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JPS62230297

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DESCRIPTION JPS62230297
[0001]
INDUSTRIAL APPLICABILITY OF THE INVENTION The present invention is a directional
microphone with a working mode of electrical static conversion or electro dynamic conversion, in
which the distance between the back of the active conversion diaphragm and the back of the
diaphragm surface is separated. The directivity is defined by at least one phase rotation delay
element provided between a small number of (at least one acoustic inlet opening) provided in the
casing, and the microphone is connected to the delay element. The invention relates to a
directional microphone having at least one acoustic element coupled thereto. Prior art directional
microphones are known and are shown, for example, in DE 82 21 217 A1. This directional
microphone has several undesirable disadvantages. A delay element for phase rotation usually
acts over the entire audible range. For example, in the case of a directional microphone
configured as a pressure gradient receiver, the proximity transmission effect is impaired. This
leads to a significant sensitivity increase in the bass region, which significantly impairs the sound
image. Furthermore, the pressure gradient receiver is particularly sensitive to plosives, so that a
so-called whistling state Popen is produced. Furthermore, other microphones of the type
mentioned at the outset are known. The microphone is similarly configured and also has an
acoustic element coupled to the delay element. In this case, the directivity characteristic itself is
affected and changed by this configuration. In this known document, neither the related
description to the problem of the close-talking effect nor the related description based on the
configuration of this microphone is also shown. Problem to be solved by the invention It is an
object of the present invention to provide a directional microphone that avoids the drawbacks of
known directional microphones. The basis of the recognition in this case is that the frequencies
lower than 300 Hz hardly contribute to the localization of the sound source. Therefore, what is
proposed by the present invention configures the directional microphone as follows. In other
words, the microphone should operate as a pressure gradient receiver with directional
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characteristics in the area above 300 cm, and be configured as a simple pressure receiver
without directivity in the area below 300 & It is. The above-mentioned 300 um cut-off
frequencies are only considered as approximate mean values. The reason is that the transition
from the pressure gradient receiver to the acoustic pressure receiver is smooth rather than
jumping.
The above problem is solved according to the invention as follows: in the finger microphone
mentioned at the outset, the combined delay element device of the acoustic element is 300 H □
It is made to have a lower cutoff frequency in the region. A directional microphone in this way
has many advantages. The combination of a sound pressure receiver for the lower frequencies in
the audible range and a pressure gradient receiver for the higher and the highest frequencies
first extends the frequency response towards lower frequencies. In this case, the close-talking
effect no longer appears because the sound pressure receiver does not have this effect. As a
result, no disturbing ゝ ゝ Popen〃 occurs, which is to be transmitted, since the sound pressure
receiver does not have the characteristics present in a pressure gradient receiver. Furthermore,
the arrangement according to the invention improves the transmission factor over the whole
range of audio frequencies, since the frequency characteristics of the microphone according to
the invention are low and mid frequencies when operating as sound pressure receivers. This is
because it is increased by dB and is therefore adapted to the level of presence enhancement of
the pressure gradient receiver, which is still present at high frequencies. The realization of a
configuration with a transmission coefficient こ this frequency can be carried out without special
difficulties, and several specific solutions which are optimal for achieving an adaptation
adjustment to this kind of cut-off frequency. Is provided. The simplest concrete solution to the
task set consists of a device with a delay element and an acoustic element coupled to it,
consisting of a series connection of the two, where this acoustic element is an acoustic
capacitance Or as a passive diaphragm. In the case of capacitance, this value is chosen as follows:
this capacitance cooperates with at least one delay element to provide a 180 ° phase rotation at
frequencies below about 300 °, and so on The above selection is made such that substantially
no sound pressure acts on the back side of the active diaphragm. The passive diaphragm, on the
other hand, is adapted to be not passed through for frequencies below about 3, OO &.
Advantageously, at each of the acoustic inlet openings behind at least one delay element, a
passive diaphragm is mounted which closes this acoustic inlet opening. The microphone in both
embodiments is 3 o. It operates as a simple pressure receiver in the region below H2 and only as
a pressure gradient receiver with a pronounced directivity only above the proposed cutoff
frequency of about 300 Hz.
A series connection of an acoustic capacitance or passive diaphragm with a delay element for
phase rotation is suitable, for example, for a condenser microphone. The use of passive
diaphragms is also advantageous if it is configured as follows: these diaphragms are divided by
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strips into partial diaphragms with different resonance frequencies. This gives the person skilled
in the art a wide selection of values. Finally, the natural resonance frequency of the passive
diaphragm is set to a value higher than that of the passive transducer diaphragm. This avoids
adverse effects on the frequency characteristics and sensitivity of the microphone. The transition
from the gradient receiver to the sound pressure receiver is also achieved by a plurality of
acoustic elements being additively connected in parallel with at least one delay element. For
example, a vibration circuit composed of an acoustic inductance and an acoustic capacitance is
used, which is formed of at least two acoustic elements. At least one additional resistance can
optionally be assigned to this oscillating circuit. In a specific case, the directional microphone
configured in this way has the following features. That is to say that the acoustic inductance is
the air volume present in the small tube, which on the one hand communicates with the air
chamber behind the transducer diaphragm in common with at least one delay element and on the
other hand this air chamber as the microphone casing It combines with a large void space inside.
The series oscillator circuit targeted in this case is connected in parallel to at least one delay
element and forms a short circuit for frequencies lower than about 300 Hz, so that at least one
delay element acts Values are selected to shut off. In another advantageous embodiment, a series
oscillating circuit as described above is used, but the coupling is not effected via a common air
chamber, but rather directly, for example, in the resistor itself, in the delay element itself.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a specific first embodiment of
the present invention. The subject is a directional condenser microphone having an active
conversion diaphragm 1. The back electrode or counter electrode 2 provided with the holes 3 is
opposed to the diaphragm which is this diaphragm at a slight interval. Lower air students are
provided between the vibrating membrane 1 and the counter electrode 2. The height of the lower
air chamber has a value that allows the vibrating membrane 1 to vibrate freely with respect to
the counter electrode 2. The delay element for rotating the phase is shown at 5.
An acoustic inlet opening, which is a vent provided behind the vibrating membrane surface and
leading to the delay element 5, is formed by the air volume 7 contained in the large volume
cavity at reference numeral 8. This air volume acts as an acoustic capacitance and, together with
the air mass 6 provided as an acoustic inductance contained in the small tube, forms a vibrating
circuit. This oscillating circuit, like the delay element 5, is coupled to the lower air student behind
the oscillating membrane 1. The oscillating circuit formed from the acoustic elements 6 and 7
forms a series connection of an inductance and a capacitance, whose impedance is at a minimum
in the region of the resonant frequency. In the embodiment shown in FIG. 1, this series
connection of 6 and 7 is connected in parallel to the delay element 5. Therefore, the delay
element is substantially short-circuited in the region of the resonant frequency of the seriesconnected oscillator circuit 6, 7, ie in other words the delay element 5 no longer acts on the
conversion diaphragm 1 in this case, The microphone is considered as a sound pressure receiver
only. This is the object of the present invention. Of course, the resonant frequency of the
oscillating circuit formed by the elements 6 and 7 is such that this resonant frequency attenuates
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the region up to about 300 Hz, which is the lowest frequency to be transmitted. FIG. 2 shows a
directional microphone operating in electrical dynamic form according to the present invention,
the configuration of which is similar to the configuration of the electrical static directional
microphone shown in FIG. In this case, the conversion diaphragm is shown at 9 and supports the
voice coil 10. A lower air chamber 11 is provided behind the conversion diagram 9, to which the
delay element 12 and the small pipe communicate. This tube comprises an air mass 15 which
acts as an inductance. The acoustic inlet opening has the reference numeral 14. The other end of
the tubule is led to a large volume cavity. This cavity contains an air volume 13 which acts as an
acoustic capacitance. The operation of this device is similar to that of the embodiment shown in
FIG. The embodiment shown in FIG. 3 differs from the previous embodiment in the following
respect. That is, the additional acoustical remen) 23.24, which forms a series resonant circuit, is
directly coupled to one element of the delay element, i. The second acoustic element of the delay
element is formed by a significantly larger air chamber provided behind the counter electrode
17. The air chamber is constituted by a counter electrode 17 having an opening 18 passing
through the air chamber 19 on the one hand and a partition 25 having an acoustic passage
opening 26 on the other hand.
The air volume 20 comprising the large air chamber is provided as the acoustic capacitance of
the delay element. Further additional resistances 22 can be provided at the sound inlet opening
21, which is optionally a rear vent. In principle, the series connection 24 of the air mass 23 and
the air volume 24 again in this case acts as a short circuit for the delay element 20.22.27. As a
result, the electrical static converter having the diaphragm 16 and the counter electrode 17
operates as a sound pressure receiver below the frequency of about 300) Tz, as is the object of
the present invention. The embodiment shown in FIG. 4 also comprises an electrical static
converter having a diaphragm 28 and a counter electrode 29. An air volume 3o is formed behind
this counter electrode as in the previous embodiment. An air chamber containing this air volume
is partitioned between the counter electrode 29 and the partition 35, and has a large opening 36
which allows sound to pass well. Behind this bulkhead 35 a large flat resistance 31 is provided,
into which the air volume-expanding tube with three air volumes and the air volume 32 are in
communication There is. The large open passive diaphragm 33 of the aforementioned tube-like
tube is adapted and adjusted as follows, i.e. to prevent the ingress of sound for frequencies below
about 300 Hz, so that the microphone in this area is It is adapted and adjusted to operate as a
sound pressure receiver as desired. FIG. 5 likewise shows an embodiment with a passive
diaphragm 37. The diaphragm diaphragm 37 closes the rear acoustic entrance opening to the
delay element. The diaphragm 37 is in the form of a circular ring. This is only possible in the
following cases, i.e. only when the casing containing the air volume 41 has a smaller diameter
than the electrical static converter with the diaphragm 38 and the counter electrode 39. Here
too, the passive diaphragm 37 is adapted as follows, i.e. to prevent the ingress of sound with
frequencies lower than about 300 Hz, so that the microphone acts as a sound pressure receiver
in this region To adjust to compensate for the action of the delay element. For example, the cow
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3 is attached to the surface of the opposite electrode 39 on the side opposite to the diaphragm
38, and the air chamber 40 is connected to the lower plate after the air volume 41 is connected.
The acoustic resistor 42 and the passive diaphragm 37 are acoustically coupled.
In order to extend the working range of the passive diaphragms 33, 37, the diaphragms can be
divided into partial diaphragms, each having a different natural resonant frequency. FIG. 6 shows
this type of division in the case of a diaphragm formed as a circular surface. Bandages a, b and C
make this diaphragm 33 three partial diaphragms 44, 45. Divide into 46. A similar arrangement
can also be provided for the circular ring diaphragm 37 as shown in FIG. In this case too, the
channels a, b, c divide into three partial diaphragms 47 ° 48. 49 with different natural
resonance frequencies as described above. The simplest way is to have the partial diaphragms
have different surface areas. Next, the operation of the present invention will be described using
an electrical equivalent circuit. In order to better understand the invention, FIG. 8 first shows an
electrical equivalent circuit of a known directional microphone configured as a pressure gradient
receiver. A directional microphone of this kind has a transducing diaphragm and the mass of this
transducing diaphragm. The stiffness and the internal resistance can be represented as a series
connection of an inductance M, a carrier / F resistance CM and an ohmic resistance RM,
corresponding to the duality relationship between acoustic and electrical quantities. A 4-terminal
circuit 1 is connected to this series connection body. This small terminal circuit 1 represents the
usual delay element in the case of a pressure gradient receiver by the delay time τ. The sound
pressure acting on the front face of the transducing diaphragm is denoted PL and the sound
pressure acting on the rear acoustic inlet opening led to the delay element 1 is denoted P2. The
delay of the action of the sound pressure P2 on the back side of the conversion diaphragm due to
the delay element V has to have the following value, ie in the case of a directional microphone
with eg heart-shaped directivity, behind the microphone In the case of the acoustic radiation
(180'-acoustic radiation), the sound pressures P1 and P2 'need to be equal in amplitude and
phase. In this case, P2 'is the sound pressure that travels through the delay element 1 and
reaches the back surface of the conversion diaphragm. In this case, the transducing diaphragm is
at rest and therefore no conversion from acoustic vibration to electrical vibration takes place.
Such an ideal case can not be obtained in practice because the delay element (which is always
accompanied by losses). As a result, in the 180.degree. Acoustic emission of the microphone, the
sound wave coming from the back side only has a noise of 20 d13 -.delta. DB, which is a value
which is a little more than this, even in the most advantageous case.
The aforementioned known directional microphones operate as pressure gradient receivers
throughout the audible area. In contrast, the directional microphone according to the invention is
configured to be a pressure gradient receiver only in the region above the cut-off frequency of
about 300 Hz. In the region below this cutoff frequency, this microphone operates as a
nondirectional sound pressure receiver. FIG. 9 shows an electrical equivalent circuit diagram of a
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directional microphone according to the present invention of this kind. This is different from the
electrical equivalent circuit of FIG. 8 in that a series connection of an inductance Lk and a
capacitance Cv is connected in parallel in parallel with the input side of the delay element V. This
equivalent circuit is applicable to the embodiments shown in FIGS. 1 and 2. The series resonant
circuit consisting of Lk and Cv forms a short circuit connected in parallel to the delay element 1
in the frequency range below about 300 Hz. So, the value is chosen. This means that in this
frequency range the delay element loses its force, i.e. the microphone acts as a non-directional
sound pressure receiver as desired. As a result of losses in the series resonant circuit and
possibly also by monthly damping, the following is achieved, ie sufficiently covering the
frequency range in which the resonant bandwidth of the oscillating circuit consisting of Lk and
Cv is below about 300 Hz It is selected as a large value of The transition from the pressure
gradient receiver to the omnidirectional sound pressure receiver is also achieved by a
capacitance C5-connected in series with the delay element, referred to as a blocking capacitance.
An arrangement of this type is shown in FIG. 10 as an electrical equivalent circuit. If the blocking
capacitor C5 has a sufficiently small value, the passage of the delay element of the sound
pressure P2 incident in the case of 1800 acoustic radiation is blocked, for example at all
frequencies lower than the blocking frequency of 300 Hz. Therefore, the sound pressure P2
almost disappears on the nose side of the conversion diaphragm. Therefore, in this area, the
microphone operates as a nondirectional sound pressure receiver. Only after the abovementioned cut-off frequency does the directional effect of the microphone begin to appear as the
frequency increases. The device described above can be advantageously used, for example, in the
case of a condenser microphone. In the case of the electrical equivalent circuit shown in FIG. 11,
a passive diaphragm is connected in series with the delay element V, and its mass, stiffness and
internal resistance are represented by inductance Lp, capacitance Cp and ohmic resistance Rp. It
is done.
In principle, a series resonant circuit with damping characteristics is of interest. This series
resonates. Therefore, of the sound pressure P2 applied to the acoustic inlet opening on the back
side, only the component whose frequency exceeds the cutoff frequency of about 300 Hz reaches
the back side of the active conversion diaphragm. As a result, the microphone acts as an
omnidirectional sound pressure receiver for frequencies below this cutoff frequency and,
conversely, as a pressure gradient receiver with significant directional characteristics above this
cutoff frequency . It is not so easy to extend the passband above 300 Hz with passive diaphragms
alone to the highest frequency in the audible zone without too much attenuation. Therefore, if
the requirement is higher, as described above, the patch diaphragm (shown in FIGS. 4 to 7 and
33. 37) is used to close the rear side chain sound entrance opening to the delay element V. It is
proposed to divide into partial diaphragms by a plurality of strip paths (FIGS. 5 and 7). In this
case, the partial diaphragms are assigned different intrinsic resonance frequencies which are
assigned to the passage area. An arrangement of this kind is based on the equivalent circuit
shown in FIG. In this case, it is assumed that the noxious diaphragm is divided into three partial
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diaphragms, each of which has capacitance Cp19 Cp2. Cp3 and resistance Rp1. It is to be
expressed as a series connection composed of Rp29Rp3 and an inductance Lp11Lp2ILp3. Each
of these series resonances,-circuits covers only about one third of the passband respectively. A
sufficient solution can therefore be found with the very slight attenuation of the individual series
resonant circuits, in which the respective passage regions are in renal succession with one
another. This naturally works in favor of the entire passage area. The reason is that in this case
the total attenuation is significantly smaller than in the case of a single series resonant circuit.
FIGS. 13, 14 and 15 show the Oo and 180 ° acoustic emissions of the embodiment of FIGS. 9,
10 and 11 of the directional microphone according to the invention shown by the equivalent
circuit. Shows the frequency characteristics in the case of As shown, the amount of transmission
in the case of acoustic radiation from the front (00 acoustic radiation) fluctuates substantially
only over the entire frequency range, for example with one or more noisy diaphragms In the case
of the embodiment, the amount of transmission is almost zero.
According to the present invention, the frequency characteristic is expanded in the direction of
lower frequency, and the close electric transmission effect appears and the lower frequency
component is filled with the correct electric conversion of the timbre faithful to the original
sound, and the transmission is further carried out. A directional microphone is provided with
improved inheritance and thus reduced noise levels.
[0002]
Brief description of the drawings
[0003]
1 is a sectional view of a condenser directional microphone according to the present invention,
FIG. 2 is a sectional view of an electric dynamic directional microphone according to the present
invention, FIG. 3 is a sectional view of a condenser microphone, and FIGS. Sectional views of the
embodiment using passive diaphragms, and FIGS. 6 and 7 are plan views of the embodiments of
this type of negative diaphragm, and are shown only by blocks in FIGS. 8 to 12 Electrical
equivalent circuit diagram connected to the delay circuit, FIG. 13 is a frequency characteristic
diagram for 00 and 1800 acoustic radiation of the embodiment of FIG. 9, and FIG. 14 is a
frequency characteristic line of the directional microphone of FIG. FIG. 15 shows frequency
characteristic diagrams of the directional microphone of FIG. 11, respectively.
DESCRIPTION OF SYMBOLS 1 ... Vibrating film, 2 ... Counter electrode, 3 ... hole, 4 ... Air chamber,
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5 ... Delay element, 6 ... Air mass body, 7 ... Air volume body, 9 ... · Diaphragm, 10 · · · voice coil,
12 · · · delay element; 13 · · · air volume, 15 · · · air mass, 2.3.24 · · · acoustic element, 28. 38 ·
diaphragm, 33.37 · · · Passive diaphragm, 44 to 49 · · · Partial diaphragm, a, b, c · · · Band-like
path. FC% J l'n 4Ln% OF = 4 to 1i-1 ≦-((G of t, T J 31 'O- o ") · 1 to 1 meter total-ψ Low α α> C
) J C) γ Re 7 匁 Re 7 匁 R 乃 ≧
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