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JPS55128996

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DESCRIPTION JPS55128996
Description 1, title of the invention
Dynamic-type electroacoustic transducer
3. Detailed Description of the Invention The present invention relates to a dynamic electroacoustic transducer having a flat diaphragm disposed within an acoustically transparent flat
magnet system and having a conductive path. This type of electroacoustic transducer is currently
used only in headphones. The reason is that the diaphragm which is driven in a planar manner is
difficult to partially vibrate, and therefore, it is not possible to reproduce sufficiently low linearity
and sufficient linearity. The printed matter in which this type of transducer is described is
occasionally mentioned and it has been shown that it can be used as a ficrophone because of the
four inverse problems of the dynamic method, but the special of this type of microphone No
description has been given as to the construction, its acoustics or the construction when used as
a directional microphone. Capacitive transducers, such as electret diaphragms l, active and
passive electronic components of this kind, associated with ongoing miniaturization, clearly lead
dynamic microphones where the highest quality is required doing. However, in capacitive
transducers, amplifiers and impedance transformers are embedded in the casing, and these have
also been lost because they have been omitted from or otherwise embedded in the casing. Even if
it is lost, it may not be possible to get replacements at the required point, and when feeding via a
microphone cable KI'i needs an amplifier with appropriate connectivity that is not always at hand
Not only that, but if the microphone cable is overloaded, the microphone cable may be broken,
which naturally makes the microphone unusable. The object of the present invention is, in
particular, substantially corresponding to a capacitive converter with regard to transmission
characteristics related to iR characteristics, yet without electronic components in the casing, and
noise is hardly generated due to the low resistance output. It is possible to provide a dynamic
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converter which can be used as a microphone, for example, as a directional microphone. The
purpose of this is, in the case of a converter of the type mentioned at the outset, that the mass of
the diaphragm with the conductor path substantially corresponds to the mass of a diaphragm of
the same size for a capacitive transducer, and This is achieved by single-fingering the back of the
diaphragm via a low height air chamber. Compared to known dynamic microphones with moving
coils, in the present invention, the coupling between the diaphragm and the acoustic delay
element is relatively simple and can be made so as to cause almost no interference, so it is
further improved Directivity characteristics are also obtained.
Furthermore, as described above, the noise characteristics of the transducer of the present
invention are significantly improved as will be apparent from the following description as
compared to the noise characteristics of the moving coil microphone. That is, the diaphragms
used in the present invention, in which the conductor tracks are printed, for example made of an
extremely thin sheet of synthetic resin, are only about 17, o of the mass of the diaphragm with
the movable coil. Well, in the equation EndPage: 22C for the radiation resistance R 'S of a circular
diaphragm (a ρ 空 気-air density = 12 1 o 2 Crs, the radius of the r diaphragm is a unit of cm, Csound velocity = 344 m / s Substituting appropriate values for a diaphragm with a diameter of
3tTn, the radiation resistance 几 will be 11 for 100H2 and 0.11 for KH and 0.4.4 for 1000H2.
Become. The logarithmic damping factor is obtained from the following equation (R-frictional
force, M = mass of vibration system, ω〇-resonant frequency of vibration system). The mass of
the diaphragm with movable coil is about 0122 for a diameter of 36 n, compared to the mass of
a flat diaphragm of the same size, which is only 0,0122. Substituting this value into the above
equation, the reduction ratio for the diaphragm having the movable coil is d-Japanese Patent
Laid-Open Publication No. 55-128996 (3) 0045, while the attenuation ratio is 0 for the flat
diaphragm. It will be .45. This value is already an important value in particular for damping
oscillating systems, especially when mass-constrained systems are at issue. By comparison, a
value of 0045 for a diaphragm with a moving coil is of little use for damping of the vibration
system. In fact, such slight attenuation causes the microphone to exhibit disturbing sensitivity to
mechanical shock applied to the casing from the outside or to atmospheric pressure noise caused
by redundancy in close-talking of the microphone. The transducer according to the invention
with a light and flat diaphragm does not have this drawback. This has the particular advantage
that the pulse fidelity, which is particularly pronounced in the transmission of music and
languages, is high. A regen microphone, counted as one of the dynamic transducers, in which a
metallic ribbon of about 2μ thickness is a vibrating system, exhibits very good pulse
characteristics due to the extreme lightness of lidan. However, it is almost impossible to prevent
the ring tension vibration of the relay which causes transmission error. This kind of difficulty
does not occur in the transducer according to the invention, which is an essentially thin
diaphragm, which is essentially only lightly tensioned in the radial direction. The converter of the
present invention can be said to have frequency and phase characteristics and noise
characteristics which are equivalent to that of the condenser microphone in the case of being
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configured as a directional microphone, in essence the converter of the present invention is
based on the dynamic principle Since it operates, it is necessary to provide a delay element that
acts on the damping of the diaphragm so that the transmission constant is independent of
frequency.
In moving-coil microphones, the condition for obtaining a transfer constant which is independent
of the frequency is only unsatisfactory due to the mass of the oscillating system due to the
parallel arrangement of the resonant circuits. Furthermore, in order to extend the frequency
range upward, it must be manipulated by a Helmholtz resonator placed in front of the
diaphragm. In the case of the transducer according to the invention, the flat diaphragm has only
a sufficient mass of the mass of the diaphragm with moving coils, as in the case of the capacitive
transformer by connecting acoustic delay elements as well as disturbing effects Will not occur.
The RC to LR acoustic delay elements in the electrostatic transducer and the dynamic transducer
are in principle similar to one another as long as the directional characteristics match, and in fact
they are different in design value. In the case of uni-directional characteristics derived from the
vector addition of spheres and figure-eight characteristics, in an expansion receiver (e.g. an
evaporative condenser microphone) the vibration system must be resiliently damped to the
spherical characteristics, Frictional braking is required for the figure 8 character. In a dynamic
system, as in the case of a Perrositi receiver, i.e. the transducer of the invention, friction and mass
damping must be performed for unidirectional characteristics. Thus, when the diaphragm area is
equal, the capacitive element of the delay element, that is, the vacant volume (R volume must
have about 30 to 100 times the value of the dynamic converter as compared to the capacitive
transformer. Become. However, this requirement is completely fulfilled, for example, in the case
of a capacity converter with a diameter of 32 throats, the empty (torque) volume is only (10)
EndPage: 3 about 0.2 cJ, and as a result the velosity receiver π The above-mentioned conditions
can be satisfied without the need to increase the volume of the microphone body. Excluding this,
further advances in printed circuit technology in the near future can be factored into the
calculation, thus reducing the area of the diaphragm, reducing the width of the conductor track
and reducing the spacing between the conductors. It can be made 8cdl or less by doing. In this
way not only the mass of the diaphragm is reduced, but also the advantageous internal
impedance of the transducer, which is between 200 and 600 ohms, is obtained.
Dynamic-type electroacoustic transducer
In the detailed description of the invention it can be seen that the coupling of acoustic elements,
such as, for example, cavities, frictional resistance or acoustic mass, can be realized considerably
clearly and precisely as in conventional moving coil microphones. . The upward extension of the
highest frequency of the frequency range is particularly simple with the light diaphragm
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according to the invention. The reason is that due to the flatness of the diaphragm, an acoustic
damping effect can be incorporated on the back side to form a very low air chamber, and the
return force of this chamber causes the width of the upper limit of the transmission range to be
reduced. A wide resonance curve extending over about 2 octaves is obtained. Therefore, it is not
necessary to arrange a Helmholtz resonator in front of the diaphragm, which is essential in the
moving coil type microphone and causes a sharp drop in frequency characteristics above the
resonance frequency. The low air chamber behind the diaphragm is formed in the first
embodiment of the invention by the large area of acoustic friction on the side opposite the back
of the diaphragm. On the other hand, this resistance closes large acoustically active cavities in
the lower frequency range. Furthermore, from the low air chamber behind the imaging plate, a
slitted tube, with holes with frictional resistance distributed over its length, leads into the
external space. This serves as a device for forming unidirectional characteristics. In another
embodiment, an acoustic frictional resistance is attached to the back plate of the magnet system,
which is located on the back side of the diaphragm and has a hole, and this resistance is an
external air through the frictional resistance. It leads to the connected room. Furthermore, a tube
is connected directly to the back plate, which leads to a large, acoustically effective cavity in the
lower frequency range. This example shows how the arrangement of the transducer according to
the invention can be easily realized in connection with a flat magnet system. This is also shown in
the alternative embodiment in which the magnet system is located on the back side of the
diaphragm and a frictional resistance is placed on the back plate with the holes. At that time, a
casing that forms a cylindrical cavity is connected to the frictional resistance, and holes with
frictional resistance are distributed on the circumferential surface of the casing. The end face of
the casing opposite to the conversion system is closed by frictional resistance. In the last
embodiment, where a simpler and easier to understand arrangement would be almost impossible,
the back of the diaphragm is connected to the annular cylindrical passage via a low air space. On
the circumferential surface of this passage, there are distributed holes which communicate with
the external space and are sealed off by frictional resistance (13).
Also, the end of the low airspace chamber opposite the back of the diaphragm is frictionally
closed, which leads to a closed acoustical chamber in the medium and relatively high frequency
range. In the lower frequency range, an acoustically effective cavity is provided, from which a
hole with frictional resistance leads to the external space. The empty space is in turn connected
to the lower air chamber behind the diaphragm via the scooping bushing. Next, the present
invention will be described in detail using the drawings. FIG. 1 schematically shows a crosssectional view of a transducer according to the invention, consisting of a diaphragm 1, bar
magnets 2 and 3 and back plates 4 and 5 with holes. The vacant space 6 is connected to the back
plate 41 c via the acoustic friction resistance 7 on the one hand, and is connected to the
appearance via the acoustic friction resistance 8 on the other hand. Since the tube 9 is connected
to the center of the back plate, the diaphragm can deliver low frequency sound waves to the
large cavity 10. The delay element comprises elements 8, 6.7-. It is combined from 9 and 10 to
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(14) EndPage: 4. Another embodiment is shown schematically in FIG. A low height air chamber
11 is formed on the back plate ˜. From this chamber, an acoustic hole is distributed, and the hole
is provided with a frictional resistance 13 and a tube 12 provided with a slit exits into the
external space. The chamber 11 is also provided with an acoustic frictional resistance 14 which
leads to the cavity 15. The delay elements for obtaining the desired uni-directional characteristics
consist of the tube 12, the frictional resistance 14 and the cavity 1 Luca. In FIG. 3, the friction
resistance 16 provided on the back plate, the cavity 17 connected to this resistance, and the
friction resistance 18.19 provided on the holes distributed in the empty casing are similarly
obtained. It can be seen that in a narrow frequency range but with an olfactory-directed
characteristic being obtained. FIG. 4 shows a vertical microphone having a close talk direction in
the axial direction. An annular cylindrical passage 21 is followed in the transducer system via the
lower air chamber 20. Holes distributed on the circumferential surface of the passage and
provided with the frictional resistance 22 lead to the external space. At the center of the chamber
20 is connected a bushing 23 containing an acoustic mass and leading to a large chamber 24.
The acoustic frictional resistance 25 leads to the external space. The chamber 26 is connected to
the lower chamber 20 via a frictional resistance 27. Two delay elements are provided here.
Elements 22 ° 27 and 26 are valid for the medium and high frequency range and elements 25.
24 and 23 for the low frequency range.
4. Brief Description of the Drawings FIGS. 1 to 4 are schematic cross-sectional views of
embodiments of a viewing acoustic transducer used as a directional microphone according to the
present invention. DESCRIPTION OF SYMBOLS 1 ... Diaphragm 2, 3 ... Bar magnet 4,5 ... Back
plate, 6.10, 15, 17, 24.26 ... Vacancy, 7 degrees 8.13, 14 ,, 16. . 18,19,22,25 ° 27 ... acoustic
frictional resistance, Nursing 9,12 ..., 11.20 ... low air chamber, 21 ... annular cylindrical passage
23 ... Butsushingu EndPage: 5
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