Volume 127, Issue 2, February 2010
- jasa express letters
- letters to the editor
- general linear acoustics 
- nonlinear acoustics 
- aeroacoustics, atmospheric sound 
- underwater sound 
- ultrasonics, quantum acoustics, and physical effects of sound 
- structural acoustics and vibration 
- noise: its effects and control 
- architectural acoustics 
- acoustical measurements and instrumentation 
- acoustic signal processing 
- physiological acoustics 
- psychological acoustics 
- speech production 
- speech perception 
- speech processing and communication systems 
- music and musical instruments 
- bioacoustics 
- acoustical news
- book reviews
- reviews of acoustical patents
Index of content:
- JASA EXPRESS LETTERS
127(2010); http://dx.doi.org/10.1121/1.3280234View Description Hide Description
Although the spatial focusing property of the conventional time reversal approach facilitates multiuser communications, there always is residual crosstalk between users. A recent paper [Kim and Shin, J. Acoust. Soc. Am.115, 600–606 (2004)] proposed an adaptive active time reversal approach for simultaneous multiple focusing with minimal interference. This letter applies the adaptive approach to passive time reversal, multiuser communications for additional suppression of crosstalk among users. Experimental data at with a bandwidth demonstrate as much as improvement per user in terms of output signal-to-noise ratio for three-user communications over a range in deep shallow water.
127(2010); http://dx.doi.org/10.1121/1.3280236View Description Hide Description
This study investigated temporal integration processes underlying cochlear implant(CI) users’ amplitude modulation processing. Thresholds for modulation detection (AMDTs) and modulation frequency discrimination (AMFDTs) were measured for 50-, 100-, and 200-Hz modulation frequencies with stimulus durations from 50 to 400 ms in eight adult CI users. The results showed significant interactions between modulation frequency and stimulus duration for AMDTs and AMFDTs. The data suggest that temporal integration limits CI users’ sensitivity to low temporal pitch over short durations, and that temporal integration over longer durations may not enhance CI users’ sensitivity to high temporal pitch.
127(2010); http://dx.doi.org/10.1121/1.3280237View Description Hide Description
The transfer matrix method based is extensively used and well-validated for predicting the transmission loss of multilayer structures. However, this method leads to poor results at low frequencies due to the infinite extent assumption it is based on. This paper presents an efficient implementation of a Rayleigh-integral based method to account for the finite size effects. The accuracy of the method is illustrated by various examples.
127(2010); http://dx.doi.org/10.1121/1.3284544View Description Hide Description
Cochlear implant(CI) and normally hearing (NH) listeners’ recognition of periodically interrupted sentences was investigated. CI listeners’ scores declined drastically when the sentences were interrupted. The NH listeners showed a significant decline in performance with increasing spectral degradation using CI-simulated, noise-band-vocodedspeech. It is inferred that the success of top-down processes necessary for the perceptual reconstruction of interrupted speech is limited by even mild degradations of the bottom-up information stream (16 and 24 band processing). A hypothesis that the natural voice-pitch variations in speech would help in the perceptual reconstruction of the sentences was not supported by experimental results.
127(2010); http://dx.doi.org/10.1121/1.3284548View Description Hide Description
This letter describes a ray-based blind deconvolution technique for oceansound channels that produces broadband estimates of the source-to-array impulse response and the original source waveform from array-measured signals corrupted by (unknown) multipath propagation. The technique merely requires elementary knowledge of array geometry and sound speed at the array location. It is based on identifying a ray arrival direction to separate source waveform and acoustic-propagation phase contributions to the received signals. This technique successfully decoded underwater telecommunicationsequences in the bandwidth 3–4 kHz that were broadcast 4 km in a 120-m-deep oceansound channel without a-priori knowledge of sound channel characteristics.
127(2010); http://dx.doi.org/10.1121/1.3290175View Description Hide Description
A nonlinear structural intensity concept is presented as an approach for the identification of defects displaying nonlinear vibration behavior. The nonlinear structural dynamic response exhibited by a riveted joint with loosened fasteners connecting a stiffener with a flat panel is investigated. The excitation, generating elastic waves with dominant bending components, triggers the nonlinear contact between the plate and the stiffener inducing a dynamic response rich with nonlinear harmonics. Experimental structural intensity maps are evaluated at the super-harmonic frequencies. This technique provides an experimental approach for the characterization and two dimensional visualization of nonlinear types of defects.
127(2010); http://dx.doi.org/10.1121/1.3292286View Description Hide Description
The role of consciously directed attention toward speech input in learning has not yet been determined. Previous phonetic learning studies have manipulated acoustic signals and response feedback, but not conscious control over attentional orienting. This study tests whether directed attention facilitates learning of phoneticinformation. Two monolingual English-speaking groups were trained with feedback on the same auditory stimuli: Hindi words. One group was instructed to attend to the consonants and the other to the vowels. The consonant-oriented group, but not the vowel-oriented group, demonstrated post-training improvement in consonant perception, confirming a role for consciously directed attentional mechanisms during phonetic learning.
127(2010); http://dx.doi.org/10.1121/1.3290744View Description Hide Description
A magnetoencephalography study was conducted to reveal the neural code of interaural time difference(ITD) in the human cortex. Widely used crosscorrelator models predict that the code consists of narrow receptive fields distributed to all ITDs. The present findings are, however, more in line with a neural code formed by two opponent neural populations: one tuned to the left and the other to the right hemifield. The results are consistent with models of ITD extraction in the auditory brainstem of small mammals and, therefore, suggest that similar computational principles underlie human sound source localization.
Verification of a near-field error sensor placement method in active control of compact noise sources127(2010); http://dx.doi.org/10.1121/1.3272632View Description Hide Description
Recent experiments in active noise control (ANC) have used near-field error sensors whose locations are determined according to the minimization of sound power. Sensors should be placed in regions where the sound pressure reductions are the greatest during sound power minimization of the ANC system. Near-field pressure measurements of noise sources with and without ANC were made. With the error sensors in theoretically ideal locations, the measured near-field pressure map approximates the theoretical map created under the condition of minimized radiated power. Moving the error sensors to theoretically nonideal locations greatly reduces the attenuation of radiated sound power.
127(2010); http://dx.doi.org/10.1121/1.3284545View Description Hide Description
It is shown that robust dimension-reduction of a feature set for speech recognition can be based on a model of the human auditory system. Whereas conventional methods optimize classification performance, the proposed method exploits knowledge implicit in the auditory periphery, inheriting its robustness. Features are selected to maximize the similarity of the Euclidean geometry of the feature domain and the perceptual domain. Recognition experiments using mel-frequency cepstral coefficients (MFCCs) confirm the effectiveness of the approach, which does not require labeled training data. For noisy data the method outperforms commonly used discriminant-analysis based dimension-reduction methods that rely on labeling. The results indicate that selecting MFCCs in their natural order results in subsets with good performance.
127(2010); http://dx.doi.org/10.1121/1.3292562View Description Hide Description
A three-dimensional non-linear model for simulating microbubble response to acoustic insonation is presented. A radius microbubble stimulated using positive and inverted 2.4 MHz pulses produced radius-time curves that matched (error ) with the experimental observation. A bound radius microbubble insonated using 2.25 MHz 6 cycle pulse was observed to oscillate with max/min oscillations 45% lower than that of the free microbubble, this correlated ( error) with the observations of Garbin et al. [Appl. Phys. Lett.90, 114103 (2007)]. The adherent microbubbleoscillated asymmetrically in the plan view and symmetrically in the elevation view, consistent with the previous experimental results.
- LETTERS TO THE EDITOR
Scattering by an arrangement of eccentric cylinders embedded on a coated cylinder with applications to tomographic density imaging127(2010); http://dx.doi.org/10.1121/1.3277154View Description Hide Description
The solution to the scattering of an incident pressure wave by an arrangement of eccentric cylinders embedded inside a pair of concentric cylinders is derived here using a combination of -matrix and mode-matching approaches. This method allows the generation of synthetic data from relatively complex structures to be used for the validation of acoustic tomography methods. An application of the solution derived here is illustrated by reconstructing sound speed and density profiles from a complex phantom using inverse scattering.
127(2010); http://dx.doi.org/10.1121/1.3278607View Description Hide Description
It has been reported recently through high speed optical observations of phospholipid-coated contrast microbubbles that there is a threshold value for the acoustic pressure amplitude below which the radial oscillation of the microbubbles does not occur. In this Letter, it is suggested that this threshold behavior results from the fact that a phospholipid layer, as a physical material, has a certain value of the limiting shear stress so that its deformation does not start until this limiting value is exceeded. A theoretical model is proposed for the description of this phenomenon. The model explains the experimentally observed dependence of the threshold onset of microbubble oscillation on the initial bubble radius.
The influence on predicted harmonic and distortion product generation of the position of the nonlinearity within cochlear micromechanical models127(2010); http://dx.doi.org/10.1121/1.3279812View Description Hide Description
Numerical techniques are used to explore the influence on the predicted basilar membrane (BM) response of the position of the nonlinearity within the micromechanical feedback loop of an active nonlinear cochlear model. This position is found to influence both the harmonic and distortion product spectra of the predicted BM response. The BM motion at the fundamental or primary frequencies is not significantly altered by the position of the nonlinearity, however, provided that the gain is appropriately adjusted. The observed effects are explained in terms of the frequency responses of the elements within the micromechanical feedback loop.
Modulation rate discrimination using half-wave rectified and sinusoidally amplitude modulated stimuli in cochlear-implant users127(2010); http://dx.doi.org/10.1121/1.3282947View Description Hide Description
Detection and modulation rate discrimination were measured in cochlear-implant users for pulse-trains that were either sinusoidally amplitude modulated or were modulated with half-wave rectified sinusoids, which in acoustic hearing have been used to simulate the response to low-frequency temporal fine structure. In contrast to comparable results from acoustic hearing, modulation rate discrimination was not statistically different for the two stimulus types. The results suggest that, in contrast to binaural perception, pitch perception in cochlear-implant users does not benefit from using stimuli designed to more closely simulate the cochlear response to low-frequency pure tones.
Psychophysical tuning curves and recognition of highpass and lowpass filtered speech for a person with an inverted V-shaped audiogram127(2010); http://dx.doi.org/10.1121/1.3277218View Description Hide Description
A single subject whose audiogram resembled an inverted V shape (good hearing at 4000 Hz, and poorer hearing at other frequencies) was tested. Results of the threshold-equalizing noise test suggested that a dead region (DR) in the cochlea was present at all test frequencies from 500 to 3000 Hz, but no DR was present at 4000 Hz. Psychophysical tuning curves (PTCs) obtained using signal frequencies of 2000, 3000, 4000, and 6000 Hz showed upward shifted tips for the lowest two signal frequencies, and a downward shifted tip for the highest frequency. The results of the PTCs suggested a functioning region extending from 3900 to 5100 Hz, with DRs outside that range. The identification of nonsense syllables, amplified according to the “Cambridge formula,” was measured as a function of lowpass or highpass filter cutoff frequency. The results suggested that useful speech information could only be extracted from a limited frequency range around 4000 Hz.
- GENERAL LINEAR ACOUSTICS 
127(2010); http://dx.doi.org/10.1121/1.3273891View Description Hide Description
The classical problem of sound scattering by an acoustically hard cylinder due to a point monopole and a line airborne source is extended in the present study. The solution to the homogeneous Helmholtz equation is expressed in a cylindrical coordinate system and represented by an expansion of Fourier integrals. Incorporating the image source method and the Bessel function addition theorem, the analytical solution is derived for the prediction of multiple scattering of sound by a hard cylinder placed above a ground surface of finite impedance. The total sound field can be expressed as a sum of four components: the incident field, the reflected wave, and the scattered fields from the cylinder and its image. The total far-field scattered potential was evaluated asymptotically by the method of stationary phase. Experimental measurements by using a point source were conducted in an anechoic chamber to validate the theoretical formulations. The numerical predictions of using a point source model give good agreements with all the experimental data but there are obvious discrepancies in the spectral magnitudes between the calculation and experimental results when a line source model is used to simulate the scattering problem due to a point source excitation.
A residual-potential boundary for time-dependent, infinite-domain problems in computational acoustics127(2010); http://dx.doi.org/10.1121/1.3273900View Description Hide Description
A theoretically exact computational boundary is introduced that is based on modal residual potentials for the spherical geometry. The boundary produces a set of first-order, uncoupled ordinary differential equations for nodal boundary responses, and a set of uncoupled time-stepping equations for modal boundary responses. The two sets are coupled through nodal-modal transformation based on the orthogonal surface functions for the spherical boundary. Numerical results generated with the boundary are presented for a step-wave-excited, elastic, spherical shell submerged in an infinite acoustic medium. Extension of the method to other separable geometries for partial differential equations defined in unbounded domains is mentioned.
- NONLINEAR ACOUSTICS 
127(2010); http://dx.doi.org/10.1121/1.3277202View Description Hide Description
For fluids, the theoretical investigation of shock wave reflection has a good agreement with experiments when the incident shock Mach number is large. But when it is small, theory predicts that Mach reflections are physically unrealistic, which contradicts experimental evidence. This von Neumann paradox is investigated for shear shock waves in soft elastic solids with theory and simulations. The nonlinear elasticwave equation is approximated by a paraxial wave equation with a cubic nonlinear term. This equation is solved numerically with finite differences and the Godunov scheme. Three reflection regimes are observed. Theory is developed for shock propagation by applying the Rankine–Hugoniot relations and entropic constraints. A characteristic parameter relating diffraction and non-linearity is introduced and its theoretical values are shown to match numerical observations. The numerical solution is then applied to von Neumann reflection, where curved reflected and Mach shocks are observed. Finally, the case of weak von Neumann reflection, where there is no reflected shock, is examined. The smooth but non-monotonic transition between these three reflection regimes, from linear Snell–Descartes to perfect grazing case, provides a solution to the acoustical von Neumann paradox for the shear wave equation. This transition is similar to the quadratic non-linearity in fluids.
127(2010); http://dx.doi.org/10.1121/1.3277190View Description Hide Description
The nonlinear propagation through porous media is investigated in the framework of Biot theory. For illustration, and considering the current interest for the determination of the elastic properties of granular media, the case of nonlinear propagation in “model” granular media (disordered packings of noncohesive elastic beads of the same size embedded in a visco-thermal fluid) is considered. The solutions of linear Biot waves are first obtained, considering the appropriate geometrical and physical parameters of the medium. Then, making use of the method of successive approximations of nonlinear acoustics, the solutions for the second harmonic Biot waves are derived by considering a quadratic nonlinearity in the solid frame constitutive law (which takes its origin from the high nonlinearity of contacts between grains). The propagation in a semi-infinite medium with velocity dispersion, frequency dependent dissipation, and nonlinearity is first analyzed. The case of a granular medium slab with rigid boundaries, often considered in experiments, is then presented. Finally, the importance of mode coupling between solid and fluid waves is evaluated, depending on the actual fluid, the bead diameter, or the applied static stress on the beads. The application of these results to other media supporting Biot waves (porous ceramics, polymer foams, etc.) is straightforward.