Optimal source placement for sound zone reproduction with first order reflections.

The problem of delivering personal audio content to listeners sharing the same acoustic space has recently attracted attention. It has been shown that a perceptually acceptable level of acoustic separation between the listening zones is difficult to achieve with active control in non-anechoic conditions. A common problem of strong first order reflections has not been examined in detail for systems with practical constraints. Acoustic contrast maximization combined with optimization of source positions is identified as a potentially effective control strategy when strong individual reflections occur. An analytic study is carried out to describe the relationship between the performance of a 2 × 2 (two sources and two control sensors) system and its geometry in a single-reflection scenario. The expression for acoustic contrast is used to formulate guidelines for optimizing source positions, based on three distinct techniques: Null-Split, Far-Align, and Near-Align. The applicability of the techniques to larger systems with up to two reflections is demonstrated using numerical optimization. Simulation results show that optimized systems produce higher acoustic contrast than non-optimized source arrangements and an alternative method for reducing the impact of reflections (sound power minimization).

Personal audio with a planar bright zone.

Reproduction of multiple sound zones, in which personal audio programs may be consumed without the need for headphones, is an active topic in acoustical signal processing. Many approaches to sound zone reproduction do not consider control of the bright zone phase, which may lead to self-cancellation problems if the loudspeakers surround the zones. Conversely, control of the phase in a least-squares sense comes at a cost of decreased level difference between the zones and frequency range of cancellation. Single-zone approaches have considered plane wave reproduction by focusing the sound energy in to a point in the wavenumber domain. In this article, a planar bright zone is reproduced via planarity control, which constrains the bright zone energy to impinge from a narrow range of angles via projection in to a spatial domain. Simulation results using a circular array surrounding two zones show the method to produce superior contrast to the least-squares approach, and superior planarity to the contrast maximization approach. Practical performance measurements obtained in an acoustically treated room verify the conclusions drawn under free-field conditions.

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

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.