JPS5828958B2 - Device to cancel acoustic feedback - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical device that is combined with an acoustic device to cancel noise and acoustic feedback.

The device of the invention can be applied to voice-to-voice communication devices, telephone devices, and sound reproduction public address devices.

The acoustic feedback found in these types of devices is due to three main causes.

The first source of direct acoustic feedback is sound that reaches the microphone from the loudspeaker of the device by sending the sound directly into the air.

A second source of conducted acoustic return delay is the associated mechanical equipment, such as the microphone and loudspeaker or housing, and the structures associated with the loudspeaker and microphone transducer, as well as any damage to these parts of the equipment. This is the sound that reaches the diaphragm of the microphone from the loudspeaker as a result of vibrations of the supporting member or stand of the loudspeaker.

Third, there is indirect acoustic return, which is sound that reaches the microphone diaphragm after reflecting from objects such as walls and furniture around the device.

The present invention relates to providing an apparatus and method for canceling noise and acoustic feedback using electrical circuits that handle acoustic feedback arising from all three sources when combined with acoustic means.

Therefore, the present invention includes at least two microphones and one speaker housed in the same housing, and adds and subtracts signals outputted from each of the microphones and consisting of a necessary component and an unnecessary component. 1st
a circuit device; adjusting the phase and amplitude of the addition signal and the subtraction signal output from the first circuit device, and outputting a signal consisting only of the useless component and a signal containing the useless component and the necessary component; a phase/amplitude adjustment circuit, and either a signal output from the at least two microphones or a signal output from the phase/amplitude adjustment circuit and containing a useful component and an unnecessary component, and a signal consisting only of the unnecessary component. combination,
To provide a device for canceling acoustic feedback, which includes a second circuit device for canceling unnecessary components and outputting a signal to the speaker from almost only useful components, and forming a closed loop.

In addition, the present invention separates a noise signal from an electrical signal obtained as an output of a microphone device, and separates a noise signal from an electrical signal obtained as an output of a microphone device.
processing the two signals so as to derive from these two signals two more signals having a phase difference of about 180° and an equal amplitude,
and a device for combining the two other signals to cancel the noise signal, thereby providing a device that provides a stable audible signal substantially free of acoustic feedback noise signals.

Needless to say, said third signal is obtained by combining said first and second signals in such a way as to cancel out the desired components, and thus said third signal is substantially a pure noise signal and/or an echo signal. .

If the first signal and the second signal both have similar necessary components, and those necessary components include unnecessary components whose phases are mutually different and different from the phase of the necessary component, then these signals can be easily offset.

In other words, one signal is shifted in phase by 180°,
The two signals are combined.

Since the inequalities of these unwanted components depend on the sources of the various unwanted components, which may vary from time to time, they can be I can get a signal.

The first and second signals may be obtained by any suitable method.

The invention does not exclude adjusting the phase and/or amplitude of the signals before combining them into the appropriate form.

Next, the desired signal having almost only the above-mentioned input component has the same amplitude as the unnecessary component of the third signal and the third signal, which is necessary to make the unnecessary component of the fourth signal equal in amplitude and opposite in phase After any processing of either or both of the four signals, another combination step is obtained from said fourth signal.

If said first and second signals are as described above, they are conveniently simply added, so that the amplitude of said input component is effectively doubled in said fourth signal, and its combined useless component is always 90° out of phase with the third signal.

Before combining the third and fourth signals, all that is required to obtain the desired output is appropriate amplification or attenuation and this 90° phase shift.

Obviously, said fourth signal can be a completely independent signal obtained from only one of the first and second signals, ie from another microphone.

To create the necessary cancellation of the third and fourth signals, adjustments to the phase or amplitude of either or both are performed before the signals are combined to obtain the desired output signal.

Conventional circuit arrangements are used to effect the necessary phase and amplitude adjustments and the desired combinations of the various signals.

The method and apparatus of the present invention provide an effective means of canceling noise and acoustic feedback from the output of a microphone, and for best results, these electrical devices should be used in the "Microphone" filed by the same applicant on the same date as the present application. in line with the mechanical or physical means disclosed in the patent application entitled ``Apparatus''.

That is, the two said microphones have identical sound-sensitive elements, i.e., mounted adjacently and separately within the housing, in such a way that approximately equal outputs can be created by vibrations of the housing and by random incoming noise and echoes. It is desirable to have a diaphragm.

Direct acoustic feedback also arranges the sound waves propagated from the loudspeaker to travel parallel to both sides of each microphone's diaphragm so that the output due to the movement of each diaphragm has almost no component due to these directly propagated sound waves. minimized by

Furthermore, conducted feedback can be minimized by a laminated or multi-material housing structure, also as described in the above-mentioned co-pending application.

Combining these measures with the circuit of the invention makes it possible to almost completely eliminate all forms of acoustic feedback mentioned above.

It is believed that the present invention will be more easily understood from the following description with reference to the accompanying drawings.

The illustrative circuit arrangement of the invention includes one or more loudspeakers represented by one loudspeaker 12 and a pair of microphones each having one or more microphones represented by one microphone 14 and 16. The device is shown in combination with a transducer device having a device.

The microphone and loudspeaker devices are used in close proximity and are then mounted in a common housing 10 as shown.

The relative positions of the loudspeaker 12 and the microphones 14 and 16 as shown in FIG. It should be stored in such a position that it will

In the apparatus of the invention, the outputs of microphones 14 and 16 are both applied to a summing circuit element 20 and a subtracting circuit element 22, each element being, for example, a transformer or a differential amplifier.

Next, the added and subtracted outputs are outputted to the phase and amplitude adjustment control device 24.
and 24, respectively, and are simply summed or repeatedly summed in another circuit element 26, which can be an amplifier as shown, to provide a further electrical output signal.

The various circuit elements 20-26 are themselves conventional and are preferably adjustable with presetting or control from outside the device.

The output of the device described and the input to the loudspeaker 12 and associated amplifier 28 may be connected to lines connected to similar devices at the remote station, if necessary through a hybrid 30 as shown.

To control the loudspeaker output amplifier 28, an automatic gain control circuit 32 may be included as shown.

The operation of the apparatus shown in FIG. 1 is therefore similar to that shown in FIGS.
As shown in the figure.

Each of the microphones 14 and 16 produces an output as shown in FIGS. 2 and 3, respectively, containing a desired component or signal S of sound produced remotely from the device, such as the voice of a person using the device. .

The signals S in the microphone output are considered to be effectively equal in all respects.

Furthermore, each output includes an unwanted component or noise due to the sound from the loudspeaker.

The noise component N1. N2 differs in phase and amplitude from each other and from the signal S, as shown.

By circuits 20.22, the two microphone outputs are added and subtracted, respectively.

As shown in FIG. 4, the output of circuit 20 is the signal S whose amplitude has been effectively doubled and the components N1. It includes a noise signal N1+2 which is a composite of N2.

From the output of the circuit 22 shown in FIG. 5, there is almost no signal S, but a composite noise N1-2 is present.

In this way, the microphone output is analyzed and components N1-2, representing more or less pure noise, are separated.

Therefore, a signal such as that obtained by either microphone will be free of its noise component if it is suitably processed in phase and amplitude so that the pure noise signal from circuit 22 is equal to this noise component.

The pure noise component mentioned above is actually the noise component N1. N2
and the summed noise signal N1+2, or are of course 90' out of phase with them.

Therefore, signal N1. It can be easily processed so that both N2 and N1+2 are canceled out almost equally.

In the illustrative apparatus, the noise composite signal N1+2 is amplified and 90 degrees
1 and then summed or combined in amplifier 26 with the output of circuit 20 as shown in FIG.

Of course, amplification and phase shifting can be added to or in place of the output of the circuit 20 to produce the output to the amplifier 26 in this desired relationship, with the second circuit 24 shown in FIG. is placed for this purpose between the circuit 20 and the amplifier 26 as shown in FIG.

That is, the amplifier 2 constituting the common microphone output
The output of No. 6 contains almost no components due to loudspeaker noise.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram in block form of an apparatus for carrying out the invention in combination with a converter, and FIGS. 2 to 5 are vector diagrams representing the phases and amplitudes of signals generated in the circuit of FIG. . 12... Loudspeaker, 14.16... Microphone, 10... Housing, 20...
... Addition circuit element, 22 ... Subtraction circuit element, 2
4... Amplitude and phase control device, 26...
・Amplifier, 28...Amplifier, 30...
Hybrid, 32... Automatic gain control circuit.

Claims (1)

[Claims] 1. At least two microphones and one speaker housed in the same housing, and mutual addition and subtraction processing of signals output from the microphones and consisting of a necessary component and an unnecessary component. First thing to do
a circuit device; adjusting the phase and amplitude of the addition signal and the subtraction signal output from the first circuit device, and outputting a signal consisting only of the useless component and a signal containing the useless component and the necessary component; a phase/amplitude adjustment circuit, and either a signal output from the at least two microphones or a signal output from the phase/amplitude adjustment circuit and containing a useful component and an unnecessary component, and a signal consisting only of the unnecessary component. combination,
and a second circuit device configured to cancel unnecessary components and output a signal consisting almost only of useful components to the speaker, and to form a closed loop.