PURPOSE: To eliminate external noise components by dividing electroacoustic transducers into two groups and combining them so that outputs of each group are inverted together.

CONSTITUTION: Many electroacoustic transducers 1, 1' arranged in parallel are polarized respectively in directions of arrows A, B. That is, the electroacoustic transducers 1 are polarized in the direction of arrow A and the electroacoustic transducer 1' are polarized in the direction of arrow B. With respect to the noise component N picked up by the lead wire of the electroacoustic transducers 1, 1', since one group of electroacoustic transducers 1' are connected to an adder 10 via a phase inverter 12, the noise component is opposite in phase to that from the other transducers 1 at the adder 12 and the noise components are cancelled together.