| 摘要 |
PROBLEM TO BE SOLVED: To set acoustic impedance on a rear part acoustic terminal side so that successful directivity is obtained even in a high sound area.SOLUTION: When an encapsulation member 30A forming an air chamber A with predetermined capacity on a rear surface side of an acoustic electric transducer 20 is engaged into a rear end part of a unit case 10, a part from an apex part 301 adjacent to a center part of the acoustic electric transducer 20 of the encapsulation member 30A to a skirt part 302 adjacent to a rear part acoustic terminal 12 is made into a projection spherical surface shape, and an acoustic distribution constant circuit including: a first part 310 in which a cross section of a sound path reaching the rear part acoustic terminal 12 via the air chamber A from an acoustic resistance part AR by a sound hole 28a of the acoustic electric transducer 20 continuously increases; and a second part 320 in which the cross section continuously decreases toward a direction going farther from a sound collection source on a side of the rear part acoustic terminal 12 is constituted by the encapsulation member 30A. |
