Patent ID: 8705786

Claim:
A dynamic microphone unit comprising: a diaphragm vibrating in response to sound waves; a voice coil fixed to the diaphragm and vibrating in cooperation with the diaphragm; a magnetic circuit comprising an inner yoke, an outer yoke and a pole piece, the magnetic circuit generating a magnetic field in a magnetic gap, and the voice coil being disposed in the magnetic gap; a first air chamber adjacent to a reverse of the diaphragm and holding an acoustic resistance therein; a second air chamber behind the voice coil; and a communication passage for sound waves between the first air chamber and the second air chamber, the communication passage comprising a groove provided on the inner yoke, wherein the magnetic gap is defined between an inner circumference wall of the outer yoke and an outer circumference wall of the pole piece, wherein the magnetic circuit comprises a magnet surrounded by a ring spacer, wherein the ring spacer has a notch on an outer circumference wall of the ring spacer, the notch is in communication with the communication passage, and wherein the groove is in communication with the notch.