Microphone unit
View Patent ↗A microphone unit includes a case; a diaphragm arranged inside the case; and an electric circuit unit that processes an electric signal generated in accordance with vibration of the diaphragm. The case has a first sound introducing space that introduces a sound from outside of the case to a first surface of the diaphragm via a first sound hole; and a second sound introducing space that introduces a sound from outside of the case to a second diaphragm, via a second sound hole. A resonance frequency of the diaphragm is set in the range of ±4 kHz based on the resonance frequency of at least one of the first sound introducing space and the second sound introducing space.
1. A microphone unit, comprising:
a case; and
a diaphragm arranged inside the case;
wherein:
the case includes a first sound introducing space that introduces a sound from outside of the case to a first surface of the diaphragm via a first sound hole and a second sound introducing space that introduces a sound from outside of the case to a second surface of the diaphragm, which is an opposite surface of the first surface of the diaphragm, via a second sound hole;
wherein the first and second sound holes are formed in the same surface; and a distance between the centers of the first and second sound holes is not less than 4 mm and not more than 6 mm; and
a resonance frequency fd of the diaphragm fulfills formula below:
7000<fd<15000,
Where
f
d
=
2
t
3
π
a
2
*
(
5
E
)
/
(
ρ
(
1
-
v
2
)
)
fd represents the resonance frequency (Hz) of the diaphragm;
α represents a radius (m) of the diaphragm;
ρ represents a density (kg/m3) of the diaphragm;
υ represents a Poisson's ratio of the diaphragm;
Ε represents a Young's modulus (Pa) of the diaphragm; and
t represents a thickness (m) of the diaphragm.
2. The microphone unit according to claim 1 , wherein the resonance frequencies of the first and second sound introducing spaces are substantially equal.
3. The microphone unit according to claim 1 , wherein
inside the case, an opening is formed through which two spaces communicate with each other, and
in one of the two spaces, a microphone having the diaphragm is arranged so as to stop the opening such that the first and second sound introducing spaces are formed.
4. The microphone unit according to claim 1 , wherein the diaphragm is formed of silicon, and
the diaphragm fulfills formula below:
0.15<t/a 2 <0.35.