JPH0217981B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a loudspeaker system such as a loudspeaker telephone, and more specifically, to the problem of deterioration of speech quality due to acoustic coupling between a loudspeaker and a handset and the rotation of side sound protection circuits, and abnormal oscillation (howling) caused by a closed-loop loop. ) Regarding a public address system that prevents

In conventional loudspeaker systems, various audio switches are used to prevent abnormal oscillations caused by the formation of a round loop due to acoustic coupling between the loudspeaker and the transmitter. In a device using this audio switch circuit, the level of the transmitting audio signal and the receiving audio signal are compared, and if the level on the transmitter side is high, it is sent to the receiving side, and if the level on the receiver side is high, it is sent to the sending side. Howling is prevented by suppressing the amount of loss. As a result, the level may pulsate, and if the device is a public address telephone and both parties are talking, the end or beginning of a sentence may be cut off. The only thing left to do was to prevent howling.

An object of the present invention is to provide a public address system that can prevent the aforementioned deterioration of speech quality and prevent abnormal oscillations in a single loop.

In order to achieve the above object, the anti-echo loudspeaker according to the present invention is a loudspeaker having an acousto-electrical transducer and an electro-acoustic transducer, which has a certain frequency spread on the drive side of the electro-acoustic transducer, and has a receiving transmission line. The degree of acoustic coupling is detected by constantly adding a reference signal having a lower level than the audio signal and extracting the reference signal that has been routed to the acoustoelectric transducer, and comparing this extracted signal with the added reference signal. ,
A signal equivalent to a loop signal is created from the received signal of the electroacoustic transducer according to the degree of acoustic coupling, and a signal equivalent to the loop signal created at that time is subtracted from the acoustoelectric transducer. It is structured as follows.

According to the above configuration, good communication can be made and the object of the present invention is completely achieved.

Hereinafter, the present invention will be explained in more detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a loudspeaker according to the present invention. In the figure, A is the receiving side, and the signal input from the receiving terminal 7 is sent to the amplifiers 8 and 9.
is amplified by the speaker 2, which is an electroacoustic transducer.
is output by Reference numeral B denotes a transmitting side, and the voice inputted from the microphone, which is an acousto-electrical transducer, is sent out from the transmitting terminal via amplifiers 4 and 5. 10 is a reference signal generator which generates a signal (such as background music) having a certain frequency spread. A detector 11 extracts a reference signal included in the transmitted signal from the transmitting side. A comparator 12 compares the amplitude and phase of the reference signal from the reference signal generator 10 and the output of the detector 11. 13 is a delay circuit which delays the signal taken out from the receiving side. 14 is a tap gain adjuster, and the tap output signal is adjusted by the output of the comparator 12.

A signal from the reference signal generation circuit 10 is always added to the receiving side, and is output from the speaker 2 as a sound wave. This sound travels through the air 3 to the microphone 1. The signal thus transmitted is extracted by a detector 11, and compared in amplitude and phase by a comparator 12. Based on the comparison result, the tap gain adjuster 14 is controlled, the tap output signal of the delay circuit 13 is adjusted, and the signal corresponding to the wrap-around characteristic is eliminated. Although the above example deals with controlling the tap gain of the delay circuit, it can also be realized by using an adaptive filter instead and controlling the characteristics.

The present invention constantly controls output and input coupling characteristics with high precision. For example, by constantly sending a reference signal such as music that is not unpleasant even if it is generated as a sound at a lower level than the audio signal, and extracting the reference signal that has passed to the input side from among other signals. , the bond state is detected with high accuracy. Depending on the detection result, a signal having output and input coupling characteristics is always created with high precision using, for example, a delay circuit with a tap (transversal filter), and the loop signal is eliminated.

In conventional examples where a public address system is used in a public address telephone, howling is prevented by controlling a voice switch using a conventional voice detection method.

However, according to the present invention, since the degree of coupling from the loudspeaker to the transmitter is always detected and the loop is controlled from the signal, it is possible to have a natural conversation. Abnormal oscillation is prevented.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of an anti-reverberation loudspeaker system according to the present invention. 1... Acoustoelectric transducer (microphone), 2... Electroacoustic transducer (speaker), 3... Sound transmission space, 4, 5,
8, 9... Amplifier, 6... Sending terminal, 7... Receiving terminal,
10...Reference signal generator, 11...Detector, 12...Comparator, 13...Delay circuit, 14...Tap gain adjuster.

Claims (1)

[Claims] 1. In a public address system having an acousto-electric transducer and an electro-acoustic transducer, a reference signal having a certain frequency spread and having a lower level than the audio signal on the reception transmission path is always added to the electro-acoustic transducer driving side. The degree of acoustic coupling is detected by extracting the reference signal that has passed into the acousto-electrical transducer and comparing the extracted signal with the added reference signal, and the reception of the electro-acoustic transducer is determined according to the degree of acoustic coupling. A loudspeaker for preventing echoes, characterized in that a signal equivalent to a loop signal is created from the signal, and a signal equivalent to the loop signal created at that time is subtracted from the signal on the acoustoelectric transducer side. Device.