JP5269569B2 - Condenser microphone unit and condenser microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a condenser microphone unit and a condenser microphone capable of obtaining a favorable frequency response characteristic in a lower frequency region while having a simple structure and also facilitating adjustment. <P>SOLUTION: A unidirectional condenser microphone unit includes: a diaphragm 3 which vibrates by receiving sound waves; a stationary electrode 4 facing the diaphragm 3 with a thin air layer therebetween; and a back air chamber 6 formed behind the stationary electrode 4. The unidirectional condenser microphone unit has an acoustic terminal including a plurality of holes 51 for opening the back air chamber 6 to the outside, and has a second air chamber 10 communicating with the back air chamber 6 through at least one of the plurality of the holes 51. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a condenser microphone unit and a condenser microphone, and in particular, provides a technique for improving a low-frequency response in a unidirectional one.

A typical configuration example of the condenser microphone unit is shown in FIGS. 5 to 7, in the unit case 1 of the cylindrical diaphragm retaining ring 2, the diaphragm 3, the spacer 9, the fixed electrode 4, the air chamber 6, a built-in-chip components, such as an insulating base 5 Yes. The front end (left end in FIG. 5) of the unit case 1 is an inward flange 11, and the diaphragm holding ring 2 is pressed against the inner surface of the inward flange 11. A diaphragm 3 made of a thin film is attached to the back side of the diaphragm holding ring 2. On the back side of the diaphragm 3, a ring-shaped spacer 9 is disposed on the outer peripheral edge thereof, and the fixed electrode 4 is disposed on the back side of the spacer 9.

The insulating base 5 is formed in the same shape as the inner shape of the unit case 1, and as shown in FIG. 6, a recess 53 is formed leaving a jetty 52 at the outer peripheral edge of the front end side. A step portion 54 is formed in a portion corresponding to the bottom of the depression 53, and another depression 55 is formed on the inner peripheral side following the step portion 54. The fixed electrode 4 is dropped into the depression 53 and hits the stepped portion 54. The air chamber 6 is formed by the depression 55 whose front side is partitioned by the fixed electrode 4. For example, a sponge is packed in the air chamber 6. The opened rear end of the unit case 1 to prevent detachment of the built parts within including the insulating base 5, and is suitably of the pressing member for pressing against the built parts in the front of the unit case 1 It is fitted.

  The insulating base 5 is pushed forward by the pressing member, the step 54 pushes the fixed electrode 4 forward, and the fixed electrode 4 moves the spacer 9, the diaphragm 3, and the diaphragm holding ring 2 forward in this order. Pushing towards. Since the diaphragm holding ring 2 hits the inward flange 11 of the unit case 1, the built-in component is held in the unit case 1 with an appropriate pressing force. A step between the jetty 52 and the step portion 54 is set so that a gap is generated between the jetty 52 of the unit case 1 and the diaphragm 3. Thus, a minute gap corresponding to the thickness of the spacer 9 is formed between the diaphragm 3 and the fixed electrode 4.

  The diaphragm 3 and the fixed electrode 4 constitute a capacitor by the presence of an air layer therebetween. When the diaphragm 3 receives a sound wave and vibrates, the capacitance of the capacitor changes. This change in capacitance is converted into a change in voltage, which is used as the output of the microphone unit. The fixed electrode 4 constitutes one electrode of the capacitor, and this electrode communicates with the diaphragm holding ring 2 and the unit case 1. The fixed electrode 4 constituting the other electrode of the capacitor communicates with a columnar lead electrode 7 fixed through the central portion of the insulating base 5. The lead electrode 7 is electrically connected to an FET that is a main component of an impedance converter mounted on a circuit board (not shown).

  The front end of the unit case 1 is an entrance of sound waves from the front side of the diaphragm 3 with the inner peripheral side of the inward flange 11 being opened. Although not shown in the drawings, the fixed electrode 4 is formed with appropriate through holes. An appropriate number of through holes 51 are also formed in the insulating base 5, and the through holes 51 constitute a rear acoustic terminal. Therefore, the rear surface of the diaphragm 3 communicates with the through hole of the fixed electrode 4, the air chamber 6, and the through hole 51 of the insulating base 5. Some of the plurality of through holes 51 are covered with the acoustic resistance material 8. In the illustrated conventional example, twelve through holes 51 are formed, and one of the through holes 51 is covered with the acoustic resistance material 8.

A unidirectional condenser microphone unit can be obtained by providing an acoustic terminal behind the diaphragm 3 as in the conventional example described above. FIG. 8 shows the acoustic equivalent circuit. The elements constituting the equivalent circuit are defined as follows.
P1: Sound pressure of sound waves coming from the front side P2: Sound pressure of sound waves coming from the rear acoustic terminal side m0: Mass of the diaphragm 3 s0: Stiffness of the diaphragm 3 r0: Acoustic resistance of the front side of the diaphragm 3 r1: Rear part Acoustic resistance of acoustic terminal s1: Stiffness of air chamber 6 In the above conventional example, the acoustic resistance of the rear acoustic terminal increases as the number of acoustic resistance members 8 covering the 12 through holes 51 formed in the insulating base 5 increases. Resistance increases and directivity tends to be more omnidirectional.

  FIG. 9 shows the frequency response characteristics of the above conventional example. When the sound wave enters from an angle of 0 degrees, that is, from the front, 90 degrees, that is, from the side, and 180 degrees, that is, from the back. They are shown separately. As is clear from FIG. 9, the characteristics of 90 degrees and 180 degrees are reversed in the low band, and the characteristics of 180 degrees are close to the characteristics of 0 degree in the lower band. This is called “proximity effect”, and one problem for improving the frequency response in the low frequency range is to eliminate the “proximity effect”.

  By the way, the low frequency limit of the frequency response from the front in the unidirectional condenser microphone is a frequency higher than that of the omnidirectional condenser microphone, and there is no low frequency limit in omnidirectionality. Therefore, in a unidirectional condenser microphone, if the directivity in the low band is controlled to be non-directional, the pressure operation can be increased with respect to the low frequency, and the characteristic in the low band can be reduced. Can compensate.

Conventionally, various techniques for improving a low-frequency response in a unidirectional condenser microphone have been proposed.
In the first technique, diaphragms are provided on the front side and the rear side, and each diaphragm is used as an acoustic terminal. More specifically, two unidirectional microphone units are back-to-back and both are acoustically coupled. According to the microphone unit having such a structure, the distance between the front and rear acoustic terminals is twice that of one microphone unit, and therefore, it is often used for relatively large microphone units. Since the distance between the front and rear acoustic terminals is long, it is difficult to obtain good directional frequency characteristics up to a high frequency range.

  The second technique for improving the low-frequency response in a unidirectional condenser microphone is to acoustically connect an air chamber with an acoustic resistance attached to the air inlet to the back chamber of the microphone unit. is there. In the case of the conventional structure shown in FIGS. 5 to 7, an air chamber is provided on the back side of the insulating base 5, and this air chamber communicates with the air chamber 6.

  As a conventional example corresponding to the second technique, for example, the invention described in Patent Document 1 can be cited. The invention described in Patent Document 1 will be described with reference to the conventional examples shown in FIGS. 5 to 7. In the insulating base 5, the through holes 51 are formed concentrically at intervals, and these through holes are formed. An acoustic resistance material is disposed in the hole 51, and a back air chamber communicating with the air chamber 6 is provided on the back side of the acoustic resistance material. On the back side of the acoustic resistance material, a disk that can change the degree of polymerization with the through-hole 51 of the insulating base 5 by changing the rotation position is arranged, and by changing the rotation position of the disk The acoustic resistance value of the acoustic resistance material can be changed.

Japanese Utility Model Publication No. 6-46158

  According to the invention described in Patent Document 1, unidirectionality is achieved by varying the acoustic resistance between the air chamber behind the fixed electrode and the back air chamber formed on the back side of the acoustic resistance material. It is possible to adjust the low-frequency response in the condenser microphone to the optimum position. In addition, since the distance between the front and rear acoustic terminals can be avoided as in the first technique for improving the frequency response in the low frequency range, the directional frequency response characteristic is excellent in the single direction up to the high frequency range. A capacitive condenser microphone can be obtained. The aforementioned “proximity effect” can also be improved.

  However, according to the invention described in Patent Document 1, it is necessary to adjust the acoustic resistance of the acoustic resistance material by providing a compression degree adjustment mechanism of the acoustic resistance material in addition to the rotational position adjustment mechanism of the rotating plate. Is complicated and difficult to adjust.

  The present invention further improves the invention described in Patent Document 1, that is, obtains a condenser microphone unit and a condenser microphone that are simple in structure, easy to adjust, and can obtain a good low-frequency response characteristic. With the goal.

The present invention is unidirectional with a diaphragm that vibrates by receiving a sound wave, and the fixed electrode facing at the diaphragm and the thin air layer, and a back air chamber formed at the back of the stationary electrode a sexual condenser microphone unit, the acoustic terminal comprising a plurality of holes for releasing the back air chamber to the outside, a second in communication with the back air chamber via at least one of said plurality of holes And the second air chamber has an insertion portion that can be inserted into one of a plurality of holes constituting the acoustic terminal .

  The acoustic terminal that opens the back air chamber to the outside is configured by a plurality of holes, and a second air chamber that communicates with the back air chamber through at least one of the holes is provided. The frequency response characteristic of the front of the low frequency band could be improved without impairing the directional frequency response characteristic of the low frequency band. The frequency response in the 180 degree direction was also improved. That is, the proximity effect can be reduced, and good characteristics can be obtained as a unidirectional condenser microphone unit or microphone.

  Hereinafter, embodiments of a condenser microphone unit and a condenser microphone according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same component as the component of the above-mentioned prior art example.

In Figure 1, within the unit case 1 of the cylindrical diaphragm retaining ring 2, the diaphragm 3, the spacer 9, the fixed electrode 4, the air chamber 6, is the built parts such as insulating base 5 are incorporated. The front end (left end in FIG. 1) of the unit case 1 is an inward flange 11, and the diaphragm holding ring 2 is pressed against the inner surface of the inward flange 11. A diaphragm-like diaphragm 3 made of a thin film is attached to the rear side of the diaphragm holding ring 2 with an appropriate tension applied. On the back side of the diaphragm 3, a spacer 9 made of a ring-shaped thin plate is disposed on the outer peripheral edge thereof, and the fixed electrode 4 is disposed on the back side of the spacer 9.

  The outer shape of the insulating base 5 is the same as that of the inner surface of the unit case 1, and a recess 53 is formed on the outer peripheral edge of the front end side, leaving a jetty 52, similar to the insulating base in the conventional example shown in FIG. Has been. A step portion 54 is formed in a portion corresponding to the bottom of the depression 53, and another depression 55 is formed on the inner peripheral side following the step portion 54. The fixed electrode 4 is dropped into the depression 53 and hits the stepped portion 54. The air chamber 6 is formed by the depression 55 whose front side is partitioned by the fixed electrode 4 and has a predetermined volume. For example, a sponge is packed in the air chamber 6. An appropriate pressing member for preventing the internal parts such as the insulating base 5 from falling off and pressing the internal parts toward the front side of the unit case 1 is provided at the opened rear end of the unit case 1. It is fitted.

  The insulating base 5 is pushed forward by the pressing member, the step 54 pushes the fixed electrode 4 forward, and the fixed electrode 4 moves the spacer 9, the diaphragm 3, and the diaphragm holding ring 2 forward in this order. Pushing towards. Since the diaphragm holding ring 2 hits the inward flange 11 of the unit case 1, the built-in component is held in the unit case 1 with an appropriate pressing force. A step between the jetty 52 and the step portion 54 is set so that a gap is generated between the jetty 52 of the unit case 1 and the diaphragm 3. Thus, a thin air layer composed of a minute gap corresponding to the thickness of the spacer 9 is formed between the diaphragm 3 and the fixed electrode 4.

  The diaphragm 3 and the fixed electrode 4 constitute a capacitor by the presence of a thin air layer therebetween. When the diaphragm 3 receives a sound wave and vibrates, the capacitance of the capacitor changes. This change in capacitance is converted into a change in voltage, which is used as the output of the microphone unit. The fixed electrode 4 constitutes one electrode of the capacitor, and this electrode communicates with the diaphragm holding ring 2 and the unit case 1. The fixed electrode 4 constituting the other electrode of the capacitor communicates with a columnar lead electrode 7 fixed through the central portion of the insulating base 5. The lead electrode 7 is electrically connected to an FET that is a main component of an impedance converter mounted on a circuit board (not shown).

The front end of the unit case 1 is an entrance of sound waves from the front side of the diaphragm 3 with the inner peripheral side of the inward flange 11 being opened. Although not shown in the drawings, the fixed electrode 4 is formed with appropriate through holes. An appropriate number of through holes 51 are also formed in the insulating base 5, and the through holes 51 constitute a rear acoustic terminal. Therefore, the rear surface of the diaphragm 3 communicates with the through hole of the fixed electrode 4, the air chamber 6, and the through hole 51 of the insulating base 5.
The configuration described so far is almost the same as the configuration of the conventional example shown in FIG. The characteristic configuration of the present invention will be described below.

  In FIG. 1, the plurality of through holes 51 constituting the acoustic terminal open the back air chamber 6 to the outside, and one of the plurality of through holes 51 is the second air chamber 10. Communicating with In other words, the back air chamber 6 and the second air chamber 10 communicate with each other through one of the through holes 51. The second air chamber 10 communicates with the back air chamber 6 and communicates with the thin air layer between the diaphragm 3 and the fixed electrode 4 through the through hole of the fixed electrode 4. The second air chamber 10 is a bottle-like member that is hermetically sealed except for the insertion portion 12 at the tip, and the insertion portion 12 is inserted into one through hole 51. Therefore, the volume of the back air chamber 6 is increased by the volume of the second air chamber 10 through one through hole 51 and the insertion portion 12, and the other through holes 51 except the one through hole 51 are opened. Has been.

  The volume of the second air chamber 10 is appropriately set according to the design specifications of the basic components of the condenser microphone unit including the diaphragm 3, the fixed electrode 4, the insulating base 5, the back air chamber 6, and the like. In order to set the volume of the second air chamber 10, in the prototype stage, for example, the tip of the cylinder of the syringe is inserted into the through hole 51, and the volume of the cylinder is changed by changing the amount of the plunger inserted into the cylinder. The frequency response was measured by changing the volume of the second air chamber 10 substantially. In the embodiment, a favorable frequency response characteristic can be obtained by setting to about 2 cc.

  In the embodiment shown in FIG. 1, twelve through holes 51 constituting the rear acoustic terminal are formed and the second air chamber 10 is connected to one of them, but the second air is connected to the plurality of through holes 51. The chambers 10 may be connected. Further, the second air chamber 10 may be individually connected to the plurality of through holes 51. The through hole 51 to which the second air chamber 10 is not connected may be opened as it is, or may be covered with an acoustic resistance material as appropriate.

FIG. 2 shows an acoustic equivalent circuit of the above embodiment. The elements constituting the equivalent circuit are defined as follows.
P1: Sound pressure of sound waves coming from the front side P2: Sound pressure of sound waves coming from the rear acoustic terminal side m0: Mass of the diaphragm 3 s0: Stiffness of the diaphragm 3 r0: Acoustic resistance of the front side of the diaphragm 3 r1: Rear part Acoustic resistance of acoustic terminal s1: Stiffness of air chamber 6 r2: Acoustic resistance of communication portion between air chamber 6 and second air chamber 10 s2: Stiffness of second air chamber 10

When the equivalent circuit shown in FIG. 2 is compared with the equivalent circuit of the conventional example shown in FIG. 8, the acoustic resistance r2 of the communication portion between the air chamber 6 and the second air chamber 10 is added to the stiffness s1 of the air chamber 6, and The difference is that a series connection of the stiffness s2 of the two air chambers 10 is added in parallel.
FIG. 4 shows frequency response characteristics of the unidirectional condenser microphone unit according to the present embodiment in which the acoustic resistance r2 and the stiffness s2 are added. The sound wave is divided into a case where the sound wave enters from an angle of 0 degrees, that is, from the front, a case where the sound wave enters from an angle of 90 degrees, that is, from the side, and a case where the sound wave enters from 180 degrees, that is, the case where the sound enters from behind.

  As is clear from the comparison between the characteristics shown in FIG. 4 and the characteristics shown in FIG. 9, the frequency response from the front is improved in the low frequency range, and the frequency response from the 180 degree direction is lowered. As the characteristics have been improved. As a result, the aforementioned “proximity effect” is also eliminated. In addition, the mid-high range is almost the same as the conventional example. Therefore, the low-frequency response can be improved without impairing the mid-high frequency response characteristics. A condenser microphone unit having such excellent characteristics can be obtained with a relatively simple configuration in which the second air chamber is provided, and adjustment is also easy.

  Next, a second embodiment of the present invention will be described. FIG. 3 shows the main part of the second embodiment. In this embodiment, the second air chamber 10 has a plurality of communication passages 14, and at least one of the plurality of communication passages 14 is connected to one of the through holes 51 of the insulating base 5 through the pipe 15. It is configured to be able to. The pipe 15 is flexible and has a sufficient length necessary to be connected to the through hole 51. One of the plurality of through holes 51 is selected and inserted into the through hole 51. It is configured to be able to. Another communication path 14 included in the second air chamber 10 may also be connected to another through hole 51. The communication path 14 that is not connected to the through hole 51 is configured to close the tip thereof with an appropriate closing member 16.

  According to the embodiment shown in FIG. 3, the same effect as that of the first embodiment can be obtained, and an arbitrary communication path can be selected from the plurality of communication paths 14 included in the second air chamber 10. Since the insulating base 5 can be connected to any of the plurality of through holes 51, the frequency response of the low band can be most effectively improved without impairing the frequency response characteristics of the middle and high band. You can adjust as you can.

  By incorporating the condenser microphone unit according to the present invention into a microphone case and appropriately attaching a cable connector or the like to the microphone case, a unidirectional condenser microphone having the effects as described above can be configured. .

1 is a longitudinal sectional view showing a first embodiment of a unidirectional condenser microphone unit according to the present invention. It is the acoustic equivalent circuit schematic of the said Example. It is a longitudinal cross-sectional view which shows the principal part of 2nd Example of the unidirectional condenser microphone unit which concerns on this invention. It is a graph which shows the frequency response characteristic of the microphone unit of the said 1st Example. It is a longitudinal cross-sectional view which shows the example of the conventional unidirectional condenser microphone unit. It is a longitudinal cross-sectional view which shows the insulation base in the said prior art example. It is a bottom view of the said insulation base. It is an acoustic equivalent circuit diagram of the conventional condenser microphone unit. It is a graph which shows the frequency response characteristic of the said conventional microphone unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Unit case 2 Diaphragm holding ring 3 Diaphragm 4 Fixed electrode 5 Insulation base 6 Back air chamber 9 Spacer 10 2nd air chamber 12 Insertion part 51 Through-hole

Claims (6)

A vibration plate that vibrates by receiving a sound wave, and the diaphragm and a fixed electrode facing at a thin air layer, the back air chamber formed at the back of the fixed electrode,
A unidirectional condenser microphone unit with
An acoustic terminal comprising a plurality of holes for opening the back air chamber to the outside ;
A second air chamber in communication with the back air chamber via at least one of said plurality of holes,
Have,
The second air chamber, the condenser microphone unit, characterized in that has an insertion portion which can be inserted into one of a plurality of holes constituting the acoustic terminal. Said second air chamber is selected an appropriate communication path includes a plurality of communication passages can the back air chamber and communicating, according to claim 1 wherein the blocked in the communication path that is not used Condenser microphone unit. The back air chamber is formed by recesses of an insulating base which holds the fixed electrode and the fixed electrode, the thin air layer between the diaphragm and the fixed electrode via holes are formed in said stationary electrode claim 1 Symbol mounting the condenser microphone unit communicates with. Wherein the plurality of through holes constituting the acoustic terminal is formed in the insulating base, coupleable to be configured at least one of the plurality of communication passages which said second air chamber has at least one of the holes The condenser microphone unit according to claim 2 . Capacitor according to at least any one of claims 1 to 3 are covered with an acoustic resistance member of acoustic terminal that does not communicate with the second air chamber among the plurality of through holes constituting the acoustic terminal Microphone unit. 6. A condenser microphone in which a unidirectional condenser microphone unit is incorporated in a microphone case, wherein the condenser microphone unit is a condenser microphone unit according to any one of claims 1 to 5. Microphone.

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