JP2781193B2 - 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 so as 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 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, the monitoring microphone is located at a side position of the muffling speaker, and a canceling sound and a negative pressure surface radiated from a positive pressure surface of the muffling speaker. It is specially positioned at a position where the radiated cancel sound cancels out. It was used as a sign.

(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. .

By the way, the cancel sound radiated from the sound deadening speaker has phases opposite to each other between the sound from the positive pressure surface and the sound from the negative pressure surface of the sound deadening speaker. Therefore, at a position acoustically equidistant from the pressure surface and the suction surface, that is, at the position where the monitoring microphone is provided in the present invention,
Canceling sounds from both the positive pressure and the negative pressure cancel each other out and become zero.

Therefore, when used under external noise, the monitoring microphone ideally receives only the external noise, and this is caused by adding the original signal and the feedback signal of an integral multiple of 360 °. The occurrence of howling can be prevented, and the monitoring microphone does not disturb the sound field of the muffling speaker.

Further, the position where the canceling sound from the positive pressure surface and the negative pressure surface cancel each other to become 0 can be a position close to the sound deadening speaker if acoustically equidistant from both surfaces.

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.

 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, 2 is a monitoring microphone that inputs external noise, and 3 is a canceling sound that is substantially in phase with the input sound of the monitoring microphone. This is a noise canceling circuit that outputs a canceling sound generation signal to the muffling speaker 1 so as to cause the sound to be canceled.

The mute speaker 1 is supported by a housing 1a,
It has a diaphragm 1b, a magnet 1c, and a coil 1d. That is, when the surface 1e of the diaphragm 1b is the positive pressure surface of the muffling speaker 1 and a cancel sound generation signal is given to the coil 1d, the diaphragm 1b generates and emits a cancel sound to the ear cavity E of the user. ing. The space between the diaphragm 1b and the ear cavity E and the muffling speaker 1 are covered with a cover (not shown) in the form of a so-called headphone. The surface 1f of the housing 1a is a negative pressure surface of the muffling speaker 1, and the diaphragm 1b
The sound radiated in the opposite phase to the sound radiated from is emitted.

The monitoring microphone 2 is located at a position close to the side surface of the sound deadening speaker 1, and the canceling sound radiated from the diaphragm surface 1 e (positive pressure surface) of the sound deadening speaker 1 and the cancel sound radiated from the housing surface 1 f (negative pressure surface). It is arranged at a position where the sound is canceled. The position where the monitoring microphone 2 is provided is not limited to the position close to the muffling speaker 1, but is preferably within a distance equal to or less than the diameter of the diaphragm 1b.

The noise canceling circuit 3 shifts the phase of the input sound by 180 degrees, the preamplifier 3b for pre-amplifying the input sound of the monitoring microphone 2, the filter circuit 3c for removing an unnecessary frequency range from the canceling sound, the power amplifier 3d, and the like. Inverting circuit 3
It is formed including e.

 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 2 and the noise canceling circuit 3 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 canceling sound is radiated from the muffling speaker 1, as shown in FIG. 2, the canceling sound a is radiated from the diaphragm surface (positive pressure surface) 1e of the muffling speaker 1 and the housing surface (negative pressure surface) 1f. Thus, the cancel sound b is emitted, and the two cancel sounds ab have opposite phases as shown in the figure. Therefore, at a position where the monitoring microphone 2 is provided, that is, at a position acoustically equidistant from the diaphragm surface (positive pressure surface) 1e and the housing surface (negative pressure surface) 1f, the cancel sound ab from both surfaces 1e.1f. Cancel each other out and become 0.

Accordingly, in the monitoring microphone 2, 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 2 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.

In addition, the monitoring microphone 2 is a mute speaker 1
, 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.

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

In the second embodiment, three muffling speakers 21.21.21 are provided.
This is an example in which the monitor microphones 2 are arranged on the same circumference and attached to the support frame 4, and the monitor microphone 2 is arranged at the center of the circumference. Note that the muffling speaker 21 has a cone as a vibrating membrane.
It shows a type having 21b.

Thus, the number of muffling speakers may be one or more.

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, a mixer for inputting another microphone, an external signal, or the like may be provided in the noise canceling circuit, and a necessary conversation sound, ringing sound, or the like may be output from the muffling speaker.

(Effects of the Invention) As described above, in the active noise canceller of the present invention, the monitoring microphone is placed at the side position of the muffling speaker and the cancellation sound radiated from the positive pressure surface of the muffling speaker. And the cancel sound radiated from the negative pressure surface are arranged at positions where they cancel each other out, so that the following effects can be obtained at the same time.

The monitoring microphone can input only the external noise without inputting the cancel sound, thereby obtaining an effect of preventing howling from occurring and improving the sound deadening performance.

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, and Can be easily 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 perspective view showing a main part of an active noise canceller according to a second embodiment of the present invention. E: Ear cavity 1: Silent speaker 1e: Diaphragm surface (positive pressure surface) 1f: Housing surface (negative pressure surface) 2: Monitor microphone 3: Noise canceling circuit 21: Silent speaker

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04R 3/00 G10K 11/16 H04R 1/10

Claims (1)

(57) [Claims] 1. A mute speaker for generating and radiating a predetermined cancel sound to an ear cavity of a user, a monitor microphone for inputting external noise, and a cancel sound having a phase opposite to the input sound of the monitor microphone. A noise canceling circuit that outputs a canceling sound generation signal to a muffling speaker so as to mitigate the external noise by canceling the canceling sound having a phase opposite to that of the external noise. An active noise sensor, wherein the microphone is disposed at a side position of the muffling speaker, where the canceling sound radiated from the pressure surface and the cancellation sound radiated from the suction surface of the muffling speaker cancel each other. Cancellation.