Low frequency sound reproduction in irregular rooms using CABS (Control Acoustic Bass System)

Early investigations on low frequency sound reproduction in rectangular rooms using CABS (Controlled Acoustic Bass System) have shown good results on simulations and measurements in real rooms. CABS takes the advantage of having a rectangular room with parallel walls. By using two low frequency loudspeakers well positioned at the end of the room a virtual array is formed propagating plane waves along the length of the room in one direction. This will correct the sound field distribution in the room. When plane wave arrives to the end wall two more loudspeakers have to be placed connected with the same signal in counter phase and with a delay corresponding to approximately the length of the room. This is to cancel the reflection and maintain the plane wave propagating along the room. Real life rooms are not necessary rectangular and can be of different shapes. In this paper simulations of an irregular room model using the FDTD (Finite Difference Time Domain) method has been presented. CABS has been simulated in the irregular room model. Measurements of CABS in a real irregular room haven been performed. The performance of CABS was affected by the irregular shape of the room due to the corner diffracting the plane wave. Nevertheless CABS improves spatial and magnitude deviations. In general it was observed that the symmetrical place of the rear loudspeakers was not necessary the best placement. The deviations suggest that the amplitude and the delay to each of the rear loudspeakers need to be slightly different.