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A compact end-fire loudspeaker array based on the linearly constrained minimum variance has been investigated in various reverberation rooms. In the linearly constrained minimum variance beamformer, the coherent matrix that determines the suppression direction of the radiation sound is important. Therefore, we evaluated the directivities of a loudspeaker array for four different coherent matrices that were calculated using the following methods in which the array will not radiate the sound: (I) for any direction except the reproduction direction, (II) in the direction of several measured room transfer functions, (III) in the direction of several ideal (free field) room transfer functions, and (IV) in the direction of the weighted ideal room transfer functions. To evaluate performance, a 4-element line array of 28-mm-diameter loudspeakers with equal spacing of 48 mm was implemented. The array used loudspeaker units without enclosures to shorten the spaces between the units. The directivities of the prototype loudspeaker array were measured in an anechoic room and three reverberant rooms by using the above four methods. The prototype arrays achieved higher directivity of 6 to 15 dB for wideband frequencies (300 Hz to 3.4 kHz) than the single loudspeaker for all methods. Moreover, the experimental results clarified that the array with method (IV), which did not use prior measured room transfer functions, had efficient performance in comparison with the array with method (II), especially when the reverberation time was 120 ms or less.

Evaluating small end-fire loudspeaker array under various reverberations