JPH0456499A - Active noise canceler - Google Patents

Abstract

PURPOSE:To omit the trouble of a switch operation and to reduce energy consumption by providing a condition setting circuit for prohibiting the output of a cancel sound generating signal and an auxiliary cancel sound generating signal to a noise cancel circuit when set sound information cannot be obtained. CONSTITUTION:A condition setting circuit 4a interrupts a signal from a pre- amplifier 4c when the sound pressure level of a input signal (g) obtained through the pre-amprifier 4c is under a set level, and the circuit 4a makes the signal (g) pass to a filter circuit 4d side when the sound pressure level of the singal (g) exceeds the set level. Thus, on the occasion that the noise cancel circuit executes a muffling operation for outputting the cancel sound generating signal and the auxiliary cancel sound ganerating signal, when a sound to be muffled is inputted, the muffling operation is automatically executed, and in other cases the operation is stopped, so there is no trouble of an ON/OFF operation and it is possible to contrive to save energy.

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, active noise cancellers such as those described in US Pat. No. 44,556'75 are known. This active noise canceller outputs a canceling sound that is in the opposite phase to the input sound from the monitoring microphone from a silencing speaker, and cancels the external noise by canceling the external noise and the canceling sound.

However, according to this conventional technique, there is a problem in that it is difficult to input the canceling sound evenly and to install a monitoring microphone so as not to disturb the sound field of the canceling sound.

Moreover, since the monitoring microphone needs to input external noise, it is necessary to provide a certain distance from the muffling speaker, which causes a problem of phase lag and howling.

Therefore, the applicant of the present application proposed an active noise canceller (hereinafter referred to as prior art) described in Japanese Patent Application No. 1-44790 as a means to solve the above conventional problems with a simple control circuit that does not require feedback control. ) was proposed.

This prior art is equipped with a sub-speaker that emits a sub-cancelling sound having the same phase as the canceling sound on the negative pressure surface of the muffling speaker, and a sound (negative canceling sound) having an opposite phase to the canceling sound emitted from the negative pressure surface of the muffling speaker. ) and the sub-cancellation sound cancel each other out.
Only external noise is input to the monitor microphone.

(Problem to be Solved by the Invention) In the above-mentioned prior art, when canceling external sounds such as noise and stopping canceling, the switch is set to 0N-
It requires an OFF operation, which is cumbersome to operate.

There is also the problem that if the cancellation operation is always performed, the power consumption increases.

The present invention was made with attention to the above-mentioned problems, and the objective is to develop an active noise canceller that can eliminate the troublesome operation of switches and reduce power consumption to save energy. do.

(Means for Solving the Problems) The active noise canceller of the present invention outputs a canceling sound generation signal and a sub-cancelling sound generation signal when the input sound from the monitor microphone indicates preset sound information. The above problem is solved by providing the noise canceling circuit with a condition setting circuit that allows the operation and prohibits the output of both generated signals when the set sound information cannot be obtained.

That is, the active noise canceller of the present invention includes a silencing speaker that emits a predetermined canceling sound from one positive and negative side toward a space to be silenced, and a silencing speaker that radiates a predetermined canceling sound from one positive and negative side toward the other side of the silencing speaker. A sub-speaker that emits sub-cancelled sound in phase, a monitoring microphone placed at a position where the sounds emitted from both speakers cancel each other out, and a speaker that mutes canceling sound that is in opposite phase to the input sound from the monitor microphone. outputs a canceling sound generation signal to be emitted from one surface of the silencing speaker, and outputs a sub-cancelling sound generating signal to cause the sub-speaker to emit a sub-cancelling sound having the same phase as the canceling sound from the sub-speaker to the other surface of the silencing speaker. a noise canceling circuit; and a noise canceling circuit provided in the noise canceling circuit to enable and set an operation of outputting a canceling sound generation signal and a sub-cancelling sound generation signal when the input sound from the monitor microphone indicates preset sound information. A condition setting circuit is provided that prohibits the output of both generated signals when the generated sound information cannot be obtained.

(Function) When performing sound muffling, based on the sound input from the monitor microphone, a canceling sound is emitted from the muffling speaker toward the space to be muffled.

Therefore, in the muffling target space, the extraneous sound is canceled by the canceling sound having the opposite phase.

In addition, the monitoring microphone is placed in a position where the sounds from both speakers are canceled out. In other words, in this position, the canceled sound is emitted from one side of the muffling speaker, and the canceled sound is emitted from the other side. Negative cancellation sound with a phase opposite to that of the cancellation sound is emitted from the positive and negative sides of the sub speaker, respectively (negative side canceller) and sub cancellation sound (=cancellation sound) This cancels out the sound from both speakers, and only external sound can be input.

By the way, in the present invention, the above-mentioned silencing of external sounds is performed by
This is done when the external sound input from the monitor microphone in the condition setting circuit indicates the set sound information.

In other words, if the sound pressure of the external sound is above the setting, the frequency of the external sound is above the setting frequency, or conversely, it is below the setting frequency, the width of the setting frequency, or the setting waveform. In the noise canceling circuit, the above-described canceling sound generation signal and sub-cancelling sound generation signal are outputted.

Because of this, when the input sound from the monitor microphone does not indicate the set sound information, the noise canceling circuit does not output both generation signals, and in this case, no power is consumed.

Further, ON-OFF operation of the device is not necessary.

(Example) Embodiments of the present invention will be described below based on the drawings.

First, I will explain the configuration.

FIG. 1 is an overall view showing the configuration of an active noise canceller according to an embodiment of the present invention. In the figure, 1 is a muffling speaker that generates and radiates a predetermined canceling sound into the user's ear cavity E, and 2 is a muffling speaker. 3 is a monitor microphone for inputting external sound A; 4 is the muffling speaker 1;
A noise canceling circuit outputs a canceling sound generation signal a to the sub speaker 2 and a sub canceling sound generating signal a to the sub speaker 2, 5 is a partition wall, and 6 is a cover.

The muffling speaker 1 includes a diaphragm Ib, a coil Ic, and a magnet 1d. When the coil 1c is energized, it attracts the magnet 1d and the diaphragm 1b.
The diaphragm surface 1e is a positive pressure surface, and the diaphragm back surface 1f is a negative pressure surface.

The sub speaker 2 is the same speaker as the muffling speaker 1, that is, an acoustically equivalent speaker, and includes a diaphragm 2b, a coil 2c, and a magnet 2d, with the diaphragm surface 2e being a positive pressure surface, and the diaphragm surface 2e being a positive pressure surface. The back surface 2f is a negative pressure surface.

The partition wall 5 defines the interior of the headphone-shaped cover 6 into a sound deadening space B and an extraneous sound side space C, and supports both speakers 1.2. This support structure supports both speakers 1.2 symmetrically at the center of the partition wall 5, and
The structure is such that an intermediate chamber is formed between both speakers 1 and 2.

Incidentally, the partition wall 5 is formed with a communication hole 5a that communicates the intermediate chamber and the external sound side space C.

The monitor microphone 3 is attached to an attachment hole 5b formed in the partition wall 5 at a lower position between both speakers 1.2.

The monitor microphone 3 and both speakers 1.2 are
It is connected to the noise canceling circuit 4. That is, the noise canceling circuit 4 causes both the speakers 1 and 2 to emit a canceling sound 81 and a sub-cancelling sound s2 based on the sound input from the monitor microphone 3, and includes a preamplifier 4c and a condition setting circuit 4a. , filter circuit 4
d.

It has a power amplifier 4e and an inversion circuit 4f.

The preamplifier 4c receives a signal from the monitor microphone 3 and preamplifies this input signal.

The filter circuit 4d removes unnecessary frequency ranges from the canceling sound from the signal that has passed through the preamplifier 4c and is obtained through the condition setting circuit 4. In other words, the filter circuit 4d removes unnecessary frequency ranges from the canceled sound that cannot be output from both speakers 1 and 2. Configured to filter out sounds in a frequency range.

The power amplifier 4e mainly amplifies the signal that has passed through the filter circuit 4d so that the sound pressure of the canceling sound s1, which will be described later, is equal to that of the external sound A.

The inverting circuit 4f is a circuit that shifts the phase of the signal from the power amplifier 4c by 180 degrees and outputs the signal to the silencing speaker 1.

The condition setting circuit 4a passes the signal to the filter circuit 4d when the sound pressure of the input sound indicated by the signal passing through the preamplifier 4c is above a predetermined level, and cuts the signal when it is below a predetermined level. It is.

The circuit diagram of FIG. 2 shows the configuration of this condition setting circuit, and the symbols ``■'' and ``■'' correspond to those in FIG. 1.

Partly, this condition setting circuit 4a includes operational amplifiers 41 and 42.
,43. As shown in FIG. 3, the sound pressure level of the input signal 9 obtained through the preamplifier 4c is set to the set level 1.
If the value is less than 1, the relay switch 45 is open and the signal from the preamplifier 4c is cut off. As shown in FIG. 4, when the sound pressure level of the human input signal 9 exceeds the set level h, the relay switch 45 is closed and the input signal 9 is passed to the filter circuit 4d side. , a cancellation sound generation signal a, and a sub-cancellation sound generation signal S are generated.

Next, the effect will be explained.

For example, when it is desired to prevent the user from hearing the external noise in a factory or the like where intermittent noise is generated, the device of this embodiment is used by placing it in the ear cavity E as shown in the figure.

The operation at this time will be briefly explained.

First, monitor microphone 3 is connected to external sound (external noise).
A is input, converted into an electrical signal, and input to the noise canceling circuit 4.

After this signal is preamplified by the preamplifier 4c, it is determined in the condition setting circuit 4a whether the sound pressure level of the input signal 9 is equal to or higher than the set level 1, and the sound pressure level exceeds the set level h. is transmitted to the filter circuit 4d only when it is input.

When the signal is transmitted to the filter circuit 4d in this way, this signal is amplified and filtered to generate a canceling sound, which is a signal whose phase is reversed from that of the external sound A, to the muffling speaker 1. On the other hand, a sub-cancelling sound generation signal S, which is a signal having the same phase as the external sound A, is output to the sub-speaker 2.

Therefore, from the muffling speaker 1, a canceling sound s1 having an opposite phase to that of the external sound A is emitted toward the muffling space B, and in this muffling space, the external sound A is canceled by the canceling sound s1 having an opposite phase. received and muted.

When the sound pressure level of the input signal 9 stops generating such a large noise that it exceeds the set level h, the condition setting circuit 4
The relay switch 44 a is opened to cut off the input signal 9, and the generation of the cancellation sound generation signal a and the sub-cancellation sound generation signal S is stopped.

Therefore, since there is no loud noise and there is no cancellation effect, it is possible to have a conversation.

By the way, when the canceling sound $1 is emitted from the muffling speaker 1, a negative canceling sound t1 having an opposite phase to the canceling sound s1 is emitted from the back surface 1f of the diaphragm, which is a negative pressure surface.

On the other hand, the sub-speaker 2 is given a sub-cancellation sound generation signal a which has an opposite phase to the cancellation sound generation signal a.
That is, a sub-cancelling sound s2 having the same phase as the canceling sound s1 is emitted from the diaphragm back surface 2f toward the muffling speaker 1, and a sub-cancelling sound s1 (=cancelling sound s) is emitted from the diaphragm surface 2e toward the extraneous sound side space C.
2), a negative side cancellation stage t2 (=negative cancellation sound t1) having an opposite phase is emitted.

Therefore, in the intermediate room between both speakers 1.2, the negative canceling sound t1 emitted from the muffling speaker 1 and the sub-cancelling sound s2 emitted from the sub-speaker 2 are canceled because they are in opposite phases. In the monitoring microphone 3, the sounds from both the speakers 1 and 2 are not input, and only the external sound A can be input.

Although the embodiment has been described above based on the drawings, the specific configuration is not attached to this embodiment.

For example, in the embodiment, the sound pressure of the input sound is shown as the sound information preset in the condition setting circuit, but the frequency or waveform of the sound may also be set.

In other words, if you want to mute only certain high-pitched noises or low-pitched noises, but not mute intermediate frequencies such as conversation sounds, you can install a bypass filter, low-pass filter, etc. in the condition setting circuit, and use this filter. Only when the signal passes,
It may be configured to allow the signal to pass through and form a canceling sound generation signal and a sub-cancelling sound generation signal.

Further, if it is desired to mute only a predetermined sound, the waveform thereof may be set and the configuration may be such that the signal is passed only when a signal of that waveform is input.

In addition, in the embodiment, the diaphragm + of both speakers 1.2
An example is shown in which the positive pressure surfaces 1e and 2e of b and 2b are placed facing the silencing target space B and the extraneous sound side space C. Good too.

(Effects of the Invention) As explained above, in the Acti7 noise canceller of the present invention, when the input sound from the monitor microphone indicates preset sound information, the cancel sound generation signal and the sub The noise cancellation circuit is configured to include a condition setting circuit that allows the operation to output the cancellation sound generation signal and prohibits the output of both generation signals when the set sound information cannot be obtained. When performing the muting operation that outputs the canceling sound generation signal and the sub-cancelling sound generation signal, the muting operation is automatically performed when the sound to be muted is input without performing an ON/OFF operation, and is activated at other times. Since it is stopped, there is no need for troublesome ON/FF operations, and there is no unnecessary power consumption, resulting in the effect that energy can be saved.

[Brief explanation of the drawing]

Fig. 1 is an overall diagram showing the configuration of the Acti7 noise canceller according to the embodiment of the present invention, Fig. 2 is a circuit diagram showing the main parts of the embodiment, and Figs. 3 and 4 are the input sound level and set level. This is Kula 7, which shows the relationship with 1... Silence speaker 1e... Diaphragm surface (positive pressure side) 1f - Diaphragm back side (negative pressure side) 2... Sub-speaker 3... Monitor microphone 4... Noise canceling circuit 4 days...・Condition setting circuit a...Cancellation sound generation signal b...-Sub-cancellation sound generation signal sl...-Cancellation sound s2...Sub-cancellation sound 2nd figure 41, 42, 43... Operational amplifier 44... Transistor 45...Relay inch

Claims (1)

[Scope of Claims] 1) A silencing speaker that radiates a predetermined canceling sound from one positive and negative surface toward a space to be silenced, and a sub-cancellation having the same phase as the canceling sound toward the other positive and negative surface of the silencing speaker. A sub-speaker that emits sound, a monitoring microphone placed at a position where the sounds emitted from both speakers cancel each other out, and a canceling sound that is in the opposite phase to the input sound from the monitoring microphone is placed on one side of the silencing speaker. a noise canceling circuit that outputs a canceling sound generation signal to be emitted from the sub-speaker, and outputs a sub-cancelling sound generating signal to cause the sub-speaker to emit a sub-cancelling sound having the same phase as the canceling sound from the sub-speaker to the other surface of the silencing speaker; , which is provided in the noise canceling circuit and allows an operation of outputting a canceling sound generation signal and a sub-cancelling sound generation signal when the input sound from the monitor microphone indicates preset sound information, and outputs a canceling sound generation signal and a sub-cancelling sound generation signal, and the set sound information. An active noise canceller characterized by comprising: a condition setting circuit that prohibits output of both generated signals when the above cannot be obtained;