JP3326063B2 - Omnidirectional microphone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffraction effect (a straight line extending toward a sound source (hereinafter referred to as a "reference axis")) which always occurs in a normal omnidirectional microphone. The present invention relates to a high-sensitivity, low-noise omnidirectional microphone capable of reducing an increase in sensitivity caused at a very high frequency) and achieving ideal omnidirectional performance over a wide frequency band.

[0002]

2. Description of the Related Art Omnidirectional microphones are considered to exhibit the same sensitivity to sound arriving from all directions. In practice, they have such ideal omnidirectional directional characteristics. The range is only in the frequency band where the size of the microphone is sufficiently small compared to the wavelength of the sound wave. For this reason, in the conventional omnidirectional microphone constituted by one microphone unit, it is necessary to obtain an ideal omnidirectional sound pickup pattern over a frequency range up to 20 kHz required for sound pickup of music or the like. Has to be a very small microphone having an outer diameter of 5 mm or less.

On the other hand, the sensitivity of a microphone is substantially correlated with the size of the area of a vibrating membrane that receives sound waves. Therefore, it is difficult to obtain high sensitivity with the above-described ultra-small microphone and it is difficult to reduce the noise level. Become. For these reasons, most omnidirectional microphones used for ordinary music pickup have an outer diameter of about 20 mm, and their output sensitivity frequency characteristics are such that even if the intensity of incoming sound waves is the same in all directions. A large difference in output sensitivity occurs in a high frequency range of about 2 to 5 kHz or more in the front and side directions of the microphone due to the diffraction effect, as shown in FIG. In the same figure (the same applies to the characteristic diagrams described below), 0 ° and 90 ° indicate the front direction and the lateral direction of the microphone, respectively.

Some omnidirectional microphones have two unidirectional microphone units arranged back to back, and the outputs of these microphone units are added to obtain omnidirectional directional characteristics. In this case, since the directions of the two microphone units are opposite to each other, the effect of reducing the diffraction effect is hardly obtained. The output sensitivity frequency characteristic of the microphone in this case is as shown in FIG. 4 because the diffraction effect is not reduced.

[0005]

When an omnidirectional microphone having a diffraction effect is used for sound collection of an orchestra or the like, the output sensitivity frequency characteristics differ between the front direction and the lateral direction of the microphone at high frequencies. Since the tone of the instrument changes depending on how the direction is set, and the effects of reflections on the wall, etc., it is very difficult to set the microphone when trying to obtain good sound pickup sound quality in consideration of these difficult problems. . Further, it is a fact that the sensitivity difference between the high-frequency sensitivity in the front direction and the horizontal direction due to the diffraction effect deteriorates the quality of the sound pickup software.

Further, an omnidirectional microphone for measurement such as a sound level meter requires an ideal omnidirectional directional characteristic especially in a measurement frequency band. In order to satisfy the demand, the microphone is miniaturized. If you try to make it SN
Due to the ratio, the miniaturization is limited, and the diffraction effect is inevitable.

Generally, the sensitivity of an omnidirectional microphone tends to be slightly lower than that of a directional microphone. This is because the omnidirectional microphone has greater acoustic control in the microphone unit than the directional microphone, and therefore, the input-converted noise level of the omnidirectional microphone is slightly higher.

An object of the present invention is to reduce the diffraction effect without reducing the size of the omnidirectional microphone, thereby realizing an omnidirectional microphone having high sensitivity, low noise and extremely little diffraction effect. Is to do.

[0009]

In order to achieve the above object, the omnidirectional microphone of the present invention comprises two omnidirectional microphone units so that the respective diaphragm surfaces face the sound source. The microphones are arranged so as to be spaced apart from each other on a reference axis, and the output signals of the two omnidirectional microphone units arranged are added.

Further, in the omnidirectional microphone according to the present invention, when the microphones are spaced apart from each other, the distance between the microphones is set to a radius of the two omnidirectional microphone units or a value near the radius. Is what you do.

The omnidirectional microphone according to the present invention, when adding the respective output signals of the two omnidirectional microphone units, uses the output of one of the two omnidirectional microphone units. The signal is passed through a low-pass filter for fine adjustment of the frequency characteristic and then added later.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments with reference to the accompanying drawings. FIG. 1 is a block diagram showing one embodiment of the omnidirectional microphone of the present invention. In FIG. 1, reference numerals 1 and 2 denote two omnidirectional microphone units arranged at a required distance from each other on the reference axis (specifically, described later), and 3 denotes a frequency characteristic fine adjustment unit. Is a low pass filter. Here, the two omnidirectional microphone units 1 and 2 are respectively arranged on the reference axis such that the diaphragm surfaces of the microphone units face the direction of the sound source. Also, 4
Is an adder for adding each output signal of the microphone unit 2 and the low-pass filter 3. The low-pass filter 3 is not an essential circuit element for the omnidirectional microphone of the present invention, and may be omitted in some cases.

Next, the operation principle of the omnidirectional microphone of the present invention will be described. As described above, when the two microphone units 1 and 2 are arranged on the reference axis so that the directions of the reference axes are aligned and separated from each other, and the outputs of the microphone units are added while increasing the distance, a high level is obtained. The sensitivity after the addition gradually decreases at the band frequency, and the output becomes the minimum at a frequency at which the interval between the two microphone units becomes a half wavelength. This decrease in sensitivity at high frequencies is greatest in the front direction of the microphone and becomes smaller as it goes in the lateral direction.

Since this phenomenon has the opposite tendency to the diffraction effect, the interval between the two microphone units is appropriately set, and the output ratio and the frequency characteristics are finely adjusted by an electric circuit to make the angle from 0 ° to 90 °. This makes it possible to realize a state in which there is almost no sensitivity difference between the microphones, thereby realizing an omnidirectional microphone having high sensitivity, low noise, and extremely little diffraction effect.

In addition, since the omnidirectional microphone of the present invention adds the outputs of two microphone units due to its configuration, the sensitivity increases by 6 dB and the SN ratio becomes 3 by this addition.
It is improved by dB.

In the microphone of the present invention, the separation distance between the two microphone units arranged on the reference axis is, for example, a value that is substantially close to the radius of the microphone unit to be used. It depends on the shape and the high frequency characteristics of the microphone unit.

FIG. 2 shows the measurement results of the output sensitivity frequency characteristics of the omnidirectional microphone of the present invention when two microphone units having a diameter of 16 mm are arranged at a distance of 8.8 mm on the reference axis. I have. The output sensitivity frequency characteristic shown in FIG. 2 is constructed by arranging the frequency characteristic of the conventional omnidirectional microphone shown in FIG. 3 and the two unidirectional microphone units shown in FIG. 4 back to back on the reference axis. Compared with the frequency characteristics of the omnidirectional microphone described above, in the omnidirectional microphone according to the present invention, there is almost no sensitivity difference between 0 ° and 90 ° in the high frequency range (in particular, up to around 15 kHz). From this,
With the microphone of the present invention, it can be seen that the effect of reducing the diffraction effect has occurred.

[0018]

According to the omnidirectional microphone of the present invention,
2 so that each diaphragm face faces the sound source
The two omnidirectional microphone units are arranged apart from each other on the reference axis, and the output signals of the two arranged omnidirectional microphone units are added, so that the microphones at high frequencies are It is possible to suppress an increase in sensitivity with the maximum value of the sound source direction (0 ° direction) of the unit and realize an ideal omnidirectional microphone with a small diffraction effect in a wide frequency range.

The configuration of the microphone according to the present invention is extremely simple, and it is possible to reduce the diffraction effect of the omnidirectional microphone, which has been conventionally difficult, without increasing the sensitivity without deteriorating the performance of the two microphone units used. This is achieved in the direction of improving performance such as improvement of the SN ratio.

In addition, as an application aspect, the use of the omnidirectional microphone according to the present invention in a measurement microphone such as a sound level meter can improve the measurement accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the omnidirectional microphone of the present invention.

FIG. 2 shows a measurement result of an output sensitivity frequency characteristic of the omnidirectional microphone of the present invention.

FIG. 3 shows an output sensitivity frequency characteristic of a conventional omnidirectional microphone.

FIG. 4 shows an output sensitivity frequency characteristic of a unidirectional microphone in which two unidirectional microphone units are arranged back to back on a reference axis.

[Explanation of symbols]

 1, 2 microphone unit 3 low-pass filter 4 adder

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yasuhiko Kanno 2-8-8 Ogikubo, Suginami-ku, Tokyo Sanken Microphone Co., Ltd. (56) References JP-A-60-16739 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04R 1/40 320 H04R 3/00 320

Claims (3)

(57) [Claims] 1. A so that each of the diaphragm surface are in the direction of both the sound source, as well as arranged two omnidirectional microphone units spaced from each other on the reference axis, two omni-directional that the arranged An omnidirectional microphone characterized in that the output signals of the microphone units are added to each other. 2. The omnidirectional microphone according to claim 1, wherein, when the microphones are spaced apart from each other, the distance between the microphones is a radius of the two omnidirectional microphone units or a value near the radius. Omnidirectional microphone characterized by the following. 3. The omni-directional microphone according to claim 1 or 2, wherein, when adding each output signal of the two omnidirectional microphones units, one omni-directional among the two An omnidirectional microphone characterized in that the output signal of the microphone unit is passed through a low-pass filter for fine adjustment of frequency characteristics and then added.