Low frequency sound field control for loudspeakers in rectangular rooms using CABS (Controlled Acoustical Bass System)

Rectangular rooms are the most common shape for sound reproduction, but at low frequencies the reflections from the boundaries of the room cause large spatial variations in the sound pressure level.  Variations up to 30 dB are normal, not only at the room modes, but basically at all frequencies. As sound propagates in time, it seems natural that the problems can best be analyzed and solved in the time domain. A time based room correction system named CABS (Controlled Acoustical Bass System) has been developed for sound reproduction in rectangular listening rooms. It can control the sound distribution in the room at low frequencies by using multiple loudspeakers together with an optimal placement of the loudspeakers.  At low frequencies CABS will create a plane wave from the front wall loudspeakers which will be absorbed by additional loudspeakers at the rear wall giving an almost homogeneous sound field in the whole room, and short impulse response.  In a standard listening room (180 m³) only 4 loudspeakers are needed, 2 more than a traditional stereo setup. CABS is controlled by a developed DSP system. The time based approached might help with the understanding of sound field control and its solutions and limitations.