JPS62318Y2 - - Google Patents

Description

[Detailed description of the invention] This invention consists of 2 ⁿ (n is an integer of 1 or more) omnidirectional microphone cartridges of the same type and same sensitivity or 2 ⁿ unidirectional microphone cartridges arranged in a straight line. arranged axially in the gap,
This invention relates to an n-order sound pressure gradient type directional microphone which obtains directivity by differentially synthesizing these outputs through an appropriate phase shift circuit.

This type of n-order sound pressure gradient type directional microphone consists of a set of (n-1) order sound pressure gradient type microphones, and an (n-1) order sound pressure gradient type microphone consists of a set of (n-1) order sound pressure gradient type microphones. 2) Consists of an order sound pressure gradient type microphone, and similarly, a second order sound pressure gradient type microphone consists of a set of first order sound pressure gradient type microphones, and a first order sound pressure gradient type microphone consists of a set of zero order gradient type microphones. It consists of a type microphone.

Then, in order to obtain a higher-order r-order sound pressure gradient microphone using a pair of (r-1)-order sound pressure gradient microphones, the (r-1)-order sound pressure gradient microphones are placed at intervals of d _r . , and create a phase delay (kd _r cosθ) by spatial path difference (d _r cosθ) based on the spacing, and further insert a delay circuit (τ _r ) as a transfer circuit. A phase delay ωτ _r (=kd _r α _r ) is created and the signals are differentially synthesized.

However, d _r (r=1,...,n);
Spacing between a pair of r-1st-order sound pressure gradient microphones α _r =Cτ _r /d _r (r=1,...,n);
Constant determining directivity τ _r (r=1,...,n); delay time k=ω/C (ω: angular frequency of sound wave; C: speed of sound); θ: direction of sound source.

Therefore, the output of the synthesized r-th sound pressure gradient microphone is obtained by multiplying the output of the (r-1)th-th sound pressure gradient microphone by the coefficient of {1-e ^-jkd r(α _r +cosθ)}. Generally, the output voltage _E〓o of this type of n-order sound pressure gradient microphone is given by the following equation.

Here, α _i ; When the cartridge is elastically controlled; α _i = 1/jω 〃 When it is resistance controlled; α _i = 1 〃 When it is inertially controlled; α _i = jω K; Proportionality constant V _n ; Speed of the diaphragm The configuration of the n-th gradient type microphone is n=3.
FIG. 1 shows an example of a third-order gradient type microphone. In the figure, 1 is a pressure type microphone cartridge used as a zero-order gradient type microphone, and 2, 2', and 2'' are delay circuits.

Now, considering the mid-low range of kd _r (α _r + cos θ) << 1, from equation (1) we can calculate the directivity of the n-th sound pressure gradient microphone, that is, the output in the θ direction, in the axial direction (θ = 0
The value D _o (θ) normalized by the output of It can be seen that the directivity becomes sharper as n becomes larger.

On the other hand, considering the frequency characteristics of this n-order sound pressure gradient microphone in the mid-bass range, kd _r
Since (α _r +cosθ)≪1, the above equation (1) becomes the following approximate equation Equation (3) can be replaced by E〓 _o ∝k ⁿ = (ω/C) ⁿ , that is, the output voltage E〓 _o of this microphone is a function of frequency and the low-frequency sensitivity attenuation. It is shown that the frequency characteristics shown in the graph of FIG.

Therefore, the audio band (20Hz~20000
Hz) is approximately 10 octaves, the sensitivity attenuation of the low frequency range relative to the high frequency range of this n-order sound pressure gradient microphone is n x 6 (dB/oct.) x 10 (oct.) = 60 x n (dB) (4) Therefore, sensitivity attenuation of an integral multiple of 60 dB occurs over the entire audio band.

In order to eliminate such significant sensitivity attenuation and obtain a flat frequency response, the low frequency should be adjusted to 6×n (dB/oct.
) can be corrected using an equalizer, but in that case, the noise level increases, the SN ratio deteriorates, and the dynamic range becomes narrower.

Two unidirectional microphones (one
There is a second-order sound pressure gradient microphone that uses a second-order sound pressure gradient microphone.
The flat frequency characteristics of the unidirectional microphone, which is used as a pressure gradient microphone, suppresses the low-frequency sensitivity attenuation to 6 dB/octave.
Sensitivity is attenuated by approximately 60 dB over the entire audio band, resulting in a signal-to-noise ratio of approximately 60 dB compared to a unidirectional microphone.
Deteriorate.

In addition, in the above-mentioned secondary sound pressure gradient type microphone, if an omnidirectional microphone is used as the primary sound pressure gradient type microphone, the sensitivity attenuation in the entire audio band will be approximately 12 dB, and the S/N ratio will be even worse. Practical application will be extremely difficult.

Therefore, the purpose of this invention is to solve the above-mentioned problems in the conventional example and provide a high-order sound pressure gradient type microphone with a good signal-to-noise ratio.

An embodiment of this invention is shown in FIGS. 2 and 3. In other words, this directional microphone divides the audio band into multiple bands, arranges high-order sound pressure gradient microphones in correspondence with each band, and synthesizes the outputs of these. Yes, in the block diagram shown in Figure 2, the audio band is divided into three bands: low, mid, and high. Inclined microphone _3L ,
_3M and _3H are arranged in correspondence with each other, and the output of the respective tertiary sound pressure gradient type microphones _3L , _3M , and _3H is configured to be synthesized with the equalizers _4L , _4M , and _4H . ing.

Each of the tertiary sound pressure gradient microphones 3 _L , 3 _M , and 3 _H corresponding to the three bands is composed of two secondary sound pressure gradient microphones 5 L , 5 L , and two secondary sound pressure gradient microphones 5 _L , 5 _L , respectively. _5M , _5M , _5H , _5H
are connected so that their outputs are differentially synthesized, and the two secondary sound pressure gradient microphones 5 _L , 5 _L , 5 _M , 5 _M , 5 _H , and 5 _H are configured so that their outputs are differentially combined. One unidirectional microphone cartridge _7L , with head amplifiers _6L , _6M , _6H connected to the next stage.
_7M , _7H , another unidirectional microphone cartridge _7L , 7M, ₇ in which head amplifiers _6L , _6M , _6H and delay circuits _8L , _8M , _8H are connected.
_H and are configured by connecting these outputs so that they are differentially synthesized. In this embodiment, the delay time of each of the delay circuits _8L , _8M , and _8H is 0.368 msec for the low range and 0.368 msec for the middle range.
It is set to 0.0735msec and 0.0147mesc for the high range.

In addition, low-pass filters with an attenuation characteristic of -12 dB/oct. are adopted as the equalizers 4 _L , 4 _M , and 4 _H , and each cut-off frequency is set for the low range.
_C = 120Hz, _C = 600Hz for the midrange, and _C = 3KHz for the high range.

Further, the unidirectional microphone cartridges _7L , _7M , _7L are spaced apart from each other at appropriate intervals as shown in FIG. 3 in order to create a phase delay due to path difference. However, in this example, this interval is set to
125mm, 25mm for midrange, 5mm for high range
It is set to mm. In addition, the center of the arrangement of the unidirectional microphone cartridge group corresponding to the midrange
Unidirectional microphone that supports _M and low frequencies.
The distance from the center O _L of the cartridge group is 283.3
mm, and the distances between the mid-range arrangement center O _M and the high-range arrangement center O _H are set to 56.7 mm to serve as means for preventing phase shift at the crossover frequency of each output of the multiway.

In this case, the distance l between both ends of the entire unidirectional microphone cartridge is the above-mentioned intervals (125 mm, 25 mm, 5 mm) and the distances (283.3 mm, 283.3 mm,
56.7mm) to 535mm.

Here, the cause of the phase shift occurring at the crossover frequency will be explained. This is because the output voltages of the n-order sound pressure gradient microphones configured for each band have different phases relative to the incoming sound waves depending on their spatial arrangement. The band was divided because a single n-order sound pressure gradient microphone cannot cover the entire audio band, and especially in the frequency range where the distance between the microphone cartridges exceeds half the wavelength of the incoming sound wave, peaks and valleys are severe. arise. Therefore, the phase also changes drastically correspondingly. For these two reasons, it is necessary to perform phase adjustment when combining the outputs of the low, middle, and high ranges. If phase adjustment is not performed by some means, peaks and valleys will occur in the frequency characteristics later. The phase shift prevention means is for performing this phase adjustment.

Next, the distance between the centers of the microphone cartridge groups will be explained.

The distance between the centers of the microphone cartridge groups is determined to be a predetermined value in order to configure the phase shift prevention means by utilizing the spatial arrangement as described above. The distance between the centers of the microphone cartridge groups is the output voltage (vector quantity) of each microphone cartridge group,
It is uniquely determined by the set value of the crossover frequency and the transfer function (vector quantity) of the equalizer. However, it may be determined to such an extent that the frequency characteristics of the microphone are not impaired.
In this embodiment, the distance between the centers of arrangement is selected so that the front sensitivity characteristic is as flat as possible.

Next, the distance between the centers of the microphone cartridge groups will be explained in detail. First, the basic configuration of the secondary sound pressure gradient type microphone will be explained. A secondary sound pressure gradient type microphone is constructed using two directional microphone units or four non-directional microphone units. For example, FIG. 8 shows the basic configuration of a secondary sound pressure gradient type microphone constructed using two directional microphone units (primary sound pressure gradient type). In FIG. 8, 21 and 22 are directional microphone units arranged one behind the other in the front direction with an interval d ₁ between them, 23 is a delay circuit with a delay time τ _{1, and 24 is a delay circuit having a delay time τ 1} .
is a differential circuit that outputs the difference between the output of the directional microphone unit 21 and the output of the delay circuit 23.
R ₀ is the distance from the midpoint O ₀ between the directional microphone units 21 and 22 to the sound source 25, θ ₀ is the angle from the midpoint O ₀ toward the sound source 25 with respect to the front direction, and R ₁ is the distance between the directional microphone unit 2
1 is the distance from the center point O ₁ of the directional microphone unit 22 to the sound source 25, θ ₁ is the angle from the center point O ₁ to the sound source 25 with respect to the front direction, and R ₂ is the distance from the center point O ₂ of the directional microphone unit 22 to the sound source 25. distance, θ
₂ is the angle of the direction from the center point O ₂ toward the sound source 25 with respect to the front direction.

e ₁ (R ₁ , θ ₁ ) is the output voltage of the directional microphone unit 21, e ₂ (R ₂ , θ ₂ ) is the output voltage of the directional microphone unit 22, e _TO (R ₀ , θ
₀ ) is the output voltage of the differential circuit 24, that is, the output voltage of the secondary sound pressure gradient type microphone, and C is the speed of sound.

From FIG. 8, the output voltage e _TO (R ₀ , θ ₀ ) of the secondary sound pressure gradient microphone is expressed as e _TO (R ₀ , θ ₀ )=e ₁ (R ₁ , θ ₁ )−e ₂ (R ₂ , θ ₂ )×exp(−jωτ ₁ ). When d ₁ <<R ₀ , e ₂ (R ₂ , θ ₂ )≒e ₁ (R ₁ , θ ₁ )×exp(−jω/Cd ₁ cos _{θ 0} ). Therefore, the output voltage e _TO (R ₀ , θ ₀ ) of the secondary sound pressure gradient microphone is e _TO (R ₀ , θ ₀ ) = e ₁ (R ₁ , θ ₁ ) × [1−exp(− jω/Cd ₁ cosθ ₀ )×exp(−jωτ ₁ )] = e ₁ (R ₁ , θ ₁ )×[1−exp{−jω/Cd ₁ (cosθ ₀ +α ₁ )}]. However, α ₁ =Cτ ₁ /d ₁ .

Now, let us consider the low-mid range where ω/Cd ₁ (cos θ ₀ + α ₁ )≪1 and focus on its directivity D (θ ₀ ). Directional microphone units 21, 22
_{Let Z be the} directivity _of Then, e _TO (R ₀ , θ ₀ ) = F×{co/Cd ₁ (cos θ ₀ +α ₁ )}. That is, when the frequency characteristics F of the directional microphone units 21 and 22 are flat, the frequency characteristics of the secondary sound pressure gradient type microphone have a slope of -6 dB/octave in the low and middle range. Note that in a secondary sound pressure gradient type microphone constructed using four omnidirectional microphone units, its frequency characteristics have a slope of -12 dB/octave in the low and middle range.

Figure 9 shows two directional microphone units 2.
1 and 22 are shown. In FIG. 9, _H1 is a cutoff frequency in the high range and is expressed as _H1 = C/d ₁ (cos θ ₀ +α ₁ ), and as d ₁ and α ₁ become larger, the cutoff frequency _H1 becomes lower.

Here, consider a third-order sound pressure gradient type microphone. This third-order sound pressure gradient microphone has two
It consists of two secondary sound pressure gradient type microphones.

The center distance between the secondary sound pressure gradient microphones is d ₂
Then, the cutoff frequency _H2 at that time is determined by the spatial arrangement and is given by the following formula. That is, the cutoff frequency _H2 is _H2 = C/d ₂ (cos θ ₀ +α ₂ ). In this case, since α ₂ =1, _H2 = C/d ₂ (cosθ ₀ +1). Therefore, when the cutoff frequency _H2 is determined, for example, when it is set to the crossover frequency, the center distance _d2 is uniquely determined. Normally,
In order to smooth the frequency characteristics after synthesis, the center distance d ₂ is set slightly smaller than the calculated value. In addition,
Since the value of the cut-off frequency _H2 changes depending on the value of the angle θ ₀ , it will be considered based on θ ₀ =0 (on the axis).

Similarly, a second-order sound pressure gradient microphone is composed of two (n-1)th-order sound pressure gradient microphones, and the cutoff frequency _Ho-1
The relationship between and the center distance d _o-1 is as follows.

_Ho-1 = C/d _o-1 (cos θ ₀ +1) When θ ₀ = 0, _Ho-1 C/2×d _o-1 ) In Fig. 3, 10 is the shield case, 12 is the electrical This is the circuit section.

In _this way, _the audio band can be adjusted to low _or
Since it is divided into three bands, medium and high, and the output of each band is corrected with separate equalizers 4 _L , 4 _M , and 4 _H , sensitivity attenuation is less than that of the conventional example.
The signal-to-noise ratio can be greatly improved, and the dynamic range can therefore be increased.

In addition, the center positions O _L , O _M , O _M of the unidirectional microphone cartridge group for each band are O _L −O
Since the distance between _M and O _M is different from each other by 2833mm and the distance between _O The occurrence of dips due to the structure can be completely prevented.

In the above embodiment, the primary sound pressure gradient microphone was constructed using a unidirectional microphone cartridge, but the same effect can be obtained by using an omnidirectional microphone cartridge.

FIG. 4 shows the sensitivity characteristics in the axial direction (θ=0 degree) in each band in the above embodiment. A in the same figure is low range,
B in the same figure shows the characteristics in the middle range, and C in the same figure shows the characteristics in the high range. In the figure, a is the characteristic curve of the low-pass filter adopted as the equalizers 4 _L , 4 _M , and 4 _H , and b is the output characteristic curve before input to the low-pass filter. , c shows the output characteristic curve after passing through the low-pass filter.

The directivity characteristics according to the above embodiment are shown in FIG.
In the figure, a, b, c, d, e, and g indicate the direction of the sound source at 0 degrees, 30 degrees, 60 degrees, 75 degrees, 105 degrees, and 120 degrees, respectively.
It shows the sensitivity characteristics at 150 degrees and 150 degrees. Note that the sensitivity at 90 degrees and 180 degrees is infinitesimal.

Other embodiments of this invention are shown in FIGS. 6 and 7. That is, this directional microphone differs from the embodiment described above in which the center positions of the unidirectional microphone cartridge groups for each band are made different as a means to prevent a phase shift at the crossover frequency when the respective outputs of the multiway are combined. Instead, as shown in FIG. 4, the delay circuit 11 corrects the phase of the output of the tertiary sound pressure gradient microphones arranged corresponding to the low, middle and high frequencies of the audio band.
This is done using _M and _11H .
In this embodiment, the output of the 3rd order sound pressure gradient type microphone _3L for the low range is directly outputted via the equalizer _4L , and the output of the 3rd order sound pressure gradient type microphone _3M for the mid range is directly output. A delay circuit _11M with a predetermined delay time is connected to the output stage of the equalizer _4M , and a delay circuit with a longer delay time than that for the middle range is connected to the output of the tertiary sound pressure gradient microphone _3H for high frequencies. _11H is connected to the output stage of the equalizer _4M , and the center positions of the unidirectional microphone cartridge groups for each band are aligned at the same position 0 as shown in FIG.

That is, the difference is that the phase matching at the crossover frequency is performed by spatial processing in the previous embodiment, whereas it is performed by electrical processing in this embodiment, and the other configurations and their effects are the same as in the previous embodiment. It is similar to

As described above, the directional microphone of this invention has 2 ⁿ (n is an integer of 1 or more) microphone cartridges of the same type and the same sensitivity arranged in a straight line, and the outputs of these microphone cartridges are transferred through a phase shift circuit. A multi-way system in which high-order sound pressure gradient type microphones for differential synthesis are arranged corresponding to each of the audio bands divided into multiple bands, and the output of each of the above-mentioned high-order sound pressure gradient type microphones. an equalizer that performs sensitivity correction; an output unit that combines multiple outputs of the multiway;
Since it is equipped with a phase shift prevention means that prevents phase shift at the crossover frequency of each output of the multiway, sharp directivity without frequency dependence can be achieved without reducing the SN ratio or dynamic range. This has the effect that it can be used as a microphone with a microphone. Moreover, since the phase shift prevention means is provided, it is possible to eliminate the phase shift of the output of the high-order sound pressure gradient type microphone at the multiway crossover frequency, and it is possible to improve the frequency characteristics.

[Brief explanation of the drawing]

Fig. 1 is a basic wiring diagram showing a conventional example, Fig. 2 is a basic wiring diagram showing an embodiment of this invention, Fig. 3 is a layout configuration diagram of the unidirectional microphone cartridge, and Fig. 4 is each The axial direction (θ=
0 degree), Figure 5 is a diagram showing its directional characteristics, Figure 6 is a basic wiring diagram showing another embodiment of this invention, and Figure 7 is its unidirectional microphone cartridge. FIG. 8 is a schematic diagram showing the basic configuration of the secondary sound pressure gradient type microphone, and FIG. 9 is an output frequency characteristic diagram of the secondary sound pressure gradient type microphone. 3 _L , 3 _M , 3 _H ...Third sound pressure gradient microphone, 4 _L , 4 _M , 4 _H ...Equalizer, 5 _L , 5 _M ,
5 _H ... Secondary sound pressure gradient microphone, 6 _L , 6
_M , 6 _H ...head amplifier, 7 _L , 7 _M , 7 _H ...unidirectional microphone cartridge, 8 _L , 8
_M , 8 _H , 11 _M , 11 _H ...Delay circuit, 9... Axis line.

Claims (1)

[Claims for Utility Model Registration] (1) The audio frequency band is divided into a plurality of bands, and 2 ⁿ (n is an integer of 1 or more) microphone cartridges of the same type and the same sensitivity are made to correspond to each divided band. High-order sound pressure that is arranged in a straight line and differentially synthesizes the outputs of these microphone cartridges via a phase shift circuit to obtain directivity, and then corrects the sensitivity characteristics of the synthesized output via an equalizer. A high-order multi-way configuration in which gradient-type microphones are configured for each of the divided bands, and the outputs of these high-order sound pressure gradient-type microphones are synthesized via phase shift prevention means that prevents phase shift at each crossover frequency. Sound pressure gradient type directional microphone. (2) The phase shift prevention means is such that the center position of the microphone cartridge group constituting the high-order sound pressure gradient microphone is made different for each high-order sound pressure gradient microphone corresponding to each band. A directional microphone according to claim (1) of the utility model registration. (3) The phase shift prevention means is configured by connecting delay circuits having different delay times corresponding to each band to the output stage of each of the high-order sound pressure gradient microphones. Directional microphone described in ).