Superdirectional Microphone Arrays

Noise and reverberation can seriously degrade both the microphone reception and the loudspeaker transmission of speech signals in hands-free telecommunication. Directional loudspeakers and microphone arrays, can be effective in combating these problems. This chapter covers the design and implementation of differential arrays that are small compared to the acoustic wavelength. Differential arrays are therefore also superdirectional arrays since their directivity is higher than that of a uniformly summed array with the same geometry. Aside from the small size, another beneficial feature of these differential arrays is that their directivity is independent of frequency. Derivations are included for several optimal differntial arrays that may be useful for teleconferencing and speech pickup in noisy and reverberant environments. Novel experssions and design details covering multiple-order hypercardioid and supercardioid-type differential arrays are given. Also, the design of Dolph-Chebyshev equi-sidelobe differential arrays is covered for the general multiple-order case. The results shown here should be useful in designing a nd selecting directional microphones for a variety of applications.