JP2501445B2 - Loud call circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention, in a loudspeaker communication circuit such as a so-called hands-free telephone, describes howling, which occurs when a voice circulates from a receiver such as a microphone to a transmitter such as a speaker, as a communication voice. The present invention relates to a loudspeaker communication circuit that can be prevented without affecting.

[Background Art] This type of public-speaking speech circuit conventionally provided has a configuration including a transmission / reception switching circuit for preventing howling. As shown in FIG. 4, a transmission signal line Lt and a reception signal line are provided. A protection side sound circuit 11 which is arranged between the signal line Lr and branches the signal on the external line L into a transmission signal and a reception signal, a microphone M for receiving the transmission voice, and a transmission signal line Amplifiers OP ₁₁ and OP ₁₂ provided in Lt for amplifying the voice received by the microphone M, and a voice that amplifies the received signal input through the protection side sound circuit 11 provided in the received signal line Lr Amplifiers OP ₁₃ and OP ₁₄ for outputting a signal, and a speaker Sp for outputting a received voice by a voice signal from the amplifier OP ₁₄
And a transmission / reception switching circuit arranged between the transmission signal line Lt and the reception signal line Lr. As shown in the figure, the transmission / reception switching circuit consists of a transmission signal line Lt and a reception signal line.
It is provided with a pair of variable loss elements D ₁ and D ₂ respectively inserted in Lr, and the transmission and reception signals of the transmission signal line Lt and the reception signal line Lr are respectively smoothed by smoothing circuits Rc ₁ and Rc _2. After smoothing, these signal levels are compared by the comparator CO and a level detection signal corresponding to the magnitude relation of the signal levels is output. Diode Dd, resistance R ₂ , capacitor C, resistance
The control circuit 12 including the R ₁ and the inverter Iv controls the transmission loss of the variable loss elements D ₁ and D ₂ in accordance with the level detection signal, so that the transmission signal line having the smaller signal level is transmitted.
Variable loss element inserted in Lt or receiving signal line Lr
The configuration is such that the transmission loss of D ₁ and D ₂ is larger than that of the other. That is, when the other party is talking and the level of the reception signal is higher than the signal level of the transmission signal, the level detection signal of the comparator CO becomes LOW, the point A is LOW, and the variable loss element D ₁
Remains switched off, a loss is added to the transmission signal line Lt, and the reception state is established. On the other hand, when the signal level of the transmission signal is higher than the signal level of the reception signal during transmission, the level detection signal becomes HIGH and the connection point A becomes HIGH according to the time constant of the capacitor C and the resistor R ₁ , The variable loss element D ₂ via the inverter Iv is switched off, and loss is added to the reception signal line Lr to enter the transmission state.

In this way, a transmission loop including the microphone M, which is the receiver, and the speaker Sp, which is the transmitter, that is, the protection sound circuit 11, the amplifier OP ₁₃ , the amplifier OP ₁₄ , the speaker Sp, the microphone M, and the amplifier OP ₁₁ , The amplification factor in the closed loop that reaches the anti-sidephone circuit 11 again via the amplifier OP ₁₂ is set to 1 or less to prevent howling from occurring due to the wraparound of the sound from the speaker Sp to the microphone M. However, in such a system, switching between the receiving state and the transmitting state by the operation switching operation of both variable loss elements D ₁ and D ₂ is not performed well at the beginning or ending of the voice, and the ending of the receiving voice is interrupted, There is a drawback that the head of the transmitted voice is cut off and the transmitted and received voice is adversely affected to prevent howling.

[Object of the Invention] The present invention has been made in view of the above problems,
It is an object of the present invention to provide a loudspeaker communication circuit which does not require a transmission / reception switching circuit and can easily prevent howling without misleading or ending of the ending.

DISCLOSURE OF THE INVENTION A method for preventing howling in a loudspeaker communication circuit according to the present invention is provided between a transmitting signal line and a receiving signal line and an external line to separate a transmitting signal and a receiving signal from each other. A sound circuit, a wave receiving means for receiving the transmitted voice, and a voice for amplifying the voice received by the wave receiving means and for outputting a voice transmitting signal to a protection side sound circuit via a voice transmitting signal line. And a second amplifier for amplifying a reception signal input through the protection side sound circuit and outputting a voice by a speaker, in the loudspeaker communication circuit, the receiving means is the center of the speaker. It is composed of a directional microphone and an omnidirectional microphone that are arranged symmetrically with respect to the axis, and a differential amplifier that outputs the difference between the outputs from the omnidirectional microphone and the directional microphone. The speaker The force voice is equally received by the directional and omnidirectional microphones and canceled by the differential amplifier, and only the voice on the transmitting side input to the omnidirectional microphone becomes the transmitting voice. It is possible to prevent howling without leading and ending of a word due to a switching operation of a variable loss element without using a transmission / reception switching circuit in which a variable loss element is arranged in a signal circuit for receiving a voice.

EXAMPLE As shown in FIG. 1, the loudspeaker circuit of the present invention is arranged between the transmission signal line Lt and the reception signal line Lr and the external line L to separate the transmission signal and the reception signal. For preventing noise, a wave receiving means 2 for receiving the transmitted voice and outputting a signal corresponding to the received voice, and a wave receiving means 2 provided on the transmitted signal line Lt for receiving the wave. A first amplifier OP ₁ that amplifies a voice and outputs a transmission signal, and a first amplifier OP ₁ that is provided in the reception signal line Lr and amplifies the reception signal input from the protection side sound circuit 1 to output the sound by the speaker Sp. Second output audio signal
Amplifier OP ₂ of.

The wave receiving means 2 includes directional and omnidirectional microphones M ₁ and M ₂ embedded in a microphone box B and a first amplifier OP _1.
And a differential amplifier Dop that is provided in the preceding stage and outputs only the difference between the two audio signals by the output of a pair of audio signals from both microphones M ₁ and M ₂ . The pair of microphones M ₁ and M ₂ of the wave receiving means 2 may be similar omnidirectional microphones, and by being embedded in a microphone box B formed in a predetermined shape, one of them is a directional microphone M ₁ , The other is an omnidirectional microphone M ₂ . The microphone box B is the second
As shown in the figure, a recess 6 for embedding _one microphone M ₁ is formed, and the embedded microphone M
_{In the case of 1} , only one surface is exposed on the front surface of the microphone box B as a wave receiving surface, and therefore, it has unidirectionality. Further, the microphone box B, and for embedding the other microphones M _2, to form a cavity 5 extending from the front surface to the rear surface is opened 7,8 formed on the front and rear surfaces, the microphone M ₂ is the cavity 5 Microphone box B is buried inside and the front surface is the receiving surface.
Exposed in front of. The back side of the microphone M ₂ is a cavity 5
The microphone M ₂ is exposed on the rear surface side of the microphone box B through the opening 7 as another receiving surface.
It will have directivity in the front and rear. In this way, the microphone box B in which the pair of microphones M ₁ and M ₂ are embedded
Is installed in front of the speaker Sp vibrating surface, the front surface of the microphone box B faces the speaker Sp vibrating surface, and the receiving surfaces of both microphones M ₁ and M ₂ face the speaker Sp front surface.
By arranging the receiving surfaces of the microphones M ₁ and M ₂ toward the vibration surface of the speaker Sp and symmetrically with respect to the center axis of the speaker Sp, both microphones M ₁ and M ₂ output the sound output from the speaker Sp similarly. It is possible to receive at the voice level.

With such a configuration, the voice of the caller is input only to the omnidirectional microphone M ₂ , and the output voice from the speaker Sp is input to both the directional and omnidirectional microphones M ₁ and M ₂ . Only the speaker Sp voice is erased from the output of the differential amplifier Dop and only the transmitted voice becomes. The operation will be described below.

When the caller makes a voice toward the microphone box B side, the voice of the caller is received only by the omnidirectional microphone M ₂ exposed through the opening 7 on the rear side of the microphone box B, and the other directivity is received. No input to the microphone M ₁ . Therefore, only the voice signal of the caller's voice is input to the differential amplifier Dop, and no voice is input from the directional microphone M _1. Therefore, only the caller's voice is input to the first amplifier OP.
Amplified by ₁ and transmitted as a transmission signal to the other party through the protection side sound circuit 1 and the external line L.

Further, the reception signal input from the other side to the second amplifier OP ₂ via the external line L and the soundproofing sound circuit 1 is amplified and output by the speaker Sp. The voice output from the speaker Sp is simultaneously received by the pair of microphones M ₁ and M ₂ embedded in the microphone box B at the same voice level, and a voice signal of the same shape and at the same time is output by the differential amplifier Do.
entered in p. Therefore, the voice signal of the speaker Sp is not included in the transmission signal from the differential amplifier Dop to the _first amplifier OP ₁ , and the protection side sound circuit 1 and the second amplifier existing in the conventional circuit are present.
The closed loop of howling generation, which reaches OPD 1 again via OP ₂ , speaker Sp, wave receiving means 2, differential amplifier Dop, and first amplifier OP ₁ , is interrupted in differential amplifier Dop. The occurrence of howling formed in the communication device is prevented.

As described in the above embodiment, in the howling prevention method of the present invention, the speaker output sound is equally received by the directional and omnidirectional microphones M ₁ and M ₂ , and is erased by the differential amplifier Dop. Since only the voice on the transmitting side that is input to the directional microphone M ₂ becomes the transmitting voice, there is no use of a transmission / reception switching circuit that arranges a variable loss element as in the conventional case, and there is no beginning or ending disconnection. Howling can be prevented.

Here, in the above embodiment, the shape of the microphone box B having the shape shown in FIG. 2 was used.
The shape of the rear surface side of the cavity portion 5 of B ₁ is a horn shape having a cross-sectional shape as shown in FIG. 3, and this horn H enhances the directivity of the receiving side receiving surface of the omnidirectional microphone M ₂ . The microphone box B ₁ may be used to prevent the output sound of the speaker Sp from wrapping around from the side of the micro box B ₁ to the rear surface and preventing the speaker Sp output from being received by the receiving surface of the receiving side. Alternatively, the characteristics of the microphones M ₁ and M ₂ themselves may be directional and omnidirectional, and a special microphone box or the like may not be used.

[Advantage of the Invention] A method for preventing howling of a loudspeaker communication circuit according to the present invention is provided between a transmission signal line and a reception signal line and an external line to prevent the transmission signal and the reception signal from being separated. A sound circuit, a wave receiving means for receiving the transmitted voice, and a voice for amplifying the voice received by the wave receiving means and for outputting a voice transmitting signal to a protection side sound circuit via a voice transmitting signal line. And a second amplifier for amplifying a received signal input through the protection side sound circuit and outputting the sound by a speaker, in the loudspeaker communication circuit, the receiving means is the center of the speaker. It is composed of a directional microphone and an omnidirectional microphone that are arranged symmetrically with respect to the axis, and a differential amplifier that outputs the difference between the outputs from the omnidirectional microphone and the directional microphone. The speaker The force voice is equally received by the directional and omnidirectional microphones and is erased by the differential amplifier of the wave receiving means, and only the voice on the transmitting side input to the omnidirectional microphone becomes the transmitting voice. It is possible to prevent howling without disconnection of the beginning and the ending of a word due to the switching operation of the variable loss element without using a transmission / reception switching circuit in which a variable loss element is arranged in a signal circuit for transmission and reception.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a structure of a howling prevention system according to an embodiment of the present invention, and FIG. 2 is a partial cross-sectional view showing a state in which a pair of similar microphones M ₁ and M ₂ are embedded in a microphone box B, FIG. 3 is a partial cross-sectional view showing another example of the same microphone box B, and FIG. 4 is a block circuit diagram showing a conventional transmission / reception switching circuit arranged in a loudspeaker communication circuit, and 1 is a protection side. Sound circuit, 2 is a receiving means, Dop is a differential amplifier, L is an external line, Lr is a receiving signal line, Lt is a transmitting signal line, M ₁ is a directional microphone, M ₂ is an omnidirectional microphone, OP
₁ is a first amplifier, OP ₂ is a second amplifier, and Sp is a speaker.

Claims (1)

(57) [Claims] 1. An anti-sidetone circuit arranged between a transmission signal line and a reception signal line and an external line for separating a transmission signal and a reception signal, and for receiving a transmission voice. And a sound receiving means for amplifying the sound received by the wave receiving means and outputting a transmission signal to the protection side sound circuit via the transmission signal line.
And a second amplifier for amplifying a received signal input through the protection side sound circuit and outputting a voice by a speaker, the wave receiving means comprises:
It consists of a directional microphone and an omnidirectional microphone that are arranged symmetrically with respect to the center axis of the speaker, and a differential amplifier that outputs the difference between the outputs of the omnidirectional microphone and the directional microphone. Loudspeaker call circuit.