As shown in FIG. 10, a speaker 100 that is a related-art common electromechanical acoustic transducer has a housing 101 having a sound port 101a at the center portion of the housing 101, and an essentially-plate-shaped frame 103 is attached to an interior surface 101b of the housing 101 through an rising portion 102 so as to generate an internal space 104.
A cylindrical closed-end yoke 105 supported in correspondence with the internal space 104 is attached to the center portion of the frame 103. A magnet 106 is attached to the inside of a bottom 105a of the yoke 105, and a magnetic gap 107 is formed between an interior surface of the yoke 105 and the magnet 106.
A plate 108 is attached to an apical surface of the magnet 106. A voice coil 109 is inserted in the magnetic gap 107. One end of the voice coil is attached to the bottom 105a of the yoke 105, and the other end of the voice coil 109 is attached to the center portion of a diaphragm 110.
A protector 111 for protecting the diaphragm 110 is provided in front of the diaphragm 110, and first air holes 111a are provided in the protector 111, and second air holes 103a are provided in the frame 103.
In such a speaker 100, the bottom 105a of the yoke 105 is arranged so as to face from the interior surface 101b of the housing 101 toward a departing direction (a downward direction in FIG. 10). Since the yoke 105 is smaller in diameter than the frame 103, a space exists between the frame 103 and another electronic component M housed in the housing 101.
In order to achieve a superior acoustic characteristic, a necessity for assuring a sufficient space around the second air holes 103a for producing superior resonances of sound emitted from the second air holes 103a to the internal space 104 of the housing 101 has commonly been known (see; for instance, Patent Document 1).
Patent Document 1: JP-A-2002-171596