JP3143200U - Sound protection equipment - Google Patents

Abstract

To provide a soundproof protector capable of preventing unpleasant ultra-low noise even if the atmospheric pressure changes suddenly due to, for example, door opening / closing sound or movement of a user's head.
A main body casing 20 that can be mounted on a person's head so as to cover a person's ear, and a microphone 10 that is disposed in the main body casing 20 and detects a sound wave that enters the main body casing and converts the sound wave into an audio signal. And a phase inverter 32 that generates a signal having a phase opposite to that of the audio signal converted by the microphone 10, and a speaker 35 that is driven by the phase-inverted signal generated by the phase inverter 32 and that generates a canceling sound having the opposite phase. The microphone 10 is a speed-type condenser microphone that attenuates the output in the low sound range.
[Selection] Figure 1

Description

  The present invention relates to an earmuff type soundproof protector, and in particular, a device equipped with an active noise reduction device has been devised so as not to generate unpleasant ultra-low frequency noise. Is.

  When it is necessary to act in a loud noise, for example, when performing maintenance work in a loud engine sound, such as at an airport or aircraft maintenance site, the worker must be able to prevent the earmuff from being damaged by the loud noise. Wear protective equipment. The soundproofing protector has a passive type that enhances its own external noise blocking effect, and detects noise that has entered inside with a microphone, and cancels noise by generating a canceling sound that is in reverse phase to the noise. There is an active type. The noise is referred to as “environmental noise”, the signal for generating the opposite phase sound is referred to as “mute signal”, and the opposite phase sound source is referred to as “secondary sound source”. The present invention relates to an active sound protection device.

  In conventional active soundproofing protective equipment, a pressure-type omnidirectional microphone whose frequency characteristics of the output signal are flat from low to high is used as a microphone for obtaining an anti-phase canceling sound from environmental noise. Yes. FIG. 5 shows an example of a pressure-type omnidirectional microphone. In FIG. 5, a bottomed cylindrical unit case 1 includes a diaphragm ring 2, a diaphragm 3 having an outer peripheral edge fixed to one surface of the diaphragm ring 2, a ring-shaped spacer 4, and a fixed electrode 5. The insulating holder 6 and the circuit board 7 are accommodated in this order. The diaphragm 3 is made of a resin thin film, and one surface is an electrode. A spacer 4 is interposed between the outer periphery of the diaphragm 3 and the outer periphery of the fixed electrode 5, and a slight gap corresponding to the thickness of the spacer 4 is formed between the diaphragm 3 and the fixed electrode 5. . An appropriate number of holes 11 through which sound waves enter is formed at the bottom of the unit case 1, and the diaphragm 11 faces these holes 11. The edge on the opening end side of the unit case 1 is bent inward to press the outer peripheral edge of the circuit board 7, and with this pressing force, the insulating holder 6, the fixed electrode 5, the spacer 4, the diaphragm 3, and the diaphragm ring 2 is pressed toward the inner bottom surface of the case 1 in this order, and is fixed in the case 1.

  When a sound wave enters from the hole 11, the diaphragm 3 receives the sound wave and vibrates. The diaphragm 3 and the fixed electrode 5 constitute a capacitor, and the capacitance of the capacitor changes according to the vibration of the diaphragm 3. This change in the capacitor capacity is output as a change in voltage. In this way, electroacoustic conversion is performed by the microphone. This condenser microphone is a pressure-type omnidirectional microphone in which the space on the fixed electrode 5 side of the diaphragm 3 is sealed.

  The pressure-type condenser microphone is a condenser microphone that converts air pressure fluctuation into an electric signal. From this operating principle, when the atmospheric pressure applied to the diaphragm 3 is rapidly changed by the opening / closing sound of the door or the movement of the user's head, the fluctuation of the atmospheric pressure is detected as a sound wave in a very low frequency range with a large amplitude. Therefore, according to the soundproofing protector equipped with the pressure type condenser microphone as the environmental noise detecting means, the muffler signal is generated based on the signal detected as the sound wave of the above-mentioned large amplitude ultra low frequency range. Based on this mute signal, a sound in the very low frequency range is emitted from the secondary sound source. Since the sound in the very low frequency range does not cancel the environmental noise, it becomes a very low frequency noise, which makes the user of the soundproofing protective equipment uncomfortable.

In order to attenuate the sound wave in the ultra-low frequency range that does not contribute to the cancellation of environmental noise in the secondary sound source, (1) a method of attenuating the mute signal in the signal processing circuit, and (2) connecting the inside and outside of the soundproof protector. A method of forming an air passage and forming an acoustic circuit between the inside and the outside is conceivable.
As described in (1) above, in order to attenuate the low frequency range in the signal processing circuit, a filter circuit including a capacitor C and a resistor R is generally used. However, when such a filter circuit with C and R is used, the frequency characteristic of the phase changes in the delay direction, so that the noise reduction effect by the secondary sound source may be impaired. It is also conceivable to use a filter circuit including a low frequency coil L and a resistor R instead of the capacitor C. However, the low-frequency coil L needs to have a large inductance, and the dimensions of the parts increase, making it unsuitable for portable instruments such as earmuff-type soundproofing protectors.
According to the method of constructing the acoustic circuit between the inside and outside of the soundproofing protector as in the conventional example of (2) above, the soundproofing protector itself has by the air passage connecting the inside and outside of the soundproofing protector. Sound insulation characteristics in the low frequency range may be sacrificed.

  As a prior art related to the present invention, a bidirectional microphone is disposed in the main body casing, and a voice intake hole is provided in the front of the main body casing, through which the voice sensing surface and noise canceling of the microphone are provided. There are microphone devices each formed with an audio passage that leads to a surface (see, for example, Patent Document 1 and Patent Document 2). An object of this microphone device is to prevent the bidirectionality of the microphone from being impaired.

  As another prior art, there is a voice input device that cancels ambient noise while using an omnidirectional microphone (see Patent Document 3). In this audio input device, the first and second omnidirectional microphones are arranged so that there is an acoustic time difference, and the audio signal input from the second omnidirectional microphone is delayed by a delay circuit and then inverted. The phase is inverted by a circuit, and the audio signal from the second omnidirectional microphone whose phase is inverted and the audio signal from the first omnidirectional microphone are added by an adding amplifier.

  Although the device described in each of the above patent documents is partially similar in structure to the device of the present invention, it does not suggest the device of the present invention.

JP 2000-184489 A JP-A-7-99697 Japanese Patent Laid-Open No. 5-284588

  According to the active soundproofing protector using the pressure type condenser microphone as shown in FIG. 5 as the environmental noise detecting means, as described above, the frequency characteristic of the output signal is flat pressure type omnidirectional from the low range to the high range. Because of the use of the directional microphone, there is a difficulty in generating unpleasant ultra-low noise when the air pressure applied to the diaphragm 3 suddenly fluctuates due to the opening / closing sound of the door or the movement of the user's head. . This will be described using a characteristic diagram. The characteristic diagram shown in FIG. 3 shows the frequency response of the pressure type microphone and the speed type microphone. The solid line is the pressure type and the broken line is the speed type. The pressure type has a flat characteristic from the low range to the high range. Having this flat characteristic leads to the above problems. On the other hand, the low frequency range is attenuated in the speed type. If this speed type is used, even if the atmospheric pressure fluctuates suddenly due to the opening / closing sound of the door or the movement of the user's head, it is difficult to respond and it is possible to prevent the generation of unpleasant ultra-low noise There is.

The present invention has been made to solve the above-described problems of the prior art. For example, even if the air pressure suddenly fluctuates due to the opening / closing sound of the door or the movement of the user's head, the present invention is unpleasant. An object of the present invention is to provide a soundproof protector capable of preventing the occurrence of ultra-low noise.
Another object of the present invention is to provide the above soundproof protector with a simple configuration at low cost.

  The present invention includes a main body casing that can be worn on a person's head so as to cover a person's ear, a microphone that is disposed in the main body casing and detects sound waves that enter the main body casing and converts the sound wave into an audio signal, A phase inverter that generates a signal having a phase opposite to that of the audio signal converted by the microphone; and a speaker that is driven by the phase signal generated by the phase inverter and that generates a cancellation sound having the opposite phase. The most important feature is that it is a speed-type condenser microphone that attenuates the output in the low sound range.

  The speed condenser microphone has the characteristic that the output of the low frequency range is attenuated.For example, even if the atmospheric pressure fluctuates suddenly due to door opening / closing sound or user's head movement, Based on this, the output signal of the very low range is attenuated, and the generation of unpleasant ultra low range noise caused by this output signal is reduced.

Embodiments of a soundproof protector according to the present invention will be described below with reference to the drawings.
In FIG. 1, the soundproof protector has a main body casing 20, and a baffle plate 23 is fixed to the open end of the main body casing 20 by closing the open end. An ear pad 21 is fixed to the outer peripheral portion of the outer surface of the baffle plate 23 so as to surround the person's ear and be crimped to the side surface of the person's head. The microphone 10 is arranged by appropriate fixing means in a space 22 surrounded by the baffle plate 23 and the ear pad 21. The microphone 10 is a speed-type condenser microphone, and its specific configuration will be described later.

  A hole for attaching the speaker 35 is provided in the baffle plate 23, and the speaker 35 is attached to this hole position. A sealed space 24 is formed by the inner surface of the baffle plate 35 and the inner surface of the main casing 20. The sound signal output of the microphone 10 is amplified by the microphone amplifier 31, and the phase of the output of the amplifier 31 is inverted by the phase inverter 32. The audio signal with the phase inverted is input to the power amplifier 34 through the filter 33, and the speaker 35 is driven by the power amplifier 34. Therefore, the speaker 35 is driven by the audio signal with the phase inverted. In FIG. 1, the microphone amplifier 31, the phase inverter 32, the filter 33, and the power amplifier 34 are drawn outside the main body casing 20, but these can be incorporated in a circuit board or the like in the main body casing 20. The main body casing 20 may be loaded with a power supply battery for driving each circuit.

  The main body casing 20 itself and the ear pad 21 are of an earmuff type and function to some extent as a passive type soundproof protector so that their structure and material are selected so that environmental noise can be prevented from entering the interior. Can do. However, as described above, since the circuit from the microphone 10 to the speaker 35 is provided, the circuit operates as an active soundproofing protector. That is, the environmental noise entering the space 22 is detected by the microphone 10, amplified by the amplifier 31, and then the phase is inverted by the phase inverter 32. The frequency characteristics of the inverted signal are adjusted by the filter 33, and the power amplifier 34 drives the speaker 35 in accordance with the inverted signal. Since the sound wave generated by driving the speaker 35 is a sound wave obtained by inverting the phase of the environmental noise entering the space 22, the environmental noise entering the space 22 is canceled by the sound wave emitted from the speaker 35. Thus, even if the environmental noise is so great as to cause damage to the human ear, the sound can be protected by wearing the soundproof protector according to the illustrated embodiment, and the human ear can be protected.

  A specific configuration of the speed condenser microphone 10 is shown in FIG. In FIG. 2, a bottomed cylindrical unit case 1 includes a diaphragm ring 2, a diaphragm 3 whose outer peripheral edge is fixed to one surface of the diaphragm ring 2, a ring-shaped spacer 4, and a fixed electrode 5. The insulating holder 6 and the circuit board 7 are accommodated in this order. The diaphragm 3 is made of a resin thin film, and one surface is an electrode. A spacer 4 is interposed between the outer periphery of the diaphragm 3 and the outer periphery of the fixed electrode 5, and a slight gap corresponding to the thickness of the spacer 4 is formed between the diaphragm 3 and the fixed electrode 5. . The insulating holder 6 in this example has a cylindrical shape, and a relatively large space is generated on the back side of the fixed electrode 5. An appropriate number of holes 11 through which sound waves enter is formed at the bottom of the unit case 1, and the diaphragm 11 faces these holes 11. The edge on the opening end side of the unit case 1 is bent inward to press the outer peripheral edge of the circuit board 7, and with this pressing force, the insulating holder 6, the fixed electrode 5, the spacer 4, the diaphragm 3, and the diaphragm ring 2 is pressed toward the inner bottom surface of the case 1 in this order, and is fixed in the case 1.

  The configuration described so far differs greatly from the configuration of the pressure-type condenser microphone shown in FIG. 5 in that, for example, one hole 51 is formed in the fixed electrode 5 so as to penetrate the fixed electrode 5 in the thickness direction. is there. If the diameter of the hole 51 is too large, or if the number of the holes 51 is large (for example, about six at equal intervals in the circumferential direction), directivity is generated, so that the hole 51 can maintain omnidirectionality. Make it a size or number. By forming the hole 51 in the fixed electrode 5, the space on the back side of the diaphragm 3 communicates with the space on the back side of the fixed electrode 5, and when pressure is applied to the diaphragm 3, air is transmitted through the hole 51. Space to escape will be secured. With such a configuration, it is possible to obtain a speed-type condenser microphone that vibrates the diaphragm 3 by the air flow and performs electroacoustic conversion.

  A curve indicated by a broken line in FIG. 3 indicates the frequency response of the speed condenser microphone configured as described above, and the level in the low frequency region is attenuated. Specifically, the attenuation starts from around 200 Hz, and greatly attenuates as the frequency decreases. When this is compared with the frequency response of the pressure-type condenser microphone indicated by the solid line, it can be clearly seen that the level in the low frequency region is attenuated. FIG. 4 shows the noise reduction effect when passive in the above embodiment of the present invention by a broken line a, and the noise reduction effect when active by a solid line b. The horizontal axis is frequency. A thick solid line c indicates external noise.

FIG. 6 shows the noise reduction effect of a conventional soundproofing protector equipped with a pressure-type condenser microphone corresponding to FIG. The noise reduction effect when passive is indicated by a broken line a, and the noise reduction effect when active is indicated by a solid line b. A thick solid line c indicates external noise.
Comparing FIG. 4 and FIG. 6, the noise reduction effect when active is smaller in the embodiment of the present invention shown in FIG. 4 than in the conventional example shown in FIG. When observing in more detail, in the frequency band of 200 Hz or more that is easy for humans to perceive, the noise reduction effect when active is almost the same as the sound insulation effect of the embodiment of the present invention and the conventional example. On the other hand, in the band of 100HZ or less, the noise reduction effect when active in the embodiment of the present invention is lower than that in the conventional example. In other words, in the low frequency band of 100 Hz or less, the secondary signal is reduced in the embodiment of the present invention. In addition, at 50 Hz, the difference between the passive time and the active time is 4 dB in the case of the embodiment of the present invention compared with the case of the embodiment of the present invention and 10 dB in the case of the conventional example. is there. This also shows that in the embodiment of the present invention, the noise reduction effect in the low frequency region is lowered during active operation.

From the above, for example, when the atmospheric pressure suddenly fluctuates due to door opening / closing sound or movement of the user's head, the atmospheric pressure fluctuation is detected as environmental noise even though it is not originally environmental noise. Can be prevented, and unpleasant ultra-low noise caused by the atmospheric pressure fluctuation can be prevented.
In addition, according to the embodiment of the present invention, a great effect can be obtained by using a speed condenser microphone as a microphone, and an earmuff type active soundproof protector having a large noise reduction effect can be provided at low cost. .
The invention can be used in any case where it must act under loud noise.

It is a schematic diagram which shows the Example of the soundproof protector concerning this invention. It is a longitudinal cross-sectional view which shows the speed type | mold condenser microphone in the said Example. It is a characteristic diagram which shows the frequency response of the said speed type | mold condenser microphone compared with the frequency response of a pressure type | mold condenser microphone. It is a characteristic diagram shown with an external noise in order to compare the noise reduction effect at the time of passive in the said Example, and the noise reduction effect at the time of active. It is a longitudinal cross-sectional view which shows the pressure type condenser microphone used for the conventional soundproofing protector. It is a characteristic diagram shown with an external noise in order to compare the noise reduction effect at the time of passive in the conventional soundproof protector using a pressure type condenser microphone, and the noise reduction effect at the time of active.

Explanation of symbols

3 Diaphragm 5 Fixed Electrode 10 Microphone 20 Main Body Casing 32 Phase Inverter 33 Filter 35 Speaker 51 Hole

Claims (4)

A body casing that can be worn over a person's head to cover a person's ear;
A microphone that is arranged in the main body casing and detects sound waves that enter the main body casing and converts them into audio signals;
A phase inverter for generating a signal having a phase opposite to that of the audio signal converted by the microphone;
A speaker that is driven by an antiphase signal generated by the phase inverter and emits an antiphase canceling sound,
The microphone is a speed protection condenser microphone that attenuates the output in the low sound range.   The soundproof protector according to claim 1, wherein the speed-type condenser microphone has a hole formed in the fixed electrode facing the diaphragm so as to maintain non-directionality so as to penetrate the fixed electrode in the thickness direction.   The soundproof protector according to claim 2, wherein the hole of the fixed electrode is formed only at one place.   The soundproof protector according to claim 1, wherein the output signal of the speed condenser microphone is input to the speaker through a filter and an amplifier that adjust the frequency characteristic to a desired characteristic.

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