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JPS5957596

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DESCRIPTION JPS5957596
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
microphone device, and more particularly to a microphone device suitable for use in collecting
sound using a sound field near a rigid body plane. BACKGROUND ART In recent years, a sound
collection method using a sound field near the rigid body plane has become a hot topic. When
adopting such a sound collection method, it is necessary to clearly grasp the relationship
between the setting state of the sound receiving point and the frequency characteristics,
directivity characteristics and the like. From the end of the 19th century, many researchers have
analyzed and experimented the sound field near the rigid body plane from various angles.
Although it is necessary to take into consideration the rotation from the side of the rigid body
plane to the back in order to conduct such an exact analysis of the sound field, it is necessary to
carry out complicated calculations to obtain this exact analysis. Therefore, conventionally, a
satisfactory result is always required as a sound collection method using a sound field near the
rigid body plane, which is seldom practicable and it is difficult to realize a desired microphone
device. The SUMMARY OF THE INVENTION The present invention has been made in view of the
above circumstances, and provides a microphone device capable of realizing a sound collection
system that effectively uses the sound field near the rigid body plane. SUMMARY OF THE
INVENTION In the present invention, a microphone element is disposed at a position on the
periphery of a flat plate different from at least the center position of the flat plate on the flat
plate having a fixed area as a rigid plane, and the sound field phenomenon on the rigid plane is
effective. Can be used to obtain a microphone device having excellent sensitivity and clarity.
EXAMPLES The present invention will be described in detail based on FIGS. 1 to 13 below. First,
the basic principle of the present invention will be described with reference to FIGS. 1 and 2. In
FIG. 1, consider an example where the sound source So and the sound collection point M are
placed in a sound field surrounded by four walls W1, W2, W3 and W4. The sound pressure
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obtained by the path directly reaching the sound collection point M from the sound source So is
the sound pressure obtained by the primary mirror sound source S1 generated by the wall W1
P1. Sound pressures obtained similarly for W3 and W4 are P2. P3 and P4 更 に Furthermore, the
sound pressure obtained by the secondary mirror sound source generated by the reflection of the
two walls is P21 P131 P14 * 21 + P23 s P24 * p31 S 32 + ; 441 P 411 Pd2 and Pd2 .
Similarly, the sound pressure obtained from the mirror image sound source due to the reflection
of the third or higher order wall is also expressed as Pijk ····· (where i ′ = j #, # ······) . The S / N
obtained at this time at the sound collection point M is calculated as follows.
·······································································································································································································
······················. Considering 87H when the pickup point M is moved to the vicinity of the wall W2 in
such a state, the sound pressure PO of the direct sound reaching the pickup point M from the
sound source So and the sound of the primary reflection sound by the wall W2 The pressure P2
is a signal of the same phase at all frequencies. Therefore, the above equation (1) is given by the
following equation. ································································································································· At this time, p
(1 = P2 Therefore, the molecule of the above equation (2) is 2Po2. Since the denominators of the
above-mentioned equation (1) and the above-mentioned equation (2) are generally approximately
equal, it is understood that the S / N is improved by about 3 dB. Next, referring to FIG. 2, when a
point sound source S and a disk serving as an obstacle exist in free space, an example in which
the sound receiving point R is set to the distance of height Z on the disk surface Think. In the
same figure, the direct sound PP obtained by the route that directly reaches the sound source S
and the sound receiving point R is expressed by the following equation. PP = '-e-m ··························
(3) And the particle velocity U at the surface dS by this direct sound 粒子 P is U = (+) K) '-6-3 kLx'.
L, L, -ψ °°°°°°°°° (4), and the reflected sound d 反射 S by the surface dS is UdΦS = ds, 6-jkρ concave curve · curve · · · (5) 2πρ From this, the total Φ S of the reflected sound is
(6). Therefore, when the sound pressure P at the sound receiving point R is expressed as a ratio
to the sound pressure Pp of the direct sound, an approximate solution is expressed by the
following equation. -Fish V □ ・ ・ ・ ・ ・ · · · · · · (7) However, in the above equation (7), AZ (-L
foot 17 shoulders. Here, the on-axis characteristic (ψ-0. The characteristic at the disc center
when L and co) and the toss plane wave are perpendicularly incident on the disc of radius a is as
follows from the above (method. However, in the above equation (8), a1 = 2. As a result, it is
understood that the frequency characteristic at the center of the disk top is about 10 dB as
shown in the above equation (8). This is because the interference due to the analysis
phenomenon increases because the same boundary conditions overlap. In order to reduce this
Ritz 0, it is necessary to move the sound receiving point from the center of the disc. In this way,
smoothing of the frequency characteristic can be realized, but along with this, the directivity
characteristic also loses symmetry, and the directivity characteristic appears in the opposite
direction to the direction in which the sound receiving point is shifted.
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This is because the mirror effect (reflection effect) as described in FIG. 1 decreases in the
direction closer to the side from the sound receiving point, and the level of directivity
characteristic decreases, and conversely, the reflection surface which produces the mirror effect
in the opposite direction. In the present invention, attention is paid to the fact that the directional
characteristics appear in the opposite direction to the direction in which the sound receiving
point is shifted. It is. Embodiments of the invention will now be described with reference to FIGS.
3-12. FIG. 3 shows a first embodiment of the present invention, in which a flat plate of a
predetermined shape having a fixed area as a rigid body plane, for example, a circular flat plate
(1) having a radius a, is provided. A microphone element (2) is provided at a position on the
periphery of the flat plate different from the central position C of the flat plate (1), for example, a
position 1a away from the central position C. The flat plate (1) may have a square, rectangular or
other shape instead of a disk. Then, on the flat plate (1), a sound source (3) is provided above the
microphone element (2) K at a predetermined distance away therefrom. 4 schematically shows
the state of FIG. 3 viewed from the side and the top, respectively. In FIG. 4, φ reaches the
microphone element (2) from the sound source (3) (FIG. 3) Represents the incident angle of the
sound. The change in sound pressure of the sound source (3) with respect to the microphone
element (2) when the incident angle .phi. Is changed has directivity characteristics as shown by
black dots in FIG. 5 (measured values). The conditions for this measurement are as follows: a =
85 mm, a ˜55 throat, and the distance between the sound source (3) and the flat plate (1) is
approximately 2.5 ˜3 m It is. The solid line in FIG. 5 is a calculated value calculated by an
approximate solution in which the rotation from the side of the rigid plane is neglected from the
practical point of view as described above. It can be seen that the calculated values in FIG. 5 and
the measured values agree fairly well. And from FIG. 5, it is understood that the sound collection
sound pressure rises for the sound in the fixed direction (from the center direction position), and
is minimized at the same plane position as the plane of the flat plate (1). However, the sound
from the sound source (3) at this time is a continuous wave of a constant frequency and constant
sound pressure, which is different from a so-called bursty intermittent wave. Also, the gain of the
collected sound pressure with respect to the frequency is as shown in FIG. In FIG. 6, the solid line
is the calculated value, and the black dot is the measured value. It can be understood from FIG. 6
that the higher the frequency, the higher the rate of increase or decrease in the gain of the
collected sound pressure with respect to the frequency. 7 shows the frequency characteristics
when the plane wave incident angle φ in the same state is 4-45 °, 0 ° and −45 ° as shown in
FIG. Is shown.
In the figure, the solid line is the calculated value, and the others are the measured values. The x
marks in this measured value are the case where the incident angle φ is + 45 °, the Δ marks
are Oo, and the 印 marks are one 45 °. The relationship between the directional characteristics
of the sound collection and the frequency in this embodiment shown in FIG. 7 is that the
frequency characteristics of the sound of the flat plate (1) are remarkable compared to those of
the radial direction of the flat plate (1). It can be seen that left and right separation from Hz to 6
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kHz is obtained. As described above, in the present embodiment, by arranging the microphone
element (2) at a predetermined position, that is, 3-a, from the central position C of the flat plate
(1), the direction from the center point direction of the flat plate (1) The gain of the sound pickup
pressure of the sound is sieved, and the frequency characteristic is remarkable, and the
sensitivity and the intelligibility characteristic are improved. FIG. 8 shows a second embodiment
of the present invention, in which the microphone elements are positioned so as to be
symmetrical with respect to the central position C with respect to the device at a distance of 3-a
from the central position C of the flat plate (1). Arrange (4) and (5). These microphone elements
(4) and (5) exhibit the same characteristics if the measurement conditions are the same as those
of the first embodiment described above. Under such an arrangement condition, as shown in FIG.
9, the radius a of the flat plate (1) is 85 mm, the left side (L), the right side (I's microphone
elements (5), (4) Consider a case where the position of the sound source (3) is approximately 45
to 3 mm away from the microphone element with a position of 65 mm. Now, if the sound from
the sound source (3) is a continuous wave with constant frequency and constant sound pressure,
the sound collection pressure of the right microphone element (4) is higher than that of the left
microphone element (5) as described above. When the sound from each microphone element is
recorded or heard with the left side as the left side and the right side as the right side, it sounds
as if the localization of the sound image is located in the right direction unlike the arrangement
state of FIG. Therefore, when recording a continuous sound at a constant sound pressure with a
constant sound pressure on a recording device such as a tape recorder in the aspect of a
stereomer / one-crophone system as described above, The right side microboning element must
be input to the left side input. That is, in this case, unlike the conventional recording and
reproduction, since the directivity is in the opposite direction to the position installed to collect
the sound, the left and right localization is made during recording and reproduction. That's why.
However, assuming that the sound source (3) is a burst-like intermittent wave whose frequency is
variable as shown in FIG. 10 and the sound pressure is also different, the intermittent wave to the
right electrochromic element (4) as shown in FIG. The arrival time of is delayed by 0.26 ms from
the arrival time of the microphone element (5).
Therefore, when listening with a headphone or the like whose directivity is substantially
determined by the phase difference of sound, it is preferable to use the left microphone element
as the left input and the right microphone element as the right input. That is, when the sound of
the intermittent wave is heard using a headphone or the like whose directivity is determined by
the phase difference of the sound, the localization (the sense of direction) by the sense of hearing
is felt in the left direction. This follows the so-called first wave front law (Heath's effect), which is
said to move to a higher level with a time difference of about 5 rns or less. Therefore, as
described above, in the case of a headphone or the like, it is preferable to use the left microphone
element as the left input and the right microphone element as the right input as in the normal
recording condition. When listening to the playback sound with a speaker, the preceding sound
tends to be inconvenient, and the distance interval is reversed, so the left microphone element is
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the same as the steady state of constant frequency and constant sound pressure mentioned
above. The microphone element is input to the left input. Thus, in the present embodiment, the
same operation and effect as in the first embodiment can be obtained, and in addition, in the
present embodiment, by effectively utilizing the above-described sound field phenomenon, it is
also possible to collect stereo sound. FIG. 12 shows a third embodiment of the present invention.
In this embodiment, for example, in the arrangement state of FIG. 3, a cloth (7) having a sound
absorbing property of a fixed thickness on a flat plate (1) is used. Adhere so that the sound
absorption surface of the partial microphone element (2) is exposed to the outside. As the cloth
(7), for example, wool (wool), glass wool, felt or the like can be considered. FIG. 13 id shows the
frequency characteristics at this time, and in the same figure, the broken line is the frequency
characteristics when the cloth (in the absence of force and the solid line is in the presence of the
force). It can be understood from the characteristics of FIG. 13 that by applying a cloth (force, the
upper portion of the frequency characteristic, for example, 5000 Hz Jl) can be suppressed.
Therefore, in the present embodiment, when such a microphone device is used for sound
collection, for example, in a conference, it is possible to remove the sound of shelves, desks, etc.
having relatively high frequency components, the sound of paper etc. As a result, since
unnecessary sounds other than necessary sounds such as human voices are not collected, the
conference can be effectively advanced. In the present embodiment, it may be configured as an
aspect of the stereo sound collecting system as shown in FIG. The present invention is not limited
to the above-described embodiment, but is equally applicable to other cases requiring such a
function.
As described above, according to the present invention, according to the present invention, a
position of a flat plate having a certain area different from at least the center position of the flat
plate--the arrangement of microphone elements arranged in a microphone element; It is possible
to realize a sound collection system that effectively uses the above, and to improve the
sensitivity, clarity and the like characteristics as compared with the conventional microphone
device. Also, since the high range of about 1 kHz or more is raised, the distance is substantially
compressed to widen the sound collection range, which is extremely useful for a sound collection
system such as a conference.
[0002]
Brief description of the drawings
[0003]
1 and 2 are diagrams for explaining the basic principle of the present invention, FIG. 3 is a block
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diagram showing one embodiment of the present invention, and εP and FIG. 4 are for explaining
the operation of FIG. 5 to 7 are characteristic diagrams for explaining the operation of FIG. 3, FIG.
8 is a block diagram showing another embodiment of the present invention, and FIGS. 9 to 11 are
FIGS. FIG. 12 is a block diagram showing still another embodiment of the present invention, and
FIG. 13 is a characteristic diagram for explaining the operation of FIG.
(1) is a plate, (2), f4), (5) is a microphone element, (3) a sound source, (the force is a cloth. Figure
1 585-River 5 Kt Ltv <sz> Zhou Inu (I (,) Figure 8
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