Low frequency sound field control in rectangular listening rooms using CABS (Controlled Acoustic Bass System) will also reduce sound transmission to neighbor rooms

Sound reproduction is often taking place in small and medium sized rectangular rooms. As rectangular rooms have 3 pairs of parallel walls the reflections at especially low frequencies will cause up to 30 dB spatial variations of the sound pressure level in the room. This will take place not only at resonance frequencies, but more or less at all frequencies. A time based room correction system named CABS (Controlled Acoustic Bass System) has been developed and is able to create a homogeneous sound field in the whole room at low frequencies by proper placement of multiple loudspeakers. A normal setup using CABS is based on 2 loudspeakers like a stereo setup placed close to a wall so a plane wave is created from the front wall at low frequencies. At the opposite wall another 2 loudspeakers are placed playing the same low frequency part of the signal, but processed in order to cancel the reflection from the rear wall, and thereby leaving only the plane wave in the room. With a room size of (7.8 x 4.1 x 2.8) m. it is possible to prevent modal frequencies up to 100 Hz. An investigation has shown that the sound transmitted to a neighbour room also will be reduced if CABS is used. The principle and the understanding of why and how it works will also be discussed. CABS is controlled by a developed DSP (Digital Signal Processing) system.