bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustics in the partial deaf student school music classrooms
Authors: Bal Kocyigit Filiz , Gulec Kubra Sevim X.
Published: May 2008

Music schools need some special acoustical design for good education. If this is also for children with disabilities, the effect is more important. Research is about musical education for partially hearing disabled children. At this point architectural acoustic design acquires importance. This is not only in the shape of the room but also in using covering materials and other solutions. The question is whether architectural acoustics solutions can affect the music education of partially hearing disabled children or not. Here the first discussion is whether we need some additional components of good classrom acoustics for partially hearing disabled children in the American National Standards Institute Standard S12.60 2002 for clasroom acoustics, and the cost impact of the Standard. Childhood hearing loss is a widespread problem with significant impact, an invisible condition resulting in communication problems that can ultimately interfere with learning and social development. Included are audio files that illustrate that even a mild hearing loss can have a significant impact on a child's ability to understand the teacher. Especially children with a partial hearing loss need a more lively room to amplify the instrument sound for improved hearing capacity.
Block based physical modeling for virtual musical instruments
Authors: Rabenstein Rudolf
Published: May 2008

A variety of methods for physical modeling sound synthesis has been developed so far, mostly for single sound objects like strings, plates, etc. However, complex virtual musical instruments require not only advanced models but also methods for combining one or more sound objects with excitation mechanisms and resonating structures. This presentation shows how to derive modeling blocks from basic physical laws and how to connect them in a physically meaningful way. The first step is to establish a physical model of a dynamical structure in terms of potential and flow variables, like force and velocity. It is important to observe also the boundary conditions because firstly they shape the spectrum of the vibrating structure and thus the timbre of the sound and secondly they determine the exchange of energy with the environment. The second step is the discretization of the physical model. This procedure is shown for the functional transformation method, which delivers discrete-time models with direct access to the parameters of the physical model and which reproduces the original sound spectrum. In the last step, the resulting modeling blocks are connected by scattering elements which reflect energy back into the model or transmit it to neighboring blocks.
Passive admittance synthesis for sound synthesis applications
Authors: Bank Balázs , Karjalainen Matti
Published: May 2008

In physics-based sound synthesis, it is in general possible to incorporate a mechanical or acoustical admittance/impedance in the form of a digital filter. Examples include modeling of the termination of a string or a tube. However, when digital filters are fitted to measured admittance or impedance data, care has to be taken that the resulting filter corresponds to a passive mechanical or acoustical system, otherwise the stability of the instrument model is at risk. This paper presents a simple method for designing inherently passive admittance or impedance filters. The admittance/impedance is composed as a linear combination of positive real (PR) functions, and the weights are determined by a constrained least squares optimization. The resulting filter is a parallel set of second-order sections. For wave-based modeling, such as digital waveguides (DWGs) or wave digital filters (WDFs), the admittance/impedance is converted to a reflectance filter. The parallel filter structure is retained during conversion. As an example, a guitar model based on DWG approach is presented, using mechanical admittance measurements of a guitar bridge behavior. The model is implemented as an efficient real-time sound synthesis algorithm.
Modal parameter estimation for shape-changing geometric objects
Authors: Maxwell Cynthia
Published: May 2008

As a novel advancement in interactive sound synthesis, we would like to change the shape of a finite element model of an instrument and hear how the sound changes in real-time. Traditional modal synthesis methods require computing a new eigendecomposition for each geometric change -- a costly computation using today's hardware. However, by using the modes computed for one geometry to estimate modal frequencies for other nearby geometries, we can instantly hear the effects of changing the instrument shape on the sound produced. In this talk, we describe the process of estimating resonant frequencies of an instrument by combining information about the modes of similar instruments. We also propose a method for transferring the modal information from one finite element mesh to another. This method is used in situations where severe modifications to the object's geometry distort the finite element mesh and require an entirely new mesh to be created. We also describe the balance between computational speed and numerical accuracy of the computed resonances.
The EU FP6 research project PROBAND - Objectives and first results
Authors: Enghardt Lars
Published: May 2008

Fan broadband noise is a major aircraft noise challenge now and in the future will be even more important. Novel low-noise engine architectures, such as ultra-high-bypass-ratio engines and lower-speed fans, can help address jet noise and fan tone noise, but previous EC-funded programmes have shown they are unlikely to reduce significantly fan broadband noise without improved understanding of the source mechanisms. PROBAND will accomplish a major technical leap in providing industry with an improved understanding of the broadband noise source mechanisms, with validated broadband noise prediction methods, and with low fan broadband noise concepts. PROBAND will exploit the noise technology and methodology acquired in EC-funded projects and national programmes, to develop methods to allow the design of a fan system that will generate sufficiently low broadband noise to meet the EU noise level targets. This will be achieved by: 1. Developing a better understanding of broadband noise generation mechanisms using advanced experimental and computational techniques. 2. Developing and validating improved prediction methods using conventional computational fluid dynamics, and integrating them into industrial codes. 3. Exploring new prediction strategies using advanced computational techniques 4. Developing low broadband fan noise concepts.
Measurement strategies according to the new ISO/DIS 9612
Authors: Maue Jürgen
Published: May 2008

The European Directive 2003/10/EC on noise protection at the workplace has given the impact for the revision of the ISO 9612 describing the measurement and assessment of occupational noise. The ISO/TC 43 "Acoustics" decided that the revision should only contain requirements for the determination of the noise exposure for the purpose of assessing potential hearing damage. Meanwhile a new Draft ISO/DIS 9612 has been presented, which gives a detailed description of three alternative measurement strategies for the determination of the noise exposure level. Moreover the standard provides a method for estimating the uncertainty of the results. The measuring strategies, called "task based measurements", "job based measurements" and "full day measurements" are illustrated and compared to each other. The choice of the appropriate strategy is explained, depending on the complexity of the work situation and the movements of the worker doing his job. Based on practical experience some comments are given, which may help to reduce time and effort of measurements. The evaluation of measurement uncertainties is explained in a few words.
Stability behaviour and results of a transient boundary element method for exterior radiation problems
Authors: Stütz Michael , Ochmann Martin
Published: May 2008

Based on the Helmholtz integral equation, a boundary element method in time domain (TD-BEM) can be formulated. Because of instability issues, this method is rarely used in numerical acoustics. The stability and accuracy of the method for exterior radiation problems is investigated using some simple examples. A connection between the internal resonances of the closed structure and the instable behaviour of the method is assumed, but it is mathematically unproven. Numerical evidence of this connection is presented. Because of the sparse structure of the resulting system matrix, the use of iterative solvers is advantageous. The performances of different solvers are compared with respect to stability and numerical costs. For testing purposes, the acoustic radiation from an open turbulent flame is calculated and compared with results of a frequency domain BEM calculation.
Optimal tree canopy shape for improving downwind noise barrier efficiency
Authors: Van Renterghem Timothy , Botteldooren Dick
Published: May 2008

The presence of a row of trees behind a highway noise barrier significantly reduces the screen-induced refraction of sound by wind. In this paper, the influence of quantitative tree properties, such as the pressure resistance coefficient of the canopy and the distribution of biomass over height, was studied numerically. Three computational models were involved. First, computational fluid dynamics (CFD) software is used to accurately predict the wind fields. The finite-difference time-domain (FDTD) method is then used to simulate sound propagation in the direct vicinity of the noise barrier in combination with trees. In a last step, the Parabolic Equation (PE) method is used to predict sound fields at larger distances. As a general conclusion, it was found that coniferous trees are superior to deciduous trees to improve downwind noise barrier efficiency.
Comparative helicopter noise analysis in static and in-flight conditions
Authors: Novak Doris
Published: May 2008

Rotary wing aircraft, i.e. helicopter, is a source of intense noise, external and internal alike, in conclusion becoming serious environmental and health issue. The generated noise is in some aspects similar to propeller noise in fixed wing aircraft (airplane), while differing in main noise source alignment in respect to the relative airflow: in helicopters, both rotors, i.e. main and tail, that produce forces necessary for flight, are inline with the direction of flight, while in airplanes rotor(s) are perpendicular to it. Another distinctive noise in helicopters, well known as "slapping", comes from the rotor cutting its own wake/vortex air inflow, especially while descending. In this article main helicopter noise sources will be discussed and most significant results of various static and in-flight noise measurements on two different types of helicopters will be presented and analyzed.
Low operating temperature integral thermo acoustic devices for solar cooling and waste heat recovery
Authors: De Blok Kees
Published: May 2008

Utilizing low temperature differences from solar vacuum tube collectors or waste heat in the range 70-200 °C seems to be the most promising field of applications for thermoacoustic systems. At these reduced temperatures overall system performance is increasingly affected by the ratio between amplified (useful) power and acoustic power stored in the resonance circuitry. Well known is that this ratio can be improved by deploying multiple regenerator units (hex-reg-hex). However, in commonly used torus or coaxial bypass configurations the correct timing (real and high acoustic impedance) is hardly realized inside more than two regenerator units (soft spot). Acoustic losses in the standing wave resonator account for another fundamental limitation because of the relatively low transferred power at a given pressure amplitude. Therefore a novel acoustic geometry will be presented in which a high and near real impedance can be maintained in even more than two regenerator units and in which acoustic feedback is performed by a true traveling wave. This approach improves the overall performance of integral thermoacoustic systems. Details and experimental results of a solar driven thermoacoustic cooler and ongoing work on thermoacoustic tri-generation utilizing exhaust gas of a standard gas-engine will be presented.
Parallel detection for picosecond ultrasonics
Authors: Smith Richard , Somekh Mike , Sharples Steve , Light Roger , Johnston Nicholas , Pitter Mark
Published: May 2008

Picosecond laser ultrasonics is a powerful technique for measurement and diagnosis of micro- and nano-scale structures. Unfortunately the data acquisition speeds are slow, this is a major drawback for widespread acceptance and usually makes imaging impractical. We are engaged in a program to accelerate the data capture rate by parallel acquisition of the incoming signals. This involves electronic developments as well as optical design. In order to parallelise the electronics we have used two approaches (i) a modified commercial camera and (ii) a custom built CMOS array detector. These approaches use an integrating camera which by application of suitable algorithms can perform the task of parallel lock in detection. Modulation depths below 1 part in 106, over 512 pixels can be readily detected with the commercial detector and smaller modulation depths are possible with the custom detector on account of the large well depth and hence high signal to noise. We also discuss the novel optical detection configurations that allow parallel detection of ultrasonic waves with ultrasonic wavelengths below the optical diffraction limit. Results are presented that show image acquisition rates orders of magnitude faster than normally possible with picosecond ultrasonic systems. Prospects for ultrahigh resolution optical resolution are discussed.
The acoustic excitation mechanism of bubbles released from a nozzle
Authors: Deane Grant , Czerski Helen
Published: May 2008

At the moment of their formation, bubbles emit a short pulse of sound. Bubble noise is associated with sound from a variety of natural processes, including whitecaps, waterfalls, breaking surf and rain. A number of acoustic excitation mechanisms for bubble noise have been proposed, including the increase in internal pressure of the bubble associated with the Laplace pressure, hydrostatic pressure effects, shape mode to volume mode coupling, and a fluid jet associated with the collapse of the neck of air formed during bubble creation. Using bubbles released from a nozzle as a model system, we have determined that sound production is excited by a sudden decrease in bubble volume driven by the collapse of the neck of gas joining the bubble to its parent. A simple analytical model of neck collapse driven by surface tension energy is in agreement with high speed photographic measurements, and sufficient to explain the details of acoustic excitation. [Work supported by ONR and NSF]
Determination of cavitation bubble lifetimes using bubble-bubble coalescence data
Authors: Grieser Franz , Sunartio Devi , Ashokkumar Muthupandian
Published: May 2008

The effect that surface-active solutes, such as aliphatic alcohols and sodium dodecylsulfate, have on the extent of bubble coalescence in liquids under different sonication conditions has been investigated by measuring the volume change of the solution following a period of sonication. The data obtained led to the conclusion that SDS does not reach equilibrium adsorption level at the bubble/solution interface. On this basis, a method is proposed for estimating nonequilibrium surface excess values for solutes that do not fully equilibrate with the bubble/solution interface during sonication. For the case of SDS in the presence of excess NaCl, the method was further employed to estimate the maximum lifetime of bubbles in a multibubble field. Data obtained from this study suggests that an acoustic bubble in a multibubble field has a finite lifetime, and that this lifetime decreases with increasing applied frequency, ranging from up to 0.35 ± 0.05 ms for 213 kHz to 0.10 ± 0.05 ms for 1062 kHz. These estimated lifetimes equate to a bubble in a multibubble field undergoing an upper limit of 50-200 oscillations over its lifetime for applied acoustic frequencies between 200 kHz and 1 MHz.
Investigation of bubble dynamics and sonoluminescence in megasonic fields
Authors: Otto Andrea , Nowak Till , Mettin Robert , Holsteyns Frank , Lippert Alexander
Published: May 2008

Cavitation bubble motion and bubble structures in water are investigated for standing wave fields in the megasonic range by high-speed imaging. Larger degassing bubbles and small bubbles with high translation speeds can be resolved. Groups of bubbles arrange in lines or arrays, as reported earlier by Miller [Miller, JASA 62, 1977]. Additional, sonoluminescence is measured in overall long-term and phase-resolved (gated) long-term exposures. Several distinct luminescing islands can be detected. The findings seem to be strongly related to the standing wave nature of the pressure field in our setup. Conclusions on bubble distributions and for cleaning applications are drawn.
An acoustic resonator for determining the void fraction of bubbly mercury flows
Authors: Roy Ronald A. , Ormonde Christopher E. , Chitnis Parag V. , Cleveland Robin O. , Holt R. Glynn
Published: May 2008

An acoustic resonator for measuring free-gas void fraction of a helium-mercury mixture is investigated. We employ a vertical, stainless steel cylindrical waveguide with a 5.08-cm i.d., a 1.27-cm wall thickness, a 40-cm length, and pressure-release boundary conditions at both ends. A bubble injection flow loop produces 2-phase mixtures of varying void fraction that flows upwards through the tube, spills over, and recirculates. The resonator is driven from the top by a 2.54-cm diameter circular piston affixed to an electrodynamic shaker. A hydrophone mounted 1 cm above the tube bottom is used to measure the frequency response of the system. Sound speed is inferred by assuming a linear dependence of axial mode number on mode frequency, and void fraction is calculated assuming a mixture sound speed for a bubble population with maximum sized much smaller than the resonant sizes in the modal frequency range (Wood's limit). The system was validated using non-bubbly water and water-air mixtures of different void fractions. Void fraction measurements for Helium-Mercury mixtures will be presented. [Supported by the ORNL Spallation Neutron Source, which is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.]
Experimental investigation of the effect of heating rate on pre-existing gas nuclei in a viscoelastic medium
Authors: Webb Ian , Arora Manish , Payne Stephen , Roy Ronald A. , Coussios Constantin C.
Published: May 2008

Inertial cavitation is known to play a key role in thermal HIFU therapy, both from the point of view of treatment safety and delivery, and as a potential tool for treatment monitoring. However, bubble behaviour in rapidly changing temperature fields remains poorly understood. Using a theoretical model, we have previously shown that, for a given initial bubble radius, a critical heating rate exists, above which the bubble will grow, and below which it will dissolve. In order to test this hypothesis, an electrical resistor embedded in 0.5% Xanthan Gum solution is used to impose a known temperature profile, measured by an array of thermocouples, on a series of embedded bubbles. An optical arrangement employing a 10 Megapixel CCD and a macro lens is used to image the bubbles within the gel at sufficient resolution for accurate sizing. The radius-time profiles for a range of bubble sizes are thus extracted using image analysis techniques, allowing comparison with model predictions and subsequent refinement of the theoretical model. Future work will focus on the incorporating the effects of acoustic excitation, such as rectified diffusion, to develop a unified model of bubble behaviour in viscoelastic media under the effect of a HIFU field.
Stability and simulations of pulsating contrast agents
Authors: Pelekasis Nikos A. , Tsiglifis Kostas
Published: May 2008

The encapsulating membrane of ultrasound contrast agents, UCA's, is treated as a viscoelastic thin shell whose deviation from linear Hookean behavior is modeled as a strain softening or strain hardening effect via a parameter measuring the degree of membrane softness. As the amplitude of sound increases it controls the shift in resonance frequency until it hits the forcing frequency in which case an abrupt increase in the microbubble response takes place. Only strain softening shells exhibit this behavior. Deviations from sphericity are modeled via an additional parameter, namely the scalar bending modulus. This parameter controls static buckling of the shell, the onset of parametric instability and dynamic buckling. In this fashion phase diagrams can be constructed for a specific UCA that map regions of subharmonic growth of shape modes. Stability analysis and numerical simulations are employed in order to capture the onset, growth and break-up or saturation of shape modes. The above two parameters are added to the area dilatation modulus and viscosity of the membrane in order to construct a model that can be used to design new agents that behave optimally in different diagnostic or therapeutic modalities.
Auditory masking using Gaussian-windowed stimuli
Authors: Necciari Thibaud , Savel Sophie , Meunier Sabine , Ystad Solvi , Kronland-Martinet Richard , Laback Bernhard , Balazs Peter
Published: May 2008

This study investigates auditory masking with Gaussian-windowed tones as target and masker stimuli. On the purpose of developing a time-frequency masking model, such stimuli minimize the time-frequency uncertainty. Also, as proposed by van Schijndel et al. (1999), they activate a single spectro-temporal observation window of the auditory system. The study presented here measured auditory masking with Gaussian-windowed stimuli with an ERB of 600 Hz and an effective duration of 9.6 ms. The masker was centered at 4 kHz. Its level was 60 dB SL. Four experiments were conducted. (1) Absolute thresholds for Gaussian-windowed and 300-ms-sinusoidal targets were measured and compared for 11 frequencies. (2) Masking patterns were obtained with targets of various frequency separations from the masker. (3) Forward masking functions with 4-kHz targets were measured at 5 temporal separations. (4) Forward masking was measured for different frequency separations between masker and target. These data are compared with those typically obtained with stimuli that are broader either in the frequency or time domain. A modelling attempt is made. A companying article on multiple masker additivity based on the present results is presented at the same conference (Laback et al.). Work partly supported by EGIDE (PAI Amadeus) and the ANR.
Measurement of equal-loudness contours using eardrum pressure as reference signal
Authors: Schmidt Sebastian , Hudde Herbert
Published: May 2008

Equal-loudness contours represent the relationship of loudness perception and sound pressure at the ear. Usually, the reference pressure is defined with a standardised calibration procedure. Individual ear canal characteristics significantly influence the contours, resulting in peaks and notches. By choosing the eardrum pressure as reference for the perception measurements, individual ear canal features are cancelled, when loudness and pressure are related. Thus, flatter contours can be achieved. Finite-element simulations of the sound field in the canal have shown that signals at remote positions may differ significantly from the eardrum pressure. Thus, to achieve eardrum related measurements, it is necessary to insert probe microphones sufficiently deep into the canal. However, the desired signal has to be estimated from a distance, since measurements directly at the drum are not practical. A method is shown to determine both the probe tip distance and the transformation terms to calculate the drum pressure estimate. In this contribution, the results of equal-loudness contour measurements are discussed. The positioning and transformation processes are verified by simulations with one-dimensional and finite-element models and experiments.
A fast FFT-based integral-equation solver for simulation of elastoacoustic wave propagation in human head
Authors: Bleszynski Elizabeth , Bleszynski Marek , Jaroszewicz Thomas
Published: May 2008

We describe formulation, implementation, and representative applications of a fast integral-equation solver for modeling wave propagation in inhomogeneous visco-elastic and visco-acoustic media (e.g. in biological tissues). The present approach is an extension of our work on fast integral equation solvers in pure acoustics. It is based on Lippmann-Schwinger (L-S) integral equations. It incorporates: (i) FFT-based compression of the stiffness matrix and the corresponding fast iterative method resulting in the solution complexity proportional to the number of unknowns, and ability to solve problems of several million unknowns, (ii) piecewise-linear basis functions supported on tetrahedra, representing displacement field, and corresponding efficient algorithms for evaluation of Galerkin matrix elements, (iii) rigorous two-stage solution scheme applicable to scatterers composed of high contrast materials and consisting of transforming the L-S equations into a system of two well-conditioned problems (conventional solution schemes, when applied to such scatterers, lead to stiffness matrix of large condition number). We present applications of the developed approach to simulation of elastic wave propagation in realistic models of the human head, with the goal of comparing sound transmission through the normal auditory airways and through bone conduction, and in the presence and absence of noise-protective devices. This work is supported by the Air Force Office of Scientific Research.
Towards a transfer function used to adjust audio for bone-conduction transducers
Authors: Stanley Raymond M. , Walker Bruce N.
Published: May 2008

Bone-conduction transducers may effectively replace normal air-conduction headphones in cases where the ears need to be plugged, or else remain unoccluded. However, sounds designed to be presented via air conduction need to be adjusted to maintain optimal perception via bone conduction. This study sought to find bone-to-air amplitude and phase shifts, as preliminary data for a complete transfer function between the bone-conduction and air-conduction pathway. The variability or stability of the shift data can indicate the feasibility of making effective adjustments to sounds to account for the bone-conduction pathway. Listeners cancelled air-conducted and bone-conducted tone pairs by method of adjustment at three frequencies (500, 3150, and 8000 Hz). The amplitude adjustments were relatively consistent, while the phase adjustments were quite variable. Further analysis revealed that the variability in phase adjustments came from differences between people, but were relatively consistent within a person. Together, these data suggest that generalized adjustments for the bone-conduction pathway may not be effective, but that individualized adjustments may be both necessary and potentially quite effective. These results can be extended to continuous transfer functions applied to sounds before they are presented via bone-conduction transducers ("bonephones") in an auditory display.
Variability of hearing protection devices attenuation as a function of source location
Authors: Nelisse Hugues , Gaudreau Marc-André , Voix Jérémie , Boutin Jérôme , Laville Frédéric
Published: May 2008

It is of common knowledge, and well documented, that laboratory-measured noise attenuation values of most hearing protection devices (HPD) exceed significantly the attenuation values obtained in real-world workplace environments. Various reasons may explain such discrepancies (lack of training, wearing time, lack of comfort, bad fitting, noise environments, etc.) but very few of them have been studied in details due to the complexity of the problem. This study focuses on the variability of the attenuation of HPDs as a function of the location of the noise source. Laboratory measurements were performed where subjects, wearing a HPD and facing a loudspeaker, were asked to rotate slowly on a rotating chair to simulate different angular positions of the head relative to the source. The protected and unprotected sound pressure signals for both ears were recorded as time signals using miniature microphones placed respectively inside and outside the HPD (F-MIRE technique). The microphones signals were processed to obtain attenuation values for the different angular positions. Results for different type of HPD (ear-muffs and ear-plugs) are presented and discussed.
Effects of voice familiarity and age on perceptual organization of sound from two competing talkers
Authors: Johnsrude Ingrid S. , Mackey Allison , Alexander Elizabeth M. , Macdonald Heather , Carlyon Robert P.
Published: May 2008

We used the Coordinate Response Measure (CRM) procedure (Bolia et al, 2000) to examine whether a non-acoustic characteristic of speech -voice familiarity- can affect a listener's ability to separate competing voices. We tested 27 listeners, aged 45-79, with their spouse's and two novel voices (other listeners' spouses). Couples had been living together at least 18 years. On each trial, two different talkers produced two of four callsigns (one being the target 'Baron'), two of four colours and two of eight numbers, and the participant responded by indicating the colour-number combination to which 'Baron' was told to go. We tested three conditions: spouse-voice target phrase with a novel-voice masker phrase (F/N); novel-voice target with spouse-voice masker (N/F); novel-voice target with (different) novel-voice masker (N/N). Compared to N/N, performance was significantly better in F/N, and, crucially, N/F conditions, indicating that listeners can exploit learned characteristics of a masking voice to help them track a novel voice. Furthermore, whereas the younger participants (under 60) benefited from having a familiar voice as target or as masker, the older group (over 60) benefited only when the familiar voice was the focus of attention, suggesting that the ability to use voice familiarity to segregate sounds changes with age.
Individual differences in auditory localization of real sources in the horizontal plane
Authors: Savel Sophie
Published: May 2008

Recent studies on spatial hearing showed that individual variability is greater with virtual sources than with real ones, but that sensorial feedback provides an efficacious and rapid learning procedure. This study evaluated the degree of inter-individual variability with real sound sources in the absence of feedback. Fifty normal-hearing listeners, aged 18-62, either left- or right handed, participated. The experiment was conducted in an anechoic room. One of twelve loudspeakers placed in the frontal horizontal plane and hidden by a curtain emitted a train of low-pass pulses. Listeners had to indicate the estimated direction of that source by placing a pointer on a screen. No feedback was given to them. Each listener completed 480-720 trials. Results indicated that variability between individual was great in both resolution in bias. Precisely, individuals differed (1) in the size of their maximum error, (2) in the azimuthal region in which this maximum error occurred, and (3) in the spatial symmetry of their performance. Indeed, 25% of the listeners showed significant left-right differences in their performance, these differences always favoring the left side of space. Such asymmetries have been noticed earlier but attributed to greater front-back confusions on the right, which cannot explain the present results.
Investigating effects of spatially disparate visual stimuli on auditory localization in VR environments
Authors: Nguyen Khoa-Van , Suied Clara , Viaud-Delmon Isabelle , Warusfel Olivier
Published: May 2008

Investigating the time and spatial constraints under which visual and auditory stimuli are perceived as a unique percept or as spatially coincident has been a topic of numerous researches in neuroscience. However, these findings have been derived up to now in extremely simplified stimulation context consisting in the combination of elementary auditory and visual stimuli usually displayed in dark and anechoic conditions. The present experiment is conducted in a VR environment using a stereoscopic passive screen and binaural audio rendering. Auditory stimuli are displayed on headphones using individualized head-related transfer functions and visual stimuli are integrated in a visual background in order to convey visual perspective. The experiment investigates the effect of a spatially disparate visual stimulus on the auditory localization judgments (crossmodal bias), as well as the relation between the magnitude of the crossmodal bias and the perception of a unified bi-modal stimulus. The present study will indicate whether previous findings (Hairston et al., Journal of Cognitive Neuroscience, 2003) still hold in more complex audio-visual contexts such as those offered by VR environments.
Comparison of subjective and objective evaluation methods for audio source separation
Authors: Kornycky Josef , Gunel Banu , Kondoz Ahmet
Published: May 2008

The evaluation of audio separation algorithms can either be performed objectively by calculation of numerical measures, or subjectively through listening tests. Although objective evaluation is inherently more straightforward, subjective listening tests are still essential in determining the perceived quality of separation. This paper aims to find relationships between objective and subjective results so that numerical values can be translated into perceptual criteria. A generic audio source separation system was modelled which provided varying levels of interference, noise and artifacts. This enabled a full spread of objective measurement values to be obtained. Extensive tests were performed utilising the output synthesised by this separation model. The relationships found were presented and the factors of prime importance were determined.
An exploration of attentional monitoring of isochronous asynchronous streams in deviant detection and sensorimotor synchronization
Authors: Turgeon Martine
Published: May 2008

Past studies of auditory selective attention focused on location and/or pitch cues in stream segregation. In this study, two perceptually-segregated streams competed for attention in a perceptual-judgment task based on timbre cues and a sensorimotor task (tapping to the sounds of one stream). Both streams shared the same temporal structure (isochronous 100-ms events at 1.67 Hz) but were asynchronous (target-distractor asynchronies of -200, -100, 100, 200 ms), differed in pitch (712 or 1000 Hz) and could share or not their perceived location (diotic vs. dichotic). Deviants were amplitude modulated at 25 or 50 Hz and varied in temporal envelopes. Attentional filtering (distracting stream constant) was done using a discrimination task requiring pressing one of two keys upon hearing one of two deviants (Experiment 1) and a synchronization task requiring selective tapping to the high-pitch or low-pitch sounds (Experiment 3). Attentional monitoring (distracting stream varies) required maintaining attention to the same stream upon hearing slow-modulated deviants and switching attention to the other stream upon hearing the fast-modulated deviants. This was done for the discrimination task (Experiment 2) and synchronization task (Experiment 4). Perceptual and perceptuo-motor results suggest attentional-filtering and attentional-monitoring costs. Surprisingly, the mere presence of a non-concurrent stream in a different frequency band interferes with deviant-discrimination and synchronization-tapping performance.
Normalization in count-comparison model of interaural time difference decoding
Authors: Pulkki Ville
Published: May 2008

Recent neurophysical studies suggest that binaural decoding is based on count comparison for both ITD and ILD. In such mechanisms, the neural signals are stronger in the auditory pathways leading to the ipsilateral hemisphere when a signal is presented earlier, or with higher level, to the contralateral ear. A computational model is described implementing binaural cue decoding based on count-comparison principles for ITD decoding, which is assumed to occur in medial superior olive (MSO). Pooled response of MSO is modeled as running multiplication between inputs, which are derived from ear canal signals with GTFB filtering and phase-locked impulse generator. The contralateral and ipsilateral inputs to MSO are then convolved with different responses. The model output corresponds well to neurophysiological results. In the earlier version of the model, the MSO output was normalized only with the contralateral signal, as suggested by the neuroanatomy. It has been later found out that the output of MSO model depends on ILD, which is in contradiction with psychoacoustics studies. In this study, it is proposed that the ipsilateral input to MSO is self-normalized, which provides ILD-independent ITD decoding.
Representation of Harmonic Sounds in the Helix of the Lateral Lemniscus
Authors: Langner Gerald , Simonis Claudia , Sauck Antje , Galuske Ralf
Published: May 2008

The percept of pitch of harmonic sounds is based on temporal processing. This explains also our ability to recognize harmonic relationships between different sounds, because as a result of a neuronal correlation analysis in the auditory midbrain neurons are tuned not only to a certain pitch but to a certain degree also to integer multiples of that pitch. The responses to harmonics of a pitch are suppressed within 30 ms after signal onset by inhibition with the likely source being the ventral nucleus of the lateral lemniscus (VNLL). An investigation of spatial representation of periodicity information with the 2-Deoxyglucose method in gerbils showed that low pitch is represented dorsally and high pitch ventrally along the length-axis of the VNLL. Three-dimensional computer reconstructions of the VNLL (program AMIRA) gave evidence for a helical periodicity map with 7 to 8 turns, reminiscent of the pitch helix known from music psychology. Moreover, the spatial organization of the VNLL suggests that it is organized as a double-helix representing musical octaves and fifths. Reconstructions of the VNLL of Nissl-stained human brains gave evidence of a similar organization and therefore of a similar functional role of the VNLL for pitch processing in humans.
Dynamic behavior analysis of vehicle acoustic trim using FEM
Authors: Kobayashi Norimasa , Uno Yoshihisa , Yamaoka Hiroo
Published: May 2008

Multilayer vehicle acoustic trim containing poroelastic materials affects noise and vibration phenomena not only in the high-frequency range but also in the low and mid-frequency range. However, there are few established technology to analyze the vehicle model which includes the characteristics of the trim. In this paper, a methodology for the analysis of multilayer acoustic trim within a vehicle FEM model is derived based on Biot theory. Using this methodology, dynamic vibration, radiation and absorption behavior of three types of multilayer trim including conventional isolative type, absorptive type and isolative type with absorptive top layer backed by rectangular metal plates are analyzed. The trim model is also applied to a vehicle FEM model and its effects on interior sound pressure level are validated with experimental data.
Influence of solid phase elasticity in poroelastic liners submitted to grazing flows
Authors: Nennig Benoit , Chazot Jean-Daniel , Perrey-Debain Emmanuel , Ben Tahar Mabrouk
Published: May 2008

In the present work, we study the sound propagation in a duct treated with a poroelastic liner exposed to a grazing flow. Acoustic propagation in the liner and in the fluid domain is respectively governed by Biot's model and Galbrun's equation. Here, the coupling between Galbrun's and Biot's equation is carried out with a mixed pressure-displacement FE. On one hand, a mixed formulation is used in Galbrun's equation to avoid numerical locking. And on the other hand, in poroelastic media, the description of both phases involves the displacement of the solid phase and the pressure in the fluid phase. In addition of using the complete Biot's model, simplified models are also tested. A fluid equivalent model that does not take into account solid phase elasticity and a model that neglects only the shear stress are hence used. These two simplified models enable to evaluate the contributions of the compressional and shear waves in the solid phase. Finally, validity of each simplified model in the specific case of a liner exposed to a grazing flow is discussed for different materials.
An Evolutionary Optimization Method applied to Absorbing Poroelastic Systems
Authors: Silva Francisco , Pavanello Renato
Published: May 2008

Poroelastic materials can be used in engineering applications such as: noise control of automobiles, acoustical insulation systems for aircrafts, industrial, environmental and domestic sound quality control, etc. The insulating systems must be as light as possible and the acoustic absorption in the low frequency domain must be maximized for certain gaps. Topology Optimization is frequently used to design structures and acoustic systems in a large range of engineering applications. In this work, we propose one method to maximize the absorbing performance of insulation poroelastic systems using a coupled finite element model and Evolutionary strategies. The goal is find the best distribution of poroelastic material on insulating systems. The absorbing performance of the poroelastic material samples in a Kundt tube is simulated using a coupled poroelastic and acoustic finite element model. The Biot-Allard Coupled Model is used to represent the foam material. The porous material model is coupled to a waveguide using a modal superposition technique. A sensitivity number indicating the optimum locations for porous material removing is derived and used in a numerical hard kill scheme. The sensitivity number is used to form an evolutionary poroelastic optimization (EPO) algorithm which is verified though numerical examples.
A new hybrid passive/active cell to realize a complex impedance boundary condition
Authors: Galland Marie-Annick , Dupont Jean-Baptiste
Published: May 2008

Hybrid passive/active cells previously developed at the LMFA have proved their efficiency for global noise reduction. A hybrid cell combines passive absorbent properties of a porous layer and active control at its rear face. Active control is mainly used to increase absorption at low frequencies by cancelling the imaginary part of the surface impedance presented by the absorber. A specific decentralized control algorithm allowed realizing large panels to reduce multi-tone noise radiated by a flow duct. Generally, the design of such absorbers starts by determining the optimal impedance for the targeted application, defined as that which, for each frequency, produces the highest reduction. However, in many cases results show that this optimal impedance is complex and that both real and imaginary parts are frequency dependent. This paper investigates the potential of a new hybrid absorber intended to realize any of impedance. The new cell uses one microphone on each side of a resistive cloth. Normal velocity can then be deduced by a simple pressure difference, which allows an easy synthesis of the error signal. First experiments carried out in a standing wave tube are described and different control strategies are examined, allowing us to validate this promising concept.
Reduced models for elastoacoustic problems with intelligent interfaces
Authors: Ichchou Mohamed , Kacem Aida A.
Published: May 2008

Effective and predictive noise and vibration modelling and design tools as well as efficient and high-performance materials are essential to produce world-leading products with regards to the noise and vibration quality. In one hand, the modern trend towards virtual design and prototyping requires good analysis and modelling tools in the entire noise frequency band. In another hand, new passive, adaptive or active materials offer improved technologies issues for the vibration and noise treatment. However, there is still a lack of efficient numerical tools in the low frequency band, and an absence of tools in the mid-frequency range. Moreover, although new materials potential can be demonstrated in prototype structures, their performances are still insufficient in integrated applications. To bring advances in noise and vibration treatment using new materials, the challenge is to be capable of supporting specific aspects related to advanced materials and virtual prototyping methods. An essential requirement for this is a multi-disciplinary analysis and coupled simulation tools where effects on a very different scale need to be interconnected. The paper proposes reduced models of elastoacoustic problems with localised intelligent interface. The main focus is development of fast simulation tool for the design of new systems. Theoretical as well as numerical experiments are offered in this work.
Broad-Band Vibration Attenuation in Plates With Periodic Arrays of Shunted Piezoelectric Patches
Authors: Ruzzene Massimo , Airoldi Luca
Published: May 2008

Periodic arrays of shunted piezoelectric patches are employed for the control of waves propagating over the surface of plate structures. The shunted piezoelectric patches act as sources of impedance mismatch, which yield interference phenomena resulting from the interaction between incident, reflected and transmitted waves produced by the mismatch. The impedance mismatch corresponding to the shunted piezos can be tuned to achieve strong attenuation over frequency bands which are defined by the shunting circuit connected to the patches. Broad-band vibration attenuation can be achieved through the application of series and parallel of multiple resonant circuits, or through the implementation of negative capacitance configurations. The ability of plates with periodic shunted piezoelectric patches to attenuate vibrations over extended frequency bands is demonstrated numerically, through Finite Element models of the considered electromechanical structures. The effect of number of patches and of their periodic distributions is investigated together with the analysis and the comparison of performance achieved with various shunting strategies.
Active control of multimodal tonal noise propagated in circular duct with axial subsonic mean flow until M=0.3
Authors: Glesser Martin , Friot Emmanuel , Winninger Muriel , Pinhède Cédric , Roure Alain
Published: May 2008

As new generation of aircraft engine with lower blade passing frequency appeared in the 1990's, the fan tones radiated from the inlets had become one of the dominant source of sound. Efforts have then been made to develop active noise control. Encouraging results have been obtained but the physical limitation of the fan tones reduction have not been clearly determined, owing mainly to the complexity of the experimental rigs. This paper present an experimental investigation of the control of multimodal tonal noise propagated in circular duct in presence of a mean flow (M⩽0.3). A laboratory wind tunnel has been implemented for this purpose. Two limiting factors for the sound reduction are underlined: (i) the degradation of the secondary transfer matrix conditioning as the number of propagating modes increases in the duct and (ii) the degradation of the hypothesis of the time-invariance of the system to control as the flow velocity is increased. The effect of those limiting factors on the control efficiency are evaluated.