JP3983409B2 - Wideband directional microphone - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a directional microphone (used herein to mean a directivity other than omnidirectional), and more particularly to a directional microphone that provides a flat frequency characteristic over a wide band with a small number of microphone capsules. is there.
[0002]
[Prior art]
With a conventional unidirectional microphone in which the band of sound to be collected is 20 Hz to 20 kHz, it is possible to realize a substantially flat frequency characteristic within one band with one microphone capsule. Furthermore, in order to further improve the frequency characteristics and directivity characteristics within the band, two microphone capsules divided into a middle low band and a high band are necessary.
However, the latest state-of-the-art audio equipment already requires a band from 20 Hz to 20 kHz, and for this reason, the microphone is also required to support it.
[0003]
First, as an example, two techniques are shown as techniques for obtaining a unidirectional microphone (see FIGS. 1 and 2). FIG. 1 is a block diagram using a single unidirectional microphone capsule 1, and FIG. 2 is a block diagram using two omnidirectional microphone capsules 2 and 3. In the case of the single body of FIG. 1, in order to realize a band from 20 Hz to 100 kHz, the outer diameter of the microphone capsule 1 is about 8 mm because of the diffraction effect ⁽¹⁾ due to the relationship between the size and frequency of the microphone capsule. However, a large undulation occurs in the frequency characteristics at 20 kHz or more, and a phenomenon occurs in which the sound quality differs greatly between the front side of the microphone and other than the front side. In order to reduce this influence as much as possible, it is necessary to make the outer diameter of the microphone capsule very small, such as about 3 mm or less. However, with this size, the sensitivity is low, and the S / N cannot be sufficient, so that good sound collection is impossible. Further, as shown in FIG. 2, a method for imparting directivity by using two omnidirectional microphone capsules 2 and 3 is a known technique ⁽²⁾ . However, this method also causes deterioration of directivity characteristics at high frequencies , Similarly, a desired characteristic cannot be obtained due to a diffraction effect in a high range.
[0004]
As shown in FIG. 3, the currently considered solution is to synthesize the output of a unidirectional microphone capsule that divides and handles the mid-low range 4, high range 5, and ultra-high range 6 bands. However, in this case as well, sound quality and S / N degradation due to diffraction effects and reflections in the ultra high frequency range are inevitable.
[0005]
As a method for reducing the diffraction effect, omnidirectional microphone capsules are arranged in the same direction in the sound axis direction at a predetermined interval, and the two signal outputs are added together with an appropriate value. However, a method has been proposed that can reduce the diffraction effect in the high range and does not deteriorate the S / N (Japanese Patent Laid-Open No. 09-182184).
[0006]
Reference (1) "Acoustical Engineering" Olson D. Van Nostrand Company, INC., 1957, pp17-24
(2) "Audio Engineering" Hirataro Nakajima, Jikkyo Publishing Co., Ltd., 1973, pp204-205
[0007]
[Problems to be solved by the invention]
The issues that need to be solved in the realization of a wide-band directional microphone with a bandwidth up to the super-high frequency are: (1) The microphone capsule's desensitization that occurs in principle to widen the castle, and the undulations in the frequency characteristics due to the diffraction effect. This is a further decrease in sensitivity due to the miniaturization of microphone capsules to avoid, and a deterioration in S / N based on the decrease in sensitivity of these microphone capsules.
Furthermore, (2) since the wavelength of the sound wave becomes shorter in the ultra high frequency range, the disturbance and reflection of the sound wave due to the obstacle are likely to occur. For this reason, when a plurality of microphone capsules are used, the shape of the microphone becomes large, and such disturbance of sound waves tends to occur. Therefore, it is desirable that the number of microphone capsules be as small as possible.
[0008]
Accordingly, an object of the present invention is to provide a wide-band directional microphone with a small number of unidirectional microphone capsules, flat frequency characteristics over a wide band, and good directivity and S / N. is there.
[0009]
[Means for Solving the Problems]
The wideband directional microphone of the present invention for achieving this object is a wideband directional microphone that covers a band from 20 Hz to 100 kHz with a single directivity, and has the same configuration arranged in the same direction on the same axis . Two microphone capsules , amplification means for separately amplifying each output signal of the two microphone capsules, and addition means for adding each signal amplified by the amplification means, each of the two microphone capsules being has a circular opening shape to produce a first peak and the second peak as the front direction sensitive within the band, circular opening shape of the two microphones capsule, the peak frequencies of the first peak approximately, so that the acoustic velocity / microphone said circular opening shape diameter of the capsule, and, and, the circular opening shape So that the diameter is substantially three times the length of the peak frequency wavelength of the second peak, is determined in advance, the distance of the two microphone capsule is approximately the diameter of the circular opening shape 1/2 It is characterized by being predetermined so that
[0010]
Further, the wideband directional microphone of the present invention further includes a low-pass filter that performs low-pass filtering before inputting any one of the two microphone capsule output signals amplified by the amplifying unit to the adding unit. It is a feature.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In order to realize a directional microphone that maintains flat frequency characteristics up to an ultra-wideband, first, the stiffness of the diaphragm of a single directional microphone capsule is strengthened, or the equivalent mass is reduced to make the resonance frequency extremely high. It is necessary to extend to the area. At this time, the sensitivity drop by itself is inevitable, but it is limited to about a few dB (11 → 12, FIG. 4A). In addition, in an ultra-wideband microphone that targets a band up to 100 kHz, a microphone capsule that requires a certain size or more is required to obtain the required S / N. In this case, the outer diameter of the microphone capsule is reduced. As an example in the case of 13 mm, two or more frequency characteristic undulations due to the diffraction effect as shown in FIG. 4B occur in the band (13).
[0013]
In the present invention, the S / N can be improved by 3 dB by using two directional macrophone capsules and adding the outputs to increase the sensitivity by 6 dB. As an embodiment of the present invention, the second peak of the diffraction effect is set around 100 kHz by targeting a band up to 100 kHz. For this purpose, the outer diameter of the macrophone capsule was designed to be 10.5 mm. In this case, the frequency characteristic of the microphone capsule alone has the undulation shown in FIG. 4C due to the diffraction effect (15). This is because when the opening shape of the microphone capsule is circular, the peak frequency of the first peak among the undulations due to the diffraction effect is the speed of sound / outer diameter of the microphone capsule (that is, the diameter of the circular opening shape) , and the second This is because the peak frequency of the peak is approximately three times the peak frequency of the first peak. That is, setting the peak frequency of the second peak to around 100 kHz is equivalent to setting the outer diameter dimension of the microphone capsule to approximately three times the wavelength of the sound wave of 100 kHz. Here, the peak of the characteristic that occurs at 32 kHz is that two directional microphone capsules are arranged at a predetermined interval (a distance equal to the radius of the circular microphone capsule) in the direction of the main axis of the directivity. By adding the outputs at a predetermined ratio and using the phase difference to attenuate the diffraction effect, a substantially flat frequency characteristic can be obtained.
[0014]
The peak of the characteristic occurring around 97kHz is flattened by the following method.
As described above, since the microphone sensitivity decreases when the band is set wide, in the present invention, the outer diameter of the microphone capsule is kept as it is, for example, the gap length between the diaphragm and the back electrode and the stiffness of the diaphragm are adjusted. Therefore, the bandwidth of the microphone capsule alone is set to be narrower than 100 kHz (about 70 kHz). As a result, in the single microphone capsule, the peak near 32kHz remains due to the diffraction effect, but the peak near 97kHz becomes flat (18). Sharper directivity is obtained by using the increase in sensitivity due to the diffraction effect of the microphone capsule alone in the ultra-high range and by utilizing the fact that the sensitivity increase due to the diffraction effect is small except in the front.
By the above method, as shown in FIG. 4 (d), a directional ultra-wideband microphone (17) having a flat frequency characteristic, high sensitivity (having excellent S / N) and required directivity up to an ultra high frequency range (17). Can be realized.
[0015]
Hereinafter, embodiments of the present invention will be described more specifically with reference to the accompanying drawings. An embodiment of a microphone according to the present invention is shown in the block diagram of FIG. 5, and the basic structure of the microphone is shown in FIG. In FIG. 5, the macrophone capsule to be used has a single directivity and a characteristic that covers an ultra-wide band (however, the characteristic in a single ultra-high frequency range is a flat frequency characteristic and a directivity characteristic intended by the diffraction effect). Cannot be obtained). Then, the front directional capsule 21 and the rear directional capsule 22 are arranged on the same axis in the same direction at a distance of the capsule radius. Next, the output signal of one microphone is post-added 24 through the low-pass filter 23 for adjusting the frequency characteristics, thereby making it possible to further reduce the undulation of the frequency characteristics due to the diffraction effect in the ultra-high frequency range. Flat frequency characteristics and necessary directivity can be obtained. Note that the low-pass filter 23 is only for flattening the frequency characteristics, and is therefore a circuit that can be added and removed as necessary. Further, the target frequency characteristic can be obtained by adjusting the cutoff frequency instead of the low-pass filter.
[0016]
Explaining the above matters in more detail, the single microphone capsule 21 or 22 has a large undulation in the front characteristics in the ultra high frequency region due to the diffraction effect (31, FIG. 7 (a)). Therefore, when two identical unidirectional macrophone capsules 21 and 22 are arranged on the same axis in the same direction and the distance is adjusted, when the distance between the microphone capsules is approximately the length corresponding to the radius of the capsule, In the ultra-high frequency band, the output of the two microphones cancels out due to the phase difference, so that the front sensitivity is lowered and the lateral sensitivity is not lowered at the same time. That is, in the case of the above arrangement, since the characteristic opposite to the diffraction effect is exhibited, the desired flat unidirectional frequency characteristic can be obtained by canceling the characteristic of the single microphone (33, FIG. 7 (b)).
[0017]
【The invention's effect】
There are several challenges to realizing a microphone that can pick up sound in the ultra high range. The main one is (1) Microphone capsule sensitivity is lowered when the band up to ultra high frequency is realized. {Circle around (2)} Due to the diffraction effect, a large undulation appears in the frequency characteristics of the high frequency range or the ultra high frequency range, resulting in a difference in sound quality between the front and the front. (3) If the microphone capsule is miniaturized to reduce the influence of the diffraction effect, the sensitivity is lowered and the S / N is also deteriorated. (4) The conventional design method is three-way or four-way, the microphone becomes large, and the sound field is disturbed in the super high range.
These problems are solved by adopting the present invention in a microphone configuration, and a wide band castle microphone can be realized relatively easily.
[Brief description of the drawings]
FIG. 1 is a block diagram of a conventional unidirectional microphone (when a single microphone capsule is used).
FIG. 2 is a block diagram of a conventional unidirectional microphone (when two microphone capsules are used).
FIG. 3 is a block diagram of a microphone whose band is divided.
FIGS. 4A and 4B are diagrams showing frequency characteristics of various microphones, where FIG. 4A shows expected frequency characteristics of a conventional microphone (11) and an extended microphone (12), and FIG. 4B shows the outside of the microphone capsule. Frequency characteristics when the diameter is 13 mm (front (0 degree) 13 and lateral direction (90 degrees) 14), (c) is the frequency characteristic when the outer diameter of the microphone capsule is 10.5 mm (front (0 degree) 15 and Horizontal direction (90 degree | times) 16), (d) is a figure which shows the frequency characteristic (this invention front characteristic 17 and this invention's front characteristic 18) of the microphone by this invention when the outer diameter of a microphone capsule is 10.5 mm.
FIG. 5 is a block diagram of the microphone of the present invention.
FIG. 6 is a basic structural diagram of the microphone of the present invention.
7A and 7B are frequency characteristic diagrams shown for comparison, in which FIG. 7A is a frequency characteristic of a single microphone capsule, and FIG. 7B is a frequency characteristic of a microphone according to the present invention.
[Explanation of symbols]
1: Unidirectional capsule 2: Front omnidirectional capsule 3: Rear omnidirectional capsule 4: Unidirectional capsule for mid-low range 5: Unidirectional capsule for high range 6: Single for ultra high range Directional capsule 21: Forward directional capsule 22: Backward directional capsule 23: Low-pass filter 24: Adder 25: Head cover 26: Electronic circuit 27: Microphone case 28: Output connector

Claims (2)

A broadband directional microphone that covers a band from 20 Hz to 100 kHz with a single directivity ,
Two microphone capsules having the same configuration and spaced apart in the same direction on the same axis ;
Amplifying means for amplifying each output signal of the two microphone capsules;
Adding means for adding each signal amplified by the amplification means,
Each of the two microphone capsules has a circular aperture shape that produces a first peak and a second peak as frontal sensitivity within the band;
The circular opening shapes of the two microphone capsules are such that the peak frequency of the first peak is approximately the speed of sound / the diameter of the circular opening shape of the microphone capsule , and the diameter of the circular opening shape. Is predetermined to be approximately three times the peak frequency wavelength of the second peak,
A wideband directional microphone , wherein a distance between the two microphone capsules is predetermined to be approximately ½ of a diameter of the circular opening shape . The low-pass filter which performs low-pass filtering before either one of the two microphone capsule output signals amplified by the amplifying unit is input to the adding unit is provided. Wideband directional microphone.

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