JPH08107596A - Amplifier for microphone, microphone device and public address broadcasting system - Google Patents

Abstract

PURPOSE: To obtain a public address sound with satisfactory sound quality by reducing a proper resonance sound and to expand a howling margin by employing a filter provided with a specific band elimination center frequency as a band elimination filter connected to the output side of an amplifier. CONSTITUTION: An audio signal from a microphone 2 is supplied to a bridged T-type band elimination filter 5 whose band elimination center frequency is around 1.2kHz (for example, 0.9 to 5kHz) and also, whose Q is around 2 (for example, 1.4 to 2.6) via a two-stage directly connected amplifier 3 for low frequency amplification whose voltage gain Gv is 4.63≈13.3dB. The enhancement of a frequency component in the neighborhood of 1.2kHz can be suppressed by setting the Q of the filter 5 at such value, and the sound quality of the public address sound in the public address sound broadcasting system can be improved, and the occurrence of howling can be suppressed in advance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone amplifying device, a microphone device and a loudspeaker broadcasting device.

[0002]

2. Description of the Related Art Conventionally, there is a loudspeaker broadcasting system using a wireless microphone. This is a system in which radio waves from a wireless microphone are received by a receiver to obtain a voice signal, the voice signal is amplified and supplied to a speaker so that a large number of people can hear the loud sound.

[0003]

The conventional loudspeaker broadcasting system is not limited to wired and wireless systems, but acoustic feedback loops are a problem. This is a loop in which a voice signal from a microphone is amplified, supplied to a speaker and emitted, and the emitted sound is returned to the microphone. In this case, an audio attenuator is assumed between the speaker and the microphone, and if the amount of attenuation of the audio attenuator is small or the sound pressure of the sound emitted from the speaker is high, howling will finally occur. However, even if howling does not occur, the acoustic feedback loop causes a problem that the sound quality of the sound emitted from the speaker due to the resonance sound of a specific frequency or the like deteriorates.

Therefore, the present inventors have studied how to improve the sound quality of a sound emitted from a speaker in a loudspeaker broadcasting system. An example of the experiment is shown in FIG. In a loudspeaker broadcasting system that uses a wireless microphone, the lavalier microphone (tie-pin microphone) is stopped on the chest, tie, etc., and the microphone signal is transmitted from the transmitter by radio waves, and the receiving device receives it, amplifies it, and supplies it to the speaker. Let me speak.

Therefore, as shown in FIG. 4, a speaker 102 is provided instead of the human mouth, and 100 Hz to 20 kHz.
An oscillation signal from an oscillator 100 that continuously oscillates the frequency of z is supplied to the speaker 102 through an amplifier 101. Next, a lavalier microphone (tie-pin microphone) (unidirectional microphone) 103A is arranged on the peripheral axis in front of the speaker 102, an audio signal from the microphone 103A is amplified by an amplifier 104, and an output terminal is provided. When the frequency spectrum is measured by supplying the audio signal from the signal 105 to the frequency spectrum measuring device, the frequency (H
z) -response (dB) characteristics were obtained. Reference numeral 106 denotes an acoustic reflector / absorber corresponding to the human body or the chest thereof, but it is considered that there is almost no effect on this.

Next, the position of the speaker 102 remains unchanged, and the same microphone 10 as the microphone 103A is used.
3B was placed about 25 cm below the speaker 102 so as to face in the same direction as the direction of the speaker 102, and the same experiment as described above was performed. As a result, the frequency (Hz) shown by the alternate long and short dash line in FIG. -Response (dB) characteristics were obtained. According to this characteristic, compared with the characteristic of 1.2
A high response portion (peak) appeared near kHz. In addition, in the characteristic of, in the range of about 2 kHz or more, the level is significantly lowered as compared with that of the sound pressure directivity characteristic in the high sound range. This is the sound emitted from the speaker 102
Directly enters the microphone 103B and the speaker 1
The sound emitted from 02 is reflected by the chest to which the microphone 103B is attached, and the reflected sound is the microphone 1
Probably due to entering 03B.

Therefore, after amplifying the voice signal from the microphone, it is supplied to the modulator through a band elimination filter having a band elimination center frequency near 1.2 kHz, transmitted, and received by a receiver, which then receives it. When amplified and supplied to the speaker, a loud sound with good sound quality was realized.

In view of the above points, the present invention, when applied to a loudspeaker broadcasting system, can reduce the peculiar resonance sound to obtain a loudspeaker sound with good sound quality, and for a microphone capable of expanding the howling margin. An attempt is made to propose an amplification device, a microphone device, and a loudspeaker broadcasting device that can obtain a loud voice with good sound quality.

[0009]

The first aspect of the present invention comprises an amplifier 3 to which a microphone signal is supplied, and a band stop filter 5 connected to the output side of the amplifier 3, and the band stop filter 5 is provided. Is a microphone amplifying device characterized in that a band elimination center frequency is around 1.2 kHz.

The second aspect of the present invention is to provide a microphone 2 and an amplifier 3 to which an audio signal from the microphone 2 is supplied.
And a band stop filter 5 connected to the output side of the amplifier 3, the band stop filter 5 having a frequency of 1.2 kHz.
The microphone device is characterized in that the vicinity thereof is a band elimination center frequency.

A third aspect of the present invention is directed to a microphone 2 and an amplifier 3 to which an audio signal from the microphone 2 is supplied.
And a band stop filter 5 connected to the output side of the amplifier 3, and a modulator 7 and a transmitter 8 provided at the output side of the band stop filter 5.

A fourth aspect of the present invention is a loudspeaker broadcasting apparatus which amplifies an audio signal from the microphone 2 and supplies the amplified audio signal to the speaker 29.
A loudspeaker broadcasting apparatus is characterized in that a band elimination filter 5 having a band elimination center frequency in the vicinity of kHz is inserted.

In the first, second, third or fourth aspect of the present invention, a bridged T type band stop filter is used as the band stop filter 5.

In the first, second, third or fourth aspect of the present invention, Q of the band elimination filter 5 is set to about 2.

[0015]

According to the first aspect of the present invention, it is possible to suppress the peak of the frequency characteristic of the microphone signal in the vicinity of 1.2 kHz when the microphone 2 is attached to the chest of a person, and to reduce this peak by the acoustic feedback loop. It is possible to suppress the enhancement of the frequency component near .2 kHz, improve the sound quality of the loud sound in the loud broadcasting system, and suppress the occurrence of howling near 1.2 kHz.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a microphone amplifier and microphone device of the present invention will be described in detail below with reference to FIG. Although this embodiment is a case of a wireless loudspeaker broadcasting system, it can also be applied to a wired loudspeaker broadcasting system.

First, the transmitter 1 will be described. Reference numeral 2 is a microphone (lavalier microphone, tie-pin microphone) (relatively broad unidirectional microphone) stopped at the chest, tie, etc.
_V is, for example, through a two-stage direct-coupling amplifier (low-frequency amplifier) 3 for low-frequency amplification of G _V = 4.63≈13.3 dB,
The band elimination center frequency is around 1.2 kHz (for example, 0.
Supply to the bridged T-type band elimination filter 5 having a frequency in the range of 9 kHz to 1.5 kHz) or a Q of approximately 2 (for example, a value in the range of 1.4 to 2.6). To do. By setting the Q of the filter 5 to such a value, the frequency component near 1.2 kHz in the curve of FIG. 5 is at the same level as the frequency component near 1.2 kHz (same level, slightly higher level or slightly higher level). Can be suppressed to a lower level). The filter 5
The audio signal from the compressor through the emitter-follower amplifier 4 for impedance conversion and the coupling capacitor 23 (compander: compandor: circuit for compressing level difference)
6, and the compressed audio signal is supplied to the FM modulator 7 to be converted into a frequency-modulated signal and transmitted from the antenna 8.

The microphone 2 can be connected to a jack provided on the transmitter 1 through a cord and a plug, and
A variable attenuator can be inserted between the microphone 2 and the amplifier 3.

Next, the receiver 20 will be described. The radio wave from the transmitter 1 is received by the antenna 26, supplied to a tuner 27 having an FM demodulator to obtain an audio signal, supplied to a low frequency amplifier 28, amplified, and then supplied to a speaker 29. Let me speak. An expander corresponding to the compressor 6 in the transmitter 1 is provided in the tuner 27 after the FM demodulator.

Next, the detailed structure of the transmitter 1 will be described.
First, the configuration of the two-stage direct connection amplifier (low frequency amplifier) 3 will be described. An input terminal T to which a microphone signal (voice signal) from the microphone 2 is supplied is connected to the base of the NPN transistor Q1 through the coupling capacitor 9. The base of transistor Q1 is connected to its collector through a parallel circuit of resistor 10 and capacitor 11. The base of the transistor Q1 is grounded through the resistor 12. The collector of the transistor Q1 is connected to the power source + B through the resistor 13, and the emitter of the transistor Q1 is connected to the resistor 14
Grounded through. The base of the PNP transistor Q2 is connected to the collector of the transistor Q1, the emitter of the transistor Q2 is connected to the power source + B through the resistor 15, and the collector of the transistor Q2 is connected to the emitter of the transistor Q1 through the resistor 16. In this amplifier 3, the gain can be easily changed by changing the resistance ratio of the resistors 14 and 16.

Next, the configuration of the impedance converting amplifier 4 will be described. This is an emitter follower amplifier having an NPN transistor Q3, the emitter of which is grounded through a series circuit of resistors 20 and 21 as load resistors.

Next, the bridged T-type band elimination filter 5
The configuration of will be described. The resistor 17 is connected between the collector of the transistor Q2 and the base of the transistor Q3, the series circuit of the capacitors 18 and 19 is connected in parallel to the resistor 17, and the connection midpoint of the capacitors 18 and 19 is connected through the resistor 22. , The resistors 20 and 21 are connected to the connection midpoint.

The circuit constants of the circuit elements forming the filter 5 are as follows. Resistor 17 100 kΩ Capacitor 18 5600 pF Capacitor 19 5600 pF Resistor 20 680 Ω Resistor 21 1.8 kΩ Resistor 22 4.7 kΩ

The frequency f (Hz) of the filter 5 in this case
The voltage gain G _V is shown in FIG. However, the voltage gain G _V is G
_V = V _O / Vi, Vi is the voltage of the audio signal from the microphone 2 (50 mV), and V _O is the voltage at the test point Tp on the output side of the capacitor 23. The band elimination center frequency is actually 1.3 kHz, and Q is 1.3 (kHz) /
(1.65-0.99) (kHz) = 1.96.

The bridged T-type band elimination filter has an advantage that it is composed of a small number of circuit elements and that a filter having desired characteristics can be easily obtained.

Next, the bridged T-type band elimination filter will be described with reference to the equivalent circuit of FIG. The signal voltage Vi is passed through the bridged T-type band elimination filter 5 to form a transistor Q that constitutes a grounded-emitter amplifier.
Supply to the base. R _E represents the resistance value of the load resistor connected to the emitter of the transistor Q. R indicates the resistance value of the resistor 17 in FIG. 1, C indicates the capacitance of the capacitors 18 and 19, and R / n indicates that one end of the resistor 22 in FIG. 1 is connected to the connection midpoint of the resistors 20 and 21. Without, the resistance value when grounded is shown. n represents a damping constant.

In this bridged T-type band elimination filter, the greater the value of n of the resistance value R / n, the greater the amount of band elimination attenuation. In this filter, since the input signal and the output signal have the same amplitude and the same phase, no current flows through the R / n resistor and the output has a flat characteristic. In the case of the equivalent circuit of FIG. 2, the band elimination center frequency f ₀ is expressed as follows.

[0028]

## EQU1 ## f ₀ = √ (n) / 2πCR

In the filter 5 of FIG. 1, the resistance value connected in series with the resistor 22 is the parallel resistance value of the resistors 20 and 21, and therefore, it is about 0.494Ω when calculated. Therefore, R / n in the equivalent circuit of FIG. 2 corresponding to the filter 5 of FIG. 1 becomes a value obtained by adding 0.494Ω to the resistance value of the resistor 22 of 4.7kΩ, and R / n = 5.19kΩ.
Becomes Thus, n is n = 100 / 5.19≈2
It will be 4.4. Therefore, in the equation of the equation 1, n = 24.4, C
= 5600 pF and R = 100 kΩ are calculated, the band elimination center frequency f ₀ is f ₀ = 1.4 kHz, which is approximately equal to the measured value of 1.3 kHz.

When the present invention is applied to a cable type loudspeaker broadcasting system, the test point Tp in the transmitter 1 of FIG. 1 is connected to the input terminal of the amplifier 28 of the receiver 25 through a cable. Just do it.

According to the microphone amplifying device or the microphone device of this embodiment, the band elimination center frequency is about 1.2 kHz at the output side of the amplifier (low frequency amplifier) to which the microphone signal (voice signal from the microphone) is supplied. Since I connected a band elimination filter to
When the microphone is attached to the chest of a speaker, the enhancement (peak) of the frequency component near 1.2 kHz of the microphone signal is suppressed, and when applied to a loudspeaker broadcasting system, the characteristic resonance sound is reduced and the sound quality is improved. It is possible to obtain a good voiced sound and to expand the howling margin.

Further, according to the loudspeaker broadcasting system of this embodiment, in the microphone amplifying device or the microphone device, 1. is provided on the output side of the amplifier (low frequency amplifier) to which the microphone signal (audio signal from the microphone) is supplied. Since a band-elimination filter having a band-elimination center frequency around 2 kHz was connected, the enhancement (peak) of the frequency component near 1.2 kHz of the microphone signal when the microphone was attached to the chest of the speaker was suppressed. An audio signal from the microphone amplifying device or microphone device is supplied to the speaker side by wire or wirelessly, and the amplified signal is amplified and supplied to the speaker to reduce the inherent resonance sound and produce a loud sound with good sound quality. In addition to being able to obtain, the howling margin can be expanded.

Further, in these embodiments, when a bridged T-type band elimination filter is used as the band elimination filter, a desired band elimination characteristic can be easily set with a simple structure.

Further, in these embodiments, the Q of the band stop filter is set to about 2 so that the frequency component near 1.2 kHz of the microphone signal when the microphone is attached to the chest of the speaker ( (Peak) is almost eliminated.

[0035]

According to the above-described microphone amplifying device of the present invention, it has an amplifier to which a microphone signal is supplied and a band stop filter connected to the output side of the amplifier, and the band stop filter is 1.2 kHz. When the microphone is attached to the chest of a speaker, the enhancement (peak) of the frequency component near 1.2 kHz of the microphone signal is suppressed because the vicinity is the band elimination center frequency, and when applied to a loudspeaker broadcasting system. , It is possible to reduce the inherent resonance sound and obtain a loud voice with good sound quality, and it is possible to widen the howling margin.

According to the microphone device of the present invention described above, the microphone, the amplifier to which the audio signal from the microphone is supplied, and the band elimination filter connected to the output side of the amplifier are provided. Since the band elimination center frequency is set to around 1.2 kHz, the enhancement (peak) of the frequency component near 1.2 kHz of the microphone signal when the microphone is attached to the chest of the speaker is suppressed, and the system is used in a loudspeaker broadcasting system. When applied, it is possible to reduce the peculiar resonance sound and obtain a loud voice with good sound quality, and it is possible to expand the howling margin.

According to the above-described loudspeaker broadcasting apparatus of the present invention, in the loudspeaker broadcasting apparatus which amplifies the audio signal from the microphone and supplies the amplified audio signal to the speaker, the band elimination in the vicinity of 1.2 kHz is performed in the audio signal transmission path. Since a band stop filter with the center frequency is inserted, the frequency component around 1.2 kHz of the microphone signal when the microphone is attached to the chest of the speaker is enhanced (peak).
Is suppressed, and a peculiar resonance can be reduced to obtain a loud voice with good sound quality, and a howling margin can be widened.

In the present invention, when a bridged T-type band elimination filter is used as the band elimination filter, a desired band elimination characteristic can be easily set with a simple structure.

Further, in these inventions, the Q of the band elimination filter is set to about 2 so that the frequency component around 1.2 kHz of the microphone signal when the microphone is attached to the chest of the speaker is enhanced (peak). ) Is substantially eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an equivalent circuit of a bridged T-type band stop filter used in the embodiment.

FIG. 3 is a characteristic curve diagram showing frequency characteristics of the bridged T-type band elimination filter.

FIG. 4 is a block diagram showing an experimental example.

FIG. 5 is a frequency characteristic curve diagram of a microphone in an experimental example.

[Explanation of symbols]

 1 Transmitter 2 Microphone 3 Low-frequency amplifier 4 Impedance conversion amplifier 5 Band stop filter 6 Compressor 7 FM modulator 8 Antenna 25 Receiver 26 Antenna 27 Tuner 28 Low-frequency amplifier 29 Speaker

Claims (10)

[Claims] 1. An amplifier to which a microphone signal is supplied, and a band stop filter connected to the output side of the amplifier, wherein the band stop filter has a band stop center frequency near 1.2 kHz. Amplification device for microphone. 2. The microphone amplifying device according to claim 1, wherein a bridged T-type band canceling filter is used as the band canceling filter. 3. The microphone amplifying device according to claim 1, wherein Q of the band elimination filter is set to approximately 2. 4. A microphone, an amplifier to which an audio signal from the microphone is supplied, and a band elimination filter connected to the output side of the amplifier, the band elimination filter having a band elimination in the vicinity of 1.2 kHz. A microphone device having a center frequency. 5. The microphone device according to claim 4, wherein a modulator and a transmitter are provided on an output side of the band elimination filter. 6. The microphone device according to claim 4, wherein a bridged T-type band stop filter is used as the band stop filter. 7. The microphone device according to claim 4, 5 or 6, wherein Q of the band elimination filter is set to approximately 2. 8. A loudspeaker broadcasting apparatus for amplifying a voice signal from a microphone and supplying the amplified voice signal to a speaker, wherein a band elimination filter having a band elimination center frequency near 1.2 kHz is provided in a transmission path of the voice signal. A loudspeaker broadcasting device characterized by being inserted. 9. The loudspeaker broadcasting device according to claim 8, wherein a bridged T-type band elimination filter is used as the band elimination filter. 10. The loudspeaker broadcasting device according to claim 8 or 9, wherein Q of the band elimination filter is set to approximately 2.