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Oct 2007

Volume 122, Issue 4, pp. 1845-EL141

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Time-reversal focusing of elastic surface waves with an asymmetric surface layer

Pelham D. Norville and Waymond R. Scott, Jr.

J. Acoust. Soc. Am. Volume 122, Issue 4, pp. EL95-EL100 (2007); (6 pages) | Cited 1 time

Online Publication Date: 04 Sep 2007

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The effectiveness of time-reversal focusing is evaluated in the presence of an asymmetric surface layer that changes the direction of the propagating waves, but does not continually scatter or block the propagating wave front. Interactions between the wave front and the surface layer are dependent on the depth and material properties of the asymmetric surface layer and its orientation in the medium with respect to the incident wave. Time-reversal focusing is shown to perform significantly better than other excitation methods for the purpose of delivering energy to the location of a buried land mine.
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43.60.Tj Wave front reconstruction, acoustic time-reversal, and phase conjugation
43.35.Pt Surface waves in solids and liquids
43.20.El Reflection, refraction, diffraction of acoustic waves
43.20.Tb Interaction of vibrating structures with surrounding medium
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Searching for best exemplars in multidimensional stimulus spaces

Eric Oglesbee and Kenneth de Jong

J. Acoust. Soc. Am. Volume 122, Issue 4, pp. EL101-EL106 (2007); (6 pages)

Online Publication Date: 07 Sep 2007

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Examining phonetic categorization in multidimensional stimulus spaces poses a number of practical problems. The traditional method of forced identification becomes prohibitive when the number and size of stimulus dimensions becomes increasingly large. In response, Evans and Iverson [J. Acoust. Soc. Am. 115, 352–361 (2004) ] proposed an adaptive tracking algorithm for finding vowel best exemplars in a multidimensional space. This algorithm converged on best exemplars in a small number of trials; however, the search method was designed explicitly for vowel stimuli. In this paper, a more general multidimensional search algorithm is described, and results from simulations and experiments using the proposed algorithm are presented.
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43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.71.Hw Cross-language perception of speech
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A comparison of vocal tract perturbation patterns based on statistical and acoustic considerations

Brad H. Story

J. Acoust. Soc. Am. Volume 122, Issue 4, pp. EL107-EL114 (2007); (8 pages) | Cited 2 times

Online Publication Date: 07 Sep 2007

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The purpose of this study was to investigate the relation between vocal tract deformation patterns obtained from statistical analyses of a set of area functions representative of a vowel repertoire, and the acoustic properties of a neutral vocal tract shape. Acoustic sensitivity functions were calculated for a mean area function based on seven different speakers. Specific linear combinations of the sensitivity functions corresponding to the first two formant frequencies were shown to possess essentially the same amplitude variation along the vocal tract length as the statistically derived deformation patterns reported in previous studies.
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43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics
43.70.Bk Models and theories of speech production
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Exact wave field simulation for finite-volume scattering problems

Dirk-Jan van Manen, Johan O. A. Robertsson, and Andrew Curtis

J. Acoust. Soc. Am. Volume 122, Issue 4, pp. EL115-EL121 (2007); (7 pages) | Cited 3 times

Online Publication Date: 07 Sep 2007

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An exact boundary condition is presented for scattering problems involving spatially limited perturbations of arbitrary magnitude to a background model in generally inhomogeneous acoustic media. The boundary condition decouples the wave propagation on a perturbed domain while maintaining all interactions with the background model, thus eliminating the need to regenerate the wave field response on the full model. The method, which is explicit, relies on a Kirchhoff-type integral extrapolation to update the boundary condition at every time step of the simulation. The Green’s functions required for extrapolation through the background model are computed efficiently using wave field interferometry.
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43.20.Fn Scattering of acoustic waves
43.20.Bi Mathematical theory of wave propagation
43.60.Tj Wave front reconstruction, acoustic time-reversal, and phase conjugation
43.60.Sx Acoustic holography
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Nonperiodicity of the flow within the gap of a thermoacoustic couple at high amplitudes

Arganthaël Berson and Philippe Blanc-Benon

J. Acoust. Soc. Am. Volume 122, Issue 4, pp. EL122-EL127 (2007); (6 pages) | Cited 1 time

Online Publication Date: 17 Sep 2007

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The flow inside a thermoacoustic couple is investigated experimentally using particle image velocimetry. Measurements show the oscillation of the shear layers flowing out of a single stack, thus forming an asymmetric vortex street at high driving amplitudes. Development of vortices is also observed within the gap of a thermoacoustic couple. It causes the flow not to repeat from one acoustic period to another. The nonperiodicity of the flow will lead to unsteady heat transfer between the stack and heat exchangers and to the oscillation of the cooling load.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
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Use of a sigmoidal-shaped function for noise attenuation in cochlear implants

Yi Hu, Philipos C. Loizou, Ning Li, and Kalyan Kasturi

J. Acoust. Soc. Am. Volume 122, Issue 4, pp. EL128-EL134 (2007); (7 pages) | Cited 7 times

Online Publication Date: 17 Sep 2007

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A new noise reduction algorithm is proposed for cochlear implants that applies attenuation to the noisy envelopes inversely proportional to the estimated signal-to-noise ratio (SNR) in each channel. The performance of the proposed noise reduction algorithm is evaluated with nine Clarion CII cochlear implant patients using IEEE sentences embedded in multi-talker babble and speech-shaped noise at 0–10 dB SNR. Results indicate that the sigmoidal-shaped weighting function produces significant improvements to speech recognition compared to the subjects’ daily strategy. Much of the success of the proposed noise reduction algorithm is attributed to the improved temporal envelope contrast.
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43.66.Ts Auditory prostheses, hearing aids
43.66.Sr Deafness, audiometry, aging effects
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Speech disruption during delayed auditory feedback with simultaneous visual feedback

Jeffery A. Jones and Danielle Striemer

J. Acoust. Soc. Am. Volume 122, Issue 4, pp. EL135-EL141 (2007); (7 pages)

Online Publication Date: 17 Sep 2007

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Delayed auditory feedback (DAF) regarding speech can cause dysfluency. The purpose of this study was to explore whether providing visual feedback in addition to DAF would ameliorate speech disruption. Speakers repeated sentences and heard their auditory feedback delayed with and without simultaneous visual feedback. DAF led to increased sentence durations and an increased number of speech disruptions. Although visual feedback did not reduce DAF effects on duration, a promising but nonsignificant trend was observed for fewer speech disruptions when visual feedback was provided. This trend was significant in speakers who were overall less affected by DAF. The results suggest the possibility that speakers strategically use alternative sources of feedback.
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43.70.Bk Models and theories of speech production
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation
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