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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a sound source searching device for
searching an objective sound source out of a plurality of sound sources,
and particularly to a sound source searching device employing an intensity
probe.
In order to reduce noise produced in a large number of sound source of an
internal combustion engine or the like, it is effective to search one
sound source of which the sound pressure level is the maximum and prevent
the sound source from producing noise.
For searching the above described sound source precisely, the detector
having a sharp directivity against sound must be employed. Recently, the
intensity probe has been noted as the above described detector.
The intensity probe (hereinafter, will be called "probe") is provided with
two omnidirectional microphones 11a, 11b.
By making a frequency analysis of the sound pressure signals obtained by
the microphones 11a, 11b, combining spectrums of the above sound pressure
signals into a cross spectrum and calculating acoustic intensity
(hereinafter, will be called "intensity") from the imaginary part of the
cross spectrum, the directional characteristics as shown in FIG. 1 is
obtained.
Namely, when the sound source approaches the plane including O.sub.I, Oc,
O.sub.II, the intensity rapidly decreases.
In order to search an objective sound source, at first, by moving the probe
on the first plane, the first direction in which the absolute value of
intensity is the minimum is searched, then by moving the probe on the
second plane including the above horizontal direction, which is
perpendicular to the first plane, the second direction in which the
absolute value of intensity is the minimum is searched, as the direction
of sound source.
Conventionally, the above search has been performed by controlling the
probe by hand, so it is difficult to search the sound source precisely
even by use of great effort and a long period of time.
SUMMARY OF THE INVENTION
The sound source searching device of the present invention comprises an
intensity probe provided with one pair of microphones, a probe driving
means for supporting the above intensity probe and rotating by a
predetermined angle the above intensity probe stepwise in a first plane
and in a second plane which perpendicularly intersects the first plane
about the intermediate point of the above microphones. A frequency
analyzing means analyzes the frequency of the sound pressure signals fed
from the intensity probe at every rotating position and forming a cross
spectrum of sound pressure signals. A processing means calculates acoustic
intensity corresponding to the frequency of the objective sound source
from the cross spectrum. A direction indicating means indicates the
direction in which the absolute value of acoustic intensity is the minimum
(that is, the direction in which the sign of the acoustic intensity is
inverted) in the second plane including the direction in which the
absolute value of acoustic intensity is the minimum (that is the direction
in which the sign of the acoustic intensity is inverted) in the first
plane, as the direction in which the objective sound source is positioned.
According to the present invention, the intensity probe is rotated stepwise
by a predetermined angle on the first and second planes by means of the
probe driving means. The processing means calculates acoustic intensity
corresponding to the frequency of the sound source at every rotating
position. Then, the direction indicating means indicates the direction in
which the absolute value of acoustic intensity is the minimum on both of
the first and second planes as the direction of the objective sound
source.
One object of the present invention is to provide a sound source searching
device by which an objective sound source can be precisely searched in a
short period of time without wasting great effort.
Another object of the present invention is to provide a sound source
searching device which automatically searches an objective sound source
with precision and indicates the direction of the objective sound source.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view illustrating directional characteristics of an intensity
probe;
FIG. 2 is a view illustrating the sound source searching device of the
present invention; and
FIGS. 3 and 4 are views illustrating an interface circuit of pulse motors.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Hereinafter, the present invention will be explained in accordance with the
embodiments thereof with reference to the accompanying drawings.
FIG. 2 shows the composition of the sound source searching device of the
present invention.
An intensity probe 1 is provided with two microphones 11a, 11b. The sound
pressure signal generated by the intensity probe is amplified by an
amplifier 2. The sound pressure signal is analyzed by the frequency
thereof, then a cross spectrum is obtained by a fast Fourier transducer 3.
Then, the acoustic intensity corresponding to the frequency of the
objective sound source is calculated from the imaginary number of the
cross spectrum by a computer 4.
The reference numeral 5 designates an interface device provided with pulse
motor driving circuits which rotate the probe 1 in the horizontal and
vertical directions in accordance with the instructions of the computer 4,
the reference numerals 6, 7 designate pulse motors for rotating the probe
1 on the horizontal plane and vertical plane, respectively, and the
reference numeral 9 designates an indicator for indicating the direction
of the objective sound source.
The microphones 11a, 11b of the intensity probe 1 are mounted on the top
ends of cylindrical housings 12a, 12b, respectively, Within the housings
12a, 12b, preamplifier circuits for amplifying feeble sound pressure
signals fed from the microphones 11a, 11b, are accomodated, respectively.
The housings 12a, 12b are retained by microphone holders 13, 14 so as to
be spaced by a predetermined interval. The indicator 9 is mounted on the
microphone holder 13 so as to pass through the middle point Oc of the
microphones 11a, 11b and extend in the direction perpendicular to the line
connecting the microphones 11a, 11b.
A supporting stand 8 is formed by bending a strip-shaped plate at right
angles. A horizontal portion 81 is supported by the pulse motor 6 so as to
rotate on the horizontal plane. A vertical portion 82 is provided with the
pulse motor 7. The pulse motor 7 supports the microphone holders 13, 14 of
the probe 1 so as to rotate on the vertical plane. The middle point Oc is
positioned on the intersection of the extensions of the rotating shafts of
the pulse motors 6, 7. Thus, the microphones 11a, 11b are rotated by the
pulse motors 6, 7 on the horizontal plane and the vertical plane about the
middle point Oc. A weight 10 is installed in the horizontal portion 81 of
the supporting stand 8 for balancing the horizontal portion 81 with the
intensity probe 1 and the pulse motor 7.
FIGS. 3 and 4 illustrate an interface circuit 5 of the pulse motors 6, 7.
The reference numeral 51 designates a signal decoder circuit which is
composed of a series-parallel convertor (VART) 51A, a waveform shaping
circuit 51B, binary counters 51D, 51F, 51G, 51H, J-K flip-flops 51J, 51K,
a decoder 51E, an oscillation circuit 51L and a baud rate selecting switch
51M. The reference numerals 52, 53 designate driving circuits for driving
the pulse motors 6, 7, respectively.
The driving circuit 52 comprises J-K flip-flops 52A, 52B, 52D, drivers 52E,
52F, 52G, 52H, each of which is composed of transistors forming a
Darlington circuit, and EXCLUSIVE OR gates 52J, 52K.
As the series-parallel convertor 51A, IM 6402 made by Intercil Co., Ltd.
can be used, and as the other digital IC, CD 4000 series made by RCA Co.,
Ltd. can be used.
The pulse motor rotation directing signal 4a which is fed in series by the
computer 4 at a predetermined baud rate, is shaped by the waveform shaping
circuit 51B, and is converted into a parallel signal of 8 bits by the
series-parallel convertor 51A, which appears at the output terminals RBR.
The decoder 51E generates a output signal of 1 level at the output
terminal Q, which corresponds to the binary lower four bits of the output
signal 51a of the convertor 51A. Upon receiving the output signal from the
decoder 51E, the J-K flip flops 51J, 51K are set to determine the rotating
direction of the pulse motors 6, 7. And the binary counters 51G, 51H which
operate as the monostable multivibrators, generate pulse signals 51g, 51h
which determine the rotating step of the pulse motors 6, 7. When the
output signals 51j, 51k of the flip-flops 51J, 51K are 1 level, the
pulse motors 6, 7 rotate clockwise while when the output signals 51j, 51k
of the flip-flops 51J, 51K are 0 level, the pulse motors 6, 7 rotate
counter-clockwise.
The output signal 51j of the flip-flop 51J and the output signal of the
flip-flop 52A are fed to the EXCLUSIVE OR gates 52J, 52K. The EXCLUSIVE OR
gates 52J, 52K feed output signals which determine the order of inversion
of the output signals of the flip-flops 52B, 52D. As a result, the coils
6a, 6b and the coils 6c, 6d of the pulse motor 6 are alternately excited
through the drivers 52E, 52F, 52G, 52H. The pulse motor 6 rotates in the
direction determined by the computer 4 by steps determined by the computer
4.
The operation of the driving circuit 53 which receives the output signals
51k, 51h of the flip flop 51K and the counter 51H is similar to that of
the driving circuit 52.
For example, in order to rotate the pulse motor 6 clockwise by three steps,
character signal 2111 of ASCII Code is successively fed to the decoder
circuit 51 from the computer 4 as the pulse motor rotating signal 4a. At
first, the ASCII Code 0110010 corresponding to the character 2 is fed
to the decoder circuit 51. At the terminals RBR7 to RBR 1 of the
series-parallel convertor 51A, parallel signal 51a of 7 bits having a
signal level of 0110010 appears.
At the terminal Q.sub.2 of the decoder 51E, the output signal of 1 level
which corresponds to the lower 4 bits 0010 of the signal 51a, appears.
When the data ready signal is fed from the terminal DR of the convertor
51A, the flip-flop 51J to which the output signal of 1 level is fed from
the terminal Q.sub.2, feeds the output signal 51j of 1 level to the
driving circuit 52.
Next, the character 1 is fed to the decoder circuit 51. Parallel signal
51a of 0110001 level appears at the output terminal RBR7 to RBR1
successively. As a result, the decoder 51E generates output signal of 1
level at the output terminal Q.sub.1. When the data ready signal is fed
from the terminal DR of the convertor 51A to the counter 51G to which the
1 level signal is fed from the decoder 51E, the counter 51G feeds pulse
signal 51g having a predetermined pulse width to the driving circuit 52.
Upon receiving this pulse signal, the output signal of the flip-flop 52A is
inverted while the output signal of the flip-flop 52B is inverted to
excite the coil 6a in place of the coil 6b. As a result, the pulse motor 6
rotates clockwise by one step.
Furthermore, the character 1 is fed to the decoder circuit 51, the
counter 51G feeds pulse signal 51g to the driving circuit 52 again. Upon
receiving this pulse signal, the output signal of the flip-flop 52A is
inverted again while the output signal of the flip-flop 52D is inverted to
excite the coil 6c in place of the coil 6d. As a result, the pulse motor 6
rotates clockwise by one step further.
At last, the character 1 is fed to the decoder circuit 51. The output
signals of the flip flops 52A, 52B are inverted to excite the coil 6b in
place of the coil 6a. As a result, the pulse motor 6 rotates clockwise by
one step, furthermore.
In order to rotate the pulse motor 6 counterclockwise, the character
signals composed of the character 3 and a plurality of the character 1
of which the number corresponds to the number of rotation steps, are fed
from the computer 4 as the rotation directing signal 4a.
In order to rotate the pulse motor 7 clockwise, the character signal
composed of the character 5 and a plurality of the character 4 of
which the number corresponds to the number of rotation steps, is fed from
the computer 4 as the rotation directing signal 4a. In order to rotate the
pulse motor 7 counterclockwise, the character signal composed of the
character 6 and a plurality of the character 4 of which the number
corresponds to the number of rotation steps, is fed from the computer 4 as
the rotation directing signal 4a.
When the sound source is searched by the device of the present invention,
at first the amplifier level, the frequency of the sound source to be
searched, and the number of searching steps in the horizontal and vertical
directions are set in the computer 4. Next the microphones 11a, 11b are
horizontally positioned by means of the pulse motor 7 so that the
indicator 9 points in the vertical direction.
In the above embodiment, the directional characteristics of the intensity
probe 1 on the plane including O.sub.I, +, - as shown in FIG. 1 is applied
to the search on the horizontal plane while the directional characteristic
on the plane including O.sub.II, +, - is applied to the search on the
vertical plane. The indicator 9 is positioned on the line connecting the
points Oc and O.sub.II. In the sound source searching device of the
present invention, at first the intensity probe 1 is rotated on the
horizontal plane about the middle point Oc in steps by means of the pulse
motor 6. The intensity value at each step is successively calculated by
means of the computer 4. Next, the intensity probe 1 is returned to the
step where the absolute value of intensity is the minimum on the
horizontal plane. Then, the intensity probe is rotated by 90.degree. so
that the plane including O.sub.II, +, - shown in FIG. 1 coincides with the
vertical plane. The intensity probe 1 is rotated on the vertical plane
about the middle point Oc in steps by means of the pulse motor 7. The
intensity value at each step is successively calculated by means of the
computer 4. The intensity probe 1 returns to the step where the absolute
value of intensity is the minimum on the vertical plane. At this time, the
indicator 9 indicates the direction of sound source.
Instead of the directional characteristics on the planes used in the above
embodiment, the directional characteristics on other planes, can be used.
As described above, according to the sound source searching device of the
present invention, the sound source can be searched automatically by
rotating the intensity probe on arbitrary selected planes which are
perpendicular to each other by means of the driving means in accordance
with the instructions of the processing means. Therefore, the sound source
can be precisely and speedily searched.
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