JPH06334727A - Loudspeaker telephone set circuit - Google Patents

Abstract

PURPOSE:To prevent malfunction of the loudspeaker telephone set caused by fluctuation in an output sound pressure resulting from a minimum resonance frequency of a speaker itself with respect to the voice switch type loudspeaker telephone set provided with a microphone and a speaker. CONSTITUTION:The loudspeaker telephone set circuit in which a comparator 6 compares a signal level from a transmission signal detection circuit 9 and that of a reception signal detection circuit 10 and voice switches 4, 5 in an exclusive operation with each other are controlled by the result of comparison by the comparator 6 is provided with an F0 detection circuit 13 whose input is obtained from a connecting point B between a speaker 2 and a speaker resistor 12 and whose output is added to the reception signal detection circuit 10 and a reception signal from a reception amplifier 8 through a route A and a signal resulting from detecting a sound pressure at the point B of the speaker 2 by the detection circuit 13 are inputted to the reception signal detection circuit 10 and its output and a signal from the transmission signal detection circuit 9 in a route C are compared by the comparator 6 to provide a control signal to voice switches at a sender side and a receiver side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice switch type telephone system having a microphone and a speaker. In the operation of the loudspeaker system (or the hands-free phone system) for making a call by using the speaker and the microphone, switching control between transmission and reception is performed by the voice switch circuit. The present invention relates to a voice switch circuit for controlling the operation of the public address telephone device (hands-free telephone device).

Although a loudspeaker system has been put to practical use for a long time, since a speaker and a microphone are housed in the same housing, various acoustic or electrical methods for reducing howling due to acoustic coupling between the speaker and the microphone are used. Improved methods have been devised. Further, it is devised so that the control of switching between transmission and reception of the voice switch circuit is made smooth so that the voice of the transmission or reception is not interrupted.

[0003]

2. Description of the Related Art FIG. 3 shows a block diagram of a conventional public address telephone system. In the figure, 21 is a microphone, 22 is a speaker, 23 is a hybrid circuit, 24 is a voice switch on the transmitting side, 25 is a voice switch on the receiving side, 26 is a comparator, 27
Is a transmission amplifier, 28 is a reception amplifier, 29 is a transmission signal detection circuit, 30 is a reception signal detection circuit, and 31 is a speaker amplifier.

The hybrid circuit 23 is connected to a telephone line to perform 2-line to 4-line conversion, the comparator 26 compares the signal levels of the transmission signal detection circuit 29 and the reception signal detection circuit 30, and the comparison result of the comparator 26 Switching control between the voice switch 24 on the transmitting side and the voice switch 25 on the receiving side is performed.

The voice switch circuit comprises a voice switch 24 on the transmitting side, a voice switch 25 on the receiving side, a comparator 26, a transmitting signal detecting circuit 29 and a receiving signal detecting circuit 30. When the operation state of the public address telephone device is the receiving mode, the receiving signal from the telephone line is emitted from the speaker 22 as the speaker output via the hybrid circuit 23 → the receiving side voice switch 25 → the receiving amplifier 28 → the speaker amplifier 31. It

At this time, a reception signal detection circuit from the reception amplifier 28
Since the reception input signal from the route A to the route 30 is larger than the transmission input signal from the route C from the transmission amplifier 27 to the transmission signal detection circuit 29, the reception side voice switch 25 is controlled by the control signal of the comparator 26. Turn on the voice switch 24 on the transmitting side. As a result, sound is sent from the speaker 22 and the signal from the microphone 21 is not sent to the telephone line.

When the operation of the public address telephone device is in the transmission mode, the transmission signal from the microphone 21 is transmitted to the telephone line via the transmission amplifier 27 → the transmission side voice switch 24 → the hybrid circuit 23. At this time, the transmission input signal from the transmission amplifier 27 to the transmission signal detection circuit 29 from the route C is larger than the reception input signal from the reception amplifier 28 to the reception signal detection circuit 30 from the route A. The voice signal 24 on the transmitting side is turned on and the voice switch 25 on the receiving side is turned off by the control signal. As a result, the sound from the microphone 21 is transmitted and the signal from the speaker 22 is cut off.

Originally, the speaker 22 is designed so that predetermined characteristics (sensitivity and frequency characteristics) can be obtained by housing it in a housing having a sufficient volume. On the other hand, in a general loudspeaker system, a speaker and a microphone are housed in the same housing, so that it is often impossible to secure a sufficient space inside the phone. As a result, the output sound pressure of the speaker rises near the lowest resonance frequency (F0) of the speaker as shown in the frequency characteristics of Fig. 4, and conversely in the middle range (around 1KHz).
In that case, there was a non-uniformity in frequency characteristics that the sound pressure decreased.

[0009]

Therefore, since the frequency characteristic of the received sound pressure varies depending on the lowest resonance frequency of the speaker, the amount of acoustic coupling between the speaker and the microphone also depends on the frequency characteristic of the previous speaker. For this reason, there is a problem that the margin for erroneous operation (switching to transmission during reception) when using the loudspeaker system is also affected by the frequency characteristic of the reception sound pressure of the speaker.

It is an object of the present invention to provide a loudspeaker telephone system circuit which does not deteriorate the margin of the malfunction of the loudspeaker telephone apparatus caused by the non-uniformity of the received sound pressure frequency characteristics.

[0011]

FIG. 1 is a block diagram showing the principle of the present invention. In the figure, 1 is a microphone, 2 is a speaker, 3 is a hybrid circuit, 4 is a voice switch on the transmitting side, 5 is a voice switch on the receiving side, 6 is a comparator, 7
Is a transmission amplifier, 8 is a reception amplifier, 9 is a transmission signal detection circuit, 10 is a reception signal detection circuit, 11 is a speaker amplifier, 12 is a speaker resistance, and 13 is an F0 detection circuit.

The F0 detection circuit 13 uses the connection point B between the speaker 2 and the speaker resistor 12 as an input signal and adds the amplified output to the reception signal detection circuit 10. Received signal detection circuit 10
Inputs the output signal of the reception signal from the reception amplifier 8 (route A) and the output of the F0 detection circuit 13 to the comparator 6 and compares it with the transmission signal (route C) from the transmission signal detection circuit 9. Then, the control signal is sent from the comparator 6 to the voice switches on the transmitting side and the receiving side.

[0013]

[Function] The speaker 2 has the lowest resonance frequency (F0), and the input AC impedance becomes high at this time. Therefore, this change in impedance is electrically detected by the F0 detection circuit 13, and the output is added to the reception signal detection circuit 10. As a result, the change in the output of the speaker 2 becomes one of the control parameters for the voice switch 5 on the receiving side, and more accurate voice switch control can be performed.

FIG. 4 shows the characteristics of the AC input impedance of the speaker and the frequency, and the frequency on the horizontal axis is in the audio frequency range of 300 to 3400 Hz. In the audio frequency range, there is a peak impedance value at the lowest resonance frequency F0, and malfunctions due to howling or blocking easily occur near this frequency.

The F0 detection circuit 13 converts a change in impedance near the lowest resonance frequency (F0) of the speaker 2 into an electric signal, and the electric signal is added to the reception signal detection circuit 10 for controlling the reception side voice switch 5. As a result, the fluctuation of the output sound pressure near the lowest resonance frequency of the speaker alone is used as one of the control signals of the voice switch, and it is possible to prevent a malfunction that tends to occur near this frequency.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows an embodiment of a circuit configuration diagram of the public address telephone device of the present invention. In the figure, the same numbers as in FIG. 1 indicate the same devices. That is, 1 is a microphone, 2 is a speaker, 3 is a hybrid circuit, 4 is a voice switch on the transmitting side, 5 is a voice switch on the receiving side, and the voice switches 4 and 5 are controlled by the comparison result of the comparator 6. It should be noted that the voice switches 4 and 5 perform an antithetical operation and are not turned on at the same time. Reference numeral 7 is a transmitting amplifier, 8 is a receiving amplifier, and 11 is a speaker amplifier. The comparator 6 compares the signal levels of the transmission signal detection circuit 9 and the reception signal detection circuit 10.

For operations other than when the speaker is at the lowest resonance frequency, if the operation state of the loudspeaker system is set to the receiving mode, the receiving signal from the telephone line is the hybrid circuit 3 → the receiving side voice switch 5 → the receiving line as in the conventional case. The signal is emitted from the speaker amplifier 11 as the output of the speaker 2 via the circuit of the amplifier 8 → the speaker amplifier 11.

Since the speaker AC input impedance is low at frequencies other than the lowest resonance frequency of the speaker in the reception mode, the reception signal level at point B is a certain level. At this time, the amplifier of the reception signal detection circuit 10
If the gain of the amplifier A1 of the F0 detection circuit 13 is set so that the output of the amplifier A1 of the F0 detection circuit 13 to be added to A2 is sufficiently lower than the reception input signal from the route A, the output of the reception signal detection circuit 10 becomes The signal of only route A will be output. Therefore, only the route A (received signal) and the route C (transmitted signal) are compared.

As for the operation of the speaker at the lowest resonance frequency, if the operation state of the loudspeaker telephone system is set to the receiving mode, the receiving signal from the telephone line is the hybrid circuit 3 →
The voice switch 5 on the receiving side → the receiving amplifier 8 → the speaker amplifier 11 passes through the circuit of the speaker amplifier 11
Is emitted as the output of.

At the frequency at the lowest resonance frequency of the speaker, the speaker AC input impedance is higher than that at a frequency other than the lowest resonance frequency, and the reception signal level at point B is also high. At this time, the output of the amplifier A2 of the reception signal detection circuit 10 becomes an output obtained by adding the reception signal level input from the route A and the output of the amplifier A1 of the F0 detection circuit 13. (Addition in the same phase) At this time, the output sound pressure from the speaker 2 is in a state of increasing as compared with the non-minimum resonance frequency. As a result of the increase in the sound pressure output from the speaker 2 compared to the case of the non-minimum resonance frequency, the output level of the transmission signal detection circuit 9 generated by the acoustic coupling (α) is proportional to the amount of increase in the sound pressure output from the speaker 2. And increase. If the amount of increase at this time is too large, the output of the transmission signal detection circuit 9 will exceed the output of the reception signal detection circuit 10, resulting in malfunction. (Reversal from the reception mode to the transmission mode) However, the output level of the reception signal detection circuit 10 also increases at the lowest resonance frequency due to the above operation, so that the transmission signal detection circuit generated by acoustic coupling is generated. The increase in the output level of 9 is canceled. Therefore, even if the output sound pressure of the speaker increases at the lowest resonance frequency, the same voice switch characteristics as at the non-minimum resonance frequency can be secured, and no malfunction occurs.

[0021]

EFFECTS OF THE INVENTION It is possible to prevent malfunctions due to an increase in sound pressure at the lowest resonance frequency of a speaker in a loudspeaker system.
The following effects can also be expected. (1) The range of parts that can be selected for the speaker is expanded without being affected by the output sound pressure increase characteristics at the lowest resonance frequency. (Cost reduction effect of parts) (2) No costly mounting method or acoustic consideration to prevent increase of sound pressure at the lowest resonance frequency is required, which enables downsizing of equipment and reduction of design restrictions. To do.

[Brief description of drawings]

FIG. 1 is a block diagram of the principle of the present invention.

FIG. 2 is a circuit configuration diagram of an embodiment.

FIG. 3 is a block diagram of a conventional example.

FIG. 4 Characteristics of AC input impedance and frequency of speaker

[Explanation of symbols]

 1,21 Microphone 2,22 Speaker 3,23 Hybrid circuit 4,24 Transmitting voice switch 5,25 Receiving voice switch 6,26 Comparator 7,27 Transmitting amplifier 8,28 Receiving amplifier 9,29 Transmitting signal detection Circuit 10, 30 Received signal detection circuit 11, 31 Speaker amplifier 12 Speaker resistance 13 F0 detection circuit

Claims (1)

[Claims] 1. A voice on the transmitting side, which compares the signal levels of a transmitting signal detecting circuit (9) and a receiving signal detecting circuit (10) by a comparator (6), and operates in a contradictory manner based on the comparison result of the comparator (6). A voice switch type loudspeaker device circuit including a microphone (1) and a speaker (2) for controlling a switch (4) and a receiving side voice switch (5), a speaker (2), a speaker resistor (12), A circuit for outputting the signal taken from the connection point B of is provided, and the reception signal (route A) from the reception amplifier (8) and the output signal of the F0 detection circuit (13) are added to the reception signal detection circuit (10), The added reception signal and the transmission signal (route C) from the transmission signal detection circuit (9) are compared by the comparator (6), and the control signals for the voice switches on the transmission side and the reception side are transmitted. Features and That loudspeaker telephone device circuitry.