Development of a semi-circular speaker array system to control low-frequency radiation pattern

A back-to-back speaker system can be used to achieve a cardioid-like radiation pattern in a low-frequency range. The pattern is obtained by placing two closely spaced speakers mounted back to back with a filter. The arrangement results in two sound waves that are in opposite phases, the sound wave from the back speaker cancels the back side sound wave from the front speaker. The arrangement achieves sound cancellation only in a narrow coverage angle. On the other hand, adding two more speakers may widen the coverage angle of the cancellation. This paper reports on the result of our investigation into a speaker system that consists of a primary speaker and three secondary speakers. The primary speaker is set to point in the desired direction, and three secondary speakers with semi-circular arrangement are used to reduce the back side sound wave at low frequencies where corresponding filters of each secondary speaker create the cancellation signals as a result of the filtered-x least mean square (FXLMS) Algorithm. The system has been tested and examined with measurements in an anechoic chamber. The results obtained were also compared to the results of the back-to-back speaker system.