Evaluation of a method for the measurement of subwoofers in usual rooms

Abstract

This paper evaluates the potential of the field separation method (FSM) for performing subwoofer measurements in a small test room with poor absorbing properties, as is commonly available. The FSM requires the knowledge of both acoustic pressure and velocity fields on a closed surface surrounding the tested source. Pressures and velocities, measured using a p-p probe on a half-sphere mesh, are collected under various conditions: in a room with variable reverberation time (6.4-0.6 s) and with four measurement half-sphere radii. The measured data are expanded on spherical harmonics, separating outward and inward propagation. The pressure field reflected by walls of the surrounding room is then subtracted from the measured field to estimate the pressure field that would have been radiated under free-field conditions. Theoretical frequency response of the subwoofer is computed using an analytical formulation derived from an extended Thiele and Small model of the membrane motion, coupled to a boundary element model for computing the radiated pressure while taking into account the actual subwoofer geometry. Measurement and simulation results show a good agreement. The effects of the measurement distance, the measurement point number, and the room reverberation time on the separation process are then discussed.

Active control of outgoing noise fields in rooms

“…In this section, we introduce a method to estimate the outgoing field on a sphere. The effectiveness of this method has been confirmed by simulations and experiments, 17 and we present detailed derivations of this method here for completeness.…”

“…15,16 The primary incoming field P I (k, R, H), on the other hand, is due to room reverberations. 17 In this paper, we formulate the problem of controlling the primary noise field P(k, r, H) in the room as estimating and canceling the primary outgoing field P O (k, R, H) on the sphere S 2 . By canceling the primary outgoing field P O (k, R, H), we effectively cancel the undesired noise in the entire room.…”

“…27 The measured sound field can be regarded as symmetric with respect to the floor, and can be duplicated to the lower semisphere to use the full spherical harmonic expansion. 17…”

“…We duplicate the sound field measured on the upper semi-sphere to the lower semi-sphere. 17 We set up a Cartesian coordinate system and a spherical coordinate system based on the primary source center O. One corner of the room locates at X ¼ (À1.5, À2, 0) m with respect to the point O.…”

Theoretical and experimental analysis of the electromechanical behavior of a compact spherical loudspeaker array for directivity control

“…The resonance frequency shifts observed between free standing unit and when applying a set of mechanical perturbations (added masses and compliances) are then used in an LMS estimation of the driver compliance, mass and effective surface. 20,32 This process ensures that the parameter set is suitable for a wide range of acoustic loads. The parameters for each driver have therefore been estimated from seven electrical impedance measurements taken with the driver operating under the following conditions:…”