JP2001189987A - Narrow directivity microphone unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a narrow directivity microphone unit that obtains a narrow directivity over the entire sound band, so as to enhance articulation of human voice and hardly picks up driving noise and vibration noise. SOLUTION: Two single directivity microphones 11, 12 are placed on the same axis at a prescribed interval, an arithmetic unit 13 receiving outputs of the two microphones and subtractively provides an output to a low-pass filter 14, where high-frequency components are removed. For example, by retting the installation interval of the microphones to be 50 mm (equivalent to a half wavelength that is the upper limit of a phone voice band), a front characteristic of 6 dB/oct in terms of the phase difference caused in the microphones from a 3 kHz, that is the upper limit of the phone voice band is realized. By incorporating a low-pas filter 14, whose cut-off frequency is 500 Hz and whose characteristic is 6 dB/oct in the microphone unit, a characteristic resulting from filtering the microphone outputs through a band-pass filter having a range of 500 Hz to 3.4 kHz is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone having a narrow directivity, which is particularly suitable for use in an in-vehicle hands-free communication system and a voice recognition system.

[0002]

2. Description of the Related Art FIGS. 3 and 4 show a basic configuration of a conventional narrow directivity microphone. As shown in FIG. 3, the conventional narrow directional microphone has two unidirectional microphone units 31 and 32 whose front faces are directed in the main axis direction.
And a delay network 33 and a subtractor 34, or, as shown in FIG. 4, two unidirectional microphone units 4 oriented frontward in the main axis direction.
1, 42, a high-pass filter 43, and a subtractor 44
It consists of.

[0003] A narrow directional microphone is of a secondary sound pressure gradient type (the directivity of one omnidirectional microphone unit is f
When (θ) = 1, the directivity f (θ) = (1 + cos) when two unidirectional microphone units are used.
θ) ² ), but in order to measure the uniformity of the front characteristics, of the two microphone units 31 (41) and 32 (42) as shown in FIGS.
After the output of one microphone unit is delayed by the delay network 33 or the high-frequency component is removed through the high-pass filter 43, the output is subtracted by the subtractor 34 (43).

[0004]

According to the above-mentioned prior art, narrow directivity cannot be obtained in the entire voice band, especially in the low frequency band, so that traveling noise and vibration noise can be easily picked up, and voice clarity can be obtained. Is low. Therefore, it cannot be used in a vehicle such as a hands-free communication system.

The present invention has been made in view of the above circumstances. Two unidirectional microphone units are arranged on the same axis at an interval corresponding to a half wavelength of a telephone voice band, and the two microphones are arranged. By providing a narrow directional microphone that can obtain narrow directivity in the entire audio band from low to high by removing the high frequency component by subtracting the unit output, it is particularly suitable for use in a car. The purpose is to:

[0006]

According to a first aspect of the present invention, there is provided a narrow directional microphone comprising two unidirectional microphone units disposed on the same axis at a predetermined interval. And a calculator for calculating a difference between one output signal and the other output signal of the unidirectional microphone unit, and a low-pass filter for removing a high-frequency component of the output of the calculator.

Thus, by setting the installation interval of the microphone units to, for example, 50 mm (corresponding to a half wavelength of the upper limit of the telephone voice band), the front characteristic is changed from the upper limit of the telephone voice band of 3.4 kHz to the microphone unit. The characteristic of 6 dB / oct is realized by the resulting phase difference,
For example, a cutoff frequency of 500 Hz, 6 dB / oct
By incorporating a low-pass filter of the type described above, the microphone output has the characteristic of passing through a band-pass filter from 500 Hz to 3.4 kHz, narrow directivity can be realized over the entire voice band, and the clarity of a human voice is increased, and Since the sensitivity of the frequency component is low, it is difficult to pick up road noise, and therefore, it is possible to withstand practical use in hands-free communication in a vehicle.

[0008]

FIG. 1 is a diagram showing an embodiment of a narrow directional microphone according to the present invention. FIG. 2 is a diagram cited for explaining the operation of the embodiment of the present invention, and is a diagram showing frequency characteristics of signals at points a, b, and c in FIG.

In FIG. 1, reference numerals 11 and 12 denote unidirectional microphone units, which are installed on the same axis at an interval of 5 cm. Here, from the position close to the front, the front microphone unit 11 and the rear microphone unit 12 are referred to from the vicinity of the installation position. The interval of 5 cm is the upper limit of the telephone voice band of 3.4 kHz.
Corresponds to a half wavelength. 13 is an arithmetic unit. Arithmetic unit 13
Is to generate an output signal having a frequency characteristic shown in FIG. 2A by subtracting the output of the rear microphone unit 12 from the output of the front microphone unit 11. That is, two microphone units 1
By subtracting the outputs 1 and 12, the front characteristic becomes the frequency at which the phase is inverted due to the phase difference (3.4 MHz when the installation interval D between the microphone units 11 and 12 is 5 cm).
up to z) at 6 dB / oct. It should be noted that the sound picked up from the side face has an in-phase input at all frequencies, and is therefore subtracted to have an output of 0.

Reference numeral 14 denotes a low-pass filter. The low-pass filter 14 has a frequency characteristic shown in FIG. That is, the cutoff frequency 500H
Using a low-pass filter of z, 6 dB / oct, the high-frequency component output from the arithmetic unit 13 is removed. As a result, an output having the characteristics shown in FIG. 2C is generated. Therefore,
The output of the microphone has a characteristic of passing a band-pass filter from 500 Hz to 3.4 kHz, so that the clarity of a human voice can be increased and low-frequency components such as running noise can be suppressed.

As described above, the microphone output (the output of the subtractor 13) having the characteristics shown in FIG.
By passing through the low-pass filter 14 having the characteristics shown in FIG. 2, it is possible to obtain the characteristics whose front characteristics have passed through the desired band-pass filter, that is, the characteristics shown in FIG.

A microphone for obtaining the characteristics shown in FIG.
It can be obtained by arranging two unidirectional microphone units on the same axis, and subtracting the output of the front microphone unit 11 from the rear microphone unit 12 by the calculator 13. In these microphone units 11 and 12, by setting the installation interval to 50 mm, the front characteristics of the microphone are changed from 3.4 MHz, which is the upper limit of the telephone voice band, to the microphone unit 11.
The characteristic of 6 dB / oct is realized by the phase difference generated in (12), which lowers the sensitivity at low frequencies and makes it difficult to pick up road noise. In addition, since sounds picked up from the side surfaces of the microphone units 11 and 12 are input to the two microphone units 11 and 12 in the same phase,
The subtraction cancels each other out, and as a result, only the frontal sound is output, and narrow directivity in the entire voice band is realized.

[0013]

As described above, according to the present invention, two unidirectional microphone units are arranged at a predetermined interval on the same axis, and the outputs of these two microphone units are subtracted and output by a computing unit to obtain a high frequency signal. It is the one with the components removed. As a result, the installation interval of the microphones is set to, for example, 50 mm.
(Corresponding to a half wavelength of the upper limit of the telephone voice band), the front characteristic is 3.4k which is the upper limit of the telephone voice band.
6 dB from the phase difference generated from the Hz to the microphone unit
The characteristic of / oct is realized. For example, by incorporating a low-pass filter with a cut-off frequency of 500 Hz and 6 dB / oct, the microphone output becomes a characteristic passed through a band-pass filter from 500 Hz to 3.4 kHz. Therefore, narrow directivity can be realized over the entire voice band,
As the clarity of the human voice increases, the sensitivity of low-frequency components decreases, making it difficult to pick up road noise.
It can withstand hands-free calls in the car.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a narrow directional microphone of the present invention.

FIG. 2 is a diagram cited for describing an operation of the embodiment of the present invention, and is a diagram illustrating a frequency characteristic of a signal at each point in FIG. 1;

FIG. 3 is a diagram illustrating a configuration example of a conventional narrow directivity microphone.

FIG. 4 is a diagram showing another configuration example of a conventional narrow directivity microphone.

[Explanation of symbols]

 11 front microphone unit 12 rear microphone unit 13 arithmetic unit 14 low-pass filter

Claims (1)

[Claims] 1. A unidirectional microphone unit arranged on a same axis at a predetermined interval, and a difference between one output signal and the other output signal of the unidirectional microphone unit is calculated. A narrow directional microphone comprising: an arithmetic unit; and a low-pass filter that removes a high-frequency component of the arithmetic unit output.