U.S. patent number 3,905,448 [Application Number 05/483,154] was granted by the patent office on 1975-09-16 for loudspeaker.
This patent grant is currently assigned to Sony Corporation. Invention is credited to Kazumasa Abe, Nobuyuki Arakawa, Toshiko Harashino, Toshio Hirosawa, Hirotake Kawakami, Kozo Kokubu, Naomi Sakai, Toshio Sasabe.
United States Patent |
3,905,448 |
Kawakami , et al. |
September 16, 1975 |
Loudspeaker
Abstract
In a loudspeaker, the upper part and the lower part of a
cone-shaped diaphragm with a voice coil are suspended from a frame
by a ring shape suspension member, herein referred to as a first
suspension means, and by a ring shape suspension member, herein
referred to as a suspension means, respectively. At least one of
the suspension means is formed of a mixture of elastic material
such as rubber, with carbon fibers therein. The fibers are
needle-like and are aligned radially in the material of at least
one of the suspension means.
Inventors: |
Kawakami; Hirotake (Tokyo,
JA), Sasabe; Toshio (Tokyo, JA), Hirosawa;
Toshio (Yokohama, JA), Sakai; Naomi (Yokohama,
JA), Arakawa; Nobuyuki (Yokohama, JA),
Kokubu; Kozo (Yokohama, JA), Abe; Kazumasa
(Tokyo, JA), Harashino; Toshiko (Yokohama,
JA) |
Assignee: |
Sony Corporation (Tokyo,
JA)
|
Family
ID: |
13667237 |
Appl.
No.: |
05/483,154 |
Filed: |
June 26, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Jul 2, 1973 [JA] |
|
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48-78632[U] |
|
Current U.S.
Class: |
181/172 |
Current CPC
Class: |
H04R
7/12 (20130101); H04R 7/20 (20130101) |
Current International
Class: |
H04R
7/12 (20060101); H04R 7/00 (20060101); H04R
7/20 (20060101); G10K 013/00 (); H04R 007/00 () |
Field of
Search: |
;181/169,167,170,171,172
;162/141,146 ;252/511 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tomsky; Stephen J.
Attorney, Agent or Firm: Hill, Gross, Simpson, Van Santen,
Steadman, Chiara & Simpson
Claims
We claim as our invention:
1. A loudspeaker comprising a diaphragm with a voice coil, a frame
surrounding said diaphragm, and a suspension means for suspending
said diaphragm from said frame, said suspension means being formed
of a mixture of elastic material impregnated with carbon
fibers.
2. A loudspeaker according to claim 1, wherein said elastic
material is rubber and said carbon fibers are needle-like and are
radially aligned in said suspension means.
3. A loudspeaker according to claim 2, wherein said suspension
means is disposed between the upper portion of said diaphragm and
said frame and it defines an intermediate portion having an arcuate
cross section.
4. A loudspeaker according to claim 2, wherein said suspension
means is disposed between the lower portion of said diaphragm and
said frame and it defines an intermediate portion having a
wave-like cross section.
5. A loudspeaker according to claim 1, wherein said elastic
material is a plastic resin.
6. A loudspeaker comprising a cone-shaped diaphragm with a voice
coil, a frame surrounding said cone-shaped diaphragm, a first
suspension means for suspending the upper part of said diaphragm
from said frame, and a second suspension means for suspending the
lower part of said diaphragm from said frame, at least one of said
suspension means being formed of a mixture of elastic material
impregnated with carbon fibers.
7. A loudspeaker according to claim 6, wherein said elastic
material is rubber and said carbon fibers are needle-like and are
radially aligned in said one of said first suspension means and
said second suspension means.
8. A loudspeaker according to claim 6, wherein the other suspension
means is also formed of a mixture of elastic material with carbon
fibers.
9. A loudspeaker according to claim 8, wherein said elastic
material is rubber and said carbon fibers are needle-like and are
radially aligned in the material of said first and said second
suspension means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a dynamic, cone type loudspeaker, and
more particularly to a loudspeaker with suspension means for
supporting the cone from a frame.
2. Description of the Prior Art
In a typical conventional dynamic loudspeaker, there is found a
circular yoke, an annular yoke, an annular magnet and a central
pole fixed on the circular yoke. The vibration system comprises a
cylindrical bobbin, a voice coil wound around the cylindrical
bobbin, a suspension means or a damper suspending the bobbin from a
cone-shaped frame and a cone-shaped diaphragm fixed adhesively on
the upper end of the bobbin. An annular suspension means has its
outer edge bonded to the upper end of the frame with a suitable
binder and has its inner edge bonded to the upper end of the
diaphragm by a suitable binder.
Generally, the suspension means provides an edge for the cone which
has a curved portion with a nearly semicircular cross section
projecting upward at its center, which is elastically deformable
due to its own elasticity, whereby the diaphragm can be linearly
vibrated in the vertical direction. The stiffness of the edge has
an important effect on the lower frequency characteristic. The
stiffness should be reduced for the lowering of the lower threshold
frequency. For such a purpose, the edge is generally formed of
urethane sponge or cotton cloth impregnated with phenol resin, or
of a mixture of nitryl butadiene rubber, styrene butadiene rubber
or isobutyl-isoprene rubber with carbonic fine grains.
For satisfactory vibration of the diaphragm, it is required that
the edge be deformable both radially and peripherally. Moreover, it
is necessary that the peripheral deformation be larger than the
radial deformation.
An edge formed of cotton cloth has the following disadvantages.
When the diaphragm is strongly vibrated, the edge is wrinkled and
its internal loss is increased, since it is little deformed in the
peripheral direction. Moreover, sounds are generated from the
edge.
An edge formed of the vulcanized mixture of the above-mentioned
rubber with carbonic fine grains has the following disadvantages:
The thickness of the edge should be relatively large for the
required stiffness. Therefore, the sound conversion efficiency is
lowered with the increase of the weight of the edge.
Generally, the damper is annular and undulated in shape, and
deformable in a radial direction. This prevents the voice coil from
contacting the yoke during vibration. It supports the diaphragm and
the voice coil.
Also, the stiffness of the damper has an important effect on the
lower threshold frequency f.sub.o. With a damper having a large
degree of stiffness, sounds cannot be reproduced with high
fidelity, since the damper does not vibrate accompanied with the
diaphragm. For that reason, the damper is manufactured in such a
manner that the cotton cloth impregnated with phenol resin is
formed under heat into undulation so as to obtain a lower
stiffness.
However, the conventional damper cannot be deformed in a peripheral
direction when the vibration system is operated. Accordingly, the
linearity of the deformability is unsatisfactory under large
vibrations. The size and the thickness of the damper are increased
for the required stiffness and so the weight of the damper is
increased. Accordingly, the internal loss of the damper is
decreased. Therefore, the mechanical impedance of the loudspeaker
is increased in the lower frequency range. As the result, the
sharpnesses of the mechanical resonance and the electrical
resonance are increased and so the quality of the reproduced sounds
is worsened.
SUMMARY OF THE INVENTION
One object of this invention is to provide a loudspeaker with a
good frequency response characteristic.
Another object of this invention is to provide a loudspeaker with a
good sound characteristic in which the suspension means is improved
for supporting the cone or the diaphragm.
Another object of this invention is to provide a loudspeaker with a
light suspension means having a high degree of stiffness, in which
a diaphragm is suspended by a suspension means formed of a mixture
of elastic material with carbon fibers.
Another object of this invention is to provide a loudspeaker
generating no radiate sound from a suspension means, in which a
diaphragm is suspended by a suspension means containing short
carbon fibers aligned radially, and in which the suspension means
is prevented from wrinkling.
Another object of this invention is to provide a loudspeaker with a
cone-type diaphragm in which the cone-type diaphragm is suspended
by an improved suspension means with a large internal loss at its
lower end.
Another object of this invention is to provide a loudspeaker with a
cone-type diaphragm in which the cone-type diaphragm is suspended
by an improved suspension means formed of a mixture of elastic
material with carbon fibers and deformable in the peripheral
direction, at its lower end, and therefore in which the sharpnesses
of mechanical and electrical resonances are decreased.
A still further object of this invention is to provide a
loudspeaker with a cone-type diaphragm in which the cone-type
diaphragm is suspended by a suspension means containing carbon
fibers at its upper end and lower end, whereby signals can be
converted into sounds with high fidelity in a higher frequency
range and vibration can be sufficiently damped in a lower frequency
range.
In accordance with an aspect of this invention, a loudspeaker
comprises a diaphragm with a voice coil, a frame surrounding the
diaphragm, and a suspension means for suspending the diaphragm from
the frame, the suspension means being formed of a mixture of
elastic material with carbon fibers.
The above, and other objects, features and advantages of the
invention will be apparent in the following detailed description of
illustrative embodiments thereof which is to be read in connection
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of a loudspeaker of one
preferred embodiment of this invention;
FIG. 2 is a plan view of a first suspension means in FIG. 1;
FIG. 3 is an enlarged plan view of a part of the first suspension
means shown in FIG. 2;
FIG. 4 is a cross-sectional view taken along the line IV--IV of
FIG. 3;
FIG. 5 is a cross-sectional view of a metal mold employed for the
manufacture of the first suspension means shown on FIG. 2;
FIG. 6 is a plan view of a second suspension means in FIG. 1;
FIG. 7 is an enlarged plan view of a part of the second suspension
means shown on FIG. 6;
FIG. 8 is a cross-sectional view taken along the line VIII--VIII of
FIG. 7;
FIG. 9 is a graph showing a frequency-response characteristic;
and
FIG. 10 is a graph showing a frequency-impedance
characteristic.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, the magnetic portion of a loudspeaker 1,
according to one embodiment of this invention, comprises a circular
yoke 2a, an annular yoke 2b, an annular magnet 3 disposed between
the circular yoke 2a and the annular yoke 2b, and a central pole 4
which extends upwardly from the center of the circular yoke 2a and
is fixed with respect thereto. A vibration system comprises a
bobbin 5 for a voice coil, a voice coil 6 wound around the bobbin 5
and a cone-shaped diaphragm 9 fixed on the upper end of the bobbin
5. The first annular suspension means 20 is bonded to the upper end
of the frame 7 and to the upper end of the diaphragm 9, with a
suitable binder. A second annular suspension means, namely a damper
28 is bonded to the lower end of the diaphragm 9 to suspend the
diaphragm 9 elastically from the frame 7. A sound absorber 11 is
fixed on the upper face of the bobbin 5. A cap 12 covers the
surface of the sound absorber 11. A clamping ring 13 is fixed on
the upper end of the edge 20 to prevent the edge 20 from peeling
from the upper end of the frame 7.
The first suspension means 20 will now be described in detail with
reference to FIGS. 2 to 4.
The first suspension means 20 defines a curved or ridge-like
portion 20a with a nearly semicircular cross section projecting
upward, an inclining portion 20b and an outer horizontal
circumferential portion 20c. The first suspension means 20 is
manufactured in such a manner that carbon fibers 21 with lengths of
0.3 to 0.8 mm are mixed into an elastic material such as synthetic
rubber, (for example, nitryl butadiene rubber, styrene butadiene
rubber and isobutyl-isoprene rubber), natural rubber or synthetic
resin (for example, soft-foamed-urethane). The carbon fibers 21 are
aligned radially as diagrammatically shown in FIG. 3.
The upper end of the diaphragm 9 is fixed on the inclined portion
20b of the first suspension means 20, and the upper end of the
frame 7 is fixed to the horizontal circumferential portion 20c of
the first suspension means 20.
The method for manufacturing the edge 20 will be described with
reference to FIG. 5.
1 to 40 percent carbon fibers, with Young's modulus 20,000
kg/mm.sup.2, diameter 8.mu. and length 3 to 6 mm, and a different
material, such for example, stearic acid, sulpher, carbon black,
etc., are mixed into solid styrene butadiene rubber by a mixing
mill, where the carbon fibers are cut needle-like into 0.3 to 0.8
mm. A resulting mixture 22 is put on the center of a metal mold 23,
heated up to a required temperature, for example 150.degree.C.,
which defines an annular groove 24 having the same cross section as
the first suspension means 20. Another metal mold 26 is provided
having a mating annular projection 25 of the same cross section as
the annular groove 24. The metal mold 26 is brought over the one
metal mold 23, heated up to the said required temperature. The
mixture 22 is put between the metal molds 23 and 26. Accordingly,
as the metal mold 26 is pressed down, the mixture 22 is radially
spread out from the center of the metal mold 23 in the direction
shown by the arrows 27 in FIG. 5 and then led into the annular
groove 24, between the metal molds 23 and 26. When the annular
projection 25 is fitted into the annular groove 24, the mixture 22
is vulcanized at a temperature over 140.degree.C., between the
metal molds 23 and 26. Thereafter, the metal molds 23 and 26 are
cooled to solidify the mixture 22. The formed mixture 22 is drawn
out from the metal mold 23. As the result, the first suspension
means 20 is obtained, as shown on FIG. 2 and FIG. 4.
In the manufacturing process, since the mixture 22 is spread out
directionally, the carbon fibers 21 contained in the mixture 22 are
displaced directionally. Therefore, the carbon fibers 21 with the
lengths of 0.3 to 0.8 mm are radially dispersed in the direction of
the diameter of the first suspension means 20 (FIG. 3).
With such a dispersion of the carbon fibers 21, the deformability
of the first suspension means 20 is improved on the peripheral
direction. There is no possibility that the first suspension means
20 will be wrinkled. The specific weight of the first suspension
means 20 is small and the stiffness of the first suspension means
20 is large, since it is manufactured in a vulcanizing process of
the mixture containing carbon fibers. Consequently, the thickness
of the curved portion 20a of the first suspension means 20 can be
reduced to the minimum for the required stiffness and so the total
weight of the first suspension means 20 can be reduced.
According to this invention, the second suspension means 28 is also
formed of the mixture of elastic material with the carbon
fibers.
Referring to FIG. 6 and FIG. 8, a second suspension means 28 has a
plurality of concentric curved portions 28a with a semicircular
cross section projecting upward. It also has curved portions 28b
with a semicircular cross section projecting downward, an inner
edge portion 28c with a U-shaped cross section projecting downward,
and a horizontal circumferential portion 28d. The second suspension
means 28 is formed of a mixture of the same elastic material as the
first suspension means 20 with the carbon fibers. As shown in FIG.
7, carbon fibers 31 with lengths of 0.3 to 0.8 mm are radially
aligned in the direction of the diameter of the second suspension
means 28. It is preferable that the Young's modulus of the carbon
fiber be more than 20,000 kg/mm.sup.2 and that the diameter of the
carbon fiber is smaller than the length of the carbon fiber, for
example, about 8.mu.. 1 to 40 percent carbon fibers 31 are
contained in the second suspension means 28.
In the loudspeaker 1, the inner end portion 28c is bonded to the
bobbin 5 and the horizontal circumferential portion 28d is bonded
to the frame 7. The second suspension means 28 can be manufactured
in the same manner as the first suspension means 20.
The deformability of the second suspension means 28 is higher in
the peripheral direction than in the radial direction, since the
carbon fibers 31 are radially dispersed in the second suspension
means 28. When a mixture of styrene butadiene rubber with the
carbon fibers is vulcanized for the manufacture of the second
suspension means 28, a small specific weight and a large stiffness
can be obtained for the second suspension means 28. Consequently,
the thickness of the second suspension means 28 can be reduced to a
minimum for the required stiffness and hence the total weight of
the second suspension means 28 can be reduced.
FIG. 9 shows the frequency-response characteristics of cone-type
dynamic speakers using the first suspension means 20 according to
this invention and the conventional first suspension means formed
of cotton cloth.
In a curve a for a speaker using cotton cloth, the response
fluctuates in frequencies above 500 Hz, where peaks or dips occur.
Therefore, the quality of tone is deteriorated. In a curbe b for
the first suspension means according to this invention, no peak or
dip occurs in the higher frequencies. The response lowers abruptly
in the frequencies above a higher threshold frequency 1,500 Hz.
Therefore, high quality of tone can be obtained. The reasons are
that the suspension means according to this invention is not
wrinkled in the vibration and no sound is generated from the
suspension means, and that the sound conversion efficiency is
improved due to the reduction of the weight.
FIG. 10 shows frequency-impedance characteristics. Curve a is for a
conventional loudspeaker using a damper formed of cotton cloth
impregnated with phenol resin, where the resonant frequency f.sub.o
is 78 Hz, the maximum impedance Z.sub.o 100 .OMEGA. and the minimum
impedance R.sub.E 6 .OMEGA.. The sharpness Q.sub.M of the
mechanical resonance is represented by an equation ##EQU1## where
f.sub.1 and f.sub.2 are frequencies for an impedance ##EQU2## From
the curve a, f.sub.1 = 67 Hz and f.sub.2 = 88 Hz are apparent.
Therefore, ##EQU3## for the curve a. The sharpness Q.sub.o of the
electrical resonance is represented by an equation ##EQU4## for the
curve b.
The values of Q.sub.M and Q.sub.o are large for the conventional
damper, as above described and so the damping effect is low for the
lower frequency range. Therefore, it will be understood that the
tone quality is inferior.
The frequency characteristic is remarkably improved by using the
second suspension means 28 according to this invention, as shown by
a curve b on FIG. 10, where the resonant frequency f.sub.o is 84
Hz, the maximum impedance Z.sub.o 24 .OMEGA. and the minimum
impedance R.sub.E 6 .OMEGA.. The frequencies f.sub.1 and f.sub.2
are 50 Hz and 143 Hz for an impedance ##EQU5## Therefore, the
sharpness Q.sub.M of the mechanical resonance is ##EQU6## And the
sharpness Q.sub.o of the electrical resonance is ##EQU7##
It will be understood that Q.sub.M and Q.sub.o can be remarkably
lowered by the second suspension means according to this invention,
compared with the conventional suspension means.
Although an illustrative embodiment of this invention has been
described in detail herein with reference to the accompanying
drawings, it is to be understood that the invention is not limited
to that precise embodiment, and that various changes and
modifications may be effected therein by one skilled in the art
without departing from the scope or spirit of this invention, as
defined in the appended claims. For example, the shape and the size
of the first and the second suspension means may be varied.
Moreover, this invention can be applied to a double cone-type
loudspeaker or a dome-type loudspeaker, too.
* * * * *