Unidirectional condenser microphone unit

Abstract

A unidirectional condenser microphone unit includes a unit case that includes a diaphragm that vibrates upon receiving a sound wave, a fixed electrode disposed to face the diaphragm, an insulating base that supports the fixed electrode to form a back air chamber between the insulating base and the fixed electrode and a fixed electrode leading terminal made of metal that is attached to the insulating base, and that leads a signal voltage generated at the fixed electrode, wherein the unit case is provided with a front acoustic terminal hole formed in a front side of the diaphragm and a rear acoustic terminal hole for communication with the back air chamber, wherein the unit case has a second air chamber different from the back air chamber and the fixed electrode leading terminal is provided with a communication path between the back air chamber and the second air chamber.

Claims

1. A unidirectional condenser microphone unit, comprising: a unit case including: a diaphragm that vibrates upon receiving a sound wave; a fixed electrode disposed to face the diaphragm; an insulating base that supports the fixed electrode to form a back air chamber between the insulating base and the fixed electrode; and a fixed electrode leading terminal made of metal that is attached to the insulating base, and that leads a signal voltage generated at the fixed electrode, wherein the unit case is provided with a front acoustic terminal hole formed in a front side of the diaphragm and a rear acoustic terminal hole for communication with the back air chamber, wherein the unit case is provided with a second air chamber different from the back air chamber and the fixed electrode leading terminal is provided with a communication path for communicating between the back air chamber and the second air chamber.

2. The unidirectional condenser microphone unit according to claim 1, wherein the fixed electrode leading terminal is formed into a pillar shape, and is provided with a shaft hole or a groove hole along an axial direction of the pillar shape, and the shaft hole or the groove hole which constitutes the communication path between the back air chamber and the second air chamber.

3. The unidirectional condenser microphone unit according to claim 1, wherein the fixed electrode leading terminal is formed into a columnar shape, and is provided with a spiral groove hole along a columnar surface, and the spiral groove hole constitutes the communication path between the back air chamber and the second air chamber.

4. The unidirectional condenser microphone unit according to claim 1, wherein the fixed electrode leading terminal is provided with plural communication paths between the back air chamber and the second air chamber in.

5. The unidirectional condenser microphone unit according to claim 1, wherein a first acoustic resistor is disposed between the back air chamber and the rear acoustic terminal hole.

6. The unidirectional condenser microphone unit according to claim 1, wherein a second acoustic resistor is disposed between the back air chamber and the second air chamber.

7. The unidirectional condenser microphone unit according to claim 6, wherein the second acoustic resistor is formed into a toroidal shape and is attached to the fixed electrode leading terminal by insertion of the fixed electrode leading terminal into a central hole, and the second acoustic resistor is formed between an adjustment ring screwed with the fixed electrode leading terminal and the insulating base to make an acoustic resistance value of the second acoustic resistor variable.

8. The unidirectional condenser microphone unit according to claim 1, wherein the second air chamber is opposing to the back air chamber with the insulating base therebetween and is disposed in the side of the fixed electrode leading terminal.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a central sectional view illustrating a first embodiment of a condenser microphone unit according to the present invention;

(2) FIG. 2 is a central sectional view illustrating a second embodiment;

(3) FIG. 3 is a central sectional view illustrating a third embodiment;

(4) FIGS. 4A to 4E are schematic diagrams illustrating favorable embodiments of a communication path provided in a fixed electrode leading terminal;

(5) FIG. 5 is an acoustic equivalent circuit diagram of a condenser microphone unit according to the present invention;

(6) FIG. 6 is an acoustic equivalent circuit diagram of a condenser microphone unit of another embodiment according to the present invention;

(7) FIG. 7 is a graph illustrating frequency response characteristics of the condenser microphone unit illustrated in FIG. 1;

(8) FIG. 8 is a central sectional view of a conventional condenser microphone unit;

(9) FIG. 9 is an acoustic equivalent circuit diagram of the condenser microphone unit illustrated in FIG. 8;

(10) FIG. 10 is a graph illustrating frequency response characteristics of the condenser microphone unit illustrated in FIG. 8; and

(11) FIG. 11 is a graph illustrating frequency response characteristics of a typical condenser microphone unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) A unidirectional condenser microphone unit according to the present invention will be described on the basis of embodiments illustrated in the drawings.

(13) FIG. 1 illustrates a first embodiment. A condenser microphone unit 1 includes a cylindrical unit case 2 including a plurality of openings 3 in a front side. Further, a plurality of openings 4 is also provided on side surface of the unit case 2. The front openings 3 are front acoustic terminal holes and the side openings 4 are rear acoustic terminal holes.

(14) Further, a diaphragm 6, a periphery of which is attached to a support ring 5, is disposed on a front side in the unit case 2, and a fixed electrode 7 is disposed to face a back of the diaphragm 6 through a small gap. The diaphragm 6 and the fixed electrode 7 face each other with a ring-like spacer although not illustrated in FIG. 1. With the configuration, a capacitor is formed between the fixed electrode 7 and an electrode film (not shown) formed on the diaphragm 6. Then, in the present embodiment, a dielectric film is formed on the fixed electrode 7, and a back electret-type electret condenser microphone unit is formed.

(15) An insulating base 8 formed of resin material is disposed on the back of the fixed electrode 7. A peripheral edge of the insulating base 8 rises toward the front side of the unit case 2, and a periphery of the fixed electrode 7 is fit in this rising portion 8a, and the rising portion presses the fixed electrode 7 toward the front side of the unit case 2. Then, a space is formed between the back of the fixed electrode 7 and the insulating base 8 to form a back air chamber 8b. Further, a plurality of communication holes 8c for communication between the back air chamber 8b and the rear acoustic terminal holes 4 of the unit case 2, is formed in the insulating base 8 along a circumference.

(16) As is known, openings with a small diameter (not shown) are provided in the entire surface of the fixed electrode 7.

(17) Further, a cylindrical portion 8d is erected in a central portion of the insulating base 8 toward the back side of the insulating base 8. Then, a tip end portion of a rod-like fixed electrode leading terminal 9 formed of metal material is fitted and fixed to inside of the cylindrical portion 8d. A lead wire is connected between the fixed electrode leading terminal 9 and the fixed electrode 7, and the fixed electrode leading terminal 9 operates to supply a signal voltage generated at the fixed electrode 7 to an impedance conversion circuit (not shown) using a field effect transistor and the like mounted in the condenser microphone unit 1.

(18) A cup member 11 is accommodated in a state where a bottom opening is fitted into the cylindrical portion 8d of the insulating base 8, and the cup member 11 is attached inside the unit case 2 with an opening edge pressed by a ring member 12. That is, a female screw is threaded on an inner peripheral surface of the unit case 2 along a periphery, and the ring member 12 is screwed with the inner peripheral surface of the unit case 2, whereby the cup member 11 is attached in the unit case 2.

(19) A first acoustic resistor 13 formed into a toroidal shape is disposed between a lower bottom surface of the cup member 11 and the insulating base 8 to block the communication holes 8c formed in the insulating base 8.

(20) The cup member 11 can be moved in an axial direction according to the degree of screwing of the ring member 12 relative to the unit case 2, thereby to control the apparent density of the first acoustic resistor 13. With this means, a bi-directional component applied through the rear acoustic terminal holes 4 to the back air chamber 8b can be adjusted.

(21) Meanwhile, a shaft hole 9a, which reaches a vicinity of a central portion from the tip end portion along an axial center, is provided in the rod-like fixed electrode leading terminal 9, and an intersecting hole 9b is further provided, which is perpendicular to the shaft hole 9a and communicates with the shaft hole 9a in a radial direction. A communication path by the shaft hole 9a and the intersecting hole 9b allows communication between the back air chamber 8b formed in the insulating base 8 and a second air chamber 16 formed in the cup member 11 described below, and effectively functions as an acoustic mass (inertance).

(22) Then, a low height cylindrical member 14 is screwed with the unit case 2 in the further rear of the ring member 12 that is screwed with the unit case 2, and a lid member 15 provided with an opening 15a in a central area is attached to the low height cylindrical member 14.

(23) The fixed electrode leading terminal 9 enters the central opening 15a of the lid member 15, and the lid member 15 closes the cup member 11. The cup member 11 and the lid member 15 closing the cup member 11 form the above-described second air chamber 16. That is, the second air chamber 16 is an air chamber provided in the unit case 2, being separate from the back air chamber 8b.

(24) A second acoustic resistor 18 formed into a toroidal shape is mounted to cover a vicinity of the intersecting hole 9b of the fixed electrode leading terminal 9. That is, the second acoustic resistor 18 is attached to the fixed electrode leading terminal 9 by insertion of the fixed electrode leading terminal 9 into a central hole of the second acoustic resistor 18. Then, the second acoustic resistor 18 is disposed in a sandwiched state between an adjustment ring 17 screwed with a male screw threaded on an outer peripheral surface of the fixed electrode leading terminal 9 and an end portion of the cylindrical portion 8d formed in the insulating base 8.

(25) With this arrangement, the second acoustic resistor 18 lies between the back air chamber 8b and the second air chamber 16 through the communication path by the shaft hole 9a and the intersecting hole 9b. Then, the apparent density of the second acoustic resistor 18 can be adjusted according to the degree of screwing of the adjustment ring 17 with the fixed electrode leading terminal 9. Thus, adjustment of the second acoustic resistor 18 allows to adjust a non-directional component applied to the back air chamber 8b from the second air chamber 16.

(26) In the condenser microphone unit 1 shown in FIG. 1, the communication path formed by the shaft hole 9a and the intersecting hole 9b that is provided in the fixed electrode leading terminal 9 made of metal functions as a pipe with an extremely small diameter, and acts as an acoustic mass, as described above.

(27) FIG. 5 shows an acoustic equivalent circuit of the condenser microphone unit 1 shown in FIG. 1, and this equivalent circuit shows a state in which an acoustic mass m2 formed by the shaft hole 9a and the intersecting hole 9b is added to the equivalent circuit shown in FIG. 9.

(28) According to the equivalent circuit shown in FIG. 5, a low-cut filter composed of an equivalent coil L for the acoustic mass m2 and an equivalent capacitor C for the stiffness s2 of the second air chamber 16 is formed in the acoustic circuit.

(29) With the configuration, a low-frequency component entering the second air chamber 16 through the acoustic mass m2 formed by the shaft hole 9a and the intersecting hole 9b is substantially moved to a lower frequency band. That is, since the non-directional component is moved to the lower-frequency band, the low-frequency directional component can be effectively compensated without affecting directivity in an audio band at about 1 kHz, for example.

(30) The frequency response characteristics illustrated in FIG. 7 supports the effect, and characteristic curves A to C illustrate characteristics of respective angles with respect to a sound collecting axis being 0 degrees, 90 degrees, and 180 degrees, similarly to the graphs shown in FIGS. 10 and 11.

(31) FIG. 7 illustrates the frequency response characteristics in a case where an opening diameter of the communication path (pipe) that functions as the acoustic mass m2 is set to 0.2 mm and its length is set to 3.5 mm, and the volume of the second air chamber 16 is set to 0.27 mL.

(32) As shown in the measured values in FIG. 7, the second air chamber 16 can improve the low-frequency response with the volume kept small, as shown in FIG. 1.

(33) Since the volume of the second air chamber 16 can be designed to be small, a condenser microphone unit can be achieved which is small in size and has an improved low-frequency response and in which the proximity effect is reduced.

(34) FIG. 2 illustrates a second embodiment of a unidirectional condenser microphone according to the present invention. In the second embodiment, a groove hole 9c that reaches a vicinity of a central portion from a tip end portion is provided on a side surface of a rod-like fixed electrode leading terminal 9. Other configurations are not changed from the configurations of the first embodiment shown in FIG. 1, and corresponding portions are denoted with the same reference signs and its detailed description is omitted.

(35) According to the second embodiment, a formed portion of the groove hole 9c in the fixed electrode leading terminal 9 is fitted and fixed to a cylindrical portion 8d that is integrally formed in the insulating base 8, and thus the groove hole 9c constitutes a communication hole with a small diameter between the groove hole 9c and the cylindrical portion 8d. This communication hole with a small diameter functions as the above-described acoustic mass m2, and an acoustic equivalent circuit similar to the example illustrated in FIG. 5 is formed.

(36) The second embodiment shown in FIG. 2 can allow to obtain functions and effects similar to the first embodiment shown in FIG. 1.

(37) FIG. 3 illustrates a third embodiment of a unidirectional condenser microphone according to the present invention. In the third embodiment, a spiral groove hole 9d is provided on a columnar surface of a rod-like fixed electrode leading terminal 9 to reach a vicinity of a central portion from a tip end portion. Note that other configurations are not changed from the configurations of the first embodiment illustrated in FIG. 1, and corresponding portions are denoted with the same reference signs and its detailed description is omitted.

(38) According to the third embodiment, a portion to which the spiral groove hole 9d is formed of the fixed electrode leading terminal 9 is fitted and fixed to a cylindrical portion 8d integrally formed in the insulating base 8, and thus the spiral groove hole 9d constitutes a communication hole with a small diameter between the spiral groove hole 9d and the cylindrical portion 8d. This communication hole with a small diameter functions as the above-described acoustic mass m2, and an acoustic equivalent circuit similar to the example shown in FIG. 5 is formed.

(39) According to the third embodiment, with the spiral groove hole 9d provided on a columnar surface of the fixed electrode leading terminal 9, the longer communication hole with a small diameter can be formed. With the configuration, the acoustic mass m2 having a larger value is added to the equivalent circuit shown in FIG. 5.

(40) Correspondingly, the value of the equivalent coil L obtained for the acoustic mass m2 is increased, which contributes to more remarkably improve low-frequency characteristics.

(41) FIGS. 4A to 4E schematically illustrate configuration examples of a shaft hole or a groove hole provided in a fixed electrode leading terminal 9, and these configuration examples are illustrated in a state where the fixed electrode leading terminal 9 is viewed from its tip end portion.

(42) FIG. 4A illustrates an example in which a shaft hole 9a along an axial center of the fixed electrode leading terminal 9 and an intersecting hole 9b that is perpendicular to the shaft hole 9a and communicating with the shaft hole 9a in a radial direction are provided. This configuration has been employed in the first embodiment shown in FIG. 1.

(43) FIG. 4B illustrates an example in which a groove hole 9c is provided on a side surface of the fixed electrode leading terminal 9 along an axial direction. This configuration has been employed in the second embodiment shown in FIG. 2.

(44) FIG. 4C illustrates an example in which the shaft hole 9a and the intersecting hole 9b both shown in FIG. 4A and the groove hole 9c shown in FIG. 4B are further provided in the fixed electrode leading terminal 9. According to this example, an acoustic mass m2a due to the shaft hole and an acoustic mass m2b due to the groove hole are disposed in parallel.

(45) Its acoustic equivalent circuit, therefore, becomes to one where have an equivalent coil L for the acoustic mass m2a and the acoustic mass m2b is connected in parallel, as shown in FIG. 6.

(46) FIG. 4D illustrates a case where the position at which the groove hole 9c to be provided is shifted by 90 degrees in the peripheral direction from the position in the configuration shown in FIG. 4C, and its acoustic equivalent circuit is nearly similar to the example shown in FIG. 6.

(47) Further, FIG. 4E illustrates an example in which the groove holes 9c are respectively provided on opposing side surfaces (side surfaces opposing at 180 degrees) of the fixed electrode leading terminal 9, and its acoustic equivalent circuit is nearly similar to the example of FIG. 6.

(48) The above described unidirectional condenser microphone unit according to the present invention allows to achieve a configuration in which the acoustic mass (inertance) between the back air chamber and the second air chamber is disposed by forming the communication path with a small diameter utilizing the fixed electrode leading terminal, made of metal, which leads the signal voltage generated at the fixed electrode.

(49) A low-pass filter formed of the acoustic mass and stiffness of the second air chamber can lower its cutoff frequency. As a result, a condenser microphone unit with improved low-frequency response without affecting intermediate-frequency response can be provided, which is as described above, as functions and effects of the present invention.

(50) The unidirectional condenser microphone according to the present invention is configured to enable to vary each of the bulk density of the first acoustic resistor and the second acoustic resistor. This configuration allows to independently adjust the bidirectional component and the unidirectional component both of which are applied to the back air chamber.