Performance evaluation of a back-to-back speaker system using a low-cost single board computer as a digital signal processor

A back-to-back speaker system with a user-designed filter results in a low-frequency cardioid-like radiation pattern where a back-facing loudspeaker is used to suppress the radiation in the rear direction. This paper presents an application of a low-cost single board computer as a digital signal processor on a back-to-back speaker system to obtain a cardioid-like radiation pattern in the low-frequency range. The system consists of two loudspeakers and a US$7 Orange Pi Zero PC. The loudspeakers are closely spaced and mounted in a back-to-back arrangement. A cancellation filter, which is identified in advance in an anechoic chamber using the filtered-x least mean square (FxLMS) algorithm, is used in the Orange Pi Zero PC. A buffering technique is used to make the PC act as a real-time-like signal processing unit. The performance evaluation was conducted under two conditions which were offline and online filtering. In offline filtering, sounds with and without cancellation were pre-prepared. On the other hand, in online filtering, the sound was simultaneously filtered and played. This paper also indicates conditions, for which the system exhibits great performance.