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The present invention relates to expansion of a reproduction frequency band of an
electromagnetic drive type earphone. In the conventional electromagnetic drive type earphone,
as shown in FIG. 1, a thin plate of magnetic material, for example, iron, is used for the diaphragm
1 and its periphery is used as the annular projection of the magnet 2 and the case 60 or the case
60 or Are divided and fixed by a fixing method such as sandwiching or bonding between them. In
addition to the above, the diaphragm 1 may be a thin plate disc 9 of magnetic material attached
to the center of a plastic film 10 as shown in FIG. In any of the diaphragms, a method of fixing
the periphery of the diaphragm is used. The behavior of the diaphragm of FIG. 2 roughly
corresponds to that of the peripheral fixed circular film. However, in the case of earphones, it is
difficult to apply a strong tension to the membrane for low cost and simple configuration, and
the resonance frequency is generally low and the variation is large. On the other hand, in the
diaphragm 1 shown in FIG. 1, its vibration behavior matches the resonance of the peripherally
fixed disc, and its resonance frequency is higher than that of the diaphragm shown in FIG. It
becomes smaller. However, even in this case, the reproduction frequency band is extremely
narrow compared to that of the HiFi headphones, and it is impossible to reproduce a good sound.
An object of the present invention is to provide an earphone which can reproduce a good sound
by improving the resonance frequency of a diaphragm compared to the conventional one. In the
present invention, in order to raise the resonance frequency of the diaphragm, the method of
fixing the diaphragm is improved. In the present invention, as shown in FIG. 4, the diameter A of
the diaphragm is 0.5 to 0.8 times the diameter A of the diaphragm made of a magnetic thin plate,
as opposed to the conventional fixing around the diaphragm. By fixing the portion of diameter B,
it is possible to increase the resonance frequency of the diaphragm by 5 to 5 times. The
resonance frequency referred to here is a so-called lowest resonance frequency, (0, 0) mode
resonance frequency in which both the nodal circle and the nodal diameter are present. That is,
as shown in FIG. 1, in the system in which the diaphragm 1 is made of a magnetic thin plate so as
to obtain a wide band in the earphone and fixed around it, the resonance frequency of the
diaphragm is Corresponds to the case where the coefficient λ in the above is λ = 3.2. Where f:
resonant frequency (Hz) λ: constant 2h determined by resonant mode I plate thickness [α] a:
radius [α] E: Young's modulus [y / w] g: acceleration of gravity − 980 (cIL / 5 ec2 :] Σ:
Poisson's ratio γ: density (kg /-) identical diaphragm = o, fixed at sA to 0.8 A, λ becomes λ = 4
to 7, and the resonance frequency is 1.5 to 5 times It will improve.
However, in practice, the fixing portion can not be pressed by a wire, but is pressed by a certain
degree. Therefore, the improvement of the resonance frequency is not ideally 15 to 5 times as
shown by the equation, but is about 12 to 4 times. The structural example of the present
invention is shown in FIG. 3 and described with reference to the drawings. An annular projection
for fixing the diaphragm 1 is provided on the surface of the magnet 2 on the diaphragm side. The
projection may be a part of the magnet 2 or may be a separate part between the magnet 2 and
the diaphragm 10. The diameter of this annular projection (corresponding to B in FIG. 4) is 0.5 to
0.8 times the diameter of the diaphragm. Further, the case 6 on the front surface of the
diaphragm 1 is also provided with projections arranged in a circular ring shape with the same
diameter as the annular projections provided on the magnet 2. The diaphragm 1 is fixed by being
pinched by the projection of the magnet 2 and the projection of the case 6. A sound wave
generated outside the fixed portion of the diaphragm 1 passes between the projections of the
case 6 and passes through the earpiece 7 to the ear. According to the present invention, the high
frequency band of the conventional earphone is expanded about 1.2 to 4 times, and the narrow
band feeling of the sound heard by the earphone can be removed.
Brief description of the drawings
FIG. 1 is a cross-sectional view of a conventional electromagnetic earphone, FIG. 2 is a crosssectional view of a second example of a diaphragm for a conventional electromagnetic earphone,
and FIG. 6 is a structure of the electromagnetic earphone according to one embodiment of the
present invention FIG. 4 is an explanatory view of the diameter direction of the diaphragm and
the diameter of the fixed portion (iii).
1 ... diaphragm 2 ... ... magnet 3 ... coil 4 ... magnetic pin 5 ... substrate 6 ... case. 0 years old 3 bad