JP2781194B2 - Active noise canceller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an active noise canceller having a function of actively canceling external noise.

(Prior art) Conventionally, as an active noise canceller,
For example, those described in U.S. Pat. No. 4,455,675 are known. This active noise canceller provides a monitoring microphone that inputs a synthetic sound of external noise and a canceling sound, a mute speaker that generates a canceling sound, and a canceling sound that is in opposite phase to the input sound picked up by the monitoring microphone. A noise canceling circuit for outputting a canceling sound generation signal to be generated by the muffling speaker, wherein the external noise is muted by canceling the canceling sound having a phase opposite to that of the external noise.

(Problems to be Solved by the Invention) However, in such a conventional active noise canceller, the monitoring microphone inputs both the external noise and the cancel sound to form a closed loop. There was a problem described in.

That is, the monitor speaker is disposed at a position immediately in front of the mute speaker in order to input the cancel sound emitted from the mute speaker without bias. Therefore, the monitoring microphone and the supporting member disturb the sound field radiated from the sound deadening speaker, and particularly, remarkably disturb the high-frequency sound field having a short wavelength, for example, 1000 Hz or more. Therefore, the silencing volume in the high frequency range is reduced, and the silencing becomes unstable.

Furthermore, in order to prevent the disturbance of the sound field as described above, not to hinder the vibration of the diaphragm of the sound deadening speaker, not to be affected by the magnet of the sound deadening speaker, It is necessary to provide a certain distance between the muffling speaker and the monitoring microphone so as not to obstruct the intrusion path.
For this reason, a phase delay occurs while the canceling sound emitted from the muffling speaker propagates in the air and is input to the monitoring microphone, thereby causing audible frequency howling and deteriorating the muffling performance.

By the way, as a solution to the conventional problem as described above,
It is conceivable to provide a monitoring microphone dedicated to external noise input at a position away from the muffling speaker. However, in this case, the monitoring microphone is also separated from the ear cavity of the user, and the sound inputted to the microphone is different from the sound actually heard by the user, so that the sound deadening performance is low. Becomes Therefore, in order to improve the noise reduction performance, it is necessary to provide a feedback microphone near the ear cavity of the user separately from the monitoring microphone for external noise and perform feedback control. Becomes complicated.

The present invention has been made in view of the above-described problems, and prevents occurrence of howling, prevents disturbance of the sound field, provides stable high noise reduction performance, and has a simple structure. The task is to develop an active noise canceller.

(Means for Solving the Problems) In order to solve the above problems, in the active noise canceller of the present invention, a muffling speaker that generates and emits a predetermined canceling sound to a user's ear cavity and external noise are input. A monitoring microphone, and a noise canceling circuit that outputs a canceling sound generation signal to a muffling speaker so as to generate a canceling sound having a phase substantially opposite to the input sound of the monitoring microphone, and canceling a phase substantially opposite to external noise. In an active noise canceller configured to mitigate external noise by a sound canceling action, a sub-speaker is provided to emit a generated sound with respect to a negative pressure surface of the muffling speaker, and the noise canceling circuit includes a muffler of the muffling speaker. The sub-phase of the cancellation sound radiated from the pressure side of the muffling speaker is in phase with the suction side. The sub-speaker is configured to output a sub-cancellation sound generation signal to the sub-speaker so that the cancellation sound is radiated from the sub-speaker, and the cancellation sound radiated from the negative pressure surface of the muffling speaker cancels the sub-cancel sound radiated from the sub-speaker. This means is provided with the monitoring microphone at the position.

(Operation) When used under external noise, a canceling sound is emitted from the sound deadening speaker toward the user's ear cavity, and the external noise heard by the user is canceled out by the canceling action due to the opposite phase due to the canceling sound. .

Meanwhile, a (negative) cancel sound having a phase opposite to that of the (positive) cancel sound radiated from the negative pressure surface of the muffling speaker is emitted from the negative pressure surface of the muffling speaker. On the other hand, the sub-speaker emits a sub-cancel sound having the same phase as the (positive) cancel sound to the negative pressure surface of the muffling speaker.

Therefore, a (negative) cancellation sound and a sub-cancellation sound [(positive) cancellation sound] having opposite phases are radiated between the negative pressure surface of the muffling speaker and the sub-speaker in the facing state, and the two sounds cancel each other out to become 0. Occurs.

And, since the monitor microphone is placed at the position where both cancellation sounds cancel each other, when used under external noise, the monitor microphone ideally receives only external noise, so that ,
Howling caused by the addition of the original signal and the feedback signal of an integral multiple of 360 ° can be prevented, and the monitoring microphone is located at a position off the radiation front of the positive pressure surface of the silencing speaker. It does not disturb the sound field of the speaker.

Further, the monitoring microphone may be arranged at a position where the cancellation sound and the sub-cancellation sound between both speakers cancel each other out. Therefore, this condition can be satisfied, and the monitoring microphone can be arranged close to the muffling speaker.

Therefore, it is possible to input only the same external noise as the external noise heard by the user at a position close to the muffling speaker.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.
In describing the embodiments, the same reference numerals indicate the same objects in each drawing.

 First, the configuration will be described.

FIG. 1 is an overall view showing a configuration of an active noise canceller according to a first embodiment of the present invention.
1 is a muffling speaker that generates and emits a predetermined canceling sound to the user's ear cavity E, 2 is an auxiliary speaker, 3 is a monitoring microphone for inputting external noise, and 4 is substantially the same as the input sound of the monitoring microphone. To output a cancel sound generation signal to the muffling speaker 1 so as to generate an anti-phase cancel sound, and to generate a sub-cancel sound having a phase opposite to the cancel sound (the same as the input sound of the monitoring microphone 3). This is a noise cancellation circuit that outputs a sub cancellation sound generation signal to the sub speaker 2.

The silencing speaker 1 includes a housing 1a, a diaphragm 1
b, a coil 1c, and a magnet 1d, the diaphragm surface 1e is a positive pressure surface, and the housing surface 1f is a negative pressure surface.

The auxiliary speaker 2 is the same speaker as the mute speaker 1, that is, an acoustically equivalent speaker, having a housing 2a, a diaphragm 2b, a coil 2c, a magnet 2d, and a housing surface (negative pressure surface) 2f. The silencing speaker 1 is provided so as to be symmetrically opposed to the housing surface (negative pressure surface) 1f of the sound deadening speaker 1. Note that the alternate long and short dash line A indicates the plane of symmetry of the speakers 1 and 2. The diaphragm surface 2e of the sub speaker 2 is a positive pressure surface.

The space between the speakers 1 and 2 and the space between the speakers 1 and 2 and the ear cavity E are covered by a cover (not shown) in the form of a so-called headphone, and the diaphragm 1b of the sound deadening speaker 1 and the ear cavity. A noise removing space B is formed between the space E and the noise removing space B.

The monitoring microphone 3 is located at a position on the symmetry plane of the speakers 1 and 2 and close to the speakers 1 and 2.

The mute cancellation circuit 4 is a circuit that forms a cancellation sound generation signal and a sub cancellation sound generation signal based on the input sound of the monitoring microphone 3, and cancels a preamplifier 4a for pre-amplification and an unnecessary frequency range. It is formed to include a filter circuit 4b for removing from the sound, a power amplifier 4c for main amplification, and an inverting circuit 4d for shifting the phase of the input sound by 180 degrees. The mute speaker 1 is provided with a cancel sound generation signal having a phase opposite to that of the input signal from the monitoring microphone 3 via an inversion circuit. On the other hand, the sub-speaker 2 is supplied with a sub-cancellation sound generation signal having the same phase as the input signal from the monitoring microphone 3 without passing through an inverting circuit. The sub-cancellation sound having the same phase as the (positive) cancellation sound is radiated to one housing surface 1f.

 Next, the operation will be described.

When used under external noise such as in the cockpit of an aircraft, external noise is input by the monitoring microphone 3 and a noise canceling circuit 4 forms a canceling sound generation signal having a phase opposite to that of the input signal. The canceling sound is emitted from the muffling speaker 1 toward the user's ear cavity E, and the external noise heard by the user is canceled out by the canceling effect of the canceling sound due to the opposite phase.

When the cancellation sound is emitted from the muffling speaker 1, a (positive) cancellation sound a as shown in FIG. 2 is emitted from the diaphragm surface (positive pressure surface) 1e of the muffling speaker 1, and the housing surface ( A negative pressure cancellation sound b is radiated from the negative pressure surface 1f.

On the other hand, in the sub-speaker 2, a signal having a phase opposite to that of the mute speaker 1 is given, that is, the diaphragm surface 2e.
(Negative) cancel sound b is radiated from the housing surface
A (correct) cancel sound a is emitted from 2f.

Therefore, on the symmetry plane A of the two speakers 1 and 2 where the monitoring microphone 3 is provided, the (negative) cancellation sound b from the housing surface 1f of the sound deadening speaker 1 and the housing surface of the sub speaker 2 The (correct) cancel sound a from 2f cancels each other and becomes zero.

Therefore, in the monitoring microphone 3, the external noise c
(FIG. 2) is input only. This prevents the occurrence of howling caused by the addition of the original signal and the feedback signal of an integral multiple of 360 °, and reduces the noise reduction performance due to the occurrence of howling. This has the effect of preventing it.

In addition, the monitoring microphone 3 is a diaphragm
Radiation of the canceling sound from 1b Since it is arranged on the side face away from the front face, the sound field of the sound deadening speaker 1 is not disturbed. Therefore, stable noise reduction performance can be obtained up to a high frequency range.

The monitoring microphone 3 is connected to both speakers 1, 2
, It is possible to input only the same external noise as the external noise heard by the user. Therefore, a stable noise reduction performance is obtained, and an effect that a circuit for feedback control and a microphone are not required and the configuration is simple is obtained.

Further, in the present embodiment, the same speaker as the silencing speaker 1 is used as the sub-speaker 2 to cancel the (negative) canceling sound radiated from the negative pressure surface (housing surface 1f) of the silencing speaker 1 and is acoustically equivalent. Therefore, the input signal from the monitoring microphone 3 can be used as it is as the sub-cancellation generation signal, so that it is not necessary to make the output different from the cancellation sound generation signal, and the configuration can be simplified.

Next, a second embodiment of the present invention shown in FIG. 3 will be described.

In the second embodiment, a mixer 24e is provided in the middle of the noise canceling circuit 24, an external signal d is input, and this signal sound can be given to the user (the ear cavity E) through the muffling speaker 1. This is an example of forming.

Examples of the external signal d include a communication sound, an emergency alarm sound, and other operation monitor sound of an instrument. In other words, when used in the cockpit of an aircraft, external noise can be cut off while necessary sounds such as communication sound, emergency alarm sound, and other instrument operation monitor sound can be generated and emitted from the sound deadening speaker 1. I have.

In this embodiment, two filter circuits, a pre-filter 24f and a main filter 24g, are provided in the noise canceling circuit 24.

 Next, a third embodiment shown in FIG. 4 will be described.

This third embodiment is similar to the mixer 24e of the second embodiment.
Preamplifier 30a for noise canceling circuit 24 having
And an environmental sound circuit for inputting an environmental sound signal from the non-directional environmental sound input microphone 31 via the pre-filter 30b
This is an example in which 30 is provided.

Therefore, it is possible to arbitrarily adjust the environmental sound signal from the environmental sound input microphone 31 and leave only the desired environmental sound among the external environmental sounds in the noise removal space B.

As described above, the embodiments have been described based on the drawings. However, the specific configuration is not limited to the embodiments, and even if there is a design change or the like without departing from the gist of the present invention, it is included in the present invention. .

For example, in the embodiment, the same speaker as the muffling speaker was used as the sub-speaker. Any speaker may be used. Further, as shown in the embodiment, the present invention is not limited to the configuration in which the negative pressure surfaces of both speakers are opposed to each other, and the positive pressure surface of the sub-speaker may be opposed to the negative pressure surface of the sound deadening speaker.

(Effect of the Invention) As described above, in the active noise canceller of the present invention, a sub-speaker that radiates sub-cancellation is provided opposite to the negative pressure surface of the muffling speaker, and Since the monitoring microphone is provided at a position where the radiated cancel sound and the sub-cancel sound radiated from the sub-speaker cancel each other, the following effects can be obtained at the same time.

In the monitoring microphone, it is possible to input only the external noise without inputting the cancel sound, thereby obtaining an effect that howling can be prevented and the silencing performance can be improved.

The monitoring microphone and its supporting member do not disturb the sound field of the sound deadening speaker, whereby the effect that the external noise up to the high frequency range can be stably suppressed.

A monitoring microphone is provided near the muffler speaker and the user's ear cavity, and external noise equal to the external noise heard by the user can be input, thereby eliminating the need for a microphone or circuit for feedback control. Can be easily obtained.

By providing a filter in the electric circuit, it is possible to selectively eliminate a sound to be eliminated.

[Brief description of the drawings]

FIG. 1 is an overall view showing a configuration of an active noise canceller according to a first embodiment of the present invention, and FIG. 2 is a positive pressure sound, a negative pressure sound, and external noise of a sound deadening speaker by the active noise canceller of the first embodiment. FIG. 3 is an overall view showing the configuration of the active noise canceller of the second embodiment of the present invention, and FIG. 4 is an overall view showing the configuration of the active noise canceller of the third embodiment of the present invention. . E: ear cavity 1: silencing speaker 1e: positive pressure surface (of silencing speaker) 1f: negative pressure surface (of silencing speaker) 2: auxiliary speaker 3: monitoring microphone 4: noise canceling circuit 24 Noise cancellation circuit

Continuation of the front page (56) References JP-A-62-2798 (JP, A) JP-A-63-296599 (JP, A) JP-A-62-29397 (JP, A) JP-A-63-67099 (JP, A) , A) Fully open sho 61-70486 (JP, U) Special table 63-503186 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04R 3/00 H04R 1/10 101 G10K 11/16

Claims (1)

(57) [Claims] 1. A mute speaker for generating and radiating a predetermined cancel sound from a positive pressure surface to a user's ear cavity, a monitor microphone for inputting external noise, and a cancel of an opposite phase to the input sound of the monitor microphone. A noise canceling circuit that outputs a canceling sound generation signal to a muffling speaker to generate a sound, and an active noise canceller configured to mitigate the external noise by canceling the canceling sound having a phase opposite to that of the external noise. A sub-speaker is provided to emit a generated sound with respect to the negative pressure surface of the muffling speaker, and the muffling cancellation circuit is provided with the same phase as the canceling sound radiated from the positive pressure surface of the muffling speaker with respect to the negative pressure surface of the mute speaker. A sub-cancellation sound generation signal is sent to the sub-speaker so that the sub-cancellation sound is emitted from the sub-speaker. An active noise canceller, wherein the monitoring microphone is provided at a position where a canceling sound radiated from a negative pressure surface of the muffling speaker and a sub-cancelling sound radiated from a sub-speaker cancel each other. .