JPH0354475Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a secondary sound pressure gradient type microphone which has small attenuation of sensitivity at low frequencies and high directivity at middle and high frequencies.

In general, a secondary sound pressure gradient microphone is constructed by combining two unidirectional microphone units and taking the difference in output from both units. As the value decreases, the frontal sensitivity decreases at a rate of 6 dB/octave. Therefore, if the output is used as it is, the sound quality will be unbalanced, so an equalizer is usually used to correct the frequency characteristics so that they are averaged over the audio band. However, among the noise generated by the field-effect transistors and amplifiers that make up the impedance converter built into the microphone unit, the high-frequency components are attenuated by the equalizer, but the low-frequency components are not. This results in a poor signal-to-noise ratio, and in order to take the difference between the outputs of both microphone units, it is necessary to invert the phase of the output of one microphone unit using an electric circuit, which increases the line size. There was a problem that miniaturization and cost reduction could not be achieved.

The purpose of this invention was to solve this problem by using an electret condenser microphone in the microphone unit, so that each output has a phase difference of 180° from each other at the microphone unit stage, and is placed at the front. The purpose of this invention is to provide a secondary sound pressure gradient type microphone by cutting off the lower part of the output of the microphone unit from a fairly high frequency band.

Next, the secondary sound pressure type microphone according to this invention will be explained based on an example. FIG. 2 is a block diagram showing an embodiment of the quadratic sound pressure gradient type microphone according to this invention. In the figure, numerals 1 and 2 are electric condenser-microphone units constituting each unit of a secondary sound pressure gradient type microphone, and each microphone unit includes a microphone cartridge 3, 4 and a field-effect transistor. Impedance converters 5 and 6 formed therein are built-in.
Among these two cartridges, the vibrating membrane R of one cartridge, for example cartridge 3, is formed of an electret, and the vibrating membrane R of the other cartridge 4 is formed of an electret.
The fixed electrode E is made of an electret. Therefore, cartridge 3 and cartridge 4
The two cartridges are structurally biased in opposite directions, and when the diaphragms move in the same direction, both cartridges 3 and 4 output signals with a phase difference of 180°. This eliminates the need for a phase inversion circuit, which is required in the next sound pressure gradient microphone.

The output from these cartridges 3 and 4 is
They are each amplified by amplifiers 7 and 8. Of the microphone units arranged on the same axis,
The output from the amplifier 7 of the microphone unit 1 arranged on the front side is inputted to one input terminal of the adder 10 through the high-pass filter 9, and the output from the microphone unit 2 arranged on the other side is inputted to one input terminal of the adder 10. is input to the other input terminal of the adder 10 through the amplifier 8, and the adder 10 outputs a difference signal between the two microphone units 1 and 2. This causes the attenuation of sensitivity at low frequencies to be
As shown in FIG. 3, this will be considerably alleviated.

As explained above, in the microphone of this invention, the attenuation of sensitivity in the low frequency range is alleviated, so the sensitivity over the entire audio band is equalized and a secondary sound pressure gradient type microphone is formed. This improves directivity and improves performance.Furthermore, it eliminates the need for a phase inverter circuit, which was required for conventional secondary sound pressure gradient microphones, resulting in smaller circuit size and smaller size. There are effects such as making it possible to reduce costs.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the on-axis frequency characteristics and directivity pattern of a conventional secondary sound pressure gradient microphone, FIG. 2 is a block diagram showing an embodiment of the microphone according to this invention, and FIG. The figure is a diagram showing the on-axis frequency characteristics and directivity pattern of the microphone according to this invention. 1, 2...Microphone unit, 3, 4...
Microphone cartridge, 5, 6... impedance converter, 7, 8... amplifier, 9... high pass filter, 10... adder.

Claims (1)

[Scope of utility model registration request] A secondary sound pressure gradient type microphone is constructed in which two electret condenser microphone units with unidirectionality are arranged on the axis at an appropriate distance in the front-rear direction, and the difference in output from both microphone units is taken. In the microphone, the vibrating membrane of one microphone unit is made of an electret, and the fixed electrode of the other microphone unit is made of an electret so as to have opposite polarity, and the vibrating membrane of the other microphone unit is made of an electret so as to have opposite polarity. The output of the microphone unit is inputted to one input terminal of the adder after passing through a high-pass filter, and the output of the microphone unit located at the rear side is inputted as is to the other input terminal of the adder, and is input to both microphones. A microphone characterized in that it is configured to obtain a unit differential output.