JP2786278B2 - 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.

2. Description of the Related Art Conventionally, as an active noise canceller, for example, one described in US Pat. No. 4,455,675 is 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 howling occurs.

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-cancel sound in phase with the cancel sound on the negative pressure surface of the muffling speaker, and provides a monitoring microphone at a position where the cancel sound and the sub-cancel sound cancel each other out. Only external noise is input to the microphone.

However, in this prior art, the low-frequency sound of the negative cancellation sound, the sub-cancellation sound, and the negative sub-cancellation sound is not considered because the low-frequency surrounding of the speaker is not considered. And cancels the cancel sound in the low frequency range, the output of the cancel sound in the low frequency range is reduced, and there is a possibility that the noise canceling performance in the low frequency range may be reduced.

By the way, with a speaker about 4cm in diameter, the output drops sharply in the frequency range below 300Hz.

The present invention has been made in view of the above-described problem, and has as its object to develop an active noise canceller capable of improving the sound deadening performance in a low frequency range.

(Means for Solving the Problems) In order to solve the above problems, in an active noise canceller of the present invention, a muffling speaker that emits a predetermined canceling sound from a positive pressure surface, and a positive / negative sound is provided on a negative pressure surface side of the muffling speaker. A sub-speaker provided with one surface facing the other, a monitoring microphone arranged at a position where the sounds radiated from both speakers cancel each other, and a sound for a sound to be silenced; and a monitor microphone for monitoring from the positive pressure surface of the silencer. A cancel sound generation signal is output to emit a cancel sound having a phase opposite to that of the microphone input sound, and a sub cancel sound generation signal is emitted to emit a sub cancel sound having the same phase as the cancel sound from one of the positive and negative surfaces of the sub speaker. And a noise canceling circuit that outputs
A partition wall is provided which defines a silencer-side space on the positive pressure side of the silencer, an intermediate space between the two speakers, and a sub-speaker side space on the other side of the sub-speaker.

(Operation) The active noise canceller of the present invention is the same as the prior art in that a cancellation sound having a phase opposite to that of a sound to be muffled such as noise is emitted from the muffling speaker and the sound is canceled by the canceling action.

By the way, in the case of the present invention, the silencing speaker side space, the intermediate space, and the sub speaker side space are defined by the partition walls.

The silencing speaker radiates a cancel sound from the positive pressure surface to the silencing speaker side space, and simultaneously emits a negative cancel sound having a phase opposite to that of the cancel sound from the negative pressure surface to the intermediate space.

On the other hand, the sub-loudspeaker radiates a sub-cancellation sound having the same phase as the cancellation sound to the intermediate space from one of the positive and negative surfaces, and the sub-cancellation (cancellation sound) having the opposite phase to the sub-speaker side space from the other surface. Emit a negative secondary cancel sound.

Therefore, in the intermediate space, a negative cancel sound from the silencing speaker and a sub-cancel from the sub-cancel sound having the opposite phase to the negative cancel sound are radiated, and a position where both sounds cancel each other to become 0 is generated.

Similarly, both sounds cancel each other out between the sound-suppressing speaker-side space from which the cancellation sound is radiated and the sub-speaker-side space from which the negative sub-cancellation sound of the opposite phase is radiated.
Is generated.

In the present invention, since the monitoring microphone is provided at a position where the sound radiated from both speakers cancels out, the monitoring microphone is not affected by the sound radiated from both speakers. , It is possible to input only the sound to be silenced.

Therefore, it is possible to prevent the occurrence of howling caused by the addition of the original signal and the feedback signal of an integral multiple of 360 °, thereby improving the noise reduction performance.

In addition, since the monitoring microphone may be installed at a position where the sound radiated from both speakers cancels out, if this condition is satisfied, a mute speaker is used to input a sound close to a sound that can be actually canceled by the cancel sound. It is also possible to dispose them in close proximity to each other, so that the silencing performance can be improved.

In addition, since the monitoring microphone is installed at a position separated from the radiation front of the positive pressure surface of the silencing speaker, the sound field of the silencing speaker is not disturbed. The silencing performance in a short high-frequency range can be improved.

Furthermore, in the present invention, the partition walls can block the low-frequency components of the negative cancellation sound, the sub-cancellation sound, and the negative sub-cancellation sound from flowing around the muffler speaker-side space from which the cancellation sound is radiated. Of the present invention can be improved.

(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.
Reference numeral 1 denotes a muffling speaker, 2 denotes a sub-speaker, 3 denotes a monitoring microphone for inputting external noise, and 4 denotes a cancellation sound to the muffling speaker 1 so as to generate a cancellation sound having a phase substantially opposite to the input sound of the monitoring microphone. A noise canceling circuit that outputs a signal e and outputs a sub-cancellation sound generation signal f to the sub-loudspeaker 2 to generate a sub-cancellation sound having a phase opposite to that of the cancellation sound (in phase with the input sound of the monitoring microphone 3). Numerals 5 are partitions provided on the outer periphery of the muffling speaker 1 and the sub-speaker 2.

The silencing speaker 1 includes a housing 1a, a diaphragm 1
b, the coil 1c, and the magnet 1d, and the diaphragm surface 1e is a positive pressure surface, and the diaphragm back surface 1f is a negative pressure surface. 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 and the diaphragm back surface 2f, which are negative pressure surfaces, are provided so as to face each other symmetrically with respect to the plane 2a. 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 use, and the space between the two speakers 1, 2 and the space between the two speakers 1, 2 and the ear cavity E are so-called. A cover in the form of headphones (see FIG. 5,
In FIG. 1, only the inner surface is shown).

The speakers 1 and 2 are fixed to the partition wall 5 and are supported by the cover 6 by the partition wall 5. The space inside the cover 6 is divided by the partition wall 5 into the muffler speaker 1. Of the muffling loudspeaker facing the diaphragm surface 1e, the intermediate space C between the two loudspeakers 1 and 2 and between the housings 1a and 2a, and the sub loudspeaker facing the diaphragm surface 2e of the sub loudspeaker 2. The space D is defined.

The partition 5 is provided with an air vent hole 5a for communicating the intermediate space C and the two speaker-side spaces B and D, and the two speaker-side spaces B and D are located below the two speakers 1 and 2. A communication input hole 5b is formed, and a microphone mounting hole 5c is formed at the center of the input hole 5b and at a position on the symmetry plane A.

The monitoring microphone 3 is connected to the microphone mounting hole 5c.
It is installed in.

The noise canceling circuit 4 is a circuit for forming a canceling sound generation signal e and a sub-cancelling sound generation signal f based on the input sound of the monitoring microphone 3, and includes a preamplifier 4a for pre-amplification and an unnecessary frequency range. And a power amplifier 4c for main amplification, and an inverting circuit 4d for shifting the phase of the input sound by 180 degrees.

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.

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 inverting circuit.
In the sub-speaker 2, a sub-cancellation sound having the same phase as the cancel sound is radiated from the diaphragm back surface 2f, and the sub-cancellation sound is radiated to the diaphragm back surface 1f via the hole 2g of the housing 2a and the hole 1g of the housing 1a. Is configured.

 Next, the operation will be described.

For example, when using under external noise such as in the cockpit of an aircraft, the external noise passes through a cover (not shown), and then is transmitted from the auxiliary speaker side space D or the muffling speaker side space B into the input hole 5b to be monitored. Input to the input 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,
The canceling sound is emitted from the muffling speaker 1 toward the user's ear cavity E, and the external noise transmitted to the user's ear cavity E is canceled out by the canceling effect of the canceling sound a having a phase opposite to that.

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, in the sub-speaker 2, a signal having a phase opposite to that of the muffling speaker 1 is given, that is, a sub-cancellation sound (a) having the same phase as the cancellation sound a is radiated from the rear surface 2f of the diaphragm. A negative sub-cancellation sound (b) having a phase opposite to that of the sub-cancellation sound is emitted from 2e.

Therefore, on the symmetry plane A of the two speakers 1 and 2 where the monitoring microphone 3 is provided, the cancellation sound a from the diaphragm surface 1e of the sound deadening speaker 1 and
The negative sub-cancellation sound (b) from the diaphragm surface 2e of the sub-speaker 2 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, the sound field of the sound deadening speaker 1 is not found because it is arranged on the side surface away from the front surface, so that stable sound deadening performance can be obtained up to a high frequency range.

Further, since the sound deadening speaker side space B, the intermediate space C, and the sub speaker side space D are defined by the partition wall 5, the negative cancel sound b radiated from the diaphragm back surface 1f and the negative cancellation sound b radiated from the diaphragm back surface 2f. The sub-cancellation sound (a) and the low-frequency sound of the negative sub-cancellation sound (b) radiated from the diaphragm surface 2e do not go into the muffling speaker side space B, respectively. For this reason, the output of the cancel sound a in the low frequency range does not decrease due to the canceling action due to the wraparound of the sound in the low frequency range, and stable noise canceling performance can be obtained up to the low frequency range. Note that in the intermediate space C, the negative cancellation sound b radiated from the diaphragm back surface 1f and the sub-cancellation sound (a) radiated from the diaphragm back surface 2f are canceled.

Further, since the monitoring microphone 3 is installed in the input hole 5b close to the side surfaces of the speakers 1 and 2, only the same external noise transmitted to the user's ear cavity E can be input. . 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 sub-speaker 2 for canceling the negative cancel 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, so that sub-cancellation occurs. As the 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.

Further, in the embodiment, since the partition wall 5 is also used as a support member for the speakers 1 and 2, no support member is required,
This also simplifies the configuration.

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

In this embodiment, a microphone mounting hole 25c is formed in the intermediate space C so as to be opened, and the monitoring microphone 3 is installed so as to input a sound in the intermediate space C.
This is an example in which a sound absorbing material 25h is attached to positions facing B, C, and D.
25a is an air vent hole.

Therefore, in the case of the second embodiment, the monitoring microphone 3 inputs an external sound that has passed through both speakers 1 and 2 and entered the intermediate space C from the muffling speaker side space B or the sub speaker side space D. The sounds radiated from the diaphragm back surfaces 1f and 2f of both speakers 1 and 2 cancel each other out because they have opposite phases, and are not input to the monitoring microphone 3.

Further, since the sound is absorbed by the sound absorbing material 25h, irregular reflection of extraneous sound and sound radiated from both speakers 1 and 2 is suppressed, and the noise reduction performance is improved.

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

The third embodiment is an example in which a magnet is shared between the sound deadening speaker 31 and the sub speaker 32.

That is, the magnet 30 is disposed at the center of the intermediate space C supported by the rod 37. And this magnet
Symmetrically across diaphragm 30, diaphragm 1b and diaphragm 2b
Is provided.

Therefore, sound is radiated based on the magnetic field generated by energizing the coils 1c and 2c and the attraction of the magnet 30.

As described above, in the present embodiment, the magnet 30 is shared, so that the distance between the two diaphragms 1b and 2b of the two speakers 31 and 32 can be reduced, and the size can be reduced.

 Next, a fourth embodiment shown in FIG. 5 will be described.

In the figure, reference numeral 6 denotes a cover, which is formed in a bowl shape, provided with a pad 6a on the periphery, and formed with a sound opening 6b having a grill at the bottom (right end in the figure) of the bowl. I have.

The inside of the cover 6 is partitioned by a partition wall 45 into a silencer speaker side space B and a sub speaker side space D.

Then, the sound absorbing material 45h,
6c is pasted.

Further, the monitoring microphone 3 is mounted facing the intermediate space C.

The other configuration is the same as that of the third embodiment, and the description is omitted.

Therefore, in the fourth embodiment, the external sound such as noise mainly enters the auxiliary speaker side space D from the sound passage 6b, passes through both speakers 31, 32, and attempts to reach the ear cavity E. The external sound is canceled by the cancel sound emitted from the muffling speaker 31.

In this case, in the sound absorbing speaker side space B, the sound absorbing materials 45h and 6c provided on the surface of the partition wall 45 and the inner surface of the cover 6 suppress the irregular reflection of the canceling sound and the external sound emitted from the sound deadening speaker 31, thereby improving the sound deadening performance. improves.

In the sub-speaker space D, the negative sub-cancellation sound emitted from the sub-speaker 32 is suppressed from being reflected inward on the inner surface of the cover 6.

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, a headphone type used by a person to be worn on the head and used to remove external negative noise is shown as an example, but the scope of the present invention is not limited to this. Installed in vehicles, 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.

Further, 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.

Further, in the embodiment, the example in which the partition is abutted on the cover to completely define the muffling speaker side space and the sub-speaker side space has been described. That is, the two spaces may not be completely defined, but may be partially defined at the outer peripheral positions of the two speakers.

(Effect of the Invention) As described above, in the active noise canceller of the present invention, it is possible to input only the sound to be silenced without being affected by the sound radiated from both speakers. Accordingly, an effect that the noise reduction performance can be improved can be obtained.

At the same time, it is possible to arrange the monitoring microphone close to the muffling speaker, thereby improving the muffling performance and simplifying the structure by eliminating the need for a feedback circuit or the like. Is obtained.

Moreover, in the present invention, the monitoring microphone does not disturb the sound field of the sound deadening speaker, thereby improving the sound deadening performance particularly in a high frequency range having a short wavelength.

In addition, in the present invention, the partition walls prevent the negative cancel sound, the sub cancel sound, and the negative sub cancel sound from sneaking into the muffler speaker side space, improve the output of the cancel sound in the low frequency range, and improve the output in the low frequency range. The effect that the silencing performance of the can be improved can be obtained.

[Brief description of the drawings]

FIG. 1 is an overall view (partially omitted) showing a configuration of an active noise canceller according to a first embodiment of the present invention, and FIG. 2 is a canceling sound and a negative canceling of a muffling speaker by the active noise canceller according to the first embodiment. FIG. 3 is a characteristic diagram showing sound and external noise, FIG. 3 is a sectional view showing a configuration of a main part of an active noise canceller according to a second embodiment of the present invention, and FIG. FIG. 5 is a sectional view showing a main part of an active noise canceller according to a fourth embodiment of the present invention. B: Silent speaker side space C: Intermediate space D: Sub speaker side space a: Cancel sound b: Sub cancel sound 1: Silent speaker 1e: Diaphragm surface (positive pressure surface) 1f: Back surface of diaphragm ( Negative pressure surface) 2 ... Sub-speaker 2e ... Diaphragm surface (positive pressure surface) 2f ... Diaphragm back surface (negative pressure surface) 3 ... Monitoring microphone 4 ... Noise canceling circuit 5 ... Partition wall 25 ... Partition wall 31 ... Mute Speaker 32 …… Sub speaker 45 …… Partition

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) JP-A-3-86691 (JP) , U) Japanese Utility Model Application Hei 3-86694 (JP, U) Japanese Utility Model Application Hei 3-86695 (JP, U) Japanese Utility Model Application Hei 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 predetermined canceling sound from a positive pressure surface, a sub-speaker provided with one of the positive and negative surfaces facing a negative pressure surface of the muffling speaker, and a sound radiated from both speakers. And a monitoring microphone that is arranged at a position where the noise cancels and inputs a sound to be muffled, and outputs a cancellation sound generation signal to emit a cancellation sound having a phase opposite to that of the input sound of the monitoring microphone from a positive pressure surface of the muffling speaker. A noise canceling circuit that outputs a sub-cancellation sound generation signal so as to radiate a sub-cancellation sound in phase with the cancellation sound from one of the positive and negative surfaces of the sub-speaker; The side silencer side space, the intermediate space between both speakers, and the sub speaker side space on the other side of the positive and negative sides of the sub speaker. An active noise canceller, comprising: