JPH0193295A - audio output device - Google Patents

Abstract

PURPOSE:To improve the degree of freedom in use by adopting the constitution such that an input section, an amplifier section having a variable gain amplifier function and an output section are used so as to attenuate in a very short period as to a signal being discontinuous and consecutive only for a short period thereby preventing howling. CONSTITUTION:A voice signal inputted from a microphone of an input section 1 is band-limited from 200Hz to 6kHz by a band limit circuit and reaches a variable gain amplifier section. The variable gain amplifier section has a characteristic not always being linear and changing periodically while being consecutive from an amplification factor of 0dB to 50dB at 15kHz-20kHz. The voice signal reaching the variable gain amplifier section is at a far low frequency band in comparison with the gain change of the amplifier and recognized as a voice signal as if the maximum amplification factor is constant to human ears. In general, howling is generated from a single frequency component of a very minute voltage among environmental noise in a system having a constant amplification factor in a time nearly 10msec and the howling is attenuated momentarily in the amplifier system and not recognized as the sound.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a signal transmission method and device for an audio output device that magnifies and outputs an audio signal input from an audio input device (hereinafter referred to as a microphone). .

[Conventional technology]

Conventionally, audio output devices that magnify and output audio signals input through a microphone have an integrated structure that clearly separates the speaker and microphone by covering the sounding body (hereinafter referred to as the speaker) with a special horn-shaped member. There are horn-type loudspeakers, radio cassettes, audio systems, etc., with microphone input terminals, and dedicated loudspeaker equipment that uses wired or wireless technology and has a microphone and speaker that are spatially and physically separated. Ta.

[Problem that the invention seeks to solve]

In the conventional example, the audio signal emitted from the speaker is
The oscillation phenomenon (hereinafter referred to as howling) that occurs when the same phase returns to the microphone can be avoided by blocking the microphone and speaker using a physical partition wall, and by covering the speaker with a long horn-shaped tube. A horn-type loudspeaker reduces the in-phase feedback rate of the false audio signal.

Others use wires or radio waves (mainly FM modulated waves) to slightly separate the microphone and speaker, reduce the common-mode feedback rate of the audio signal, or at the same time limit the passband of the audio signal. Methods such as limiting the range of the common-mode feedback signal have been used, and the above-mentioned methods have been combined in various ways to form so-called howling prevention means.

Even if the howling effect is improved in this way, the in-phase signal feedback rate to the microphone increases along with the signal amplification rate of the entire system, and howling will always occur outside a certain limit range, resulting in poor sound reproducibility. It is difficult to obtain a device that has sufficient performance in terms of both howling prevention effects.

Also, due to the physical limitations of the horn shape, the shape was easy to increase in size (and was not always satisfactory in terms of practicality).

In systems where the transmission path is formed between a microphone and a wired system or wirelessly using FM modulation, the howling prevention effect of the system improves depending on the distance between the microphone and the speaker, so it is more effective than a system using a horn shape. However, unfortunately, the howling prevention effect of the system using the slave wire or wireless transmission line is not perfect, and the amplification factor of the entire system and microphone Depending on the position of the speaker and the position of the speaker, howling can occur very easily under certain conditions.

Therefore, when using it, the user must always keep the following points in mind.

■Place the microphone and speaker as far apart as possible depending on the purpose of use.

■Always place the microphone and speaker in a position where they are not directly facing each other.

■Make sure to use the signal at an appropriate signal amplification factor that is permissible within the entire system, including the location of use and the structure of the building.

The present invention solves the above-mentioned problems of conventional audio output devices, and the physical shape of the audio output Hft is determined by the physical shape of the speaker and output circuit that can obtain the required output. Moreover, the shape can be freely designed within that range, and it does not depend on the mutual positional relationship of the microphone and speaker or the signal amplification factor of the entire system.
It is an object of the present invention to provide an audio output device which has an effect of preventing howling and has a large degree of freedom in use.

[Means for solving problems]

The audio output device of the present invention is an audio output device that amplifies and outputs an audio signal using a slave wire or wireless transmission means, and includes an input section, an amplification section that performs a variable gain amplification function, and an output section. It is characterized by

[Effect]

According to the above configuration of the present invention, the input section includes a microphone and an audio signal band limiting circuit, both of which are configured using a microphone and an operational amplifier.

The amplifier section having a variable gain amplification function is a variable gain amplifier that has a function of continuously repeating periodic changes from an extremely small signal amplification factor to an extremely large signal amplification factor at a relatively high speed.

The output section is a cone speaker or a piezoelectric speaker using PZT.

It may be different, but if a piezoelectric speaker is used for the output section,
The amplification section with the variable gain function described above also includes a buffer for high voltage output.

The audio signal input from the microphone ranges from 200Hz to 6K.
The band is limited to about Hz and reaches the variable gain amplification section at the subsequent stage.

The variable gain amplification section has a characteristic that changes continuously but not necessarily linearly (a linear function approximation does not hold) periodically between the amplification factor OdB and 50 dB at a frequency of about 15 KHz to 20 KHz.

The audio signal that reaches the variable gain amplification section is in a considerably lower frequency range than the change in gain of the amplifier, and is perceived by the human ear as an audio signal that appears to be constant at the maximum amplification factor.

In the amplification system configured as described above, howling occurs and attenuates during one period of gain change. In general, howling is caused by noise in the environment.
Since it can be considered that it takes about 5 ec to occur, howling is instantaneously attenuated in the amplification system with the above-mentioned configuration and is not recognized as sound.

〔Example〕

FIG. 1 is a conceptual diagram of an embodiment of the present invention, in which the one-man power section consists of a microphone, a band-limiting circuit called a band-pass filter composed of an operational amplifier, a resistor, and a capacitor. It is desirable for the attenuation characteristics to be as large as possible, so the cutoff frequency is 5K)
(Z and at least a second-order active filter is used.

FIG. 2 is a detailed diagram of the variable gain amplification section in the fourth embodiment of the present invention, and shows 4 LEDs which are IT style variable resistance elements.
Cds and Thailand? This is an example composed of an IC555, a 5 o -lot filter, and a transistor.

FIG. 3 is an operation diagram showing the operation of each part of the variable gain amplification section and gain changes in the embodiment of the present invention, and shows the operation of the timer IC.
The output of 555 is made into a triangular wave by 50-pass filter buffer 7, and when current flows through the transistor with that output, 4 LEDs
-The resistance of Cds changes periodically, and the amplification factor of the amplification system is also O
dB (it shows how it periodically changes from a value close to 50 dB).

In this embodiment, the output section is two/speaker.

〔Effect of the invention〕

As described above, according to the present invention, signals such as environmental noise that are discontinuous and last only for a short period of time can be attenuated in an extremely short period of time, thereby providing an effect of preventing howling.

Therefore, by using the present invention, the shape of the audio output device can be designed more freely compared to conventional audio output devices, and the method has an anti-howling effect that does not depend on the mutual positions of the microphone and speaker or the signal amplification factor of the amplification system. This has the effect that it is possible to configure an audio output device with a large degree of freedom in use.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing an embodiment of the audio output device of the present invention. FIG. 2 is a detailed diagram of the variable gain amplification section of FIG. 1. FIG. 3 is an operation diagram showing the operation of each part of the variable gain amplification section of FIG. 2 and changes in the signal amplification factor of the amplification system. 7 input egg 1st factor 4 L21-ρ-cds Figure 2

Claims (1)

[Claims] An audio output device that amplifies and outputs an audio signal using a wired or wireless transmission means, the audio output device comprising an input section, an amplification section having a variable gain amplification function, and an output section.