Variable-directivity microphone device

Claim 1

A variable directivity microphone device comprising: a microphone unit assembly provided and arranged with at least three microphone units, said three microphone units being mutually separated by predetermined distances, and front faces of first and second microphone units among said three microphone units being provided and arranged facing the front surface of said microphone unit assembly while the front face of a third microphone unit is provided and arranged in a direction opposite to those of said first and second microphone units; a first and second variable resistors respectively having a first terminal at one end, a second intermediate terminal, and a third terminal at the other end, wherein respective sliders are mutually linked or ganged and movable between first, second, and third positions corresponding to said first through third terminals, said first variable resistor having its first and third terminals respectively coupled to outputs of said second and third microphone units and its second intermediate terminal coupled to ground; a phase-shifter coupled between the output of said second microphone unit and said first terminal of said first variable resistor, for substantially only performing a phase shift in a high-frequency range, said phase-shifter having a phase shifting characteristic wherein the output phase approaches -180 degrees from -90 degrees as a ratio ω/ω a becomes larger than unity and approaches zero degrees from -90 degrees as the ratio ω/ω a becomes smaller than unity, where ω is the angular frequency and ω a is the angular frequency at a point lagging in phase by 90 degrees; an adder for adding and mixing the output of said first microphone unit and a signal obtained from the slider of said first variable resistor; and a frequency characteristic compensating circuit having an operational amplifier and a frequency characteristic circuit, for compensating for the frequency characteristic of an output signal of said adder, said second variable resistor having its first terminal and slider coupled to an output of said operational amplifier and its third terminal coupled to one input of said operational amplifier, said frequency characteristic circuit being connected in parallel with said second variable resistor between said first and second terminals of said second variable resistor, said microphone device having its directivity varied from non-directivity, to primary unidirectivity, and then to secondary unidirectivity, as the sliders of said first and second variable resistors vary from said third, to second, and then to first positions so that the output phase at said phase-shifter approaches zero degree from -90 degrees and then approaches -180 degrees from -90 degrees.