Spatially extended sound equalization in rectangular rooms

Abstract

The results of a theoretical study on global sound equalization in rectangular rooms at low frequencies are presented. The zone where sound equalization can be obtained is a continuous three-dimensional region that occupies almost the complete volume of the room. It is proved that the equalization of broadband signals can be achieved by the simulation of a traveling plane wave using FIR filters. The optimal solution has been calculated following the traditional least-squares approximation, where a modeling delay has been applied to minimize reverberation. An advantage of the method is that the sound field can be estimated with sensors placed in the limits of the equalization zone. As a consequence, a free space for the listeners can be obtained.

Regularization in global sound equalization based on effort variation

“…This means that the sources are 180°out of phase with the desired sound pressure at x = x R , which is necessary to avoid reflections from the receiving wall. This behavior, which has already been observed and explained theoretically by Santillán 8 for the case of rectangular rooms, remains a desired condition for good global equalization also in irregularly shaped rooms.…”

“…6,7 Based on the latter approach, it has been shown that equalization in a large region of a room can be favored by the reproduction of a freely propagating plane wave. [8][9][10][11][12][13] This is achieved by appropriate positioning of sound sources at two opposite walls perpendicular to the direction of propagation. In this way the equalization can be extended to a spatial region that covers almost the complete volume of the room.…”

Sound equalization in a large region of a rectangular enclosure (L)

“…The traditional least-squares approximation has been employed to estimate the coefficients of FIR filters for the equalization of broadband signals. 3 However, some issues remained unaddressed in the original study, and thus the purpose of this paper is to extend the previous work and discuss some matters more thoroughly on the basis of simulation and experimental results.…”

“…2 The problems that traditional equalization methods face were overcome in Santillán's approach. 3 In this work a plane wave moving along a rectangular enclosure was generated in order to equalize the sound field at low frequencies in a continuous three-dimensional region that occupied almost the complete volume of the enclosure. Theoretical results showed that the generation of a traveling plane wave is possible within a rectangular enclosure provided that sets of sources are arranged in the two walls that are perpendicular to the direction of propagation.…”

Enhanced Wide-Area Low-Frequency Sound Reproduction in Cinemas: Effective and Practical Alternatives to Current Calibration Strategies

“…There exist numerous approaches to spatial variance minimization (largely targeted for home-cinema applications, but are often applicable to large-scale venues) that typically achieve their results through the application of least mean squares (LMS) based optimization algorithms, including a series of frequency response measurements taken from across the listening area [31][32][33][34][35]. Other methods use loudspeaker polar response control in order to avoid room-mode buildup along certain dimensions and to focus the sound energy towards the listeners [12,36,37].…”