Showing papers in "Canadian Acoustics in 2000"

Temporal jitter mimics the effects of aging on word identification and word recall in noise

Abstract: The simulation of the neural jitter disrupting the ability to phase-lock to lower frequencies in the aging auditory system was done. The applied jitter was determined to affect young adults performance so that it resembles that of older adults in two different tasks. Such findings helped in explaining age related decline in the ability to perceive speech, particularly in the presence of background noise, when no hearing loss is evidenced by standard clinical pure-tone audiometry. Degraded perceptual processing affects processes, such as memory, which are cognitive. Cognitive processes are employed to rescue signals degraded at the perceptual level.

Inverse characterization of the geometrical macroscopic parameters of porous materials

Abstract: The inverse problem of acoustically determining the geometrical macroscopic parameters of an open celled porous specimen is analyzed. The inverse characterization scheme is based on the equivalent fluid model, in which the solid frame is assumed to be rigid. The numerical predictions using the inversely identified parameters are compared to the measured sound absorption coefficient of the specimen for different thicknesses.

Multichannel active noise control algorithms using inverse filters

Abstract: An inverse structure, for the use of adaptive filters in active noise control (ANC) systems, is described. Multichannel adaptive filter learning algorithms, based on the filtered least mean square (LMS) algorithm was introduced for the inverse structure. It is shown with simulations, that the some versions of the introduced algorithms can achieve both a reduction of the computational load and an increase of the convergence speed, compared to the standard algorithms for ANC.

Wavelet noise reduction : application to speech enhancement

Abstract: An approach is proposed to remove noise by wavelet transform. The proposed method uses singularity information analysis and thresholding of the wavelet coefficients for noise reduction. The proposed approach is tested using speech sound corrupted by white noise and speech recorded in real environments.

Active noise control in enclosure with virtual microphone

Abstract: This study concerns local active noise control (ANC) in confined spaces. In cases where an active zone of quiet is intended in an enclosure, it is not always practical to place error microphones in this zone. Error microphones placed on the enclosure walls would sometimes be a more convenient solution. This article discusses the concept of a “virtual” microphone, which consists to generate a quiet zone distant from the error microphone used during control. Two virtual microphone algorithms are presented and experimentally tested. Such a virtual microphone technique has been implemented in the past for essentially fixed primary sources with respect to the enclosure (e.g. active control of propeller-induced aircraft cabin noise). The virtual microphone technique is especially examined here in the context of a moving primary source with respect to the enclosure (such as road traffic noise)

An evaluation of three-dimensional audio displays for use in military environments

Abstract: A relatively new technology, the three-dimensional (3-D) audio display, has been proposed for improving operator performance. However, many of the studies supporting 3-D audio displays have been conducted in controlled laboratory settings and it is not clear if all gains in performance will transfer into corresponding real-world applications. The Canadian Department of National Defence (DND) and the defence forces in allied nations are presently investigating 3-D technology for use in operational environments. The implications of the use of 3-D audio technology in real-world applications and recommendations for further research are discussed in this paper.

Strategies for active and passive noise control

Abstract: Noise control is a very crucial issue to be handled since the environmental concerns have become quite important. It involves careful diagnosis of the noise problem, prediction and design of various elements of the problem and application of best technology to solve the problem. Proper tools should be designed by the practicing engineers to curb the problem. Researchers should work to develop new technology. Noise will be effectively controlled once everyone contributes in this direction.

Comparison of three distortion product otoacoustic emission devices

Abstract: A comparison of noise susceptibility and distortion product otoacoustic emissions (DPOAE) variability was performed using DPOAE device prototype and two different DPOAE recording devices, on a small sample of adults, in quite and noisy conditions. To compare machine susceptibility to noise the effect of background noise level on the measured DPOAE values for each machine was examined. To compare data variability over repeated testing the standard deviations of the DPOAE amplitude values in the `low noise' and `high noise' sections were calculated.

Comparison of objective functions for engine mounts optimization

Abstract: A straightforward method is presented to model the behavior of an elastically supported engine attached to a rigid or a flexible structure. The proposed suspension optimization approach seeks to minimize passenger's perception of noise and vibration inside vehicles. It allows designers to model structure borne noise generated by the engine.

Binaural technology for application to active noise reduction communication headsets: design considerations

Abstract: This article examines the fundamental basis and the technical aspects involved in integrating two emerging technologies in the design of communication headsets for use in noisy environments. The first technology, active noise reduction (ANR), can improve signal detection and speech intelligibility by reducing the amount of interfering noise from the environment. The second technology, known as binaural technology, allows the creation of 3D auditory displays, which can improve signal detection and speech intelligibility in noise, and situational awareness, over monaural listening. For an optimal integration of binaural technology into ANR headsets, digital devices are preferred over analog devices. The complexity of the integrated system, particularly the features of the binaural simulation, is found to be largely dependent on the specific demands of the application targeted. Two extreme cases relevant to an aircraft cockpit environment are analyzed. The greatest benefit is likely to be found in situations of divided attention listening in relatively low signal-to-noise environments.

Rider influence on modal properties of bicycle frames

Abstract: Modal analysis of bicycles was carried out to find their dynamic behavior and the influence of rider and boundary conditions on the modal parameters of road bikes. Out-of-plane motion analysis and in-plane analysis were performed to identify the modes of the bicycle. The analyses were performed in the free-free condition and with the bicycle standing stationary on the floor with a rider. The dynamic behavior of bicycle was found to increase with the interaction of rider.

Transmission loss through barriers lined with heterogeneous porous materials

Abstract: The effect of solid heterogeneities and acoustic cavities on the normal incidence transmission loss of heterogeneous porous materials inserted in an infinite rectangular waveguide is investigated. The model is based on a finite element Biot-Allard's formulation for the porous patches. The modal behavior of the waveguide accounts for the coupling between the porous material and the waveguide. Numerical results are presented regarding the effect of geometric and physical parameters on the transmission loss performance of highly resistive plastic foam.

A comparison of modal decomposition algorithms for matched-mode processing

Abstract: This paper compares a variety of modal decomposition methods used in matched-mode processing (MMP) for ocean acoustic source localization. MMP consists of decomposing far-field acoustic measurements at an array of sensors to obtain the constituent mode excitations (modal decomposition), and then matching these excitations with modelled replica excitations computed for a grid of possible source locations. Modal decomposition can be ill-posed and unstable if the sensor array does not provide an adequate spatial sampling of the acoustic field, so the results of different approaches can vary substantially. Solutions can be characterized by modal resolution and solution covariance; however the ultimate test of the utility of the various methods is how well they perform as part of a MMP source localization algorithm. In this paper, the resolution and variance of the methods are examined using an ideal ocean environment, and MMP results are compared for a series of realistic synthetic test cases, including a variety of noise levels and sensor array configurations. Zeroth order regularized inversion is found to give the best results.

Sound transmission characteristics of elastomeric sealing systems

Abstract: A simple sound transmission model of the sealing system is presented. Finite element method and transfer function matrix were used to develop the model. Dynamic mechanical properties of seal material were measured and used as inputs to material property for the simulation. The effect of seal compression and material property of the bulb seal can be investigated. The seal vibration at the receiver was measured by the laser vibrometer.

Transmission loss optimization of multi-layer noise control treatments

Abstract: The optimization of the diffuse field transmission loss through double-wall sound barriers is discussed. The sound barriers are made from a porous decoupling material sandwiched between an elastic skin and a septum. The study aims at optimizing the frequency band averaged diffuse field transmission loss of the three layer system. The optimization problem is implemented by combining the optimization engine to an acoustic-indicator engine for the transmission loss calculation. The aim is to tailor certain material properties of the porous layer to achieve the minimum noise condition.

Index to predict the stability of decentralized adaptive feedback active noise control system

Abstract: A decentralized adaptive feedback control system of periodic noise is developed for control of periodic disturbances. The stability of feedback loop and the stability of the control is effectuated in the frequency domain. A condition derived from the Nyquist criterion is given in order to predict the stability of the control. The results show that the positions of the control filters on their convergence path play an important role on the stability and the performance of the control system.

Array element localisation of rapidly deployed systems

Abstract: Array processing techniques such as beamforming or matched field processing require accurate knowledge of the location of individual elements in the array. For horizontal arrays laid on the ocean floor, relative arrival times measured across the array from nearby implosive sources are often used to aid in estimating the sensor positions. However, the inverse problem of determining the sensor positions from the relative arrival times is both nonunique and ill-conditioned. Standard grid search techniques rely on very accurate measurements of the source locations and some knowledge of the array. This paper shows how simulated annealing can be used to solve the inverse problem with limited knowledge of the array or source locations. Synthetic studies show that relative sensor locations can be exactly found while tests with real data show an improvement in array gain comparable to the theoretical limit obtained from a perfectly known array.

Speaker identification by computer and human evaluated on the SPIDRE corpus

Abstract: Closed set speaker identification experiments were performed on a SPIDRE subset of the switchboard corpus with matched and mismatched telephone handset conditions. The impact of mismatched and matched conditions was evaluated. The tested conversations were divided into fixed block lengths of 10 ms. It was found that the confusion between speakers was mainly due to the strong telephone handset influence.

Formulation of an equation of diffusion for heterogeneous rods

Abstract: A new formulation for predicting the energy flow in heterogeneous rods id developed on the basis of an equation of diffusion. It succeeds in surpassing traditional studies for homogeneous ones, for which vibratory responses are often easily known by simple displacement formulation. However, one stays difficult to describe the mechanical behavior for heterogeneous structures: in this case, the energy flow is governed by structural damping, as for homogeneous medium, but by discontinuities too. The study presented here proposes to identify for heterogeneous structures a factor of diffusion involving proportionality between transmitted power and energy gradient. An equation of diffusion is then formulated considering an energetic balance. The formulation is semi-local, that is spatial average is locally made to take into account several heterogeneities in studied element. An analytical formulation is first developed for rod with area discontinuities. The proposed theoretical factor of diffusion is in good agreements with the numerical predictions.

Hybrid image/energy approach for acoustical predictions of industrial rooms

Abstract: A hybrid approach based on geometry acoustics and on energy acoustics was developed for acoustical prediction computation. A user-friendly interface was also developed to facilitate the use of this model. Observations reveal that the results obtained from this model were similar to the ones obtained from accurate methods.

Effect on sound attenuation provided by earmuffs of other safety gear worn in combination

Abstract: It is shown whether the sound attenuation afforded by hearing protective earmuffs is compromised, if the muffs are worn in combination with other safety gear. Seventy-two working-aged adults were tested. Speech understanding was assessed using the four alternative auditory feature test (FAAF) of constant discrimination. The results revealed that for young listeners the wearing of other safety gear alone or in combination significantly decreased the attenuation provided by class A muffs.

Validation of 3-D poroelastic finite element from the impedance measurement of a vibrating foam sample

Abstract: The real 3-D motion of porous materials was validated by comparing it with skeleton motion and acoustic coupling. The impedance of a resonant porous sample in a duct with lateral air gap was measured. A quasistatic measurement method was used to investigate both isotropic and axisymmetrical viscoelastic skeletons. For the experiment, the porous sample and the boundary conditions are so chosen that one resonance of the skeleton can be observed in the frequency range of 50 Hz to 500 Hz. The use of isotropic law is efficient when mechanical parameters are related to the kind of deformation of the material.

Modelling structure-borne sound transmission at bolted joints

Abstract: A model based on the wave approach for semi-infinite plates was used to calculate the coupling loss factors for statistical energy analysis. The coupling loss factors are expressed in terms of point mobility functions. The concept of an effective connection length is evaluated for a bolted joint between a plate and a stiffening rib. A parametric calculation is carried out with varying width to evaluate the concept of an equivalent connection length.

Integration of acoustic absorbing porous components in vehicle environment using a novel finite element solver

Abstract: A new mixed finite element formulation very well adapted to analyze the propagation of elastic and acoustic waves in porous absorbing media is presented. The proposed new formulation is based on modified Biot's equations written in terms of the skeleton displacement and the acoustic pressure in the interstitial fluid. It generalizes the previous formulation proposed by Professor Atalla & Co-authors, and has the great advantage over existing formulations of automatically satisfying all boundary conditions without having to compute surface coupling integrals at porous sub-domain interfaces. When elastic forces in the skeleton are neglected, the formulation automatically degenerates to an equivalent fluid model taking into account inertial coupling with the skeleton. This generalized mixed formulation and associated equivalent fluid model has been implemented by STRACO (France) in RAYON-PEM Solver. It is shown in this paper, that the numerical results predicted with RAYON-PEM agrees very well with experimental results using impedance tube tests and vibration measurements on multi-layered plates.

Acoustic absorption of non-homogeneous poro-elastic materials

Abstract: A model to evaluate the acoustic absorption performance of configurations consisting of a porous material, bonded onto the hard termination of a semi-infinite rectangular waveguide is presented. A power balance approach is used to evaluate the performance of the porus material using the absorption coefficient. An experimental validation is performed for a macro-perforated material, which consists in a mineral wool with periodic holes containing air. The absorption coefficient of non-homogeneous porous-elastic layers is predicted.

Modeling of multilayered structures including porous materials using hierarchical elements and non coincident meshes

Abstract: The coupling of mixed displacement-pressure formulation using hierarchical elements with a finite element plate modeling of an elastic domain assuming non-coincident meshes can be done. It can be used to predict the mean quadratic velocity and the transmission loss of a plate coated with porous materials. The results are very accurate and are with a reduced number of unknowns as compared to classical finite element modeling of the structure with the coincident meshes.

Piezoelectric actuator optimization for simultaneous aircraft cabin noise and vibration control

Abstract: The use of the piezoelectric (PZT) actuator optimization for simultaneous aircraft cabin noise and vibration control is effective in reducing both noise and vibration. The study explores PZT elements into different control groups as means to simplify the control systems while increasing the control authority. A genetic algorithm is developed to optimize the noise and vibration separately and independently. By the application of Pareto cooperative optimization approach the present work can be extended to both noise and vibration reduction performance.