Conference PaperPDF Available

On the Comparison of Two Room Compensation / Dereverberation Methods Employing Active Acoustic Boundary Absorption

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Abstract

In this paper, we compare the performance of two active dereverberation techniques using a planar array of microphones and loudspeakers. The two techniques are based on a solution to the Kirchhoff-Helmholtz Integral Equation (KHIE). We adapt a Wave Field Synthesis (WFS) based method to the application of real-time 3D dereverberation by using a low-latency pre-filter design. The use of First-Order Differential (FOD) models is also proposed as an alternative method to the use of monopoles with WFS and which does not assume knowledge of the room geometry or primary sources. The two methods are compared by observing the suppression of reflections off a single active wall over the volume of a room in the time and (temporal) frequency domain. The FOD method provides better suppression of reflections than the WFS based method but at the expense of using higher order models. The equivalent absorption coefficients are comparable to passive fibre panel absorbers.
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... • A minimum-phase weighted least square (WLS) compensation pre-filter for WFS/SDM is proposed. It allows for delayless real-time suppression of acoustic reflections [120]. The WLS-based method does not assume knowledge of the room. ...
... • A first-order differential (FOD) source/receiver model is proposed for active dereverberation [120]. The FOD-based method does not assume knowledge of the room. ...
... • A comparison of the proposed WLS-based and FOD-based dereverberation methods is given for acoustic suppression in the time domain and frequency domain [120]. ...
Thesis
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The experience and utility of personal sound is a highly sought after characteristic of shared spaces. Personal sound allows individuals, or small groups of individuals, to listen to separate streams of audio content without external interruption from a third-party. The desired effects of personal acoustic environments can also be areas of minimal sound, where quiet spaces facilitate an effortless mode of communication. These characteristics have become exceedingly difficult to produce in busy environments such as cafes, restaurants, open plan offices and entertainment venues. The concept of, and the ability to provide, spaces of such nature has been of significant interest to researchers in the past two decades. This thesis answers open questions in the area of personal sound reproduction using loudspeaker arrays, which is the active reproduction of soundfields over extended spatial regions of interest. We first provide a review of the mathematical foundations of acoustics theory, single zone and multiple zone soundfield reproduction, as well as background on the human perception of sound. We then introduce novel approaches for the integration of psychoacoustic models in multizone soundfield reproductions and describe implementations that facilitate the efficient computation of complex soundfield synthesis. The psychoacoustic based zone weighting is shown to considerably improve soundfield accuracy, as measured by the soundfield error, and the proposed computational methods are shown capable of providing several orders of magnitude better performance with insignificant effects on synthesis quality. Consideration is then given to the enhancement of privacy and quality in personal sound zones and in particular on the effects of unwanted sound leaking between zones. Optimisation algorithms, along with a priori estimations of cascaded zone leakage filters, are then established so as to provide privacy between the sound zones without diminishing quality. Simulations and real-world experiments are performed, using linear and part-circle loudspeaker arrays, to confirm the practical feasibility of the proposed privacy and quality control techniques. The experiments show that good quality and confidential privacy are achievable simultaneously. The concept of personal sound is then extended to the active suppression of speech across loudspeaker boundaries. Novel suppression techniques are derived for linear and planar loudspeaker boundaries, which are then used to simulate the reduction of speech levels over open spaces and suppression of acoustic reflections from walls. The suppression is shown to be as effective as passive fibre panel absorbers. Finally, we propose a novel ultrasonic parametric and electrodynamic loudspeaker hybrid design for acoustic contrast enhancement in multizone reproduction scenarios and show that significant acoustic contrast can be achieved above the fundamental spatial aliasing frequency.
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