JP2786285B2 - 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. The active noise canceller outputs a cancel sound having a phase opposite to that of the input sound from the monitoring microphone from a muffling speaker, and cancels the external noise by canceling the external noise and the cancel sound.

However, according to this conventional technique, there is a problem that it is difficult to input a cancel sound without bias and to install a monitoring microphone so as not to disturb the sound field of the cancel sound.

In addition, the monitoring microphone needs to be provided with a certain distance from the muffling speaker because it is necessary to input external noise, which causes a problem that a phase delay occurs and a housing is generated.

Therefore, the applicant of the present application has solved the above conventional problems,
As a means for solving the problem with a simple control circuit that does not require feedback control, an active noise canceller (hereinafter referred to as prior art) described in Japanese Patent Application No. 44790/1994 has been proposed.

This prior art provides a sub-speaker that radiates a sub-cancellation sound having the same phase as the canceling sound on the negative pressure surface of the muffling speaker, and provides a monitoring microphone at a position where the canceling sound and the sub-cancellation sound cancel each other out. Only external noise is input to the microphone.

(Problems to be Solved by the Invention) However, in this prior art, the sound deadening speaker side space and the sub speaker side space are not always acoustically uniform. In other words, when the active noise canceller is of a type that is mounted on the head of a person, the sound-emitting speaker-side space from which the cancellation sound is radiated is inconsistent with the head of the person and the device. The sub-speaker-side space on the opposite side is formed only by the case, not only the shape and volume, but also
The material forming the space was different. for that reason,
The phase shift occurs in the respective reflected sounds of the sounds radiated from the two speakers generated on the walls of both spaces, and the reflected sounds do not cancel each other at the position of the monitoring microphone.
There was a residual sound.

Therefore, by misidentifying the residual sound input from the monitoring microphone as an extraneous sound, the muffling speaker amplifies an extra sound as a cancel sound, or
There is a problem that howling occurs when this residual sound enters the howling cycle.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problem, and eliminates the residual sound of the reflected sound, thereby eliminating the unnecessary amplification and howling of the sound, thereby increasing the noise reduction effect. The task is to develop a 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 emits a cancellation sound having a phase opposite to that of the sound to be muffled from one of the positive and negative surfaces;
A sub-speaker that emits a sub-cancellation sound having the same phase as the cancellation sound from one of the positive and negative sides of the mute speaker, and a muffler that is arranged at a position where the sounds radiated from both speakers cancel each other. A monitoring microphone for inputting a visitor including sound, a canceling sound generation signal for emitting a canceling sound to the muffling speaker based on the input sound from the monitoring microphone, and a sub canceling sound for the sub speaker. A noise canceling circuit for outputting a sub-cancellation sound generation signal for emitting
A housing is provided which symmetrically forms a space on the muffler speaker side in front of one of the positive and negative sides of the muffler speaker and a space on the sub-speaker side in front of the other side of the sub-speaker.

(Operation) In the active noise canceller of the present invention, a noise canceling sound such as noise is radiated from the sound deadening speaker in a phase opposite to that of the sound to be muffled, and the sound is canceled by the canceling action.
The monitoring microphone can input only the sound to be silenced without being affected by the sound radiated from both speakers, and aims to prevent the occurrence of howling caused by re-input of the phase delay canceling sound. Points that can be
The microphone for monitoring can be placed close to the muffling speaker to improve muffling performance, and the mike for monitoring is installed at a position off the radiating front of the positive pressure surface of the vibrating member of the muffling speaker to muffle performance in the high frequency range The point that can be improved is the same as in the prior art, and the description is omitted.

Furthermore, in the active noise canceller of the present invention, since the housing that forms the muffling speaker side space and the sub speaker side space symmetrically is provided, the shape and volume of both spaces are equal, and the reflection of sound radiated from both speakers is provided. If there is no phase shift in the sound, and if the materials of the housings forming the two spaces are made equal, the two spaces will be more acoustically uniform.

Therefore, the monitoring microphone does not input the residual sound, so that the mute speaker does not amplify the extra sound by erroneously recognizing the residual sound as an extraneous sound, and the residual sound enters the howling cycle. There is no howling caused by this.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.
In describing the embodiments, a headphone type device used by a person to be worn on the head and used to cancel noise will be described as an example. Further, in each drawing, the same reference numeral indicates the same object.

 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 silencing speaker, 2 is a sub speaker, 3 is a monitoring microphone, 4 is a noise canceling circuit, 5 is a supporting member, 6
Is a headphone cover, 7 is a muffler speaker side housing,
8 is a sub speaker side housing.

The silencing speaker 1 is for emitting a canceling sound toward the ear cavity E in order to eliminate a sound to be silenced, and includes a housing 1a, a diaphragm 1b, a coil 1c, and a magnet 1b. 1e is a positive pressure surface that emits a cancel sound a, and the diaphragm back surface 1f is a negative pressure surface that emits a negative cancel sound b having a phase opposite to that of the cancel sound a. The housing 1a is formed with an air vent hole 1g.

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, and a magnet 2d. The diaphragm back surface 1f, which is a negative pressure surface, and the diaphragm back surface 2f are provided so as to face symmetrically with the surface 1a. Note that the alternate long and short dash line A indicates the plane of symmetry of the speakers 1 and 2. In addition, the diaphragm surface of the sub speaker 2
2e is a positive pressure surface, and the housing 2a has a hole for venting air.
2 g are formed.

By the way, the muffling speaker 1 is mounted so as to face the ear cavity E of the user in the use state, and the space between the two speakers 1, 2 and the space between the two speakers 1, 2 and the ear cavity E are headphones. Covered by the cover 6, the two speakers 1, 2
Is fixed by a support member 5 inside the headphone cover 6.

Further, a muffler speaker side housing 7 and a sub speaker side housing 8 are provided so as to cover the diaphragm surfaces 1e and 2e of both speakers 1 and 2, respectively. The two housings 7, 8 are formed in the same material in a symmetrical shape, and
An opening 7a for outputting a cancellation sound a is formed in the sound deadening space B on the side of the ear cavity E, and an opening 8a for inputting an external sound c is formed in the sub-speaker housing 8 with a diaphragm 1b. , 2b are provided on substantially the front surface in the same area and the same shape.

Therefore, the space in the headphone cover 6 is provided by the support member 5, the muffling speaker-side housing 7, and the multipurpose speaker-side housing 8, and a muffling space B between the ear cavity E and the muffling speaker-side housing 7 is provided. Speaker 1
Of the muffling speaker side space C covered by the muffling speaker side housing 7 in front of the diaphragm surface 1e,
The intermediate space D between the two diaphragms 1b and 2b and the auxiliary speaker 2
The sub-speaker-side space E covered by the sub-speaker-side housing 8 on the front surface of the diaphragm surface 2e, and an extraneous sound-side space F between the sub-speaker-side housing 8 and the headphone cover.

An opening 6a for inputting an external sound c is formed in a portion of the headphone cover 6 on the external sound side space F side.

Further, the support member 5 is provided with a communication path 5a for communicating the muffling speaker side space C, the middle D and the sub speaker side space E.

The monitoring microphone 3 is provided with its tip protruding from the communication path 5a.

The noise canceling circuit 4 causes the sound deadening speaker 1 to generate a cancellation sound a having a phase substantially opposite to the input sound of the monitoring microphone 3 (external sound c in FIG. 2) based on the input sound of the monitoring microphone 3. The sub-speaker 2 outputs a cancel sound generation signal e and causes the sub-speaker 2 to generate and radiate a sub-cancel sound (a) having the same phase as the cancel sound a (the same phase as the input sound of the monitoring microphone 3) on the rear surface 2f of the diaphragm. A circuit for outputting a cancel sound generation signal f, a preamplifier 4a for pre-amplification, and a filter circuit 4b for removing unnecessary frequency ranges from the cancel sound
And the main amplifier power amplifier 4c and the phase of the input sound
It is formed to include a reversing circuit 4d for shifting the degree.

Then, for the mute speaker 1, an inversion circuit 4d
, A cancel sound generation signal e having a phase opposite to that of the input signal from the monitoring microphone 3 is given. At this time, in the sound deadening speaker 1, from the rear surface 1f of the diaphragm,
A negative cancel sound b having a phase opposite to that of the cancel sound a is emitted.

On the other hand, the sub-speaker 2 is provided with the sub-cancellation sound generation signal f having the same phase as the input signal from the monitoring microphone 3 without passing through the conversion circuit, that is,
In the sub-speaker 2, a sub-cancel sound (a) having the same phase as the cancel sound a is radiated from the rear surface 2f of the diaphragm, and the sub-cancel sound (a) is transmitted through the hole 2g of the housing 2a and the hole 1g of the housing 1a. It is configured to be radiated to the back surface 1f. At this time, a negative sub-cancel sound (b) having the same phase as the negative cancel sound b is emitted from the diaphragm surface 2e of the sub-speaker 2.

 Next, the operation will be described.

The active noise canceller according to the present embodiment is used under the external noise such as in the cockpit of an aircraft, for example, as shown in FIG.

In this case, after passing through the headphone cover 6, the external noise (external sound c) is transmitted to the communication path 5a via the external sound side space F and the auxiliary speaker side space E, and is input to the monitoring microphone 3.

In the noise cancellation circuit 4, a cancellation sound generation signal e having a phase opposite to that of the input signal is formed, and based on the signal e,
Canceling sound a is emitted from the muffling speaker 1 toward the user's ear cavity E, and external noise (external sound c) transmitted to the user's ear cavity E is canceled by the canceling sound a having the opposite phase. Muted.

By the way, when the canceling sound a is emitted from the muffling speaker 1, the canceling sound a as shown in FIG. 2 is emitted from the diaphragm surface (positive pressure surface) 1e of the muffling speaker 1 and the diaphragm back surface (the negative pressure surface). ) 1f emits a negative cancellation sound b having an opposite phase.

On the other hand, the sub-speaker 2 is provided with the sub-cancellation sound generation signal f having a phase opposite to that of the mute speaker 1, that is,
A sub-cancel sound (= a) having the same phase as the cancel sound a is emitted from the rear surface 2f of the diaphragm, while a negative sub-cancel sound (= b) having a phase opposite to that of the sub-cancel sound is emitted from the front surface 2e of the diaphragm. .

Therefore, on the symmetry plane A of the two speakers 1 and 2 at the position where the monitoring microphone 3 is provided, the negative cancel sound b from the rear surface 1f of the diaphragm of the sound deadening speaker 1
And the back surface of the diaphragm of the sub-speaker 2 in the opposite phase
The sub-cancellation sound (= a) from 2f is transmitted equivalently, and the cancellation sound a from the diaphragm surface 1e of the muffling speaker 1 and the negative sub-cancellation from the diaphragm surface 2e of the sub-speaker 2 having a phase opposite to that. The sound (= b) is transmitted equivalently, and both sounds cancel each other to become 0.

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 connected to the diaphragm 1b.
Since the noise canceling sound a is radiated from the front side and is disposed on the side surface, the sound field of the sound deadening speaker 1 is not disturbed, so that a stable sound deadening performance up to a high frequency range can be obtained.

Further, since the monitoring microphone 3 is installed in the input hole 5b close to the side surfaces of both speakers 1 and 2, only the same external noise as transmitted to the ear cavity E near the user's ear cavity E is generated. Can be entered. 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, since the sub-speaker 2 for canceling the negative cancellation sound b radiated from the diaphragm back surface 1f of the muffling speaker 1 is acoustically equivalent using the same speaker as the muffling speaker 1, the sub-cancellation generation signal f
The input signal from the monitoring microphone 3 can be used as it is, and there is no need to make the output different from the cancel sound generation signal e, and the configuration can be simplified.

Furthermore, the sound radiated from both speakers 1 and 2 is reflected by hitting the wall surface of the radiation front. In the present embodiment, the sound loudspeaker side housing 7 and the sub speaker side housing 8
Since the sound-absorbing speaker-side space C and the sub-speaker-side space E are acoustically uniform, reflected sounds generated on the inner surfaces of both housings 7 and 8 are evenly generated, and the two cancel each other out, resulting in a residual sound. Further, the reflected sound generated on the inner surface of the headphone cover 6 in the sound deadening space B and the extraneous sound side space F is hard to be re-input into the two speaker side spaces C and E by the two housings 7 and 8, and the reflected sound causes the reflected sound. The residual sound is hard to occur.

Therefore, the monitoring microphone 3 does not input the residual sound, and the mute speaker 1 does not amplify the residual sound by erroneously recognizing the residual sound as the extraneous sound c. Does not enter the howling cycle and howling does not occur, and the noise reduction performance is improved.

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

This embodiment is an example in which sound absorbing members 7c and 8c are attached to inner surfaces of both housings 7 and 8, respectively.

Therefore, in the case of the second embodiment, the sound absorbing materials 7c and 8c make it difficult for reflected sound to be generated on the inner surfaces of the sound deadening speaker side space C and the sub speaker side space E, and the amount of reflected sound is reduced, so that the sound deadening performance is improved. .

In this embodiment, the output of the cancel sound is not hindered by the sound absorbing materials 7c and 8c, and the input of the foreign sound is not hindered.

As described above, the embodiments have been described based on the drawings. However, the specific configuration is not limited to this embodiment, and even if there is a design change or the like within a range not departing from the gist of the present invention, it is included in the present invention. .

For example, in the embodiment, a headphone type used by a person for removing external noise by wearing it on the head is shown as an example, but the scope of the present invention is not limited to this.・ Installed in ships, aircraft, factories, houses, etc. to cancel indoor noise, etc.
It may be used to cancel mechanical noise of an air conditioner or other industrial equipment of a vehicle.

In addition, since the present invention cancels the sound to be silenced, the sound to be silenced is not limited to the above-described noise.For example, for the purpose of harmonizing sounds, only an arbitrary sound may be used. There are also uses such as canceling.

(Effects of the Invention) As described below, in the active noise canceller of the present invention, a monitoring microphone is provided at a position where the cancel sound and the sub-cancel sound cancel each other. Only the sound to be silenced can be input, and only the sound to be silenced can be input, and the microphone for monitoring can be placed close to the silencer at a position off the front of the cancellation sound emission. The effect of being able to improve is obtained.

In addition, in the present invention, since the housing that forms the muffler speaker side space and the sub speaker side space symmetrically is provided,
The residual sound due to the phase shift of the reflected sound does not occur, and no extra sound is amplified as a cancel sound due to misidentifying the residual sound as an extraneous sound, and at the same time howling due to the residual sound Does not occur, and the effect of improving the silencing effect can be obtained.

[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 a sectional view of a main part of an active noise canceller according to a second embodiment of the present invention. C: Silent speaker side space E: Sub speaker side space a: Canceling sound c: External sound 1 ... Silencing speaker 1e ... Diaphragm surface (positive pressure surface) 1f ... Diaphragm back surface (negative pressure surface) 2 ... Sub-speaker 2e ... Diaphragm surface (positive pressure surface) 2f ... Diaphragm back surface (negative pressure surface) 3 ... Monitor microphone 4 ... Noise cancellation circuit 7 ... Housing 8 ... Housing

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-54900 (JP, A) JP-A-2-224498 (JP, A) JP-A-2-224499 (JP, A) Jpn. 86691 (JP, U) JP-A-3-86694 (JP, U) JP-A-3-86695 (JP, U) JP-A 3-86696 (JP, U) (58) Fields surveyed (Int. Cl. ⁶ , DB name) H04R 3/00 H04R 3/02 G10K 11/16

Claims (1)

(57) [Claims] 1. A muffling speaker that emits a cancellation sound having a phase opposite to the sound to be muffled from one of the positive and negative surfaces, and a sub-sound having the same phase as the cancellation sound from one of the positive and negative surfaces of the muffler speaker. A sub-speaker that radiates a cancel sound, a monitor microphone that is disposed at a position where the sounds radiated from both speakers cancel each other, and that inputs an extraneous sound including a sound to be silenced, based on the input sound from the monitor microphone. A noise canceling circuit that outputs a cancel sound generating signal that emits a cancel sound to the muffling speaker, and outputs a sub cancel sound generating signal that emits a sub cancel sound to the sub speaker, and one of the positive and negative of the muffling speaker The space on the mute speaker side in front of the sub-speaker and the space on the sub-speaker side in front of the other side of the sub-speaker are symmetrically formed. An active noise canceller, comprising: