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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
band-limited microphone unit capable of arbitrarily cutting low or high frequencies. Prior Art
FIG. 7 is a cross-sectional view of a microphone unit of a conventional electret condenser
microphone. The configuration of this conventional example will be described below with
reference to FIG. In FIG. 7, 1 is a drawing cloth, 2 is a cylindrical metal case having a sound hole
2a on the top surface, 3 is a film ring formed by uniformly stretching a vibrating film 4 having a
metal surface by metal deposition or the like, 5 is Reference numeral 6 denotes a fixed electrode,
7 denotes an insulator, 8 denotes a FET, 9 denotes a printed circuit board, 10 denotes a back air
chamber, and 11 denotes a front air chamber. In this description, a wheel electret type using an
electret material for the vibrating membrane 4 is taken as an example, but the same applies to a
back electret type where an electret material is provided on the fixed electrode 6 side. The fixed
electrode 6, the insulator 7, the FET 8, and the printed circuit board 9 can be considered as one
amplifier block, and the above-described components are fixed to the metal case 2 by caulking
portions 2b and the like after being inserted into the metal case 2. In the electret condenser
microphone configured as described above, a typical frequency exception is shown in FIG. 8, but
theoretically the low band is almost flat and the high band has Q near the resonance frequency of
the diaphragm, This point is the reproducible band. In recent years, electret condenser
microphones are mass-produced as built-in microphones for cassette tape recorders or
telephones etc. However, the frequency characteristic shown in FIG. 8 requires a wider band due
to AGC level, intelligibility and other reasons. In the past, low cut or high cut was used outside
the required band in the electric circuit. Therefore, the number of circuit parts is increased, and
the cost is increased. An object of the present invention is to eliminate the above-mentioned
drawbacks and to provide a microphone unit which does not require band limitation on the
circuit side. Means for Solving the Problems In order to achieve the above object, according to
the present invention, a differential microphone unit is used, inserted and fixed to a holder
having a pot shape, and the holder is ventilated to the back air chamber to the outside. The
groove is provided in the A band-limited microphone unit capable of acoustically low-pass cutting
is obtained. In accordance with the invention it is therefore possible to band-limit acoustically by
means of the holder. Embodiment The configuration of an embodiment of the present invention
will be described below with reference to the drawings.
FIG. 1 is a sectional view, and the same parts as FIG. 7 are indicated by the same reference
numerals. In FIG. 1, reference numeral 7a denotes a hole provided in one or more in the insulator
7, and reference numeral 9a denotes a hole similarly provided in the printed circuit board 9. That
is, in the case of FIG. 1, it is a differential microphone unit in which the back air chamber 10 is
ventilated to the outside through the hole 7a 19a. Reference numeral 12 denotes a holder in the
form of a pot whose perspective view is shown in FIG. 2, and the differential microphone unit is
inserted and fixed by press fitting or the like. Therefore, the back air chamber 10 is configured to
be ventilated to the outside through the back air chamber 12 a of the holder 12 and by a
ventilation groove 12 b or the like provided on the side wall of the holder 12. The reference
numeral 13 denotes a lead terminal for taking out the output of the microphone unit (in the
present embodiment, the output lead terminal of the FET 8 is directly used), and the lead-out
portion 12c from the holder 12 is sealed. FIG. 3 shows a simple equivalent circuit when
configured as described above, and the same reference numerals as in FIGS. 1 and 2 indicate the
same parts. From FIG. 3, by setting the acoustic constants of the A block and the B block
appropriately, it is possible to cut the high band of the A block and cut the low band of the B
block to perform band limitation. FIG. 4 is an example of the frequency characteristic in the case
of the present embodiment, and the range of band limitation is arbitrary. FIG. 5 is another
embodiment of the present invention. The same parts as in FIG. 1 are indicated by the same
numbers. In FIG. 5, the difference from FIG. 1 is that the groove 12b of the holder 12 has a
configuration in which the back air chambers IO and 12a are ventilated to the outside by the
vibrator 14 provided on the side wall of the holder 12 . Therefore, the same results as in FIG. 1
can be obtained. FIG. 6 shows a perspective view of the holder 12. Effects of the Invention As
described above, according to the present invention, since it is possible to provide a microphone
unit capable of acoustically arbitrary band limitation, band limitation on the electric circuit side is
unnecessary, and a tape recorder, a telephone, etc. The total cost can be reduced, and further, the
performance of recording and intelligibility can be improved. Further, in the case of the present
invention, since band limitation is implemented by the addition of a simple holder, there is also
an advantage that a small and relatively inexpensive microphone unit can be supplied.
Brief description of the drawings
1 is a sectional view of a microphone unit according to an embodiment of the present invention,
FIG. 2 is a perspective view of an essential part of FIG. 1, FIG. 3 is an equivalent circuit diagram
of FIG. Frequency characteristics, FIG. 5 is a cross-sectional view showing another embodiment,
FIG. 6 is a perspective view of an essential part of FIG. 5, FIG. 7 is a cross-sectional view showing
a conventional microphone unit, and FIG. Is a frequency characteristic diagram of FIG.
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Figure 2 Figure 4 Figure 5 Figure 6
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