JPH0685541B2 - Loudspeaker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a voice call using a voice switch.
The present invention relates to a device that significantly reduces the feeling of disconnecting a call voice when switching voice switches.

(Prior Art) FIG. 4 is a block diagram for explaining a problem in a voice call. Reference numeral 1 is a microphone, 2 is an amplifier having an amplification factor At for amplifying a microphone output to a rated transmission power, and 3 is 2. Hybrid for line-to-line conversion, 4 is a communication line that attenuates to 1 / K, 5 is an amplifier having an amplification factor K that amplifies received power that is attenuated to 1 / K, and 6 is K by the amplifier 5.
An amplifier having an amplification factor As that gives the speaker a drive power that amplifies the doubled power and listens to the required volume, 7 is a speaker, 8 is the speaker output attenuated to 1 / α The amount of acoustic coupling that indicates that sound is collected,
Reference numeral 9 is the side sound attenuation amount indicating that what is obtained by amplifying the microphone output by At times attenuates to 1 / β and wraps around to the receiving side.
It should be noted that, in the figure, two receiver-type amplifiers are arranged for the purpose of helping understanding of the following description.

It is a well-known fact that in the loud voice communication system of FIG. 4, there exists a near-end Howlin group of loop A and a far-end Howlin group of loop B. The loop gain of these howlin groups is given as follows.

Near-end Howlin Group Gain G _A = K ・ As ・ 1 / α ・ At ・ 1 /
β (1) Far-end Howlin group gain G _B = (At · As · 1 / α) ² …
(2) Actually, howling will occur at G _A or G _B 1, which will hinder the call. Therefore, in order to avoid this, a voice switch is generally used.

FIG. 5 is a block diagram showing a configuration to which a conventional voice switch is applied, where 11 ₁ and 11 ₂ are insertion losses. For example, during transmission, the insertion loss 11 ₁ on the transmitting side is set to zero and the insertion loss 11 ₂ on the receiving side is set to L, so that the near-end howling group gain is set to G _A / L and the far-end howling group gain is set. the _{G B}
It is reduced to / L ² . In the figure, the circuit block for switching the transmission / reception of the insertion loss of the voice switch is omitted.

(Problems to be Solved by the Invention) However, in the device having the above configuration, the loop gain G _A increases in proportion to the loss of the communication line, and the loop gain G _B increases in the communication, as is clear from the equation (1). Does not depend on line loss. In general, the side sound attenuation β is 10 to 15 dB, while the line loss in Japan may exceed 30 dB. In such a case, the insertion loss L of the voice switch required to suppress the near-end howling becomes 15 dB or more. As a result, there is a problem that many people feel disconnection of voice when switching the voice switch. (IEEE Trans.Vol COM-16
[No. 1] (1963) p.163) Therefore, the present invention solves the problems of the above-described technology. When the voice switch is used, the near-end Howlin group is removed and the line loss is eliminated. It is possible to provide a voice communication device with less feeling of voice disconnection by eliminating the need to increase the insertion loss of the voice switch even in the case of a large voice.

(Means for Solving the Problems) In order to solve the above problems, the present invention relates to a loudspeaker call unit for performing a loudspeaker call between two telephone subscribers for transmitting and receiving two subscriber lines respectively. The telephone basic function unit that calls two lines for each line and closes the DC circuit, the line holding function unit that holds the two lines where the DC circuit is closed, and the held two lines respectively It is configured by providing a voice call mode switching unit connected to the transmitting side and the receiving side of the voice call section. The principle of the present invention will be described below with reference to FIG. In the figure, the same reference numerals are assigned to the same functional parts as in FIG. In addition, communication lines 4, 4 ', amplifier 5,
5'is indicated by adding ', because the communication line loss is different due to the difference between one subscriber line and the other subscriber line when two subscriber lines are used. Is the same as that used in the description of FIG. Also, in the figure, the circuit block for switching the transmission / reception of the insertion loss of the voice switch is omitted.

(Operation) With such a configuration, the Howlin group is only the loop B ′ in the figure, and its loop gain G _B ′ is the fourth loop.
It is equal to the far-end Howlin group gain G _B described in the figure.
That is, G _B ′ = G _B = (At · As · 1 / α) ² (3) Therefore, since the gain G _B ′ does not include the amplification factors K and K ′ in the variables, even if the communication line loss increases. However, it is not necessary to increase loss L of the voice switch in proportion to prevent G _B '1.

Next, the magnitude relationship between the gain G _B ′ and the gain G _A will be described.
The reason why the insertion loss of the voice switch can be reduced by the present invention will be described. FIG. 3 shows the gain G _B ′ and the gain G _A.
The relationship between and is illustrated by using As, At, and 1 / as variables. The region in which howling prevention is required is the case where the gain is 1 or more, and therefore the region satisfying G _B ′, G _A 1 will be described below. As is clear from the figure, At ・ As ・ 1 / α
In K / beta> 1 area is 1, in the conventional method it is necessary to suppress the loop gain in the audio switch only G _A corresponds to, for example, l ₁ Since exceeds unity gain, but in this system G _{B '<1}
Therefore, it is not necessary to suppress the loop gain with the voice switch. In the region of At · As · 1 / α1 where K / β> 1, At
When As · 1 / αK / β, in the conventional method, G _A exceeds a gain of 1, so it is necessary to suppress the loop gain by a voice switch corresponding to l ₂ + l ₃ , whereas in this method, G _B ′
Although it exceeds the gain of 1, it suffices to suppress the loop gain with the voice switch only for l ₂ . At / As / 1 /
In the region of α1 and K / β> 1, when At · As · 1 / αK / β, the present method is not more advantageous than the conventional method on the contrary, but this is the reason of the present invention. It does not compromise the benefits. That is, when designing a normal device of this type,
Loop gain l ₃ + l ₂ as much as possible to eliminate voice disconnection during a call
Is designed to be small. Next, the case of K / β1 will be described. In this case, as is apparent from FIG. 3, G _B ′> G _{A in the} region where the gain is 1 or more, but in order to suppress howling, only the voice corresponding to l ₂ that exceeds the gain 1 is used. It is necessary to suppress the loop gain with a switch, but K / β> 1 at all times
The loop gain to be suppressed is smaller than that in the case of. Therefore, in a system designed so that voice disconnection does not occur even with K / β> 1, compared with the insertion loss of the voice switch in the K / β> 1 region, the K / β <1 region (for example, communication line loss A small insertion loss is sufficient for the voice switch inserted to prevent howling due to G _B ′ in a small area). Therefore, the above problems can be eliminated.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the voice communication device of the present invention.

In the figure, 21 and 22 are communication lines, 23 is a basic telephone function unit having a call originating / receiving function, 24 is a changeover switch for switching the communication lines, and 25 is a line holding function unit for holding the communication lines 21 and 22. 26 and 27 are changeover switches for switching the line to the voice call section 29 which will be described later after holding the communication lines 21 and 22, and 28 is the voice call mode for this device by switching the held line to the voice call section 29. A voice call mode switching unit for switching, 29 is a voice call unit with a built-in voice switch, etc.
Is a microphone group, 31 is a microphone mixer amplifier,
32 and 35 are insertion loss circuits, 33 is a line amplifier, 34 is a reception amplifier, 36 is a speaker amplifier, 37 is a speaker, 38 is a transmission / reception signal A and B branched from a transmission / reception channel, and the signals are detected. Is a voice switch control unit that compares the level of the voice switch loss, removes the voice switch loss of the higher level, and inserts the voice switch loss of the lower level.

Next, the operation will be described in steps.

First, the telephone basic function unit 23 is used to call the other party's terminal through the communication line 21, and if there is a response, the line holding function unit 25 switches the changeover switch 24 and holds the communication line 21 using the changeover switch 26. . Next, the telephone basic function unit 23 is used to call the other party's terminal through the communication line 22, and if there is a response, the line holding function unit 25 uses the changeover switch 27 to hold the communication line 22. In this way, when the lines 21 and 22 are put on hold, the basic telephone function unit 23 is disconnected from any of the lines 21 and 22, but this is easily done because it corresponds to the on-hook of a normal telephone.

Now, the communication line 2 held by the line holding function unit 25
1,22 is the voice call section 29 by the voice call mode switching section 28.
Are connected by changeover switches 26 and 27. This switching operation may be performed, for example, by providing a switching button in the voice call mode switching unit 28 and operating it, or automatically immediately after the communication lines 21 and 22 are held by the line holding function unit 25. You can go. In this way communication lines 21,2
When 2 and the voice call unit 29 are connected, a voice call becomes possible.

Next, the operation of the voice call section 29 will be described. The voice of the speaker is collected by the microphone 30 and input to the mixer amplifier 31. The mixer amplifier 31 amplifies the collected sound and outputs it. The output sound of the mixer amplifier 31 passes through the insertion loss circuit 32, is amplified by the line amplifier 33, and is sent to the communication line 21. On the other hand, the reception signal input to the communication line 22 is amplified by the reception amplifier 34, and is received through the insertion loss circuit 35, the speaker amplifier 36, and the speaker 37. At this time, the voice switch control unit 38 sends / receives signals branched from the sending / receiving channel.
Received signals A and B are detected, and the signal level
Small is compared, the voice switch with the higher level is removed, and the voice switch loss is inserted into the lower level.

The above description is for the sender side, but the same applies to the receiver side. That is, when an incoming call is answered, the line holding function unit 25 may hold the communication line in the same manner as on the caller side, and the subsequent operations may be the same as on the caller side.

Further, in this description, the transmission signal is output to the communication line 21 and the reception signal is received via the communication line 22, but it is needless to say that the reverse configuration may be used.

As described above, the present invention can reduce the insertion loss and can significantly reduce the voice disconnection during the voice call.

(Effects of the Invention) As described in detail above, according to the present invention, a voice communication system is configured by using two communication lines. Therefore, one line with a large communication line loss is used for communication. Since the insertion loss can be reduced as compared with the case of configuring a loudspeaker communication system that enables the above, a loudspeaker communication device with less voice disconnection can be realized. Therefore, by applying the present invention to a voice communication device connected to an analog public network in which the communication line loss varies over a wide range depending on the communication distance, it is possible to provide a conference device of high quality voice quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a voice communication device of the present invention, FIG. 2 is an explanatory view of the principle of the present invention, and FIG. 3 is a gain G _B ′.
Is a characteristic curve diagram showing the relationship between the gain G _A and As · At · 1 / α as a variable, FIG. 4 is an explanatory diagram in a voice call, and FIG. 5 is a block diagram of a configuration to which a conventional voice switch is applied. 21,22 …… communication line, 23 …… telephone basic function part, 24,26,27
...... Changeover switch, 25 ...... Line hold function part, 28 ...... Public call mode switching part, 29 ...... Public call part, 30 …… Microphone group, 32,35 …… Insertion loss circuit, 37 …… Speaker, 38
...... Voice switch control unit.

Claims (2)

[Claims] 1. A loudspeaker communication apparatus installed in a subscriber terminal for performing a loudspeaker call between subscribers, each accommodating a plurality of telephone subscriber lines, wherein two lines of the plurality of subscriber lines are respectively transmitted. And a dedicated loudspeaker section for performing a loudspeaker call for reception, a changeover switch connected to each of the two lines and selecting one of the two lines, and a common contact of the changeover switch. Via the line, call the calling subscriber,
A telephone basic function unit that closes a DC circuit for each line according to the response of the other party, two changeover switches to which a common contact is connected to each of the two lines, and the two changeover switches are individually driven. And a line holding function unit for holding the two lines in which the DC circuit is closed, and the other of the changeover switches by driving the two changeover switches in reverse through one of the changeover contacts of the respective changeover switches. Via the switching contact of
A loudspeaker communication device comprising: a loudspeaker call mode switching unit that switches to connect to the transmitting side and the receiving side of the loudspeaker call unit. 2. The loudspeaker unit includes a plurality of microphones, a microphone mixer amplifier that mixes and amplifies respective output signals of the plurality of microphones, and an insertion loss of a voice switch on a transmitting side connected to the amplifier. A circuit, a line amplifier that is connected to the insertion loss circuit, amplifies an output signal of the circuit, and outputs the amplified signal to the transmission-dedicated line, and a reception amplifier that is connected to the reception-dedicated line and amplifies a reception signal, An insertion loss circuit of the voice switch on the receiving side connected to the amplifier, a speaker amplifier connected to the circuit for amplifying the output signal of the circuit, a speaker, and a level difference between the signals on the transmitting side and the receiving side are detected. The voice communication device according to claim 1, further comprising: a voice switch control unit that controls a loss amount of an insertion loss circuit of the two voice switches.