JPH01895A - directional microphone - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a directional microphone for a video camera.

Background of the Invention In recent years, video cameras have become increasingly smaller, more sophisticated, and less expensive, and their popularity is increasing year by year.

Under these circumstances, there is a strong demand for microphones installed in such devices to be more compact and super-directional, and research and development toward this goal is becoming more active. Currently, various methods have been proposed, and among them, the representative method that is in the practical stage is a high-order sound pressure gradient type directivity technology. (For example, see "Audiology" by Heitabe Nakajima, Jikkyo Publishing Co., Ltd., pp. 203-205).

An example of the conventional directional microphone mentioned above will be described below with reference to the drawings.

FIG. 6 shows a block diagram of a conventional directional microphone that uses a high-order sound pressure gradient type directional technology. In FIG. 6, 1a and 1b are a first microphone element and a second microphone element of the same type, which have the same direction of the main axis of directivity and are arranged on a straight line at a constant interval d. 20 is a phase shifter connected to the second microphone element 1b, 3 is a combiner connected to the first microphone element 1a and the phase shifter 20, 4 is an equalizer connected to the combiner 3, and 6 is a It is an output terminal.

In order to simplify the explanation here, the directivity of the microphone elements 1a and 1b is omnidirectional, and the cutoff frequency of the equalizer 4 is 1608. , the − next low-pass filter toshita.

Next, the main parts of the configuration will be explained in detail using FIGS. 6 and 7.

FIG. 6 shows the relationship between the first microphone element 12L, the second microphone element 1b, and the sound source.

In FIG. 6, d is the distance between the first microphone element 1a and the second microphone element 1b, θ, as described above.
is the angle between the main axis direction of the directivity of the first microphone element 1a and the second microphone element 1b and the sound source direction, and δL is the angle between the first microphone element 1a and the second microphone element 1b from the sound source.
This is the path difference between the microphone element 1b and the microphone element 1b. Path difference δL
is given by equation (1).

δL: d-CoS(of ・
...(1) Also, the phase delay of the second microphone element 1b with respect to the first microphone element 1& due to the path difference δL is given by an exponential function as shown in equation (2) when expressed by the transfer function 01. It will be done.

Ga = exp (-j 2πf ・δL/
c) ·------(2) However, C represents the speed of sound, f represents the frequency of the sound wave, and j represents the imaginary part.

FIG. 7 shows a typical example of a circuit diagram of the phase shifter 2o. In FIG. 7, R, , R2, and R3 are resistors, and C is a capacitor. Assuming that the transfer function of this phase shifter 2o is 00, it is given by equation (3).

G, = (1-j2πfCR3R, /R2)/(1+j2
πfcR,) ......(3) Here, when R1:R2, Go=(1-j2πfcR3)/(1+j2πfCR,
)=(1-j2πfτ)/(1+i2πfτ)...
...(4) is given by. However, the phase shifter 200 time constant τ=Q, i
It is 13.

Regarding the directional microphone configured as above,
The operation will be explained below.

Sound waves arriving at an angle θ with respect to the main axis direction of the directivity of the microphone element enter the first microphone element 1a and the second microphone element 1b with a phase difference given by equation (2). The output of the second microphone element 1b is delayed in phase by the phase shifter 20 given by equation (4), then subtracted from the output of the first microphone element 1a by the synthesizer 3, and then passed through the equalizer 4. is output. If this composite output is Gt, then the (6th)
It becomes like the expression. However, microphone elements 11L, 1
The transfer function of b is 00, the transfer function of equalizer 4 is Go,
shall be.

Gt=G0(1-GaGe)Geq-e・
(5) FIG. 2 is a phase characteristic diagram of the phase shifter shown on the stage number side. In FIG. 2, curve a is the phase characteristic of the transfer function 00 of the conventional phase shifter 20, that is, the negative stage.

Note that the curve e shown by the dotted line is the phase characteristic of the transfer function G& when θ=0 degrees. Here, the distance between the first microphone element 1a and the second microphone element 1b is d=23
, the time constant τ of the phase shifter 2o satisfies the condition (
τ=d/C/2).

Figure 8 shows the directional characteristic of the directional microphone given by equation (6), that is, the directional characteristic of the directional microphone when the conventional phase shifter is one stage, and is the directional characteristic of the directional microphone with two 0th-order sound pressure gradient types. A certain omnidirectional microphone element provides unidirectionality of the first-order sound pressure gradient type. Similarly below,
By using the directivity technology of the high-order sound pressure gradient type, the second-order sound pressure gradient type is generated by the two first-order sound pressure gradient types, and the third-order sound pressure gradient type is generated by the two second-order sound pressure gradient types. The second sound pressure gradient type is smaller and has even higher order directivity.

Problems to be Solved by the Invention However, in the above-described force configuration, the curves a and e do not match in phase at high frequencies, as shown in FIG. Therefore, as shown in FIG. 8, there is a problem in that its directional characteristics, especially its 180 degree characteristics, deteriorate at high frequencies.

In view of the above-mentioned problems, the present invention improves the phase characteristics at high frequencies by dividing the phase shifter into multiple stages, and provides a directional microphone that is excellent even at high frequencies.

Means for Solving the Problems In order to achieve this object, the directional microphone of the present invention includes a first microphone element and a first microphone element of the same type, which are arranged in a straight line at regular intervals and have the same direction of the main axis of directivity. a second microphone element, a multistage phase shifter connected to the second microphone element, a combiner connected to the first microphone element and the multistage phase shifter, and a nine equalizer connected to the combiner. It is made up of.

Effect: With this configuration, it is compact, has sharp directivity, and can provide good directivity characteristics even at high frequencies.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a directional microphone in an embodiment of the present invention. In Figure 1, 1a
and 1b are omnidirectional first and second microphone elements of the same type that have the same main axis direction of directivity and are arranged in a straight line at a constant interval d, and 2 is the second microphone element 1b. A collection of phase shifters connected in series in multiple stages, 2a, 2b and 2C are individual phase shifters constituting the phase shifter collection 2, 3 is a combination of the first microphone element 1& and the phase shifter. A combiner is connected to the aggregate 2, 4 is an equalizer connected to the combiner 3, and 6 is an output terminal. n is the number of 20 stages of phase shifters. here,
As in the conventional example, the distance between the first microphone element 11L and the second microphone element 1b is (i=2α), and the equalizer 4 is a first-order low-pass filter with a cutoff frequency of 1 sot-1z.

However, the time constant τ4 of each phase shifter. τ2,...
τ. For example, τ1=τ2=...=τ. =d/c/2
/n...(6). The transfer function of the phase shifter assembly 2 in which this phase shifter is connected in series in n stages is G. is given by the following equation.

G, = ((1-j2πfτ,)/(1+j2πfτ1)
)0...(7) Regarding the directional microphone configured as above,
The operation will be explained below.

A sound wave arriving at an angle θ with respect to the direction of the main axis of directivity of the microphone element is incident on the first microphone element 1a and the second microphone element 1b with a phase difference given by the angle θ. The output of the microphone element is delayed in phase by the multistage phase shifter assembly 2 given by equation (7'), and then subtracted by the synthesizer 3 from the output of the first microphone element 1&, and then the equalizer 4. If this combined output is Gt, the following equation is obtained as in the conventional example.

Gt200(1-ζG, ) G,,...
(8) In Figure 2, curves c and d each have two stages.

This is the phase characteristic of the transfer function 06 of the phase shifter assembly 2 consisting of four stages and eight stages.

FIG. 3 shows the directional characteristics of the directional microphone when the phase shifter has two stages. Moreover, FIG. 4 shows the directional characteristics of the directional microphone when the phase shifter has four stages.

As shown above, according to the present embodiment, by providing a multi-stage phase shifter, it is possible to obtain a small size, sharp directivity, and good directivity characteristics even at high frequencies.

Effects of the Invention The directional microphone of the present invention is small and has sharp directivity.
Moreover, good directional characteristics can be achieved even at high frequencies.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a directional microphone according to an embodiment of the present invention, Fig. 2 is a phase characteristic diagram of a phase shifter, and Fig. 3 is a diagram of a directional microphone when the phase shifter of the present invention has two stages. Directional characteristic diagram. Figure 4 is a directional characteristic diagram of a directional microphone with four stages of phase shifters. Figure 5 is a block diagram of a conventional directional microphone. Figure 6 shows the relationship between the microphone element and the sound source. 7 is a circuit diagram of a phase shifter, and FIG. 8 is a directional characteristic diagram of a directional microphone when the conventional phase shifter has one stage. 1a, 1b...Microphone element, 2...
...Aggregation of phase shifters, 2&, 2b, 2Q...Phase shifter, 3...Synthesizer, 4...Equalizer. Name of agent Patent attorney Toshio Nakao and 1 other person fsu, fb --- Iikuroho + 2, 2L Ripe S - - ~ Output 4JjF Fig. 2 Circumference rl-IZJ Fig. 3 Fig. 4 Fig. 6 Fig. 7, '? / Figure 8

Claims (1)

[Claims] a first microphone element and a second microphone element of the same type arranged in a straight line at regular intervals with the same main axis direction of directivity; a multistage phase shifter connected to the second microphone element; A directional microphone comprising: a combiner connected to a first microphone element and the multistage phase shifter; and an equalizer connected to the combiner.