JPH02224500A - Active noise canceler - Google Patents

Abstract

PURPOSE:To attain stable high noise eliminating performance by providing a bypass equivalent circuit in parallel with a noise eliminating speaker and a monitor microphone and using a subtraction circuit so as to subtract one of two signals being an input signal from the monitor microphone and a bypass signal from the bypass equivalent circuit from the other. CONSTITUTION:A cancel tone generating signal F outputted from a noise cancel circuit 3 is inputted to a parallel bypass equivalent circuit 4. The bypass equivalent circuit 4 gives a signal change equivalent to a signal change (phase lag and gain change) when the cancel tone generating signal reaches a preamplifier 3a from a branch point G via a noise eliminating speaker 1 and the monitor microphone 2 to form a bypass signal H. Thus, when a subtraction circuit 3b subtracts the bypass signal H from the bypass equivalent circuit 4 from the input signal D from the monitor microphone 2, since the component of the cancel tone A included in the input signal D is equivalent to the bypass tone signal H, the component is eliminated completely by the subtraction to prevent production of howling.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an active noise canceller having a function of actively canceling external noise.

(Prior Art) Conventionally, a monitor microphone inputs a synthesized sound of external noise and a canceling sound, a muffling speaker generates a canceling sound, and a canceling sound having an opposite phase to the input sound picked up by the monitor microphone is inputted. An active noise canceller that includes a noise canceling circuit that outputs a cancellation sound generation signal to be generated by a silencer speaker and that cancels external noise by canceling out canceling sound of opposite phase is disclosed in, for example, U.S. Pat. No. 4,455,675. Those described are known.

This active noise canceller forms a closed loop with a monitor microphone, a silencing cancellation circuit, and a silencing speaker, allowing a single microphone to input a synthesized sound of external noise and cancellation sound, and is used for external noise input and feedback. This made it possible to eliminate the need for two microphones.

(Problem to be solved by the invention) However, such conventional active noise
When installing a monitor microphone in a canceller, it is important to ensure that it does not interfere with the vibration of the diaphragm of the monitor microphone or the silencer speaker, or that it is not affected by the magnet of the silencer speaker. In order to arrange the speaker at a position where the intrusion of external noise is not obstructed by the speaker, it is necessary to provide a certain amount of space between the muffling speaker and the monitoring microphone.

For this reason, it takes a certain amount of time for the canceling sound emitted from the muffled speaker to propagate through the air and be input to the monitor microphone. A phase lag occurs between the input cancellation sound and the newly input external noise.

Therefore, in the closed loop as described above, when the phase difference due to such phase delay becomes an integer multiple of 360 degrees, the signals are added and howling occurs, and this howling significantly deteriorates the silencing performance.

The present invention has been made with attention to the above-mentioned problems, and an object of the present invention is to develop an active noise canceller that suppresses the occurrence of howling, provides stable and high sound deadening performance, and has a simple structure. .

(Means for Solving the Problems) In order to solve the above problems, the active noise canceller of the present invention includes a muffling speaker that emits canceling sound into the user's ear cavity, and a synthesis of the canceling sound and external noise. A monitor microphone that inputs sound,
A noise canceling circuit outputs a canceling sound generation signal to a silencing speaker to generate a canceling sound having an opposite phase to the input sound of the monitoring microphone, and external noise is muffled by the canceling action of the canceling sound having an opposite phase. In the active noise canceller, a bypass equivalent circuit is provided which is connected to a noise canceling circuit in parallel with the silencing speaker and the monitoring microphone, and gives an equivalent signal change to the input signal on the silencing speaker and monitoring microphone side, The noise canceling circuit was provided with a subtraction circuit that inputs an input signal from a monitoring microphone and a bypass signal from a bypass equivalent circuit, and subtracts one signal from the other.

(Function) When used under external noise, a canceling sound is emitted from the muffling speaker toward the ear cavity of the user, and the external noise entering the ear cavity is muffled by the canceling effect of the opposite phase of this canceling sound.

That is, the monitoring microphone inputs a synthesized sound of external noise and canceling sound, and outputs a signal indicating this input sound to the noise canceling circuit. Based on this input signal, the noise canceling circuit forms a canceling sound generation signal for emitting a canceling sound having a phase opposite to that of the external noise in the muffling speaker, and outputs it to the muffling speaker. The muffling speaker, which receives this canceling sound generation signal, emits a canceling sound and muffles external noise by canceling out the opposite phase.

By the way, in the noise canceling circuit, a signal is output to the silencing speaker side and a bypass equivalent circuit parallel to the silencing speaker side.

Of these signals, the signal output to the mute speaker side undergoes a predetermined signal change due to, for example, a phase delay occurring while being input from the mute speaker to the monitoring microphone.

On the other hand, the signal output to the bypass equivalent circuit is also given a signal change equivalent to the amount of signal change on the monitor microphone side.

Therefore, in the subtraction circuit of the noise cancellation circuit, the input signal, which is a signal from the monitor microphone and is a composite sound of the cancellation sound and the external noise, in which a predetermined signal change has occurred, and a predetermined ( Two signals are input, a bypass signal with a signal change (equivalent to that on the muted speaker side), and the other signal is subtracted (processed) from one signal.

Therefore, in this subtraction circuit, the remaining signal is a signal indicating only external noise.

As described above, in one aspect of the present invention, the cancellation sound is eliminated by the subtraction circuit and is not circulated, so that it is possible to prevent the occurrence of howling caused by the phase delay that occurs when the cancellation sound is circulated in a closed loop.

(Example) Hereinafter, an example of the present invention will be described based on the drawings. still,
In describing the embodiments, the same reference numerals in each figure indicate the same objects.

First, the configuration will be explained.

FIG. 1 is an overall diagram showing the configuration of an active noise canceller according to a first embodiment of the present invention.

In the figure, ■ is a muffling speaker that generates and radiates a predetermined canceling sound A into the ear cavity E of the user. The space between the muffling speaker I and the ear cavity E is covered with a cover (not shown) shaped like a so-called headphone, and a noise removal space B is formed.

A monitor microphone 2 is provided at the center of the front surface of the silencing speaker 1 where the canceled sound A is emitted.

That is, the monitoring microphone 2 is provided to input the canceling sound A evenly into the noise elimination space B, and to input the external noise C that enters the noise elimination space B from the outside. There is.

The muffling speaker 2 outputs an input signal representing a composite sound of the canceling sound A and the external noise C to the noise canceling circuit 3. This noise canceling circuit 3 forms a canceling sound generation signal F in order to cause the muffling speaker 2 to emit a canceling sound A having a phase opposite to that of the external noise C, and outputs this signal F to the muffling speaker l. As shown in the figure, the circuit includes a preamplifier 3a for preamplification, a subtraction circuit 3b to be described later, a filter circuit 3c for removing a predetermined unnecessary sound, a power amplifier 3d for main amplification, and a circuit for reversing the phase of the signal. (I80° phase delay) Inversion circuit 3
It is composed of e.

Further, a bypass equivalent circuit 4 is connected to the noise canceling circuit 3 in parallel with the muffling speaker 1 and the monitoring microphone 2. This bypass circuit 4
inputs the canceling sound generation signal F, and this signal F
This is a circuit that forms a bypass signal H by giving a signal change equivalent to the signal change on the muffling speaker l and monitoring microphone 2 side to C, gain compensation circuit 4.
a and a delay circuit 4b. That is, while the canceling sound generation signal F passes from the branch point G, passes through the muffling speaker 1, becomes the canceling sound A, and reaches from the monitor microphone 2 to the preamplifier 3a, a phase delay occurs and a gain change occurs at the same time. The gain compensation circuit 4a applies a gain change corresponding to the above gain change to the canceling sound generation signal F, and the delay circuit 4b delays it by one phase delay.

The subtraction circuit 3b performs subtraction by subtracting the bypass signal H passed through the bypass equivalent circuit 4 from the input signal passed through the preamplifier 3a.

Next, the operation of the embodiment will be explained.

When the device of this embodiment is used under external noise C such as inside the cockpit of an aircraft, the monitoring microphone 2
A synthesized sound of cancellation sound A and external noise C in noise removal space B is input. The noise canceling circuit 3 forms a canceling sound generation signal F based on the input signal and outputs it to the muffling speaker l.

Then, the canceling sound A is emitted from the muffling speaker I to the noise removing space B, and the external noise C that has entered the noise removing space B is canceled by the canceling sound A due to its opposite phase and is muffled.

By the way, the canceling sound generation signal F output from the noise canceling circuit 3 is outputted to the muffling speaker l as described above, and at the same time is inputted to the bypass equivalent circuit 4 in parallel thereto.

In this bypass equivalent circuit 4, the cancellation sound generation signal F
The signal change (
The bypass signal H is formed by applying a signal change equivalent to the phase delay or gain change).

Therefore, when the subtraction circuit 3b subtracts the bypass signal H from the bypass equivalent circuit 4 from the input signal from the pie monitor microphone 2, the component of the canceled sound A included in one input signal becomes the bypass signal. H
Because it is equivalent to

This subtraction completely erases the subtraction circuit 3b.
The signal passing through becomes a component of only external noise C.

Expressing this in the formula, D = f' fAl + δ (s-,) + f
Ic) −・・■H= f tAl +δ (, −
1-...■,', D-H= f (C1...■
However, f(Al is a signal indicating cancellation sound A.

δ(,, l is a phase and gain change component of the canceling sound A, and f fcl is a signal indicating the external noise C.

As described above, in this embodiment, the canceling sound A is canceled by the subtracting circuit 3b and is not circulated through the noise canceling circuit 3 including the muffling speaker 1 and the monitoring microphone 2, so that the canceling sound A does not pass through the closed loop. This can prevent the occurrence of howling caused by phase lag that occurs during circulation.

Therefore, it is possible to prevent the occurrence of howling and to obtain stable silencing performance.

Furthermore, phase delays and gain changes that occur while the canceling sound A reaches the monitor microphone 2 from the muffling speaker 1 are completely eliminated by the action of the bypass equivalent circuit 4 and the subtraction circuit 3b. When determining the installation position, the position is not restricted due to this phase delay or gain change, and the effect is that the degree of freedom in the arrangement of the monitoring microphone 2 is improved.

Next, an active noise canceller according to a second embodiment of the present invention shown in FIG. 2 will be explained.

The second embodiment differs from the first embodiment in that the signal input to the bypass equivalent circuit 24 is performed before the inversion circuit 3e in the noise canceling circuit 3. Therefore, the bypass equivalent circuit 24 is configured to include an inversion circuit 24a.

Note that the first function and effect is the same as that of the first embodiment, so the explanation thereof will be omitted.

Next, an active noise canceller according to a third embodiment of the present invention shown in FIG. 3 will be explained.

This third embodiment differs from the first embodiment in the configuration of the noise canceling circuit 33.

That is, the subtraction circuit 33b subtracts the input signal H from the bypass signal H, contrary to the first embodiment.

Therefore, the component of the external noise C in the input signal H becomes negative upon passing through the subtraction circuit 33b, that is, its phase is reversed.

Therefore, there is no need to provide the inverting circuit 3e of the first embodiment in the noise canceling circuit 33, and the effect of simplifying the configuration can be obtained.

Next, an active noise canceller according to a fourth embodiment of the present invention shown in FIG. 4 will be described.

This fourth embodiment is an improved example of the third embodiment.
In addition to the configuration of the embodiment, the noise canceling circuit 43 is provided with a prefilter circuit 43a, a mixer circuit 43b, and a main filter circuit 43c.

An external signal J is input to the mixer circuit 43b. That is, the silencer speaker 1 can output an external signal J such as a special signal such as an external radio or emergency signal or a necessary monitor sound.

Next, an active noise canceller according to a fifth embodiment of the present invention shown in FIG. 5 will be explained.

This embodiment has a mixer circuit 43b compared to the fourth embodiment.
The difference is that a signal from an external microphone 51 is input.

Note that a preamplifier 52 and a prefilter circuit 53 are provided between the external microphone 51 and the mixer circuit 43b.

Therefore, the input sound from the external microphone 51 can be output from the muffling speaker l.

That is, for example, it becomes possible to output the conversation sounds of fellow passengers from the muffled speaker l in the cockpit of an airplane.

Although the embodiment has been described above based on the drawings, the specific configuration is not limited to this embodiment, and even if there is a design change, etc. within the scope of the gist of the present invention, it is included in the present invention. .

For example, the position where the monitoring microphone is provided is not limited to the central position in the front surface of the canceling sound emission of the muffling speaker.

(Effects of the Invention) As explained above, in the active noise canceller of the present invention, a bypass equivalent circuit is provided in parallel with the silencing speaker and the monitoring microphone, and the subtraction circuit further includes a bypass equivalent circuit in parallel with the silencing speaker and the monitoring microphone. Two input signals and a bypass signal from the bypass equivalent circuit
By subtracting one of the two signals from the other,
The noise canceling circuit can eliminate the canceling sound component from the input signal to produce a signal containing only the external noise component. Therefore, it is possible to prevent howling from occurring due to the components of the canceling sound circulating in a closed loop. This produces the effect that stable and high silencing performance can be obtained.

In addition, as described above, the bypass equivalent circuit can eliminate the phase delay between the muffling speaker and the monitor microphone, so that the degree of freedom in installing the monitor microphone can be improved.

[Brief explanation of the drawing]

FIG. 1 is an overall view showing the configuration of an active noise canceller according to the first embodiment of the present invention, FIG. 2 is an overall view showing the active noise canceller according to the second embodiment, and FIG. 3 is an overall view showing the active noise canceller according to the second embodiment.・An overall view showing the noise canceller, FIG. 4 is an overall view showing the active noise canceller of the fourth embodiment, and FIG. 5 is an overall view showing the active noise canceller of the fifth embodiment.
FIG. 2 is an overall diagram showing a noise canceller. 33b...-Subtraction circuit 4...Bypass equivalent circuit 24...Bypass equivalent circuit

Claims (1)

[Scope of Claims] 1) A muffling speaker that emits a canceling sound into the user's ear cavity, a monitoring microphone that inputs a synthesized sound of the canceling sound and external noise, and an input sound of the monitoring microphone. In an active noise canceller, the active noise canceler is equipped with a noise canceling circuit that outputs a canceling sound generation signal to a silencing speaker to generate a canceling sound of an opposite phase, and is configured to muffle external noise by canceling the canceling sound of an opposite phase. A bypass equivalent circuit is provided which is connected to a noise canceling circuit in parallel with the silencing speaker and the monitoring microphone and gives an equivalent signal change to the input signal on the silencing speaker and monitoring microphone side, and the monitoring microphone is connected to the noise canceling circuit. An active noise canceller characterized in that it is provided with a subtraction circuit that inputs an input signal from a bypass equivalent circuit and a bypass signal from a bypass equivalent circuit, and subtracts one signal from the other.