response data predicted by the simulation compare very well with experimental measurements.
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43.38.Bs Electrostatic transducers
43.38.Ja Loudspeakers and horns, practical sound sources
43.40.Dx Vibrations of membranes and plates

Design optimization of condenser microphone: A design of experiment perspective

Chee Wee Tan and Jianmin Miao

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3641-3649 (2009); (9 pages)

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A well-designed condenser microphone backplate is very important in the attainment of good frequency response characteristics—high sensitivity and wide bandwidth with flat response—and low mechanical-thermal noise. To study the design optimization of the backplate, a 26 factorial design with a single replicate, which consists of six backplate parameters and four responses, has been undertaken on a comprehensive condenser microphone model developed by Zuckerwar. Through the elimination of insignificant parameters via normal probability plots of the effect estimates, the projection of an unreplicated factorial design into a replicated one can be performed to carry out an analysis of variance on the factorial design. The air gap and slot have significant effects on the sensitivity, mechanical-thermal noise, and bandwidth while the slot/hole location interaction has major influence over the latter two responses. An organized and systematic approach of designing the backplate is summarized.
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43.38.Kb Microphones and their calibration
43.38.Bs Electrostatic transducers
43.38.Ar Transducing principles, materials, and structures: general
43.58.Ta Computers and computer programs in acoustics
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The mode shapes of a tennis racket and the effects of vibration dampers on those mode shapes

Nicholas Timme and Andrew Morrison

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3650-3656 (2009); (7 pages) | Cited 2 times

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The vibrational behavior of a tennis racket was studied using a speckle-pattern interferometry system. Specifically, the first 12 mode shapes of a racket are shown and discussed. In addition, the speckle-pattern interferometry system was used to compare the effects of four commercially available vibration damping systems. It was found that these vibration dampers produce a variety of effects on the vibrational behavior of the racket, though these effects may not be noticeable during play.
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43.40.At Experimental and theoretical studies of vibrating systems
43.20.Ks Standing waves, resonance, normal modes

Graph theory applied to noise and vibration control in statistical energy analysis models

Oriol Guasch and Lluís Cortés

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3657-3672 (2009); (16 pages) | Cited 2 times

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A fundamental aspect of noise and vibration control in statistical energy analysis (SEA) models consists in first identifying and then reducing the energy flow paths between subsystems. In this work, it is proposed to make use of some results from graph theory to address both issues. On the one hand, linear and path algebras applied to adjacency matrices of SEA graphs are used to determine the existence of any order paths between subsystems, counting and labeling them, finding extremal paths, or determining the power flow contributions from groups of paths. On the other hand, a strategy is presented that makes use of graph cut algorithms to reduce the energy flow from a source subsystem to a receiver one, modifying as few internal and coupling loss factors as possible.
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43.40.At Experimental and theoretical studies of vibrating systems
43.50.Jh Noise in buildings and general machinery noise

Modeling the dynamics of a vibrating string with a finite distributed unilateral constraint: Application to the sitar

Chandrika P. Vyasarayani, Stephen Birkett, and John McPhee

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3673-3682 (2009); (10 pages)

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The free vibration response of an ideal string impacting a distributed parabolic obstacle located at its boundary has been analyzed, the goal being to understand and simulate a sitar string. The portion of the string in contact with the obstacle is governed by a different partial differential equation (PDE) from the free portion represented by the classical string equation. These two PDEs and corresponding boundary conditions, along with the transversality condition that governs the dynamics of the moving boundary, are obtained using Hamilton’s principle. A Galerkin approximation is used to convert them into a system of nonlinear ordinary differential equations, with lower mode-shapes parametrized with respect to the location of the moving boundary as basis functions. This system is solved numerically and the behavior of the string studied from simulations. The advantages and disadvantages of the proposed method are discussed in comparison to the penalty approach for simulating wrapping contacts. Simulations with bridge-string parameters consistent with the configuration of a real sitar show that any degree of obstacle wrapping may occur during normal playing. Finally, the model is used to investigate the mechanism behind the generation of the buzzing tone in a sitar.
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43.40.Cw Vibrations of strings, rods, and beams
43.75.Gh Plucked string instruments
43.40.At Experimental and theoretical studies of vibrating systems
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  1. Active acoustical impedance using distributed electrodynamical transducers
  2. Demonstration of a wireless, self-powered, electroacoustic liner system
  3. Green's function approximation from cross-correlations of 20–100 Hz noise during a tropical storm
  4. Correction techniques for the truncation of the source field in acoustic analogies
  5. Source localization from an elevated acoustic sensor array in a refractive atmosphere

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