Dynamic microphone unit and dynamic microphone
A dynamic microphone unit includes a diaphragm vibrating upon receiving acoustic waves, a voice coil fixed to the diaphragm, vibrating together with the diaphragm, a magnetic circuit generating a magnetic field in a magnetic gap in which the voice coil is disposed, a rear air chamber formed behind the magnetic circuit, wherein holes for connecting a back side space of the diaphragm with the rear air chamber are formed in a member forming the magnetic circuit in order to reduce resonance and reduce peaks developing in frequency response characteristics, achieving uniformity of directivity.
1. A dynamic microphone unit comprising:
a diaphragm vibrating upon receiving acoustic waves;
a voice coil fixed to the diaphragm and disposed in a magnetic gap, the voice coil vibrating together with the diaphragm;
a magnetic circuit generating a magnetic field in the magnetic gap; and
a rear air chamber communicating with a back side space of the diaphragm via the magnetic gap, wherein
a member forming the magnetic circuit includes holes formed therein for connecting the back side space of the diaphragm with the rear air chamber, and
wherein the magnetic circuit is formed by a magnet, a yoke and a pole piece that are fixed across the magnet, and a ring yoke to which the yoke is fixed and whose inner periphery surface faces an outer periphery surface of the pole piece to form the magnetic gap together with the pole piece.
2. The dynamic microphone unit according to claim 1 , wherein the magnetic gap is formed between the outer periphery surface of the pole piece and the inner periphery surface of the ring yoke, and the holes for connecting the back side space of the diaphragm with the rear air chamber are formed in the ring yoke.
3. The dynamic microphone unit according to claim 1 , wherein the holes for connecting the back side space of the diaphragm with the rear air chamber are formed in a flange portion, which protrudes inward, of the ring yoke at positions deviated outward in a radial direction from an inner periphery surface of the flange portion.
4. The dynamic microphone unit according to claim 1 , wherein a second air chamber communicating with the rear air chamber is formed between an outer periphery surface of the magnet and the inner periphery surface of the ring yoke, and the holes for connecting the back side space of the diaphragm with the rear air chamber communicate with the second air chamber.
5. The dynamic microphone unit according to claim 1 , wherein the holes for connecting the back side space of the diaphragm and the rear air chamber are covered with an acoustic resistance plate.
6. The dynamic microphone unit according to claim 5 , wherein the acoustic resistance plate includes innumerable minute holes in a portion where the acoustic resistance plate covers the holes for connecting the back side space of the diaphragm with the rear air chamber.
7. The dynamic microphone unit according to claim 5 , wherein the acoustic resistance plate is formed by etching a plate-like material.
8. The dynamic microphone unit according to claim 1 , wherein a unit case is fixed to an outer periphery of the member forming the magnetic circuit, an outer periphery of the diaphragm is fixed to the unit case, and holes for connecting the back side space of the diaphragm with an external space are formed in the unit case.
9. The dynamic microphone unit according to claim 8 , wherein the holes formed in the unit case are covered with an acoustic resistance plate.
10. The dynamic microphone unit according to claim 9 , wherein the acoustic resistance plate for covering the holes formed in the unit case is formed, together with an acoustic resistance plate for covering the holes that connect the back side space of the diaphragm with the rear air chamber, by etching a single plate-like material.
11. A dynamic microphone configured by installing a dynamic microphone unit in a microphone case, wherein the dynamic microphone unit is the dynamic microphone unit according to claim 1 .