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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view showing a partial cross section of a
conventional transistor megaphone, FIG. 2 is an enlarged cross sectional view of a small piece
part, and FIG. 4 schematically shows the direction of the microphone, FIG. 4 shows an enlarged
cross-sectional view of the mouthpiece according to an embodiment of the present invention, and
FIG. 6 shows the direction of the acoustic wave. FIG. 7 is a directivity pattern diagram of a single
directional microphone unit alone, and FIG. 8 is a microphone directivity characteristic diagram.
1 иии и и и Megaho / body, 2 и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и
microphones 5a, 5b и и и и и и и hair hair, / / '1/41, 1801 '180-1 toor D Fig. 7-1
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transistor
megaphone and aims to improve the howling margin. It is well known that the use of a
unidirectional microphone as a microphone for a transistor megaphone is effective in improving
the howling margin. However, when this type of microphone is actually attached to the body, the
directivity is deteriorated due to the influence of the mouthpiece etc., and a great improvement
effect can not be expected. G-IJ ') Qj2 The reason is as follows. 1 and 2, 1 is a megaphone body, 2
is a mouthpiece, 3 is a bottom plate of the mouthpiece 2, 4 is a unidirectional microphone, 5a
and 5b are sound holes provided in the mouthpiece 2, 6 is a speaker. As shown in this figure,
when the microphone 4 is attached, the sound from the speaker 6 is low or lower than the
frequency at which the body outer diameter ? D becomes m-(where ? is the wavelength).
Because it is considered as a plane wave like this, it becomes almost the same as the 1800
directivity characteristics of the microphone unit 41 alone, but the diffraction effect is produced
by the main body as shown in FIG. Since the angle ? of the applied sound wave changes, the
directivity deteriorates. Also, it was experimentally confirmed that the directivity characteristic at
this time substantially matches the directivity characteristic of the angle ? when the microphone
unit 41 alone is present. For example, in the case of the main body outer diameter 80 mm, the
directivity f degrades at a frequency f of (sound velocity C2 main body outer diameter iD), f-
"two-thirds concave 3.3 ░ (H2) 8 и D 8 @ 8 or more It becomes. In a megaphone, the directivity
of the speaker becomes sharper at 2 KHz or higher, so it is easy to make feedback at a frequency
lower than that f. That is, in the conventional method, the directivity characteristic of the
microphone 40 is deteriorated at a frequency that is easy to feedback, and the improvement of
the wringing margin does not have a significant improvement effect on jCt'L. The present
invention shown in FIG. 4 shows an example of the directivity characteristic of the microphone.
The present invention eliminates the above-mentioned drawbacks and exerts a large effect on the
improvement of the howling margin by maximizing the directivity of the microphone. The
embodiment will be described below. FIG. 5 shows its embodiment, and the corresponding parts
are denoted by the same reference numerals as in FIG. The point different from the conventional
one is that the microphone unit 4 is fixed to the bottom plate 3 by any method by separating the
microphone unit 4 from the bottom plate 3 and the angle ? connecting the microphone 4
(vibration film portion) and the outer peripheral portion is 135 ░ or more The sound holes sa
and sb are formed in the mouthpiece 2 to the position where
In this structure, the direction of the sound wave from the spy ? 1 force 6 applied to the
microphone 4 is as shown in FIG. 6A in the low band (the frequency at which the outer diameter
of the body is less than -4). As shown in FIG. 6B, since ? ? 135 ░, the microphone B reaches
the microphone 4 at an angle close to 18 o 0 as compared with the conventional r. That is, the
directivity pattern diagram of the unidirectional microphone is generally as shown in FIG. 7, and
the directivity is sharper by 15 dB or more in the range of ? ? 136 ░. An example of the
characteristic is shown in FIG. Note that the sound holes need not be uniform, and it is not the
only one, and the position at which the microphones are added is not limited to the center. As is
apparent from the above embodiments, the directional characteristics of the microphone 4 can
be sufficiently improved in 2KH2 or less where feedback is likely to occur according to the
present invention, and a large effect can be obtained to improve the winding margin.
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jps5443908, description
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