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DESCRIPTION JPH05288600

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DESCRIPTION JPH05288600
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention adjusts the
characteristics of a plurality of microphones used for this measurement to be identical to each
other when performing measurement using a plurality of microphones, for example,
measurement of acoustic intensity. Alternatively, the present invention relates to a method of
comparing the characteristics of a plurality of microphones for grasping the difference in the
characteristics of the plurality of microphones and correcting the measurement result.
[0002]
2. Description of the Related Art Conventionally, various methods for performing measurement
using a plurality of microphones are known, and as one of them, a so-called paired microphone
for measuring an acoustic intensity is known. The prior art will be described with reference to
this pair microphone as an example (see Japanese Utility Model Laid-Open No. 1-81541).
[0003]
Paired microphones consist of two microphones placed one behind the other, and by directing
the paired microphones so that the sounding body exists on the extension of the line connecting
these two microphones, the sound of the sound emitted from the sounding body Sound intensity
is determined. The sound intensity is calculated based on the cross power spectrum obtained by
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Fourier transforming the output of this pair of microphones.
[0004]
That is, the cross power spectrum Gba (f) obtained by the above-mentioned Fourier transform
processing is Gba (f) = Sb · Sa * (1) where Sb: Fourier transform spectrum Sa * of the output of
one microphone: the other Complex conjugate spectrum of the Fourier transform spectrum of the
output of the microphone, and based on the cross power spectrum Gba (f), the acoustic intensity I
(f1 to f2) between the frequencies f1 and f2 is determined as follows: Be
[0006]
Here, Im {Gba (f)}: imaginary part of one-side cross spectrum of cross power spectrum Gba ρ:
density of medium Δr: distance between both microphones The acoustic intensity determined by
this equation (2) is three-dimensional It is a component of the linear direction which connects
both microphones in the central point between both microphones among basic sound intensity.
[0007]
In practice, however, it is difficult to produce two microphones with completely identical
characteristics, and in general, two microphones with relatively identical characteristics are
selected and used from among a large number of manufactured microphones. Even in this case,
the characteristics do not necessarily match at all, and the characteristic difference will appear as
a measurement error.
[0008]
In order to eliminate the measurement error based on this characteristic difference, in the abovementioned document (Japanese Utility Model Application Laid-Open No. 1-81541), microphones
are sequentially arranged one by one on the front of the speaker so as to be at the same position
with respect to the speaker. A closed space is formed in front of the speaker to record sound, and
Fourier transform spectra Sa and Sb of each microphone of the signal obtained by this recording
are determined, and the characteristic difference H between microphones as their ratio H = Sa
There is disclosed a technique of obtaining / Sb (3) and using the characteristic difference H to
correct the acoustic intensity by the pair microphone.
[0009]
However, with respect to a plurality of microphones whose characteristic differences are to be
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determined, their external dimensions are different from one another as well as the
characteristics are slightly different, and those microphones are one speaker at a time. The size
of the closed space and the amount of air leakage from the closed space are slightly different
when set on the front of the frame, and thus the sound field in the closed space becomes
different when the microphone is replaced.
When the sound field changes, the influence is particularly noticeable in the low frequency
region, and there is a problem that the characteristic difference H between the microphones in
the low frequency region can not be accurately obtained.
[0010]
In order to avoid such a problem, it is conceivable to simultaneously arrange a plurality of
microphones on the front of the speaker and simultaneously record sound under one sound field.
However, when multiple microphones are arranged at the same time, they will be arranged at
different positions with respect to the speaker, but the sound field also differs depending on the
arrangement position of the microphones with respect to the speaker. .
[0011]
SUMMARY OF THE INVENTION In view of the above-described circumstances, the present
invention has an object of providing a microphone characteristic comparison method capable of
accurately determining differences in the characteristics of a plurality of microphones.
[0012]
In order to achieve the above object, according to the microphone characteristic comparison
method of the present invention, a plurality of microphones are arranged in the vicinity of a
sounding body to record sound, and the arrangement positions of the plurality of microphones
are provided. To obtain an average Fourier transform spectrum of a Fourier transform spectrum
of each of a plurality of signals obtained by recording sound while exchanging positions with
each other, for each of the plurality of microphones; The characteristic differences between the
plurality of microphones are determined based on these average Fourier transform spectra.
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[0013]
According to the present invention, even if the external dimensions and the like of the
microphones are different from each other, if they are placed at the same time, the size of the
closed space as a whole and the amount of air leakage will change even if the placement
positions are alternated with each other. Therefore, it focuses on the fact that accurate
measurement can be performed.
[0014]
According to the present invention, sound is recorded while alternately arranging the positions of
a plurality of microphones, an average Fourier exchange spectrum is obtained for each of the
microphones, and a difference in characteristics is determined based on this, so a low frequency
region is included. The difference in the characteristics can be accurately determined over the
entire area required.
[0015]
Examples of the present invention will be described below.
Here, in the case of three-dimensional sound intensity measurement using four microphones, the
case of comparing the characteristics of these four microphones will be described.
FIGS. 4 and 5 are a front view showing a probe in a state in which four microphones according to
an example of the three-dimensional acoustic intensity measurement device are attached, and a
side view seen from the left of FIG.
[0016]
The microphone P4 is attached to the end of the attachment shaft 20, and the three microphones
P1, P2, P3 are attached to the respective arms 22, 24 and 26 fixed to the attachment shaft 20 so
as to surround the attachment shaft 20. It is done.
These four microphones P1, P2, P3 and P4 are constructed such that their sensor parts are at the
respective apexes of a regular tetrahedron.
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A probe in which four microphones P1, P2, P3 and P4 are attached in this way is constituted, the
extending direction of the mounting shaft 20 is taken as Z axis, and the extending direction of the
arm 22 for fixing the microphone P1 is taken as Y axis.
Although the X-axis direction is not particularly specified on the probe, it is immediately grasped
as a direction perpendicular to both the mounting shaft 20 and the arm 22.
Therefore, the probe can be easily arranged in the correct direction in measuring the acoustic
intensity.
[0017]
FIG. 6 is a block diagram showing an entire configuration of an example of a three-dimensional
sound intensity measurement apparatus. The microphone probe 1 is provided with four
microphones P1, P2, P3 and P4, and these microphones P1, P2, P3 and P4 are arranged and
fixed as shown in FIGS. The signals obtained by these microphones P 1, P 2, P 3 and P 4 are
inputted to the FFT analyzer 3 via the microphone amplifier 2.
[0018]
In the FFT analyzer 3, the A / D converter 4 converts the digital signal into a digital signal, and
the digital signal is input to the FFT calculator 5. In the FFT operation unit 5, the signals obtained
by the respective microphones P1, P2, P3 and P4 are respectively subjected to the Fourier
transform, and cross power spectra Gij (i, j = 1, 2, 3) corresponding to the respective
combinations of two microphones. , 4) are required. Where G ij is the cross power spectrum for
the signal obtained with the two microphones P i and P j.
[0019]
The cross power spectrum G ij (i, j = 1, 2, 3, 4) obtained by the FFT operation unit 5 is input to
the intensity operation unit 6, and the intensity operation unit 6 performs an operation according
to the following equation. The components SIX, SIY and SIZ in the X, Y and Z directions of the
acoustic intensity are obtained.
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[0021]
Here, Im {G}: imaginary part of one side cross spectrum of G: density of medium d: distance
between microphones The acoustic intensity (SIX, SIY, SIZ) determined in this way is the display
unit 7 Is input and displayed.
[0022]
Here, this three-dimensional sound measurement apparatus is an application of the principle of
the pair microphone described above, but the above equation holds when the characteristics of
the four microphones are the same.
However, since there is a characteristic difference in practice, the characteristic difference is
determined, and the Fourier transform spectrum for each microphone determined by the FFT
operation unit 5 is corrected, and the corrected Fourier transform spectrum is used to obtain the
above (4) The calculation of the equation (6) is performed.
[0023]
Next, how to calculate the characteristic difference of these four microphones will be described.
FIG. 1 is a side view (a) showing the microphone insertion portion of the microphone calibrator
and a front view (b) showing the upper half in cross section. A speaker 12 is built in the
microphone insertion portion 10, and four long holes 14a, 14b, 14c and 14d are formed toward
the front of the speaker 12. The four microphones P1, P2, P3, P4 removed from the microphone
probe shown in FIG. 4 are inserted into the four elongated holes 14a, 14b, 14c, 14d. The external
dimensions of the four microphones P1, P2, P3 and P4 are identical to each other except for the
tolerance point, and the four elongated holes 14a, 14b, 14c and 14d are also drilled to the same
dimensions, and therefore Any one of the four microphones P1, P2, P3, P4 can be inserted into
any one of the four holes 14a, 14b, 14c, 14d. When these four microphones P1, P2, P3, P4 are
inserted into the four elongated holes 14a, 14b, 14c, 14d, a small closed space is formed at the
position of the front surface of the speaker 12 in the microphone insertion portion 10. .
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[0024]
FIG. 2 is a diagram showing the position of the microphone with respect to the speaker when
four microphones are inserted into the long hole. As shown in this figure, the microphones P1,
P2, P3, P4 are first inserted into each long hole 14a, 14b, 14c, 14d and recorded, and then their
positions are alternated to each long hole 14a, 14b. , 14c, 14d are inserted into the respective
microphones P2, P3, P4, P1 to record the sound, and then alternated to make each of the long
holes 14a, 14b, 14c, 14d into the respective microphones P3, P4, P1, P1,. P2 is inserted to
record the sound, and at the end, the microphones P4, P1, P2 and P3 are inserted into the long
holes 14a, 14b, 14c and 14d, respectively, to record the sound. As a result, the sound is recorded
while the positions of the microphones P1, P2, P3 and P4 are all replaced.
[0025]
FIG. 3 is a block diagram of the entire apparatus for determining the microphone characteristic
difference. A signal generation unit 9 incorporated in the FFT analyzer 3 generates a steady
signal including each component within a predetermined frequency range f1 to f2, and the signal
is sent to a speaker 12 provided in the microphone insertion unit 10 The speaker 12 emits a
sound corresponding to the input signal. In this state, as described above, while alternately
changing the positions of the four microphones P1, P2, P3 and P4, the sound is recorded to
obtain each signal. The respective signals obtained by these microphones P1, P2, P3 and P4 are
inputted to the FFT analyzer 3 via the microphone amplifier 2.
[0026]
In the FFT analyzer 3, the input signal is converted into a digital signal by the A / D converter 4,
and the digital signal is input to the FFT calculator 5. In the FFT operation unit, each digital signal
obtained when each of the microphones P1, P2, P3, P4 by each of the microphones P1, P2, P3,
P4 is at each position relative to the speaker 12 is subjected to Fourier transform. An average
Fourier transform spectrum for each microphone is determined for each of the determined
Fourier transform spectra. This cancels the variation due to the difference in position. The
average Fourier transform spectrum of each of the microphones P 1, P 2, P 3 and P 4 thus
obtained by the FFT operation unit 5 is inputted to the characteristic difference operation unit 8.
The characteristic difference calculation unit 8 obtains the characteristic difference according to
the above-described equation (3) using the input average Fourier transform spectrum. That is,
assuming that each average Fourier transform spectrum obtained from the signal obtained by
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each microphone Pi (i = 1, 2, 3, 4) is Si (i = 1, 2, 3, 4), two When the characteristic difference
between the microphones Pi and Pj (i, j = 1, 2, 3, 4) is Hij, the characteristic difference Hij is Hij =
Si / Sj (7) i, j = 1, 2, 3 , 4 is required.
[0027]
The characteristic difference Hij represented by the equation (7) is a complex number, and Hij =
Ai / Ajexp [j {[phi] i- [phi] j}] (8) Ai / Aj: the amplitude of the output of the microphone Pi and the
output of the microphone Pj The ratio .phi.i -.phi.j can be expressed as the phase difference
between the output of the microphone Pi and the output of the microphone Pj. The amplitude
ratio and the phase difference are stored in the FFT analyzer 3 and referred to in the acoustic
intensity measurement (refer to FIG. 6), and the Fourier obtained by the FFT operation unit 5
based on the stored amplitude ratio and phase difference. The converted spectrum is corrected,
and the intensity calculation unit 6 obtains an accurate acoustic intensity based on the corrected
Fourier transform spectrum.
[0028]
Here, in the above embodiment, the insertion of the microphones P1, P2, P3, P4 into the long
holes 14a, 14b, 14c, 14d and the replacement of the insertion position are performed by the
operator, but the insertion was made once. After that, a rotation mechanism may be attached so
that positions are automatically changed. In the above embodiment, four elongated holes are
provided on one circumference, but in the present invention, the positions of the microphones
may be alternated with each other, and it is not necessary to be disposed on one circumference.
Furthermore, although the characteristics of the four microphones are compared in the above
embodiment, the number of microphones to be compared is not limited to four, and may be any
plural as needed.
[0029]
As described above, according to the microphone characteristic comparison method of the
present invention, a plurality of microphones are arranged, sound is recorded while alternating
positions with one another, and an average Fourier transform spectrum is obtained for each
microphone. Since the difference in the characteristics of the microphone is determined based on
the average Fourier transform spectrum, the variation due to the difference in the position is also
canceled based on the sound recorded under the same condition closed space, and the difference
in the accurate characteristics Is required.
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