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A method for measuring the diffuse field sound absorption coefficient of a material using sound field synthesis is proposed. A planar loudspeaker array is first used to generate acoustic plane waves with variable incidence angle on the surface of a material under test. Using a two-microphone probe positioned closely to the sample’s surface, the angle-dependent sound absorption coefficients are then estimated. Finally, the diffuse field absorption coefficient is computed following Paris formula. Numerical simulations are used to evaluate the respective effects of the maximum incidence angle value and the number of individual incidence angles that are required for a robust calculation of the diffuse sound field absorption. Measurements are conducted on three different materials and compared with either simulation results obtained using the Johnson-Champoux-Allard theory, or with measurement results obtained using the standard reverberation chamber method. For all considered materials and over a wide frequency range, the proposed method leads to results that are in better agreement with theoretical predictions than those obtained using standardized methods.

This paper investigates the ability of binaural recording and reproduction to be used for measuring the detectability of reversing alarms in laboratory experiments. A complex and repeatible scenario was created using a wave-field synthesis system (WFS), and in-situ recordings in a lime mine. The reproduced sound field was further recorded with a dummy-head. Participants were asked to achieve a visual task (target tracking) while detecting two types of reversing alarms (tonal and broadband), mimicking an approaching vehicle. The experiment was conducted twice : at the center of a WFS array and in a sound-proof booth, using binaural recordings presented with headphones. Results showed that the detection times measured using binaural listening were significantly different from those measured in a fully immersive sound field reproduction. These differences were also greater with tonal sounds compared to broadband sounds. This study shows the limitations of the binaural technique to be used for such applications.

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The area-averaged effective sound absorption coefficient (SAC) of a rigid-backed homogeneous porous material subjected to a monopole excitation is calculated as the absorbed-to-incident sound power ratio. Using Allard's model to describe the sound propagation above the porous material, an analytical model for this power-based SAC is proposed and proves to give a good approximation of the sound absorption performance under monopole excitation of sufficiently large areas of material. The impact of factors on the power-based SAC, such as monopole height, material radial dimension used to calculate the sound powers, and material properties is discussed. The power-based SAC frequency-dependent behavior is analyzed through sound intensity field assessments at the material surface and is compared to normal incident plane wave and diffuse field SACs. The sound absorption behavior of sound absorbers under monopole excitation exhibits notable distinctions and peculiar results compared to those observed under plane wave and diffuse fields, particularly at low frequencies and for sources close to the material. [ABSTRACT FROM AUTHOR]

Standardized methods for measuring sound absorption such as the impedance tube and reverberation chamber methods are limited to normal or diffuse incidence, respectively. Two research axes have been generally followed in the literature to develop alternative techniques, the first one focusing on the measurement part, that is from the two-microphone technique to the use of microphone arrays or pressure-velocity sensors. The second axis focuses on the excitation part with for instance the use of sound field synthesis techniques. Since acoustic impedance and sound absorption coefficient of materials are classically defined under normal and oblique plane wave excitation, synthesizing an “ideal” plane wave using a loudspeaker array would allow measuring these acoustics quantities using a simple microphone pair. In this article, the effect of the different parameters of a loudspeaker array on acoustic plane waves reproduction on a material’s surface is first numerically studied. Then, numerical and experimental results for the estimation of both impedance and absorption coefficients are reported. These results show that sound field synthesis allows to characterize a material for arbitrary incidence angles over a wide frequency range, thus offering an alternative method to standard techniques and an improvement over existing works.

The sensory perception of products influences the relationship of potential users or buyers with these products. Sound quality is part of this sensory experience and is critical for products such as sports or utility vehicles as the sound conveys the impression of power or efficiency, among others. Therefore, there is a need to provide tools based on scientific methodology to acoustical engineers designing such vehicles. The motivation of this work was the need to explore new and faster methods for quicker and simpler sound quality evaluation. In this paper, the sound quality of side-by-side utility vehicles is investigated using the rapid sensory profile measurement method, and then by creating virtual participants using bootstrapping methods. Additionally, this study also investigates the effect of loudness equalization of the sound samples used during the listening tests. Results from these studies were used to establish the sensory profiles, desire-to-buy values and desirable sound profiles regarding the tested vehicles. Equalized loudness tests provide a finer sensory profile than those obtained using non-equalized sound samples. Furthermore, statistical analysis results confirm that adding virtual participants to the original data using a bootstrapping approach helps highlighting key information without altering the validity of the results.

Digital image correlation, deflectometry and digital holography are some of the full-field optical measurement techniques that have matured in recent years. Their use in vibroacoustic applications is gaining attention and there is a need for cataloging their performance in order to provide, to a broad community of users and potential future users, quantitative and qualitative evaluations of these three approaches. This paper presents an experimental comparison of the three optical methods in the context of vibration measurements, along with classical reference measurements provided by an accelerometer and a laser Doppler vibrometer. The study is carried out on two mechanical structures exhibiting various vibration responses when submitted to an impact. [ABSTRACT FROM AUTHOR]