Sound field reconstruction: a comparison between different technologies

This presentation is an introduction to two methods for the reconstruction of a sound field:high-order Ambisonics and the Least Square Method. The theoretical background to thesetwo approaches is presented and some sound field reconstruction animations, obtainedwith numerical simulations, are shown in order to illustrate the differences in theperformance of the two methods. Finally, an important result is presented: themathematical proof that high-order Ambisonics and Least Squares Methods are formallyequivalent under certain regularity conditions of transducer arrangements. This result isconfirmed by numerical simulation

Sound reproduction systems using variable-directivity loudspeakers

Sound reproduction systems using omnidirectional loudspeakers produce reflections from room surfaces which interfere with the desired sound field within the array. While active compensation systems can reduce the reverberant level, they require calibration in each room and are processor-intensive. Directional loudspeakers allow the direct to reverberant level to be improved within the array, but still produce a finite exterior field which reflects from the room surfaces. The use of variable directivity loudspeakers allows the exterior field to be eliminated at low frequencies by implementing the Kirchhoff–Helmholtz integral equation. This paper investigates the performance of variable-directivity arrays in reducing reverberant levels and compares the results with those derived in a previous paper for fixed-directivity arrays. The results presented may have some impact on the design of commercial multi-channel systems for sound reproduction

Sound-field reproduction systems using fixed-directivity loudspeakers

Sound reproduction systems using open arrays of loudspeakers in rooms suffer from degradations due to room reflections. These reflections can be reduced using pre-compensation of the loudspeaker signals, but this requires calibration of the array in the room, and is processor-intensive. This paper examines 3D sound reproduction systems using spherical arrays of fixed-directivity loudspeakers which reduce the sound field radiated outside the array. A generalized form of the simple source formulation and a mode-matching solution are derived for the required loudspeaker weights. The exterior field is derived and expressions for the exterior power and direct to reverberant ratio are derived. The theoretical results and simulations confirm that minimum interference occurs for loudspeakers which have hyper-cardioid polar response