Patent ID: 7889873

Claim:
Microphone array ( 1 ) for achieving a substantially frequency-independent directivity using a plurality of microphones ( 5 ) disposed along a rectilinear array, where: the rectilinear array is at least as long as the wavelength of the lowest frequency, where a useful directivity is desired, the rectilinear array has a first end ( 2 ) and a second end, the microphones close to the first end ( 2 ) are intended for the highest frequencies and the microphones close to the second end are intended for the lowest frequencies, the position of the microphones is given by the formula: l n = l · 2 - ( N - n d ) wherein l is longest wavelength, for which frequency-independence is desired, N is the maximum number of microphones, l n is the position of the n′th microphone with respect to the end of the microphone array, which is intended for the highest frequencies, and d is the number of microphones per octave, the signals from the individual microphones ( 5 ) are time-delayed so that phase differences or propagation time differences caused by the spatial position of the microphones ( 5 ) are taken into account, characterised in that the signals from the individual microphones ( 5 ) each independently are band-pass filtered, the band-pass filters for the individual microphones being digital with a pole position, resulting in a constant group propagation time within the entire frequency range used and ensuring that the signals from the band-pass filters are in phase, wherein the ratio between the bandwidths and centre frequencies of the individual band-pass filters is constant, and wherein the signals after band-pass filtering are summated for obtaining the output signal.