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JPS6251900

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DESCRIPTION JPS6251900
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
full-range type speaker in which the amplitude of a voice coil is amplified to improve efficiency
and reduce distortion in a low frequency range. 2. Description of the Related Art In recent years,
audio devices have been miniaturized significantly due to advances in semiconductor technology
and the appearance of high-performance small circuit components. Speaker systems are
becoming smaller regardless of home use and in-vehicle systems, but there is a problem with the
acoustic characteristics of the bass region. That is, the on-axis sound pressure (Pr) and the
amplitude (3) of the speaker are given by the following equations. ... (1)... Is the density of air, ?
is the angular frequency of vibration, a is the effective radius of the diaphragm, r is the distance
between the speaker and the microphone, ? is the velocity of the diaphragm, X is the amplitude
of the diaphragm, 8 is the force coefficient, E is The input voltage of the signal, RE is the electric
resistance of the speaker, Mll is the vibration system mass of the speaker, Ma is the air load
mass, Qo is the sharpness of resonance, fo is the lowest resonance frequency, and f is the
frequency. Therefore, the efficiency decreases as the effective radius of the diaphragm decreases.
Further, the amplitude of the diaphragm is larger in the bass range because foJAk-T is inversely
proportional to the frequency square according to Equation (2). However, if the voice coil
winding width is reduced in order to improve efficiency, the amplitude range of the voice coil
becomes narrow, so distortion components are generated in the low frequency range. As a
driving method capable of a large amplitude, there is a speaker using a Kombu-Hoice coil, but the
utilization factor of the voice coil wire ring length is deteriorated and the efficiency can not be
improved. Therefore, in order to improve efficiency and reduce distortion, it is necessary to
amplify the amplitude of a small voice coil and transmit it to the diaphragm. As a conventional
technique, for example, as disclosed in JP-A-56-131298. Some have used cylinder acoustic
transformers. Hereinafter, the above-mentioned conventional speaker will be described with
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reference to the drawings. FIG. 3 shows a cross section of a conventional speaker using an
amplitude amplification mechanism. In FIG. 3, 1 is a bottom plate having a center pole 2, 3 is an
annular magnet, 4 is a top plate, and the bottom plate 1 and the top plate 4 sandwich the magnet
3 to form an annular magnetic gap 6 Do. A voice coil 6 is wound around a voice coil bobbin 7
and is held by a suspension (not shown) so as to be able to vibrate in the magnetic gap. The
upper end of the voice coil winding width / 7 is closed to form a piston 8 of a cross-sectional
area S1. The reference numeral 9 denotes a fixed cylinder, one end of which vibrates the piston 8
and the other end of which vibrates a piston B1o having an area S2 smaller than that of the
piston A.
A diaphragm 11 forming an acoustic transformer is thereby fixed to the upper end surface of the
piston B at its inner periphery by a diaphragm which is fixed at its outer periphery to a frame
(not shown) via an edge 12. FIG. 4 shows a mechanical equivalent circuit of the speaker of the
configuration of FIG. 3, which will be described below. The driving force F @ is given by the
product of the magnetic flux density B (Wb / m 2) in the magnetic air gap 5, the effective wire
ring length t (e) of the voice coil 6, and the current five times flowing through the voice coil 6.
ZME is electromagnetic braking resistance and is A / RE. MD is a vibrating mass of a drive system
such as the voice coil 6 and the voice coil bobbin 7. ?????????????? MR is a
vibrating mass of a sound emitting system such as the piston B 10 and the diaphragm 11, and SR
indicates the stiffness of the edge. MMa and RMa are the load mass and radiation resistance of
air by the diaphragm 11. The drive system and the sound emission system are coupled by an
acoustic transformer with a metamorphism ratio S, 82. The operation of the conventional
speaker configured as described above will be described below. A piston A (cross-sectional area
51) that can vibrate at one end of the cylinder 9 when a signal current is allowed to flow through
the bottom plate 2 having the center pole 1, the magnet 3, and the voice coil 6 in the magnetic
gap 6 formed by the top plate 4. The voice coil bobbin that forms 8) vibrates. At the other end of
the cylinder, a piston B10 having a cross-sectional area S2 smaller than the piston A is disposed
so as to be able to vibrate, and an inner periphery of the diaphragm 11 is fixed to the piston yB.
Therefore, I hear it. Problems to be solved by the invention However, the above-described
configuration has the following problems. This will be explained below. First, in the mechanical
equivalent circuit shown in FIG. 4, the impedance ZR of the sound emission system seen from the
primary side of the acoustic transformer becomes the total impedance Z seen from the drive
point according to the following equation, and the voice coil 6 of the drive system The vibration
velocity v1 of the piston 8 is given by the driving force F as V1 = F / Z. Therefore, the vibration
velocity v2 of the piston B1o of the sound output system and the diaphragm 11 becomes smaller
at a frequency higher than foH. In other words, the stiffness SP due to the volume in the cylinder
acts as a high cut filter and becomes a speaker dedicated to the bass range, which is inconvenient
as a full range speaker. The present invention has been made in view of the above problems, and
provides a full-range type speaker in which the amplitude of the voice coil is amplified to
improve the efficiency and reduce the distortion in the low frequency range.
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Means for Solving the Problems In order to achieve this object, the speaker of the present
invention has a voice coil disposed so as to be able to vibrate in an annular magnetic gap
provided in a magnetic circuit, and the voice coil wound around it. A first diaphragm fixed to the
rotated voice coil bobbin, a dust cap fixed to the diaphragm, a through hole provided in a center
pole portion of the magnetic circuit, and a back side of the through hole; An acoustic transformer
is formed from a telescopic bellows-like cylinder whose end face is closed, and a second
diaphragm fixed to the closed end face side of the bellows-like cylindrical body. According to this
configuration, when a signal current is applied to the voice coil, a driving force is generated in
the voice coil and the first diaphragm vibrates, and in the low frequency range, the voice coil
bobbin and the diaphragm and the dust cap and the center In the acoustic transformer consisting
of a through hole in a pole and a telescopic bellows-like cylindrical body, displacement on the
voice coil side with a large cross-sectional area of the enclosed space amplifies the displacement
of the bellows-like cylindrical body with a small cross-sectional area. The 2 diaphragm vibrates.
Therefore, the low range is enhanced, and the distortion can be reduced without using a long
voice coil, and a full range speaker can be realized. Embodiment An embodiment of the present
invention will be described with reference to the drawings. FIG. 1 shows a cross-sectional view of
a speaker in an embodiment of the present invention. In FIG. 1, reference numeral 13 denotes a
bottom plate having a through hole 16 in the center pole 14. ????????????????
?????????? The bottom plate 13 and the top plate 17 sandwich the magnet 16 to
form an annular magnetic gap 18. The reference numeral 19 denotes a frame, and the lower end
surface is fixed to the top plate 17. Furthermore, the frame 19 has a ring-shaped frame flat
portion 2o at the upper end face, and partially has a through hole 21 in the middle portion
thereof. A voice coil bobbin 23 wound with a voice coil 22 disposed so as to be able to vibrate in
the magnetic gap 18 is suspended from the frame 19 via a damper 24. Furthermore, the inner
peripheral side of the first diaphragm 25 is fixed to the upper end side of the voice coil bobbin
23, and the outer peripheral side is fixed to the inner peripheral side of the frame flat portion 2o
via the first edge 26. Reference numeral 27 denotes a dust cap, the outer periphery of which is
fixed to the inner surface of the first diaphragm 26. Reference numeral 28 denotes a telescopic
bellows-like cylindrical body fixed to the back side of the through hole 15 of the center pole 14,
and the free end side is closed. The inner peripheral side of the second diaphragm 29 is fixed to
the free end of the bellows-like cylindrical body 28, and the outer peripheral side is fixed to the
outermost periphery of the frame 19 via the second edge 3o.
8. The inner diameter cross-sectional area of the voice coil bobbin 23 is 81 '. The first diaphragm
26, the dust cap 27, the center pole 1 and the bellows-like cylindrical body 28 form an acoustic
transformer, whose volume is Wp. FIG. 2 is a mechanical equivalent circuit of the speaker of FIG.
The driving force F and the magnetic braking resistance ZME are the same as those shown in the
prior art. M F ? is a vibrating mass of the voice coil 22, the voice coil povin 23, the first
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3
diaphragm 25 and the like. SF ? is the stiffness of the damper 24 and the first edge 26. MMa1 '+
RMa1' is the load mass and radiation resistance of air by the first diaphragm 25. Sp 'is given by
the stiffness of the space Wp. The vibration mass of the second diaphragm 29 and the bellowslike cylinder 28 and the like on the secondary side of the acoustic transformer having the crosssectional areas S1 'and 82' of the voice coil 23 and the bellows-like cylinder 28 as the
metamorphic ratio Mw ', second edge stiffness Sw' and second diaphragm load mass of air MMa2
'? Radiation resistance RMa ? 'enters in series. The operation of the loudspeaker configured as
described above will be described below. In FIG. 2, the impedance Zw 'on the second diaphragm
29 side as viewed from the primary side of the acoustic transformer is expressed by the
following equation%. Therefore, the vibration velocity v1 of the first diaphragm 26 is obtained.
The vibration velocity v2 of the second diaphragm 29 is given by equations (8) and (9). However,
Zxx is, therefore, the sound pressure lPr11 by the first diaphragm 25 and the sound pressure IPr
by the second diaphragm 29, respectively. Since the effective radius of the second diaphragm is
a2? a4, 1v21? 1v11, the sound pressure exerted by the second diaphragm is dominant below
the frequency fOH 'given by the equation (7) . Above the frequency fOH ', the stiffness Sp' acts as
a high cut, and the vibration velocity v2 on the secondary side of the transformer becomes very
small. Therefore, the sound pressure IP in this region, 1 is as follows (13). As described above,
according to the present embodiment, the voice coil 22 disposed so as to be able to vibrate in the
annular magnetic gap 18 provided in the magnetic circuit and the voice coil bobbin 23 wound
with the voice coil 22 are fixed. The first diaphragm 1, the dust cap 27 fixed to the diaphragm,
the through hole 15 provided on the center pole 14 of the magnetic circuit, and the free end face
provided on the back side of the through hole 16 By forming a speaker from the second
diaphragm 29 fixed to the closed free end side of the bellows-like cylindrical body 28 by forming
an acoustic transformer from the closed telescopic bellows-like cylindrical body 28, the efficiency
of the bass region is realized. It is possible to realize a full range type speaker in which the
improvement and the reduction of distortion are achieved.
According to the present invention, a voice coil bobbin wound with a voice coil vibrating in an
annular magnetic gap provided in a magnetic circuit, a first diaphragm fixed to the voice coil
bobbin, and a first diaphragm fixed to the first diaphragm An acoustic transformer is formed
from a dust cap, a through hole provided in the center pole portion of the magnetic circuit, and
an expandable bellows-like cylinder with a free end closed and fixed to the back side of the
through hole. By constructing a speaker provided with a second diaphragm fixed to the free end
side of the bellows-like cylinder, full band reproduction is performed by the first diaphragm, and
further, high efficiency is achieved by the second diaphragm. And, it is possible to realize low
distortion low tone reproduction.
[0002]
Brief description of the drawings
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[0003]
1 is a cross-sectional view of a loudspeaker according to an embodiment of the present invention,
FIG. 2 is an equivalent circuit diagram of a mechanical system of the loudspeaker shown in FIG.
1, FIG. 3 is a cross-sectional view of a conventional loudspeaker, and FIG. It is a mechanical
system equivalent circuit schematic of the speaker shown to FIG.
14 ииииии Center pole, 15 ииииииииииииииииииииииии Voice coil bobbin, 25 ииииии First diaphragm, 27 иииии Dust cap,
28... Name of agent Attorney Nakao Toshio Other 1 person Figure 3 Figure 4
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