JP2014180031A - Microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microphone capable of changing the volume of an air chamber according to change of sound pressure of the air chamber which varies according to vibration of a diaphragm, and controlling impedance of the air chamber accurately.SOLUTION: A microphone comprises: a microphone unit 52 in which a diaphragm 53 vibrates with a sound wave from a sound source and the vibration of the diaphragm is converted into an audio signal; and an air chamber 56 which is formed behind the diaphragm 53 of the microphone unit 52 and whose volume varies according to the vibration of the diaphragm 53. The air chamber 56 includes: a sound pressure detection member 55 for detecting a sound pressure in the air chamber 56; and a volume adjuster 57 which is driven by an output signal from the sound pressure detection member 55 and varies the volume of the air chamber 56 according to the output signal so as to control an acoustic impedance in the air chamber 56.

Description

  The present invention actively eliminates the sound pressure generated in the air chamber even if the air chamber on the back side of the diaphragm has a small volume, and is equivalent to a device having a large air chamber, The present invention relates to a microphone that can enhance responsiveness in a low sound range.

  For example, some electroacoustic transducers such as a unidirectional dynamic microphone, an omnidirectional dynamic microphone, a headphone, and a speaker include an air chamber so that sound waves from outside do not enter. These electroacoustic transducers are provided with a vibration plate that vibrates in response to sound waves or is driven by sound signals to emit sound waves, and an air chamber is provided on the back side of the vibration plate. The air chamber operates as an acoustic capacity. When the volume of the air chamber is large, the air chamber operates as a spring having a small elasticity, and when the volume of the air chamber is small, the air chamber operates as a spring having a large elasticity. Therefore, when an acoustic capacity with a small stiffness is required, that is, when the diaphragm is easily moved, a large volume air chamber is required.

  Here, the air chamber will be further described by taking an omnidirectional or unidirectional dynamic microphone as an example. In an omnidirectional or unidirectional dynamic microphone, it is necessary to provide an acoustic resistance and an air chamber on the back side of the diaphragm in order to obtain an omnidirectional component. In the low frequency band, the stiffness of the air chamber becomes dominant, and if the volume of the air chamber is small, the stiffness increases and the directional frequency response deteriorates.Therefore, it is necessary to increase the volume of the air chamber to reduce the stiffness. is there.

  Assuming a handheld, that is, a handheld wireless microphone, it is necessary to store the circuit portion of the transmitter and the power supply battery in the grip portion. Therefore, it is not possible to provide a large air chamber like a wired microphone. Therefore, the volume of the air chamber provided on the back side of the diaphragm is limited, and it is necessary to obtain an omnidirectional component by a small air chamber, which deteriorates the directional frequency response and sound quality in the low frequency range. In short, if the volume of the air chamber is small, a large back pressure is applied to the diaphragm when the diaphragm tries to vibrate in response to low sounds, and the diaphragm becomes difficult to vibrate, and the minimum frequency to respond to increases. The output level in the low frequency range is low.

  Therefore, the present inventor previously patented a dynamic microphone that enables low-frequency sound collection by reducing the acoustic impedance of the back air chamber equivalently even when the volume of the back air chamber is small. Applied (see Patent Document 1). In the invention described in Patent Document 1, the case supporting the main microphone unit has a back air chamber on the back side of the diaphragm of the main microphone unit, and a sub microphone unit on the front side of the main microphone unit. . A configuration in which the acoustic impedance of the back air chamber is equivalently reduced by driving a membrane plate made of a piezoelectric element provided in the back air chamber with an audio signal (voltage signal) output from the sub microphone unit. doing.

JP 2009-232176 A

  In the invention described in Patent Document 1, sound waves from a sound source guided to a sub microphone unit arranged on the front side of the main microphone unit are converted into a sound signal by the sub microphone unit, and this sound signal is provided in the back air chamber. A film plate made of a piezoelectric element is driven. In other words, the output signal of the sub microphone unit arranged in front of the diaphragm of the main microphone unit is a feedforward control of the membrane plate made of piezoelectric elements. Therefore, the pressure change of the back air chamber is predicted by receiving the sound wave from the sound source arriving at the sub microphone unit, and the membrane plate is driven based on the prediction. For this reason, the membrane plate cannot be driven in a faithful manner corresponding to the pressure change in the back air chamber, and further improvement is required to perform accurate acoustic impedance control of the back air chamber.

  An object of the present invention is to solve the above-described problems of the prior art. That is, the air chamber volume can be controlled to change faithfully in response to the sound pressure change of the air chamber that changes due to the vibration of the diaphragm of the microphone unit, and the acoustic impedance control of the air chamber can be performed with high accuracy. An object is to provide a microphone.

The microphone according to the present invention is
A microphone unit that receives sound waves from a sound source and vibrates the diaphragm and converts the vibration of the diaphragm into an audio signal;
An air chamber that is formed behind the diaphragm of the microphone unit and whose volume is changed by the vibration of the diaphragm;
In the air chamber,
A sound pressure detecting member for detecting the sound pressure in the air chamber;
A volume adjuster that is driven by an output signal of the sound pressure detection member and controls the acoustic impedance of the air chamber by changing the volume of the air chamber according to the output signal;
Is the most important feature.

The electroacoustic transducer according to the present invention can be developed in the following manner.
The microphone unit may be incorporated in a unit case, and the unit case may be provided with an air chamber whose volume changes due to vibration of a diaphragm included in the microphone unit.
The unit case may be incorporated in a microphone case, and the microphone case may be provided with a power battery room.

  The detection signal of the sound pressure detection member may be input to the volume adjuster through a low-pass filter.

  The volume of the air chamber changes due to the vibration of the diaphragm of the microphone unit, and the sound pressure of the air chamber changes. The sound pressure detection member detects this change in sound pressure, and the volume adjuster is driven by this detection signal to generate sound. Control to eliminate pressure change. By this control, the acoustic impedance of the air chamber can be reduced equivalently, and in particular, the directivity frequency response in the low sound range can be enhanced. Therefore, even if the volume of the air chamber is small, reproduction can be performed at a sufficient sound pressure level up to the low sound range. For example, even if the size of the air chamber is limited due to the necessity of mounting a power supply battery in a microphone case such as a wireless microphone, it can be converted into an audio signal at a predetermined signal level up to the low sound range.

It is sectional drawing which shows the Example of the microphone which concerns on this invention. It is sectional drawing which shows typically the example of the headphones for demonstrating the technical idea of the microphone which concerns on this invention. It is an acoustic equivalent circuit diagram of the headphones. It is sectional drawing which shows typically the example of the characteristic test apparatus of an electroacoustic transducer. It is a graph which shows an example of the measurement result by the said test apparatus. It is a graph which shows another example of the measurement result by the said test apparatus. It is a graph which shows another example of the measurement result by the said test apparatus.

  Before explaining an embodiment of a microphone according to the present invention, an example in which the technical idea of the present invention is applied to headphones will be described with reference to FIGS.

[Description of the technical idea of the present invention]
In FIG. 2, the headphone indicated by reference numeral 10 includes a bowl-shaped housing 12 and a baffle plate 13 fixed to the inner peripheral side near the open end of the housing 12. The speaker unit 11 is a driver unit attached to the baffle plate 13 and surrounded by the housing 12, and an ear pad 14 attached to the open end of the housing 12.

  As is well known, the headphone 10 is used by surrounding the user's ear 21 with the ear pad 14 and pressing the ear pad 14 against the user's temporal region. Although FIG. 2 shows a state in which the headphones 10 are worn on one ear of the user, a typical headphone has left and right headphones worn on the left and right ears, and the left and right headphones are a headband or a neckband. It is connected with. FIG. 2 shows an example of an ear covering type headphone in which the ear pad 14 surrounds the ear 21, but an ear mounting type in which the ear pad 14 is placed on the ear 21 may be used.

  As shown in FIG. 2, an air chamber 15 is formed when the headphones 10 are mounted on the user's temporal region. The air chamber 15 is a space surrounded by a baffle plate 13, a diaphragm (not shown) included in the speaker unit 11, a part of the housing 12, an ear pad 14, and a user's temporal region. Sound is emitted from the speaker unit 11 toward the air chamber 15, and the sound wave reaches the eardrum behind the user's ear. The pressure of the air chamber 15, that is, the sound pressure changes according to the sound wave. A sound pressure detecting member 16 for detecting the sound pressure is disposed in the air chamber 15. For example, a non-directional microphone is suitable as the sound pressure detection member 16, but a unidirectional microphone can also be used.

  The speaker unit 11 is driven by a sound signal input from a CD player, MP3 player, or other sound source to generate sound, and is also driven by a detection signal of the sound pressure detection member 16. In the example shown in FIG. 2, the detection signal of the sound pressure detection member 16 is input to the adder 18 through a circuit block 17 such as an amplifier. The detection signal is added to the musical sound signal 20 by the adder 18 and further input to the speaker unit 11 via the amplifier 19. The amplifier 19 can be referred to as a drive circuit for the speaker unit 11, and the speaker unit 11 is driven by the detection signal of the sound pressure detection member 16 added by the adder 18 and the musical sound signal 20.

  According to the example of the headphones shown in FIG. 2 configured as described above, when the speaker unit 11 is driven by the musical sound signal 20, sound is emitted from the speaker unit 11 according to the musical sound signal. The sound pressure in the air chamber 15 changes according to the sound that is emitted. The change in sound pressure is detected by the sound pressure detection member 16 and a detection signal corresponding to the sound pressure is output. This detection signal is input to the speaker unit 11 through the circuit block 17, the adder 18, and the amplifier 19. The speaker unit 11 is driven according to the detection signal, and the sound pressure in the air chamber 15 is kept constant.

  In short, the example of the headphones shown in FIG. 2 includes a speaker unit 11 having a diaphragm that is driven by an audio signal to vibrate and generates sound, and the diaphragm of the speaker unit 11 is arranged to vibrate by vibration of the diaphragm. And an air chamber 15 whose volume changes. The air chamber 15 is driven by a sound pressure detecting member 16 for detecting the sound pressure in the air chamber 15 and an output signal of the sound pressure detecting member 16, and the volume of the air chamber 15 is changed according to the output signal to A volume adjuster (speaker unit 11) for controlling the acoustic impedance of the air chamber 15 is disposed. Therefore, the sound pressure in the air chamber 15 is detected by the sound pressure detecting member 16 and fed back to the speaker unit 11, and the speaker unit 11 is controlled so that the sound pressure in the air chamber 15 does not fluctuate.

  Specifically, when the sound pressure detection member 16 detects that the sound pressure in the air chamber 15 has increased, the diaphragm of the speaker unit 11 is controlled to move backward from the air chamber 15, Reduce acoustic impedance equivalently. Thus, even if the volume of the air chamber 15 is small, the diaphragm of the speaker unit 11 can be vibrated without resistance in accordance with the sound signal in the low sound range, and the directivity response characteristic in the low sound range can be improved. it can.

  FIG. 3 shows an acoustic equivalent circuit of the example of the headphones shown in FIG. 2 described above. 3, P1 is the sound pressure of the front sound source, that is, the front air chamber 15, P2 is the sound pressure of the rear sound source, that is, the air chamber on the back side of the diaphragm of the speaker unit 11, m0 is the mass of the diaphragm, and s0 is the vibration. The stiffness of the plate, m1 is the mass of the back side air chamber, r1 is the acoustic resistance of the back side air chamber, s1 is the stiffness of the back side air chamber, and Ps1 is the sound pressure generated by the stiffness s1.

  When the back side air chamber is small and the stiffness s1 is large, the stiffness s1 becomes dominant in the low sound range, the Ps1 becomes large, the diaphragm becomes difficult to move, and the directional frequency response in the low sound range deteriorates. . Therefore, it is desirable to make the sound pressure Ps1 as small as possible by making the stiffness s1 of the back side air chamber as small as possible so that only the acoustic resistance r1 acts effectively. For that purpose, the volume of the back side air chamber should be made as large as possible, but as already explained, there are many factors that limit the volume of the back side air chamber.

  In that respect, according to the example of the headphones shown in FIG. 2, when the sound pressure of the air chamber 15 is changed by the vibration of the diaphragm of the speaker unit 11 which is an electroacoustic conversion unit, the change of the sound pressure is detected by the sound pressure detecting means. A certain microphone unit 16 detects. The speaker unit 11 is driven by this detection signal to control the acoustic impedance of the air chamber 15 to be equivalently reduced. As a result, the stiffness s1 can be reduced equivalently, the sound pressure Ps1 can be reduced, and the directional frequency response in the low sound range can be enhanced. In addition, the sound pressure in the air chamber 15 is detected, and this sound pressure detection signal is fed back to the speaker unit 11 that also serves as a volume adjuster, and control is performed so that the sound pressure in the air chamber 15 does not vary. The equivalent acoustic impedance control can be performed with high accuracy.

[Test equipment]
In order to demonstrate the effect obtained by adopting the technical idea of the present invention, a frequency characteristic test was conducted. The test apparatus conforms to the standard of EIAJ RC-8160, and its outline is shown in FIG. In FIG. 4, the code | symbol 29 has shown the unidirectional dynamic microphone as a subject. A test sound wave is emitted from a speaker arranged 50 cm in front of the dynamic microphone 29 toward the microphone 29, and this sound wave is received by the microphone 29 and subjected to electroacoustic conversion, and this converted signal is recorded.

  A device for forming a space corresponding to the air chamber described so far is attached to the back of the microphone 29. The space forming device includes a housing 24 and a dynamic speaker unit 25 built in the housing 24. The speaker unit 25 has a diaphragm 26. Further, the housing 24 is divided into a front air chamber 27 and a back air chamber by the diaphragm 26, and a microphone unit 28 as a sound pressure detecting member is disposed in the air chamber 27.

  A detection signal of the microphone unit 28 is fed back to the speaker unit 25 as a volume adjuster via a circuit block 30 including an amplifier and the like, and the speaker unit 25 is driven by the detection signal. This feedback control system can be arbitrarily turned on and off. The volume of the air chamber 27 in a state where the feedback control system is off, that is, in a natural state where the speaker unit 25 is not driven, can be arbitrarily adjusted by a method such as changing the mounting position of the dynamic microphone 29. Yes.

Using the above test apparatus, the following three specifications were tested.
(1) Assuming a normal dynamic microphone, the volume of the air chamber 27 is set to 30 cc. The feedback control system is turned off and the acoustic impedance control of the air chamber is not performed.
(2) The volume of the air chamber 27 was set to 2 cc. The feedback control system is turned off and the acoustic impedance control of the air chamber is not performed.
(3) The volume of the air chamber 27 was set to 2 cc. The feedback control system was turned on, and the acoustic impedance of the air chamber was controlled.

  FIG. 5 shows the test result of (1), FIG. 6 shows the test result of (2), and FIG. 7 shows the test result of (3). In each figure, a graph indicated by a thick line indicates a measurement result in a case where a speaker that emits a test sound wave is disposed in the direction of 0 degrees with respect to the central axis, that is, in front. A graph indicated by an intermediate size line shows a measurement result when the speaker is arranged in a direction of 90 degrees with respect to the central axis. The graph shown by the thin line shows the measurement result when the speaker is arranged in the direction of an angle of 180 degrees with respect to the central axis.

  As is clear from the comparison between FIG. 7 and FIG. 8, by turning on the feedback control system, the directivity frequency response in the low frequency range is improved, the response frequency is expanded to the low frequency side, and the output level on the low frequency side is increased. Is high. Further, as apparent from the comparison between FIG. 6 and FIG. 8, it can be seen that when the feedback control system is turned on, the frequency response is improved in the low frequency range as compared with the case where the volume of the air chamber 27 is increased.

[Example of microphone]
FIG. 1 shows an embodiment in which the technical idea described above is applied to a dynamic microphone. In FIG. 1, a dynamic microphone 50 has a microphone case 51 that also serves as a grip. A dynamic microphone unit 52, which is an electroacoustic conversion unit, is attached to the inside of the tip of the microphone case 51 with an appropriate attachment structure.

  The microphone unit 52 has a unit case 54, and a diaphragm 53 that vibrates by receiving sound waves is disposed on the inner peripheral side of the front end of the unit case 54. The diaphragm 53 has a voice coil, and this voice coil is disposed in a magnetic gap formed by a magnetic circuit constituent member such as a permanent magnet or a yoke. When the diaphragm 53 receives a sound wave and vibrates together with the voice coil, the voice coil outputs a sound signal corresponding to the sound wave by an electromagnetic conversion action.

  In the unit case 54, an air chamber 56 is formed behind the diaphragm 53 and the magnetic circuit constituent member. A space formed on the back side of the diaphragm 53 communicates with the air chamber 56 through an appropriate hole. In the air chamber 56, a sound pressure detection member 55 made of, for example, an omnidirectional microphone unit is disposed. Further, a volume adjuster 57 that is driven by the output signal of the sound pressure detection member 55 and controls the acoustic impedance of the air chamber 56 by changing the volume of the air chamber 56 in accordance with the output signal is disposed in the air chamber 56. ing. The volume adjuster 57 can be of the same structure as a dynamic speaker. The output signal of the sound pressure detection member 55 is amplified by an amplifier 58, and the volume adjuster 57 is driven by this amplified signal.

  A connector portion 59 for connecting a cable connector is provided at the rear end portion of the microphone case 51, and a power supply battery chamber 60 is provided in the microphone case 51 between the microphone unit 52 and the connector portion 59. Yes. As apparent from the fact that the dynamic microphone 50 is provided with the power battery room 60, it is a microphone that requires a power source such as a wireless microphone and has the power battery room 60. Is limited in volume. Therefore, the stiffness of the air chamber 56 is high, the microphone unit 52 diaphragm 53 is difficult to move in the low sound range, and the directional frequency response in the low sound range is reduced.

  Especially in the case of pin type wireless microphones, for example, the overall size is small and it is necessary to load a power battery, so the capacity of the air chamber becomes smaller and the directional frequency response in the low frequency range is increasing. descend. Therefore, in the embodiment shown in FIG. 1, a volume regulator 57 is provided in the air chamber 56, and the volume regulator 57 is driven via the amplifier 58 by the output signal of the sound pressure detection member 55. In the control system from the sound pressure detection member 55 to the volume adjuster 57 via the amplifier 58, when the sound pressure in the air chamber 56 increases, the volume adjuster 57 expands the volume of the air chamber 56 and the acoustic impedance of the air chamber 56 is increased. The feedback control system is configured to control so as to be equivalently small.

  As described above, according to the embodiment of the microphone shown in FIG. 1, the volume of the air chamber 56 varies due to the vibration of the diaphragm 53 of the dynamic microphone unit 52 receiving the sound wave, and the sound pressure of the air chamber 56 varies. Then, this sound pressure fluctuation is fed back to the volume adjuster 57, the volume adjuster 57 is driven, and the sound pressure in the air chamber 56 is controlled to be constant. As a result, even if the volume of the air chamber 56 is small, the acoustic impedance of the air chamber 56 is equivalently reduced, and the diaphragm 53 can vibrate faithfully with respect to the sound pressure and has excellent directivity frequency response. A microphone can be obtained.

  Since the volume of the air chamber is small, the directivity frequency response is lowered mainly in the bass range. Therefore, in the embodiment described above, the detection signal of the sound pressure detection member is input to the volume adjuster through a low-pass filter so that the acoustic impedance in the low frequency range of the air chamber is equivalently reduced. Good.

  The present invention, for example, a pin type wireless microphone, even if a microphone having a very small air chamber formed behind a diaphragm of a microphone unit, which is an electroacoustic conversion unit, is electrically driven at a high level up to the low sound range. A high-performance microphone capable of acoustic conversion can be obtained.

  The volume adjuster used in the present invention is not limited to the same configuration as that of the dynamic speaker, and the volume controller that controls the volume of the air chamber by driving the diaphragm facing the air chamber with a member similar to an electromagnetic actuator is used. be able to. Or what controls the volume of an air chamber using a piezoelectric element like a piezoelectric bimorph, for example can be used, and it is not limited by a drive system.

52 Microphone unit 53 Diaphragm 54 Unit case 55 Sound pressure detection member 56 Air chamber 57 Volume controller

Claims (5)

A microphone unit that receives sound waves from a sound source and vibrates the diaphragm and converts the vibration of the diaphragm into an audio signal;
An air chamber that is formed behind the diaphragm of the microphone unit and whose volume is changed by the vibration of the diaphragm;
In the air chamber,
A sound pressure detecting member for detecting the sound pressure in the air chamber;
A volume adjuster that is driven by an output signal of the sound pressure detection member and controls the acoustic impedance of the air chamber by changing the volume of the air chamber according to the output signal;
A microphone is placed.   The microphone according to claim 1, wherein the microphone unit is incorporated in a unit case, and an air chamber whose volume changes due to vibration of a diaphragm included in the microphone unit is provided in the unit case.   3. The microphone according to claim 2, wherein the unit case is incorporated in a microphone case, and the power supply battery chamber is provided in the microphone case.   4. The microphone according to claim 1, wherein the microphone unit is a dynamic microphone unit. The microphone according to any one of claims 1 to 4, wherein a detection signal of the sound pressure detection member is input to the volume adjuster through a low-pass filter.

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