Acoustic focusing headphone based on delay-and-sum beamforming

A novel headphone system with microphone arrays was proposed whose objective is to boost forward sound signal, by doing so people can communicate well with a speaker during headphone playback. The main purpose of this research is to boost the sound signal from the front, particularly for a speech signal (300 Hz~3 kHz). A delay-and-sum beamforming method is applied to an end-fire microphone array to make a proposed headphone system. Three design parameters, i.e. an aperture size, the number of microphones, and a microphone arrangement of microphone arrays are decided based on performance of beamformer with respect to each parameter. To compare the performance regarding to each design parameter, a performance measure, efficiency, was defined as ratio of two resultant sound pressures between a forward and a backward direction. A sound scattering from a head of listener is modeled by using spherical head-related transfer function (HRTF). By changing an aperture size of a microphone array, 8 cm microphone array is thought to be proper when the efficiency in speech frequency range was considered. The use of four microphones is expected as the optimum by considering both good efficiency and reducing the number of microphones. By fixing the number of microphones and an aperture size of microphone array, the efficiency was calculated in various arrangements of microphones. As a result, microphone arrangement with inter-microphone spacing of decreasing interval is selected. The design parameters such as an aperture size, the number, and an arrangement of microphones can be changed regarding to a target frequency range or a direction wanted to be boosted, and the proposed methodology can be applied similarly.