1,721,285 research outputs found
Book review. Beranek, L, Riding the Waves: A Life in Sound, Science and Industry, MIT Press, 2008
No full textFundamentals of acoustics
No full textAcoustics is the science and study of sound. In this book, we concentrate on sound in air at audible frequencies. The field of acoustics extends to include many related topics such as environmental acoustics, musical acoustics, architectural acoustics, electro-acoustics, underwater acoustics and ultrasonics. This chapter introduces the physical processes involved in sound generation and propagation which form the basis for many of these related fields.</p
Improved directivity of spherical microphone arrays
No full textThe aim of this research is to create a microphone array on a rigid sphere that could be used for teleconferences and for recording of music with the aim of five-channel loudspeaker surround sound reproduction. Computer simulations have been undertaken, within a MATLAB environment, that test the directivity of circular microphone arrays. The beamformer used in the study is an extension of the "focused beamformer" that attempts to map the distribution of acoustic source strength associated with a given source distribution by changing the Green function vector in accordance with the assumed source position. In the approach used here, it is assumed that multiple sources are present and Tikhonov regularisation is used in order to enable the inversion of the system response. Using an algorithm for the reconstruction of source strength time histories, the improvement in the directivity of the array was achieved by simulating the presence of several sources around the microphone array and then using only the filter corresponding to one of the sources. In that way the directivity is maximum in the source direction and minimum in the directions of the other sources, creating a mainlobe in the main source direction and several dips in response in the directions of the other sources.</p
Aeroacoustic source characterisation using inverse methods
No full textMeasurements of the sound field radiated by aeroacoustic sources, usually acquired at a distance using some form of sensor array, can be used to reconstruct the sources that generated that sound field by using inverse methods. However, many aeroacoustic sources of practical interest are usually distributed in extent and the inverse methods can then only be applied to a discretised representation of the source. For the inversion process to yield a unique solution, the number of observations must be equal to or exceed the number of unknown source elements - the system needs to be square or over-determined, and if the source is large compared to the acoustic wavelength of interest, a prohibitively-large number of sensors is required. In addition, these measurements may be taken in a reverberant environment in the presence of significant air flow. This paper describes the practical application of a technique, known as the "Bounded Correlation Length (BCL) Inverse Method", first described by the authors at ICSV13. This method allows the number of required sensors to be significantly reduced by exploiting the fact that many aeroacoustic source distributions have finite correlation lengths. The BCL Inverse Method is applied to a real aeroacoustic source problem, in a reverberant space, and it is shown that a distributed source divided into 84 source elements can be successfully characterised by using only 20 microphones.</p
Analysis of complex-valued neural networks for audio source localisation
No full textAn increasing number of studies recently have dealt with novel methods for locating the source of a wide range of acoustic events. Applications such as teleconferencing, human-robot interaction, source separation or speech recognition can make use of the Direction of Arrival (DoA) of a sound source to improve their results. Since most of the newer localisation methods proposed recently make use of neural networks in their estimation of source position, the work will focus on comparing the use of complex-valued neural networks with real-valued networks for localising sound source in different scenarios. The data used for the comparison will be simulated using a number of geometrical microphone arrangements with the acoustic sources placed in the far-field of the microphone arrays. The simulated data used in combination with the chosen range of microphone arrangements will be used to investigate the localisation limits of the chosen algorithms. A particular objective of the work will be to evaluate any potential advantages in using complex-valued neural networks rather than real valued networks
Digital filter design for inversion problems in sound reproduction
No full textWhen it is attempted to invert, or eliminate the influence of, a single-channel system such as a loudspeaker response or a room response, some frequencies are usually boosted by an excessive amount by the inverse filter. In particular, inversion of experimentally measured data tends to cause an excessive boost of frequencies just below the Nyquist frequency. A similar problem is encountered when designing digital filters for a multichannel virtual source imaging system such as the stereo dipole. A digital filter design method is presented that allows selective attenuation of unwanted peaks in the spectrum of the reproduced sound by using frequency-dependent regularization.</p
Boundary element simulations of the transfer function of human heads and baffled pinnae using accurate geometric models
No full textThis paper investigates various aspects of numerically modelled individualised head-related (and pinna-related) transfer functions (HRTF). The computer simulations are based on the exact solution of the wave equation using the boundary element method (BEM). The basic features of the HRTF are investigated with accurate geometric models of two heads and six pinnae which are captured by using state-of-the-art three-dimensional (3-D) laser scanners and digitisers. These computer models are converted to valid BEM models and their frequency response is simulated. We present the results of simulated HRTFs, and show the inter-variability of the response among six baffled pinnae modelled in identical conditions. With current computing hardware power, and vigilant optimisation of the manipulated mesh models and the solving procedures, heads with pinnae (but without torso) can be investigated at least up to 10 kHz, and baffled pinnae can be investigated up to 20 kHz. We conclude that it is possible to implement individualised HRTFs in a 3-D sound system or an auditory display, without the need for measurements in an anechoic chamber, if highly accurate 3-D images of the head and pinnae are captured and modelled with BEM
Control of acoustic radiation pattern in a dual-dipole array
No full textThis paper proposes a control strategy for generating various acoustic radiation patterns associated with a "personalized sound field" using an acoustic source array. A dual-dipole array, which models each loudspeaker as an imperfect dipole and a source signal control algorithm, which effectively considers both energy difference maximization and radiation efficiency are introduced in order to obtain better radiation patterns for generating the desired sound field. With the proposed dual dipole array and control algorithm, a wide controllability from a comparatively low to a high frequency range is obtained, although the array size is small enough to implement in mobile applications. The conceptually novel control strategy proposed enables efficient cancellation of the backward radiation. The performance of the dual dipole source array is verified by using computer simulations.</p
Choice of inverse filter design parameters in virtual acoustic imaging systems
No full textReproducing a pair of binaural signals over loudspeakers requires crosstalk cancellation filters that create sound at the two ears corresponding to a transparent delivery of the intended source material. Such filtering is effectively inverting the actual response of the loudspeakers to the two ears. The authors explore the consequences of inversion, especially when the response lasts longer than that of a strictly anechoic environment. The choice of inverse design parameters proves more difficult than expected. The authors conclude that the required knowledge of the actual environment is equivalent to making in situ measurements.<br/
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