bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic wave band gaps in triangular and honeycomb two-dimensional phononic crystals
Authors: Hsiao Fu-Li , Khelif Abdelkrim , Aoubiza Boujemaa , Choujaa Abdelkrim , Moubchir Hanane , Chen Chii-Chang , Laude Vincent
Published: May 2008

The ultrasonic band gap properties of phononic crystals composed of arrays of steel cylinders immersed in water and arranged according to square, triangular or honeycomb lattices are compared theoretically and experimentally. In all three cases, complete band gaps are obtained, and the conditions of existence are identified by observing the complete band gap width as a function of the size of the inclusions. However, the measured transmission spectra reveal in the hexagonal symmetry cases (triangular and honeycomb lattices) the existence of deaf bands that cause strong attenuation in the transmission, with no band gap being involved. Band gaps and deaf bands are identified by comparing band structure computations for the infinite phononic crystal, obtained by a periodic-boundary finite element method (FEM), with transmission simulations for the finite phononic crystal, obtained using the finite difference time domain (FDTD) method. The possibility of managing phononic wave guides within a defect line channel inside an otherwise perfect triangular lattice phononic crystal is further demonstrated experimentally.
Experimental measurements of the band structure of Lamb waves in phononic lattices
Authors: Bonello Bernard , Brunet Thomas , Chen Jiu-Jiu
Published: May 2008

We have measured the band structure of Lamb waves propagating in 2D phononic crystals. Different cases were investigated. First we have studied the phononic film deposited on a homogeneous substrate. The phononic film is made of cylindrical iron scatterers embedded into a copper background; the substrate is a 700 μm silicon plate. The propagation is along the crystallographic direction [100] of Si. At low filling fraction, a frequency band gap for the antisymmetric mode arises at reduced Brillouin edge. At high filling fraction, a band gap opens also on the symmetric branch. We have also studied the case of phononic slabs with very high contrast between the scatterers and the matrix. The samples are made of 200 μm silicon plates with air holes lattices drilled throughout. Whatever the symmetry of the lattice, square of centered rectangular, broad band gaps open at first and second reduced Brillouin zone edges. Experimental data are then compared to theoretical predictions obtained using a plane wave expansion method.
Complete band gap in the phonon spectra of compact ceramics
Authors: Salamatov Evgenii I.
Published: May 2008

The processes of sound propagation in inhomogeneous systems have long the focus of researchers attention. The new interest in this problem i last years has been inspired by the appearance of artificial elastic periodic structures - phononic crystals. Since the lattice parameter artificial phononic crystals is about several millimetres the complete bandgap is assumed to lie in the megahertz range. It is of fundamental importance for modern radio equipment to obtain phononic crystals with forbidden bandgap in the gigahertz range, which requires generation of phononic lattices with the period of the order of tens and hundreds nanometers. The author believes nanoceramics compacted from a superfine powder in a special way to be very promising systems for the generatio such phononic lattices. In this work the phonon spectra of the model two-dimensional ceramics numerically calculated using the finite-difference time-domain (FDTD) method. To interpret the results, the analytical expressions obtained for an elastic limit are used, which enables formalization of the conditions necessary for the appearance of a gap in a phonon spectrum. The possibility of creation of bulk acoustic waves resonators is discussed.
Ultrasonic monitoring of hardening concrete
Authors: Bue Julien , Cohen Tenoudji Frederic
Published: May 2008

Monitoring results of velocities and attenuations of compressional and transverse ultrasonic waves in hardening concrete using short pulse through-transmission are presented. A fluid concrete is a highly attenuating heterogeneous medium, composed of several phases and granular classes. Different attenuation mechanisms are considered in order to account for experimental results: high impedance mismatch between air layers and solid-fluid clusters at early ages, Energy loss by viscous dissipation and wave scattering by heterogeneities (Rayleigh scattering at low frequencies, single or multi diffusion scatterings at intermediate and high frequencies) during the beginning of hardening. At early ages, the medium may be described as composed of a succession of large slabs of fresh concrete separated by very thin slabs of air. Attenuation is then computed from the effective transmission coefficient of this medium. This model is in good agreement with experiments. During the beginning of hardening, the medium may be seen as composed of big particles immersed in an effective medium formed by the ensemble of the particles of lesser granular sizes and water. Then, the Rayleigh scattering model at low frequencies and the multiple diffusion model predictions at intermediate frequencies are in good agreement with experiments.
Wave equation in non-integer-dimensional porous media
Authors: Depollier Claude , Legland Jean-Baptiste
Published: May 2008

Over some range of scales, porous media display properties of fractals. It particular both pore sizes and pore-interfaces exhibit the fractal characteristics. One of the fascinating interests of fractals is their capability to model objects with complicate structure. This is due to an important property of fractal objects that their structure is characterized by a small number of parameters. One of them is the fractal dimension which tells how the fractal fills the space in which it lies. Very early, fractal concept has been incorporated in the study of porous media to investigate various phenomena as flow in porous media, pores and fractures of geological media. We present generalized Biot's wave equations for a fractional dimensional system of 3-spatial coordinates used as an effective description of porous media. Some specific examples are given as an application of this model.
Ultrasonic critical angle reflectometry applied to porous nuclear fuel mechanical characterization
Authors: Cereser Camara Vivian , Laux Didier , Despaux Gilles , Baron Daniel
Published: May 2008

An ultrasonic reflectometer working from 2 to 10 MHz on zones around 4 mmhas been built in order to assess in a non destructive way the reflection coefficient R(θ, f) as a function of incident angle and frequency. Many experiments were performed on various materials (glass, aluminium,…) showing that with this goniometer and the related signal processing it is possible to assess very accurately R(θ, f) for bulk or thin samples (Lamb modes). Longitudinal and shear velocities (VL, Vs) deduced from R(θ, f) have been used to determine the elastic moduli E and G which values match very favourably with literature. Hence the Ultrasonic Critical angle Reflectometry is a powerful tool for materials characterization. In a second step, this device has been used on civil power plants fuel (UO2) with various volume fraction of porosity. The elastic moduli obtained are in good agreement with the literature data. The relations between VL, VS and the porosity (p) on the one hand, and E and G with p on the other hand will be presented and discussed. In particular, a link between these relations and the pores morphology (deduced with numerical simulations) will be pointed out.
Hybrid inversion technique for predicting geometrical parameters of porous materials
Authors: Shravage Paresh , Bonfiglio Paolo , Pompoli Francesco
Published: May 2008

In prediction of acoustical behavior of porous materials, five geometrical parameters play a very important role, but some of these geometrical properties are very difficult to measure directly. So many authors have suggested different inversion strategies for getting these properties from directly measured both characteristic and surface properties of the material using standing wave tube. These approaches can be divided in two different categories: analytical (based on the limit behaviour of the bulk properties) and minimization based methods (which make use of searching algorithms to determine the best solution that minimizes a cost function calculated by means of a prediction model). Recent studies have shown the reliability of the analytical methods for the determination of the airflow resistivity and the minimization based approach by using genetic algorithms for getting the other physical parameters. Consequently, a hybrid inversion technique can be proposed for the complete calculation of the geometrical quantities and here it is presented in detail. Moreover the paper compares the results from the hybrid approach with the experimentally measured parameters and the values of the five parameters obtained by using genetic algorithms. Finally, the paper presents the effect of both inversion techniques on acoustical properties using Johnson-Allard-Champoux model.
Acoustic properties of partly saturated porous soils
Authors: Horoshenkov Kirill V. , Mohamed Mostafa H. , Ting Siow N.
Published: May 2008

Controlled experiments are performed on soil samples saturated with different types of liquid such as water and oil to determine the relations between the degree of saturation, type of saturated liquid and the acoustic surface admittance. These experiments are conducted using a Buchner funnel attached directly to an acoustic impedance tube. The results show a very sensitive dependence of the acoustic admittance upon the degree of saturation irrespective of the liquid present. It is found that the relationship between the volumetric water content and the real part of the surface admittance in the frequency range of 500 - 1000 Hz can be expressed using a logarithmic equation. The coefficients of the proposed equation can be determined using a soil property called "uniformity coefficient" and the acoustic admittance of dry soil. Results of volumetric water content obtained using the proposed equation are validated using those obtained from an independent test. The results of the validation exercise demonstrate that the proposed relations can be used to determine very accurately the volumetric water content within soil from the acoustical data. The accuracy of the acoustically measured degree saturation is found to be within 2.0%.
Fiber Bragg grating applied pulsed photoacoustic detection technique for online monitoring concentration of liquid
Authors: Yarai Atsushi , Nakanishi Takuji
Published: May 2008

The need for real-time monitoring of the concentration of raw liquids and wastewater flowing in ducts is one of the significant process controls in chemical plants. A concentration sensor applicable to acidic fluids, however, has not been practically developed because of the maintenance required to sustain performance due to the metal erosion of the electrode from the acidity. To overcome this problem, we propose the fiber Bragg grating applied pulsed photoacoustic (PA) detection technique for online monitoring concentration of liquid. In our technique, optical fiber made of quartz is used for the PA signal generation and detection, for which a 0.6-mm-diameter step index fiber and Bragg grating composed of single mode fiber are used as an object, respectively, so that our metal-free sensor head is not only of small size but is also maintenance-free. The concentration of dye (Rhodamine 6G) dissolved into distilled water was measured to estimate the capability. A Q-switched frequency doubled Nd:YAG laser was used as the PA exiting beam, which is fed to the PA sensor through the fiber. It was experimentally confirmed that the detection linearity was significantly obtained in a concentration range from a few ppm to approximately 200 ppm.
Photoacoustic metrology of nanoimprint polymers
Authors: Kehoe Timothy , Bryner Juerg , Vollmann Jacqueline , Sotomayor Torres Clivia , Aebi Laurent , Dual Juerg
Published: May 2008

Nanoimprint lithography (NIL) is an alternative lithography method for patterning of thin polymer films using a rigid stamp, which is being developed as desired minimum feature sizes reduce to the scale of tens of nanometres. To characterise nanoimprinted structures, there is a need for more convenient and non-destructive wafer-scale metrologies to complement scanning electron microscopy and atomic force microscopy. The photoacoustic method, with a resolution in the range of 10 nm, and normally used to measure metal and dielectric layer thicknesses and physical properties, has been used for the first time to study nanoimprinting polymer layers. A good signal was obtained from the top and the bottom interfaces of two polymers, mr-I PMMA 75k300 and mr-NIL 6000.3, with thicknesses ranging from 100 to 500 nm. From the measured time of flight of the acoustic wave, and modelling physical parameters of the polymers, thicknesses calculated agree well with those measured by profilometry. The measurements are performed on a short pulse laser pump-probe setup, where bulk wave packets are excited and detected using near infrared laser pulses of less than 100 fs duration. The entire experimental setup is also simulated numerically.
Nonlinear scattering of a surface wave by an object buried in soil
Authors: Zabolotskaya Evgenia A. , Ilinskii Yurii A. , Hamilton Mark F.
Published: May 2008

Nonlinear scattering of a surface wave by an object buried in soil is investigated theoretically. The object is supposed to be excited by a monochromatic seismic wave and its pulsations are considered to be nonlinear. Specific features of soil are taken into account, namely, shear modulus less than compressibility modulus and anomalously high nonlinearity. Two analytical approaches are applied. One is based on theory of elasticity and the other is based on fluid mechanics. The two approaches yield identical results for the second harmonic in the scattered field. The second harmonic is evaluated in the near field where the medium can be considered as incompressible. The analysis is performed with perturbation theory for small displacement amplitudes in the soil. The second harmonic is also investigated with an asymptotic expression obtained from the general equation for the second harmonic generated by a pulsating object in a compressible medium. The equation is expanded for a small object at distances that are small compared with a wavelength. The influence of a stress-free boundary on the scattered field is evaluated using Green's functions. [Work supported by ONR.]
'Maxwellian' macroscopic acoustics and acoustic metamaterials
Authors: Lafarge Denis , Duclos Aroune
Published: May 2008

For electromagnetic wave propagation it was found that there exist composite media exhibiting strong spatial dispersion. This has raised the question of the relevance of the spatial dispersion in the characterization of the new metamaterials. The present communication intends to show that exactly the same problematic occurs in acoustics when considering long-wavelength acoustic wave propagation in a fluid in presence of solid obstacles of any arbitrary shape. When these obstacles resemble "Helmholtz" resonators the macroscopic equivalent medium may exhibit strong spatial dispersion. It is demonstrated that the corresponding Macroscopic Acoustics, which may be worked out in detail, is very similar to the general nonlocal Maxwellian Macroscopic Electrodynamics. This raises the question of the relevance of the spatial dispersion in the characterisation of porous materials, and specifically the question of the possible design of acoustic metamaterials exhibiting enhanced absorption due to spatial dispersion.
Improving source localisation in multi-source, reverberant conditions: exploiting local spectro-temporal location cues
Authors: Christensen Heidi , Ma Ning , Wrigley Stuart N. , Barker Jon
Published: May 2008

This paper examines the use of binaural cues for estimating the location of individual sources in multi-source acoustic mixtures. In most environments, location cues such as interaural time difference (ITD) and interaural intensity difference (IID) are rendered unreliable by noise due to competing sources and reverberation. We propose a method that examines spectro-temporal regions where such effects are minimised. Source location is estimated by combining two processing stages. First, following [Christensen et al, Interspeech (2007)], as pitch cues are generally less affected by noise, a multi-pitch estimation and tracking algorithm is used to identify local spectro-temporal 'fragments' in which the SNR is high. Second, the confidence of ITD and IID estimates arising from each time-frequency 'pixel' is estimated based on interaural coherence [Faller and Merimaa, J. Acoust. Soc. Am. 116, 3075--3089 (2004)] and reverberation estimation [Heckmann et al, Int. Conf. Int. Robots and Systems (2006)]. A location estimate is then constructed by integrating suitably weighted cues from each pixel within the fragment. Experiments are carried out on a large corpus of multi-speaker data, mixed from binaural recordings in a real, reverberant environment. The fragment based processing is shown to provide significant improvements when compared to competitive baseline approaches.
The acoustical bright spot and the erroneous localization of tones by human listeners
Authors: Rakerd Brad , Ryan Zach , Macaulay Eric , Hartmann William M.
Published: May 2008

In free-field sound localization experiments, human listeners estimated the locations of sine tones originating at 13 loudspeakers that spanned a range of azimuths from 0 degrees (straight ahead) to 90 degrees (extreme right). During the experiments the tone amplitudes and phases were measured in the listener's ear canals. Because of the acoustical bright spot, measured interaural level differences (ILD) were found to be a nonmonotonic function of azimuth at frequencies above about 1000 Hz. In source identification experiments at 1500 Hz, there was no correlation between estimated location and the interaural phase difference. There was high correlation with ILD, causing listeners to make large localization errors for azimuths greater than about 55 degrees. In a second experiment, listeners judged the direction of movement of sounds from one source to another. Errors in the second experiment could be well predicted from the localization responses in the source identification experiment. The ear canal measurements showed that, in principle, listeners could localize successfully by using the levels in the two ears independently. However, localization performance remained poor even after extensive training. Work supported by the NIDCD, grant DC00181.
Both prime length and prime position affect the spatial release of nonsense speech from informational masking
Authors: Yang Zhigang , Chen Jing , Huang Qiang , Huang Ying , Wu Xihong H. , Wu Yanhong , Li Liang
Published: May 2008

When masking speech is present, pre-presentation of early part of nonsense target speech improves recognition of the rest of target speech, indicating a content and/or voice priming effect (Freyman et al., 2004; Yang et al., 2007). Here, we examined both the prime-length effect and the prime-position effect on recognition of nonsense target speech with twelve syllables and three keywords. Target speech started 1 sec. after the onset of two-talker masking speech. The results show that a longer prime with 10 syllables (including the 1st and 2nd keywords) significantly improved recognition of the last (3rd) keyword in target speech. However, when the 1st four syllables (including the 1st keyword) were pre-presented, recognition of either the 2nd or 3rd keyword was not improved. Interestingly, when the 2nd four syllables (including the 2nd keyword) were pre-presented, recognition of the 1st but not the 3rd keyword was significantly improved. Thus under speech-on-speech masking conditions, both the prime length and the prime position in the sentence influence the priming effect on recognition of target speech, and listeners contribute more attentional resource to the initial part of target speech. Supported by the National Natural Science Foundation of China.
Lateralization of binaural stimuli with independent fine-structure and envelope-based temporal disparities
Authors: Dietz Mathias , Ewert Stephan D. , Hohmann Volker
Published: May 2008

A computational model for the lateralization of binaural stimuli, motivated by recent physiological findings in the literature and psychoacoustic data is presented. The model is based on the evaluation of the interaural phase difference (IPD). In the model, IPDs are separately assessed for the stimulus' fine-structure and envelope. Psychoacoustic measurements were conducted and compared to model predictions. Sinusoidally amplitude modulated 1-kHz tones with a modulation frequency of 25, 50, and 100 Hz were employed. The IPD of the fine-structure and the envelope IPD were independently matched with an interaural level difference or were traded against each other. Lateralization increased for increasing IPDs up to 135° of either the fine-structure or envelope independent of the modulation frequency. However, trading a fine-structure IPD with an opposing envelope IPD revealed a most persistent fine-structure IPD at 45°. The data could be modeled assuming a physiological distribution of the best IPDs of binaural neurons clustered around 45°. The model was also utilized to correctly predict the perceived lateralization of critical stimuli from literature. Individual differences in the perceptual salience of envelope and fine-structure cues, also known from the literature, could be modeled by a personal weighting coefficient for the fine-structure cue.
Temporal weighting of interaural level differences in high-rate click trains
Authors: Stecker Christopher
Published: May 2008

When high-carrier-frequency stimuli are amplitude modulated at rates above ̃200 Hz, lateralization based on envelope interaural time differences (ITD) becomes dominated by onset ITD. The role of onset cues in interaural-level-difference (ILD) processing, however, is less well understood. Although theoretical predictions suggest that onset dominance should have similar effects upon ILD as upon ITD, some experimental data suggest that ILD processing retains greater sensitivity during post-onset segments of a high-rate stimulus. In this study, subjects lateralized ILDs carried by trains of 16 Gaussian-filtered clicks (carrier frequency 4000 Hz) that varied in interclick interval (ICI) from 2 to 10 ms (modulation rate 100-500 Hz). ILDs of individual clicks in each train were randomly perturbed. Multiple linear regression of listener responses onto the perturbed ILD values was used to generate temporal weighting functions (TWFs) that describe how a listener's sensitivity to ILD changes over the stimulus duration. The resulting TWFs were compared to predictions from models of onset dominance as well as to TWFs measured for ITD and in free-field conditions. The results have implications for binaural processing of high-rate pulsatile stimuli experience by users of bilateral cochlear implants.
Relationship between reading and language ability and auditory temporal processing measured with the precedence effect
Authors: Zettler Cynthia M. , Sevcik Rose A. , Morris Robin D. , Romski Mary Ann , O'Rourke Colleen , Clarkson Marsha G.
Published: May 2008

Processing of timing information by the auditory system contributes to numerous abilities, including spatial hearing and higher-order language and reading skills. However, relationships among these abilities are poorly understood. The present study was aimed at investigating potential common mechanisms that involve timing. Auditory timing was measured by click stimuli presented via two loudspeakers at a rate of 1.5/sec. Fourteen-ms clicks were presented from one (single-source condition) or two (dual-source condition) loudspeakers. In the latter condition, the onset of one loudspeaker was delayed relative to the other by 5, 10, 20, 50, 100, 200, or 400 ms. Seventy-five naïve adults (mean age 21.23 years) listened to the auditory stimuli and were asked to identify the source of the leading sound. Additionally, all participants completed a battery of language and reading measures. Results on the auditory task revealed that performance was significantly above chance on single-source trials, dropped at short delays, and improved with increasing delay. The mean threshold for correctly identifying the source of the sound was 43.48 ms. A significant correlation (p < .05) found between this threshold and a measure of word identification suggests a relationship between timing required for auditory localization and timing required for reading ability.
The localization of multiple simultaneous sounds is mediated by attention
Authors: Simpson Brian D. , Brungart Douglas S. , Gilkey Robert H. , Iyer Nandini , Hamil James T.
Published: May 2008

Real-world listening experiences suggest that listeners possess a much greater ability to recover spatial information from multiple simultaneous sounds than would be predicted from the results of most multisource listening experiments. Recent data from our laboratory are consistent with these real-world experiences, and indicate that listeners can reliably report the location of a sound that has been deleted from a multisource scene. However, performance degrades as the number of competing sounds increases, and it is unclear if this 'set size effect' arises from changes in signal-to-noise ratio (SNR) related to the number of competing sources, or from attentional constraints that limit the number of simultaneous sources that can be monitored. In this study, SNR was held roughly constant by fixing the number of competing sources at 8, and the 'relevant set size' was varied by displaying on a visual monitor, prior to an observation interval, a list of 1,2,3,4,6, or 8 environmental sounds, one of which was the target sound (the sound that would be deleted). The ability to localize this target sound decreased as the relevant set size increased, suggesting that the ability to monitor complex auditory scenes is mediated by attentional constraints.
Better-ear listening strategies for normal-hearing and hearing-impaired individuals
Authors: Whitmer William M. , Coughlin Maureen , Bondy Jeff , Dittberner Andrew
Published: May 2008

The current study was designed to examine how hearing-impaired (HI) listeners use better-ear listening. Better-ear performance was initially assessed for normal-hearing (NH) and HI participants using a connected-speech recognition test at two signal-to-noise-ratio (SNR) levels presented over insert earphones. Test conditions consisted of monaural, symmetric and asymmetric combinations of better and worse SNR conditions. SNRs were different for NH and HI groups. Stimuli were presented at each participant's most comfortable level; to account for audibility with HI participants, stimuli were spectrally shaped based on audiometric data. A second experiment investigated the role of spatial information using recordings of the same stimuli presented in a sound-dampened chamber at the same SNR differences, with the speech signal at 0° azimuth/elevation, and uncorrelated babble presented from eight speakers at the corners of the chamber. Listening strategies between NH and HI groups were similar across experiments; neither group consistently used an optimal listening strategy. Results will be discussed in terms of hearing-impaired pathologies, rehabilitation and amplification strategies.
Numerical Analysis of the Effects of Pinna Shape and Position on the Characteristics of Head-Related Transfer Functions
Authors: Iwaya Yukio , Suzuki Yôiti
Published: May 2008

There are distinctive notches and peaks in Head-Related Transfer Functions (HRTFs). Some of them are considered as important cues in the perception of the elevation angle and thus the roles of these peaks and notches should be clarified. It is known that the characteristics of HRTFs are deeply related to listener's anthropometry. It is thus naturally expected that frequencies of the peaks and notches also change according to the individuality of listeners' anthropometry. Therefore, in this study, effects of ear shapes and positions on frequency positions of the peaks and notches are examined by numerical analyses. The analysis was performed with boundary element method (BEM). A three-dimensional model of a dummy-head was constructed with a three-dimensional laser scanner and HRTFs of the model were numerically computed with a BEM solver. The model was modified on some features as follows: 1) pinna position, 2) pinna size, 3) angle of pinna toward listener's head, and 4) existence of wrinkles of pinna. HRTFs of the modified models were also computed. From the comparison among the results of calculation, several systematic changes were found. For example, the frequency position of notches around 8 kHz is shifted toward lower frequency as the size of pinna increases.
Application of psychoacoustic tests for the evaluation of acoustical characteristics of Bartók Béla Concert Hall in Palace of Arts, Budapest
Authors: Alabardos Zsuzsanna , Arato-Borsi Eva
Published: May 2008

The objective characterisation of the subjective listening effect of single number quantities are well known in concert halls such: reverberation time, clarity, centre time, lateral energy fraction and so on. The Bartók Béla Concert Hall in the Palace of Arts in Budapest has been inaugurated at 15th of March 2005. The acoustic consultant office of the hall was ARTEC Ltd. A set of objective measurements has been carried out in the Concert Hall and a series of listening tests were accomplished. Results of the experiment show clear correlations in the relationship of architectural and room acoustical parameters. Apart from the important conclusions, there are some questions revealed.
Phonemic restoration with hearing-impaired listeners
Authors: Baskent Deniz , Eiler Cheryl , Edwards Brent
Published: May 2008

Baskent et al. (ISAAR 2007) showed that simulated undershoot that may happen due to release from hearing-aid compression may reduce phonemic restoration by normal-hearing (NH) listeners. Phonemic restoration was measured as the increase in recognition of interrupted speech when the silent intervals were filled with loud noise bursts. These results would be more crucial for hearing-impaired (HI) listeners who might encounter such problems in real life as hearing-aid users. However, it has not been previously shown if HI listeners benefit from phonemic restoration similar to NH listeners. Factors such as adverse effects of background noise on speech perception and increased forward masking observed with HI listeners might affect phonemic restoration. The present study explored phonemic restoration with mildly and moderately HI listeners with a method similar to the previous study. NH listeners participated as the control group. Perception of speech interrupted at rates of 1.5 and 2.2 Hz was measured with silent intervals and with noise bursts filling the silent intervals. The preliminary results showed that many HI listeners, especially with mild hearing loss, were able to benefit from phonemic restoration. However, in each subject group, there were a small number of listeners who did not show any benefit.
Electrode Discrimination and the effect on Speech Perception for Adults with Cochlear Implants
Authors: Vickers Debi A. , Meerton Leah
Published: May 2008

Zwolan et al (1997) showed that electrode discrimination can have an effect on speech perception for adult cochlear implant users with the Nucleus Mini 22 multi-channel device. The purpose of this study was to evaluate electrode discrimination in subjects using different implant systems and speech processing strategies to observe the effect that switching off undiscriminable electrodes has on speech perception. 17 postlingually deafened adults were tested; they used either a Nucleus 24 device (either using SPEAK or ACE processing strategies) or an Advanced Bionics HiRes cochlear implant (either using HiRes or HiRes120 strategies). Only electrodes that were activated in the subjects' clinical maps were tested in the electrode discrimination task. Electrode discrimination was performed using standard clinical software at comfortable listening level and pairs of electrodes that scored less than 60% were deemed undiscriminable. One of the undiscriminable pair was switched off and the electrode selected was determined from the results of the other electrode pairs. Performance was evaluated prior to and immediately after switch off and at a follow up appointment 1 month later. Zwolan T, Collins L and Wakefield G (1997). J. Acoust. Soc. Am. 102(6), 3673-3685.
A model for predicting hearing aid benefit
Authors: Nilsson Michael , Bray Victor
Published: May 2008

A 'large n' database was created incorporating demographic information as well as speech-recognition-in-noise measurements from several hundred subjects who participated in field trials with wearable DSP hearing aids. Performance measures were obtained across multiple hearing aid styles (CIC to BTE) with multiple signal processing technologies (multi-channel compression, digital noise reduction, directionality). The database was previously analyzed using various regression techniques (results presented at AAS-2005, IHCON-2006, AAS-2007). The current analysis includes additional parameters that were not in the earlier models and uses a more robust statistical analysis. Aided speech-understanding-in-noise can be predicted based on factors of (a) unaided thresholds for tones (b) unaided thresholds for speech in quiet, (c) unaided thresholds for speech in noise, (d) hearing aid technology, and (e) subject age. We conclude that a model for hearing aid benefit can be used as a new tool for evidence-based management of hearing aid clients. Patient parameters may be entered into the model to serve as a basis for prediction of benefit in speech-understanding-in-noise using various forms of amplification treatment.
Temporal manipulations in multi-channel compression effecting sound quality and performance
Authors: Nilsson Michael , Hicks Michelle , Ghent Robert , Bray Victor
Published: May 2008

Multi-channel compression (in four or more compression channels) is expected in modern hearing aids, but compression temporal characteristics vary without an understanding of what is optimal and why. This study takes a 16 channel system using linearly spaced compressors with minimal overlap and evaluates sound quality ratings and speech recognition performance with the HINT in quiet and noise with various attack and release settings in a 2 x 2 x 2 design. The first variable is the relationship between attack and release times, with asymmetric time constants (attack faster than release) or symmetric time constants (attack and release set the same). The second variable is the relationship of time constants across frequency channels, with uniform settings across frequencies, or frequency dependent time constants (faster settings for higher frequencies with shorter wavelengths). The third variable is absolute speed, with fast or slow time constants. No characteristics other than the temporal settings of the compressor were changed between conditions. Results will be presented showing optimal settings for sound quality as well as speech recognition. The interaction between compression characteristics and additional signal processing, such as single-microphone noise reduction, will be discussed.
Speech Intelligibility in Virtual Environments Simulating an Asymmetric Directional Microphone Configuration
Authors: Picinali Lorenzo , Prosser Silvano , Mancuso Antonio , Vercellesi Giancarlo
Published: May 2008

The benefit of directional processing and binaural listening in terms of speech intelligibility for frontal sound sources has been well documented in recent and past studies. Nevertheless, only the 20% of the situations in real life present a speaker located exactly in the frontal position. Different attempt have been done so far in order to allow, manually or automatically, a change in the directional pattern of the hearing aid, but the results of these studies are far from being satisfying. The purpose of this study is to explore the advantages brought by the asymmetric directional microphone configuration of hearing aids in terms of speech intelligibility for frontal, lateral and rear sound sources in noisy environments, and in terms of the quality of the "spatial perception" of the surrounding sound-scape. Through a 3D Ambisonic virtual environment manipulation, the presence of two microphones (the two hearing aids) is simulated in a noisy environment with a speech sound source. The listeners are presented with the signal recorded from the two simulated microphones, calibrated with symmetrical and asymmetrical directional patterns, and played through a pair of headphones. The speech intelligibility is measured for all the directional microphones configurations and for all the speech sound source positions.
Does induced loudness reduction explain contextual effects in loudness judgment
Authors: Marks Lawrence E.
Published: May 2008

Briefly presenting an inducing tone of 70-80 dB can substantially reduce the loudness of a subsequent test tone at or near the inducer's frequency, a phenomenon called Induced Loudness Reduction (ILR). The study of ILR emerged from earlier observations on differential contextual effects in loudness judgment: Tones of a given SPL and frequency were judged softer when presented as part of an ensemble of high rather than low SPL tones at the same frequency, relative to judgments of loudness of tones at a different sound frequency. At first, these effects of stimulus context on loudness judgment were assumed to reflect decisional processes, that is, to reflect biases in loudness judgment. On the other hand, ILR is often assumed to reflect a depression in the intensity response of the auditory system. While it is tempting to explain differential contextual effects in loudness judgment wholly in terms of ILR, the properties of ILR and the properties of contextual effects may not be identical, leaving open a possible role for decisional processes as well as sensory processes in contextual effects, and perhaps also in ILR, in both laboratory and 'real-world' settings.
Loudness asymmetry ratings between accelerating and decelerating car sounds
Authors: Susini Patrick , McAdams Stephen
Published: May 2008

Loudness change has been studied for tones with linearly varying levels revealing an asymmetry depending on the direction of change (increasing vs. decreasing) and the range of levels (high vs. low). Different assumptions were proposed to explain this asymmetry in favour of linearly increasing sounds. Teghtsoonian et al. (2005) and, more recently, Susini et al. (2006) explain that loudness of an increasing sound is influenced by the end level. Neuhoff (1999) describes this result by a survival advantage for detecting an approaching sound source. Whatever the assumption is, the results show that loudness judgments for abstract sounds (1000-Hz tones) and synthetic vowel sounds were significantly higher for increasing ramps. Those results are compared here with continuous and global ratings obtained on everyday sounds such as accelerating and decelerating car sounds with a same duration (43 s), but with different temporal functions and range of levels. Global loudness judgments made after the end of the sound are significantly higher for accelerating than decelerating car sounds, but are judged on average similar using continuous judgments. In addition, an increase in the speed (acceleration) is evaluated primarily in terms of its level at the end. These results confirm the previous studies.
Magnitude judgments of loudness change for discrete, dynamic, and hybrid stimuli
Authors: Flint Jesse D. , Pastore Richard E. , Gaston Jeremy R.
Published: May 2008

Recent investigations of loudness change across dynamically varying stimuli have identified differences between increasing versus decreasing power that depends upon stimulus complexity and intensity range [e.g., Canévet, Acustica, 62, 2136-2142 (1986); Neuhoff, Nature, 395(6698), 123-124, (Sep 1998)]. Some explanations of these findings are based upon known psychophysical effects [Teghtsoonian, Teghtsoonian & Canévet, Perception & Psychophysics, 67(4), 699-712 (2005)], whereas others posit qualitative differences in the perception of discrete laboratory and dynamic natural sound structures (Neuhoff, 1998). For discrete, static stimuli, the relationship between loudness and power is dependant upon a number of factors, including frequency, intensity range, perceptual anchoring, temporal order, and integration of power across time. The current investigation examines listener perception of loudness for sound structures that vary systematically from discrete to dynamic changes in power, allowing evaluation of the contributions of static versus dynamic change, as well as other factors in the perception of loudness change within complex stimuli. Relevant methodology, as well as commonalities and differences with predictions of traditional psychophysics, are discussed.
Local patch acoustic holography methods in enclosed spaces
Authors: Havranek Zdenek , Bejcek Ludvik
Published: May 2008

The paper compares reconstruction accuracy and computational cost of three patch acoustic holography algorithms applicable in the enclosed spaces for prediction of sound field near sources. Algorithms under investigation were DL-SONAH, IBEM and classical NAH with spatial transformations and hologram aperture enlargement. All of the selected algorithms take an advantage of using double layer microphone array for measurement of sound pressure field. The reconstruction accuracy of all algorithms is determined by using of simple 3D model of curved radiating surface on the basis of calculation of difference between true acoustic quantity (pressure, velocity or intensity) values very close to the surface and predicted sound field at same positions. All these methods use different calculation procedure to obtain predicted sound field near source surface, thus comparison of effectiveness of these algorithms including prediction accuracy-to-computational cost ratio is useful to determination their applicability in practice. Results of prediction error and calculation time including regularization with different parameter choice methods (L-curve, GCV, etc., are presented and compared. Initial comparison of the selected methods confirms shorter calculation time in non-element based methods, especially in NAH with transformations, while reconstruction error is in the same order.
Near-field Acoustic Holography for partial measurements inside complex structures
Authors: Valdivia Nicolas , Williams Earl G.
Published: May 2008

Near-field acoustical holography (NAH) requires the measurement of the near-field pressure field over a closed surface in order to recover the acoustic field on a nearby conformal surface. Very often we encounter applications where pressure measurements are available only over a patch of the measurement surface. In these cases the strict NAH theory does not hold, but still there are techniques that have been developed to overcome this difficulty. The best-known technique for planar surfaces is patch NAH and, recently proposed, for arbitrarily shaped surfaces patch IBEM and patch ESM. It was found in a recent study by the authors that these techniques will be affected by the problem of back-source contamination for interior NAH, but it was showed that this problem could be overcome by the use of "Cauchy" measurements. In this work we will compare the reconstruction of the acoustic field from patch based techniques with the technique that uses Cauchy measurements, and discuss the problem of back-source contamination in more detail. We use a cylindrical surface excited by a point force as an example to validate our results. This work was supported by the US Office of Naval Research.
The significance of cross-order terms in interface mobilities for structure-borne sound source characterization
Authors: Bonhoff Hannes A. , Petersson Björn A.
Published: May 2008

For the characterization of structure-borne sound sources and the description of the associated transmission process, the source descriptor and coupling function were introduced. The concept of source descriptor and coupling function can be reformulated by incorporating the interface mobilities. The applicability for source-receiver assemblies with a multi-point or continuous connection is thereby granted. The accuracy of the results and consequently the validity of this approach, however, depends on the significance of the so-called cross-order terms. Such cross-order terms consist of force orders and cross-order interface mobilities. In recent theoretical and experimental work, the influence of cross-order interface mobilities as well as the distribution of force-orders have been investigated. Based on this knowledge, the significance of the cross-order terms is assessed in the present contribution.
Vector intensity measurement with a rigid spherical microphone array in a vehicle cabin
Authors: Takashima Kazuhiro , Nakagawa Hiroshi , Williams Earl G.
Published: May 2008

Measurement results showing intensity vector reconstructions using a rigid spherical microphone array in a vehicle cabin are presented. The measurement equipment developed by Nittobo was used in previous demonstrations to visualize the acoustic field using a beamforming technique superimposed on a picture from an on-board camera. In the present study intensity reconstructions are shown and are successful in locating and quantifying sources, demonstrating the usefulness of this technique in an enclosed space like a vehicle cabin, aircraft cabin, small room, etc. This work was supported by the US Office of Naval Research and Nittobo Acoustic Engineering Co. Ltd.
Forced vibrations of a cylindric panel with regular orthogonal system of stiffeners
Authors: Lazarev Leonid A. , Efimtsov Boris M.
Published: May 2008

Forced vibrations of a cylindrical panel freely supported in contour, with regular orthogonal system of stiffeners (typical of aircraft fuselage structure) are investigated. The connection of all three components of displacement of the skin and of discrete stiffeners as well as of the respective elastic and inertial forces and moments are taken into account in the case of excitation by normal and tangential forces. This connection can be described correctly at joint application of the recreptance method and the method of space-harmonics. The task of forced vibrations is solved directly except the procedure of solving the task in terms of eigen-values. Some illustrative examples of the aircraft fuselage panel by a concentric harmonic force are presented. They demonstrate a high efficiency of applying this combined method. Potential possibilities of using this combined method for solving the tasks related to vibrations of a framed skin modeling the aircraft fuselage section and to the sound field in the volume bounded by it are considered.
Influence of the pre-stress state on the wave propagation in a shearable Timoshenko beam
Authors: Bideau Nicolas , Eyi-Assoumou Polynice , Le Marrec Loic , Rakotomanana Lalaonirina
Published: May 2008

It is very common to use pre-stressed beam models in the structure design. However in the nonlinear domain, the modal analysis remains difficult especially when shearability is taken into account. This work aims to study the natural vibrations of pre-stretched nonlinear shearable Timoshenko beam using Cosserat continuum mechanics. In this paper, a three dimensional nonlinear beam model is first developed. Then we analyse waves which are superimposed on a finite pre-stretch state. Namely, analytical dispersion relations are given for different values of pre-strech. The complete spectrum, including propagating and evanescent traction/compression, shear and bending modes, of a pre- stretched shearable beam is calculated through dispersion pattern. Spectrum strongly depends on initial pre-stress value. A significant qualitative and quantitative difference with the classical Timoshenko beam theory is pointed out even for small pre-stretch values.