1,720,983 research outputs found
Spherical Wave Diffraction for Microphone Arrays Operating in Near Field
No full textMicrophone arrays for spatial audio recording and reproduction became very popular in the last decade, due to the spread of virtual and augmented reality for entertainment, remote work, and teleconferencing. Several systems have been distributed on the market, and most of them are made of a rigid sphere. In this way, it is possible to rely on the theoretical solution of the plane wave diffraction to get the beamforming filters. Such filters are employed for synthesizing virtual microphones of arbitrary directivity by combining the signals recorded by the real microphones. However, the plane wave assumption corresponds to a far field condition, in which the wave fronts are planar or with negligible curvature.As the sound sources, or reflections, are closer to the array, the wave fronts tend to become spherical, and the planar hypothesis cannot be accepted. In this paper, the diffraction of spherical waves over a rigid sphere is investigated through numerical simulations based on Finite Elements Method and experimental measurements. It will be shown that the spatial performance is significantly degraded when theoretical filters are employed in near field conditions, while numerically calculated filters can provide a reliable improvement for near field beamforming
A Human Head Shaped Array of Microphones and Cameras for Automotive Applications
No full textNowadays, a growing interest in the recording and reproduction of spatial audio was observed. However, despite many microphone arrays were developed in the last years, there are still few solutions for Noise, Vibration and Harshness (NVH) applications at low frequency. In this paper, a new array of microphones and cameras is presented, for recording both acoustic and visual spatial information. It can be used for the spatial analysis and visualization of the sound field and to perform recordings that can be rendered in a virtual reality (VR) environment. The system was optimized for the low frequency range, as most of the available solutions have proved unsatisfactory for frequencies below 400 Hz. Moreover, the system is cost-effective if compared to other existing products designed for similar applications. The spatial performance of the array is evaluated in comparison with the current state of the art systems. Finally, a field application is presented. The new head shaped microphone array demonstrated its effectiveness for evaluating the performance of an automotive Active Noise Control (ANC) system
Spherical t-Design for Characterizing the Spatial Response of Microphone Arrays
No full textMicrophone arrays are usually employed for spatial audio recordings and analysis. This requires converting the raw signals of the capsules into a 3D audio format, e.g., a spherical harmonics expansion. For processing such conversion, namely beamforming, it is necessary to know the complex response of each microphone of the array for many Directions-of-Arrival of the sound waves. This information constitutes the spatial response and describes how the wave fronts are diffracted by the surface of the array. Beyond the experimental, numerical, or theoretical method employed to get the spatial response, the shape of the array and the number of capsules, the choice of the Directions-of-Arrival of the sound waves is always critical. On one side, to maximize the spatial information and so the performance, on the other side to reduce the number of directions, and so the measurement or calculation time. The paper analyzes the problem of choosing an optimal geometry for obtaining the spatial response of a microphone array. It will be shown that spherical design, or T-design, allows maximizing the spatial information with the minimum amount of testing directions. Numerical and theoretical methods have been employed for characterizing two microphone arrays, a spherical and a non-spherical one. In both cases, Ambisonics format for spatial audio has been employed
Transducer Distribution on Spherical Arrays for Ambisonics Recording and Playback
No full textMicrophone and loudspeaker arrays are nowadays more and more employed in several applications, such as automotive industry, entertainment, immersive teleconferencing, or remote assistance. The position of the transducers over the surface of the array has a great influence on the beamforming, and so on the spatial performance. In this paper, a recurring geometrical problem is discussed: choosing the optimal locations of transducers for spherical arrays, either microphones or loudspeakers.None of the existing systems is currently relying on a spherical design, or t-design, for the arrangement of the transducers on the sphere. It will be shown that such mathematically optimized geometry is an optimal solution for the design of spherical arrays. They are the only known geometries ensuring a lossless transformation back and forth between the two most common spatial audio format: Ambisonics, which makes use of spherical harmonics, and Spatial PCM Sampling, which relies on unidirectional, high directivity virtual microphones
Estimation of Diagonal Volterra Kernels of an Audio System During Normal Operation with Multiple Least Mean Squares Adaptive Filters
No full textThe usage of Complete Volterra Kernels for emulating the nonlinear behavior of sound systems has been investigated for decades. Due to the computational load, the real-time implementation is typically limited to second order distortion and not feasible for higher orders. This is usually unsatisfactory for audio systems in which the disturbing distortions occur mostly at orders three and five. The same authors of this work already solved the problem with the Diagonal Volterra Kernels technique, which allowed to model arbitrarily high distortion orders. The estimation of the coefficients was obtained by exciting the system with an Exponential Sine Sweep signal. However, the result was often suboptimal since the signal reproduced by the sound system is usually different from a sinusoid. In this paper, a new method for estimating the Diagonal Volterra Kernels coefficients is proposed, by employing any music, noise or speech signal being played by a sound system in real-time. Multiple Least Mean Square algorithms are used to estimate the coefficients up to the 5 th distortion order, thus allowing to emulate the nonlinearities of a typical audio system
Noncontact Measurements of Sound Absorption Coefficient with a Pressure-velocity Probe, a Laser Doppler Vibrometer, and a Microphone Array
No full textKundt's tube and reverberant chamber are common methods for determining the sound absorption coefficient or acoustic impedance of materials. These measurement methodologies are well-known and standardized, albeit not being practicable in-situ and requiring the isolation of samples of the material under test. Furthermore, Kundt’s tube results are affected by the size and the diameter of sample, and by the tube length, while reverberant chamber ones by the room dimensions and diffusiveness. In literature, noncontact techniques for sound absorption coefficient and acoustic impedance measurement are widely debated. In this paper, three different noncontact systems for measuring the sound absorption coefficient have been investigated: a pressure-velocity probe, a Laser Doppler Vibrometer, and a spherical microphone array featuring 64 capsules. The three methods have been evaluated through in-situ measurements of materials with known acoustic characteristics: Basotect G+ and Expanded Polystyrene. Furthermore, the results obtained with the standard test signal, i.e., white noise, are compared with the exponential sine sweep technique, which provides an increased signal to noise ratio, and allows for removing nonlinear high order distortions and acoustic reflections. As a main contribution of this work, it will be shown that microphone arrays are an optimal solution for measuring the sound absorption coefficient
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Application of laser vibrometer for the study of loudspeaker dynamics
Full text linkThis paper presents an experimental and numerical study of vibrations of loudspeakers. The experimental part consisted of measuring vibrational responses of cones of the loudspeakers to the sine sweep excitation signal. Acquisition was performed by means of a laser vibrometer. The numerical analysis employed finite element simulations of the cone and suspensions, based on estimation of viscoelastic properties for loudspeaker components. Having acquired accelerations of hundreds of points on the radiating surface, the radiated sound pressure level at one-meter distance has been computed. Confronting SPLs obtained from the two approaches the authors attempted to match the numerical model with the experiment. The matching was confirmed by the comparison between the simulated and measured operational deflection shapes
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