JPH07198470A - Acoustic intesity measuring apparatus - Google Patents

Abstract

PURPOSE:To enable the measuring of acoustic intensity corrected accurately by using a cross spectrum between sound signals obtained with a plurality of microphones. CONSTITUTION:A microphone probe 1 is provided with four microphones P1, P2, P3 and P4 and arranged to be extended at least in such three directions that segments joining two each thereof differ from each other three- dimensionally. A signal obtained in such an arrangement is inputted into an analyzer 3 via a microphone amplifier 2. Then, a digital signal converted with an A/D conversion section 4 is inputted into an arithmetic section 5. With the arithmetic section, the signals obtained with the respective microphones P1, P2, P3 and P4 undergoes a Fourier transform while a cross power spectrum is determined corresponding to the combination of two each of the microphones. The cross spectrum is inputted into a sound direction calculating section 6 to determine the direction of a sound. Acoustic intensity is obtained with an arithmetic section 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound intensity measuring device used in the field of sound measurement such as noise control, sound field visualization, sound source search, and radiation power measurement.

[0002]

2. Description of the Related Art Sound intensity is defined as the energy of sound that travels through a unit area perpendicular to the direction of travel of a sound in a sound field in a unit time. By measuring the sound intensity, it is possible to visualize the sound field by the flow of energy, which was impossible with the conventional method of measuring the sound pressure, which is a scalar quantity. As a result, in the field of noise control, sound source search is facilitated and noise countermeasures can be easily established. Further, also in the measurement of the radiation power in the actual use state, the radiation power can be measured without being significantly affected by the surrounding reflection and external noise.

Conventionally, a so-called two-microphone method has been known as a sound intensity measuring method. This method places two microphones apart from each other by a predetermined distance d in the sound field, and assuming that the sound field changes linearly between the two microphones, the midpoints of the two microphones are The sound intensity of the position is measured. However, in the two-microphone method, the above assumption, that is, the error due to the first-order approximation is included, and the difference in the phase of the sound input to each of the two microphones is a large error factor especially in the high frequency band.

As a method of correcting this error, (a) the wavelength λ of the sound and the distance d between the two microphones, which are predetermined amounts before measurement, are used to calculate the sound intensity kd / sin. (Kd),
(However, k represents the wave number (2π / λ)). (B) The obtained sound intensity is multiplied by φ / sin φ using the phase difference φ between the sound signals obtained by each of the two microphones. There are two methods.

These two methods are based on the direction of the flow of sound energy (hereinafter sometimes simply referred to as "sound direction").
And the direction of the line segment connecting the two microphones (hereinafter sometimes referred to as the “probe direction”) match,
Moreover, under the condition that there is no sound reflection, accurate correction is performed using either method.

[0006]

However, if the direction of the sound and the direction of the probe do not match or there is a reflected wave of the sound, correct correction may not be possible in some cases. Figure 8
[Fig. 4] is a graph showing a simulation result for confirming the effects of the above-described corrections (a) and (b). The vertical axis represents the sound intensity (dB) (relative value), and 0 dB represents a value without error. The horizontal axis represents the phase difference between the traveling wave and the reflected wave. That is, this graph represents the error of the sound intensity when the probe is arranged at each measurement point where the phase difference between the traveling wave and the reflected wave is different.

The conditions of the simulation for obtaining the graph of FIG. 8 are as follows: sound frequency f = 1.2 kHz, relative intensity r of the reflected wave to the traveling wave r = 0.0 (indicating no reflection), and two Distance between microphones d = 0.05
m, the angle between the direction of the probe and the direction of sound θ = 45 °
Is. The obtained sound intensity without any correction is about − as shown by the solid line in FIG.
It has an error of 0.5 dB. When this is multiplied by (a) described above, that is, kd / sin (kd),
As shown by the broken line in FIG. 3, an error of about 0.5 dB is produced. On the other hand, when the above-mentioned (b), that is, φ / sin φ is multiplied, the correction is correctly performed as shown by the alternate long and short dash line in FIG.

That is, under the condition that the direction of the probe and the direction of the sound do not match and there is no reflection of the sound, the correct correction is made by multiplying by φ / sin φ, and the correct correction is made by kd / sin (kd). Is not done. FIG. 9 shows the intensity ratio r = 0.
5. In the case of an angle θ = 0 ° formed by the direction of the probe and the direction of the sound (indicating that the directions are in agreement), FIG.
7 is a graph showing a simulation result similar to.

When no correction is made, there is an error of about -0.5 dB as shown by the solid line, and kd / sin (k
When d) is multiplied, the correction is correctly performed, and when φ / sin φ is multiplied, the error largely varies depending on the phase difference. That is, under the condition that the direction of the probe and the direction of the sound match, kd / sin (k
Corrected by multiplying d), φ / sin
Correct correction is not performed with φ.

In FIG. 10, the intensity ratio of the reflected wave to the traveling wave is r = 0.5, and the angle θ between the probe direction and the sound direction is θ =
10 is a graph showing the same simulation result as in FIGS. 8 and 9 in the case of 45 °. As shown in FIG. 10, under the condition that the reflected wave exists and the direction of the probe and the direction of the sound do not match, kd / sin (kd),
Correct correction is not performed using either of φ / sin φ.

Here, if the direction of the probe and the direction of the sound are the same even if the reflected wave exists, kd / sin
Since the correct correction is performed by multiplying (kd), a factor of the angle θ formed by the direction of the probe and the direction of the sound is added to this kd / sin (kd), and only 2 corresponding to the angle is added. Considering that the equivalent distance between two microphones is shortened, kdcosθ / sin (kdcos
It is conceivable to use θ) for correction.

FIG. 11 is a graph showing simulation results under the same conditions as in FIG. 10, where kd /
With correction by sin (kd) and φ / sin φ, k
The correction result by dcos θ / sin (kdcos θ) is shown. As shown in FIG. 11, kdcos θ / s
By using in (kdcos θ), correct correction is performed even if there is a reflected wave and the direction of the probe and the direction of the sound do not match.

However, kdcos θ / sin (kdco
In order to actually apply sθ), it is necessary to know in advance the angle formed by the direction of the probe and the direction of sound, but the direction of sound is usually unknown. In order to know the direction of the sound, it is possible to change the direction of the probe by trial and error to find the direction that maximizes the required sound intensity value, but it is very troublesome and not realistic. .

In view of the above circumstances, it is an object of the present invention to provide an acoustic intensity measuring apparatus capable of obtaining a correctly corrected acoustic intensity without repeating the trial and error.

[0015]

According to the sound intensity measuring apparatus of the present invention which achieves the above object, (1) line segments connecting two microphones each extend in at least three directions which are three-dimensionally different from each other. At least four microphones arranged at measurement points (2) Cross spectrum calculation means for obtaining a cross spectrum G _mn (m and n represent the numbers of the respective microphones) between sound signals obtained by the above microphones (3) Sound direction calculation means for obtaining the direction of the sound energy flow at the measurement point based on the cross spectrum G _mn obtained by the cross spectrum calculation means (3) The sound energy flow obtained by the sound direction calculation means When the angle formed by the direction and the line segment connecting each of the two microphones m and n is θ _mn , the cross spectrum G
Instead of _mn , the equation G ′ _mn = G _mn · {kd _mn cos θ _mn / sin (kd _mn cos θ _mn )} (1) where k is the wave number of the sound (2π / λ; λ is the wavelength of the sound), d _mn
Represents the distance between each two microphones m, n. The sound intensity calculating means for calculating the sound intensity is provided by using the corrected cross spectrum G ′ _mn obtained in (1).

[0016]

The cross spectrum G _mn of the sound signals obtained by the two microphones (allowing duplication) of the at least four microphones is calculated, and x is calculated based on the cross spectrum G _mn. The sound intensity components in the y, z and z directions can be obtained.

Those sound intensities are
Some include differences, but sound inte
Since the intensity component is required, the general direction of the sound
Can be determined. In this way the direction is fixed
Therefore, the angle between the direction of the sound and the direction of each pair is θ _mnage
Correction term kd_mncos θ_mn/ Sin (k
d_mncos θ_mn) Using cross spectrum G_mnCorrect
And the corrected cross spectrum G ′ _mnSound using
Find Hibiki Intensity. This allows you to try and
Correctly corrected without repeating error-like measurement
It is possible to obtain the sound intensity.

[0018]

EXAMPLES Examples of the present invention will be described below. Here, a probe having four microphones arranged at the positions of the vertices of a regular tetrahedron (Japanese Patent Laid-Open No. 28859/1993).
An example using the Japanese Patent No. 8) will be described.

FIG. 1 is a layout diagram of _four microphones P ₁ , P ₂ , P ₃ , P ₄ in this embodiment. These four microphones P ₁ , P ₂ , P ₃ and P ₄ are arranged at the respective vertices of a regular tetrahedron whose one side is the length d. X axis, Y
The axes and the Z-axis are defined arbitrarily, but here, the center of gravity of the regular tetrahedron is set to the origin 0, and three microphones P are arranged.
_The coordinate axes are set so that ₁ , P ₂ and P ₃ are on a plane extending parallel to the XY plane, and the microphone P ₄ is on the Z axis, and the Z axis extends from the position of the microphone P _{1 to} the Z axis. The Y-axis is defined in the direction of the line segment that intersects at right angles. In this embodiment, four microphones are attached to the shaft extending in the Z-axis direction so as to have such an arrangement.

2 and 3 are a front view showing a probe in a state in which four microphones are attached in an embodiment of the three-dimensional acoustic intensity measuring apparatus of the present invention, and a side view seen from the left side of FIG. is there. A microphone P ₄ is attached to the tip of the mounting shaft 20, and three microphones P ₁ , P ₂ , P ₃ are fixed to the mounting shaft 20 so as to surround the mounting shaft 20, and each arm 22, 24, 26 is fixed. Is attached to. These four microphones P ₁ , P
The sensor parts of ₂ , P ₃ and P ₄ are located at each vertex of the regular tetrahedron. Four microphones P ₁ , P ₂ , P ₃ ,
A probe in which P ₄ is attached in this way is configured, and here, the extension direction of the attachment shaft 20 is the Z axis, and the microphone P
The extending direction of the arm 22 for fixing ₁ is the Y axis. The X-axis direction is not particularly specified, but the direction perpendicular to both the mounting shaft 20 and the arm 22 is the X-axis direction. Therefore, this probe can be easily arranged in the correct direction when measuring the acoustic intensity. In addition, the center of gravity of the tetrahedron composed of these four microphones P ₁ , P ₂ , P ₃ , and P ₄ (the position of the measured acoustic intensity, the origin of the coordinate axis) is in the Z-axis direction of the microphone P _4. Since there is only the axis 20a extending to, the disturbance of the sound field can be minimized.

FIG. 4 is a block diagram showing the overall construction of an embodiment of the sound intensity measuring apparatus of the present invention.
The microphone probe 1 has four microphones P.
₁ , P ₂ , P ₃ , P ₄ are provided, and these microphones P ₁ , P ₂ , P ₃ , P ₄ are arranged and fixed as shown in FIGS. 2 and 3. The signals obtained by these microphones P ₁ , P ₂ , P ₃ , P ₄ are input to the FFT analyzer 3 via the microphone amplifier 2.

In the FFT analyzer 3, the A / D conversion section 4 converts the digital signal, and the digital signal is input to the cross spectrum calculation section 5. In the cross spectrum calculation unit 5, the microphones P ₁ , P ₂ , P
_The signals obtained at ₃ and P ₄ are respectively Fourier transformed,
Further, the cross power spectrum G _mn (m, n = 1, 2, 3, 4) corresponding to each combination of two microphones is obtained. Where G _mn is the two microphones P _m and P
It is a cross power spectrum about the signal obtained by _n .

Cross power spectrum G _mn (m, n = 1, 2, 3, 4) obtained by the cross spectrum calculation unit 5
Is input to the sound direction calculation unit 6, and the sound direction calculation unit 6 performs the following calculation to obtain the sound direction. In the sound direction calculation unit 6, the cross power spectrum G _mn (m, n = 1, 2, 3, 4) obtained by the cross spectrum calculation unit 5
First, each component of the sound intensity in the X, Y and Z directions is obtained.

The direction i component I _i of the sound intensity is
Generally, I _i = Im (a _i G ₁₂ + b _i G ₁₃ + c _i G ₁₄ + d _i G ₂₃
+ E _i G ₂₄ + f _i G ₃₄ ) However, Im (...) Is the imaginary part of the one-sided spectrum of ...
a _i , b _i , c _i , d _i , e _i , and f _i represent each coefficient.

.. (2) is represented. When this is applied to the coordinate system shown in FIGS. 1 to 3, the respective components I _x , I _y , and I _z of the sound intensity I in the X, Y, and Z directions are

[0026]

[Equation 1]

Here, Im {G}: imaginary part of one-sided cross spectrum of G: ω: angular frequency ρ: density of medium d: spacing between microphones. Here, any of the X, Y, and Z directions may be selected to be positive, and in this case, depending on the selection method, the signs of the calculation results of the expressions (3) to (5) may be reversed.

In the sound direction calculation unit 6, after obtaining each component of the sound intensity in the X and YZ axis directions based on the equations (3) to (5), the sound direction viewed from the measurement point where the probe is arranged. Is required. The direction cosine of the sound direction viewed from the measurement point is cos α = I _x / I cos β = I _y /, where α, β, and γ are angles formed by the sound direction and the X, Y, and Z axes, respectively. I cos γ = I _z / I (6) Here, I is the magnitude of the sound intensity, and is given by I = (I _x ² + I _y ² + I _z ² ) ^1/2 (7).

When the three direction cosines shown in the equation (6) are used, the microphones m, n (m, m) in which two four microphones P ₁ , P ₂ , P ₃ , P ₄ are combined respectively
The angle θ _mn formed by the pair direction (n = 1, 2, 3, 4) and the sound direction is obtained.

[0030]

[Equation 2]

The angle θ _mn obtained by the sound direction calculation unit 6 based on the equation (8) and the cross spectrum G _mn obtained by the cross spectrum calculation unit 5 are input to the sound intensity calculation unit 7. In the sound intensity calculation unit 7, the input angle θ _mn and the cross spectrum G _{mn are} input.
By using and, the cross spectrum G ′ _mn corrected by the equation G ′ _mn = G _mn · {kdcos θ _mn / sin (kdcos θ _mn )} (9) is obtained,
Further, using this corrected cross spectrum G ′ _mn , an equation in which G _mn in the above equations (3) to (5) is changed to G ′ _mn :

[0032]

[Equation 3]

A sound intensity corrected based on
Component I in the X, Y and Z directions_x ´, I_y ´, I_z But
Desired. In the sound intensity calculation unit 7,
Sound intensity (I _x ´, I_y ´, I_z 
′) Is returned to the sound direction calculation unit 6 again, and in the formulas (6) to (8),
Therefore, the angle θ_mnAnd re-obtained angle θ_mnTo
Input to the sound intensity calculation unit 7
And repeat the correction several times in this way
The sound intensity after playing may be obtained.

Next, the simulation result of the present invention will be described. FIG. 5 is a graph showing a simulation result for confirming the effect of the correction according to the present invention. The condition of the simulation is that the sound frequency f = 1.2 kHz
z, relative intensity of reflected wave to traveling wave r = 0.5, 2 each
Distance between two microphones d = 0.06m, Z axis and X
The angle ξ between the sound direction and the Z-axis in the plane including the axis
= 0 °, an angle ζ between the direction of sound and the X axis in the plane including the X axis and the Y axis ζ = 0 °, and the mutual phase difference (phase difference between channels) of all microphone / amplifier systems is zero. This is the case. That is, the simulation shown in FIG. 5 is for the case where the reflected wave exists but the direction of the sound matches the Z axis.

In this case, there is an error of about -1.0 dB before the correction, but even if there is a reflected wave, it is correctly corrected by the method of the present invention. FIG. 6 is a graph showing another simulation result for confirming the effect of the correction according to the present invention. The simulation conditions are as described in the figure, and the difference from the simulation in FIG. 5 is ξ = 45 °, that is, the sound is incident from the Z axis in a direction swung 45 ° in the X direction (horizontal direction). Is assumed.

FIG. 6 shows a component of the sound intensity in the X direction and a component in the Z direction. When the magnitude of the sound intensity (see the equation (7)) is 1.0, the X direction is shown. , Z-direction components I _x and I _z are expressed in decibels, and I _x = I _z = 10 · log 1.0 / √2 = −1.5 (d
B). Therefore, it means that the position of -1.5 dB in FIG. 6 is correctly corrected, and in the present invention,
In this way, correct correction is performed even if there is a reflected wave and the sound enters obliquely.

FIG. 7 is a graph showing another simulation result for confirming the effect of the correction according to the present invention. In the presence of a reflected wave, the sound is incident obliquely, and the amplifier of the microphone P ₄ is changed. It is assumed that the phase error e with the other three channels included is e = kd / 50≈1.5 °. In this case, the error due to the phase error e remains, but even in this case, the reflected wave,
The error caused by the oblique incidence of sound is corrected correctly.

Although the above description is for a three-dimensional intensity probe using four microphones, the same method can be applied to a probe using six microphones.

[0039]

As described above, according to the present invention,
It is possible to obtain the sound intensity in which both the error caused by the reflected wave and the error caused by the oblique incidence of sound are corrected correctly.

[Brief description of drawings]

FIG. 1 shows four microphones P ₁ in the present embodiment.
P _2, P _3, is a schematic representation of a P _4.

FIG. 2 is a front view showing a probe with four microphones attached thereto according to an embodiment of the three-dimensional acoustic intensity measuring apparatus of the present invention.

3 is a side view of the three-dimensional acoustic intensity measuring device shown in FIG. 2 as viewed from the left side of FIG.

FIG. 4 is a block diagram showing the overall configuration of an embodiment of the sound intensity measuring apparatus of the present invention.

FIG. 5 is a graph showing a simulation result for confirming the effect of the correction according to the present invention.

FIG. 6 is a graph showing another simulation result for confirming the effect of the correction according to the present invention.

FIG. 7 is a graph showing another simulation result for confirming the effect of the correction according to the present invention.

FIG. 8 is a graph showing a simulation result for confirming the effect of correction.

FIG. 9 is a graph showing a simulation result for confirming the effect of correction.

FIG. 10 is a graph showing a simulation result for confirming the effect of correction.

FIG. 11 is a graph showing a simulation result for confirming the effect of correction.

[Explanation of symbols]

 1 Microphone probe 2 Microphone amplifier 3 FFT analyzer 4 A-D converter 5 Cross spectrum calculation unit 6 Sound direction calculation unit 7 Sound intensity calculation unit

Claims (1)

[Claims] 1. At least four microphones arranged at a measurement point such that line segments connecting two microphones extend in at least three directions which are three-dimensionally different from each other, and a sound signal obtained by the microphones. Based on the cross spectrum calculation means for obtaining the cross spectrum G _mn (m and n represent the numbers of the respective microphones) between them, and the sound energy at the measurement point based on the cross spectrum G _mn obtained by the cross spectrum calculation means. Θ _mn is the angle formed by the sound direction calculation means for obtaining the direction of the flow of the sound and the direction of the flow of the sound energy obtained by the sound direction calculation means and the line segment connecting each of the two microphones m, n. When the cross spectrum G _mn
Instead of the equation, G ′ _mn = G _mn · {kd _mn cos θ _mn / sin (kd _mn cos θ _mn )}, where k is the wave number of the sound (2π / λ; λ is the wavelength of the sound), and d _mn
Represents the distance between each two microphones m, n. The sound intensity measuring device is provided with a sound intensity calculating means for calculating the sound intensity by using the corrected cross spectrum G ′ _mn obtained in 1.