Acoustic contrast, planarity and robustness of sound zone methods using a circular loudspeaker array

Abstract

Since the mid 1990s, acoustics research has been undertaken relating to the sound zone problem-using loudspeakers to deliver a region of high sound pressure while simultaneously creating an area where the sound is suppressed-in order to facilitate independent listening within the same acoustic enclosure. The published solutions to the sound zone problem are derived from areas such as wave field synthesis and beamforming. However, the properties of such methods differ and performance tends to be compared against similar approaches. In this study, the suitability of energy focusing, energy cancelation, and synthesis approaches for sound zone reproduction is investigated. Anechoic simulations based on two zones surrounded by a circular array show each of the methods to have a characteristic performance, quantified in terms of acoustic contrast, array control effort and target sound field planarity. Regularization is shown to have a significant effect on the array effort and achieved acoustic contrast, particularly when mismatched conditions are considered between calculation of the source weights and their application to the system.

The Relationship Between Target Quality and Interference in Sound Zone

“…The strict target field does however result in poorer contrast than ACC [11], particularly at frequencies above the array aliasing limit. As a result, we might expect that PM would produce listening scenarios with a higher distraction score than ACC but also with improved target quality.…”

“…Since ACC purely maximizes the ratio of spatially averaged squared pressures between the zones, it tends to outperform other methods in terms of contrast [11]. However, ACC does not control the phase and so may result in confusing spatial cues for the listener.…”

“…For this implementation, λ was first initialized such that the condition number of (G H B G B + λI) did not exceed 10 10 [11]. At higher frequencies where the condition number was already below this threshold, λ was instead initialized such that the condition number of (G H B G B + λI) was reduced by a factor of 10.…”

“…However, these are not designed to address the degradations to target quality caused by reproducing programs using sound zoning systems. The types of degradations caused by sound zoning systems may include spatial degradations (due to uncontrolled phase and selfcancellation) [11], temporal degradations (such as ringing or pre-echo) [12], spectral coloration, and variation in all of these across the reproduction zone that may be audible with listener head movement.…”

“…Each approach enjoys differing degrees of success according to the physical measures of contrast (the acoustic separation between the zones), control effort (the energy required for sound attenuation), and planarity (the distribution of plane wave energy with respect to direction of arrival at the bright zone) [11]. Acoustic contrast control (ACC) [13] gives the maximum contrast between the zones but does not attempt to control the phase of the resulting sound field.…”