AU486552B2 - Loudspeaker - Google Patents

Description

70.575 /74 BACKGROUND OF THE INVENTION

Field of the Invention:

This invention relates to a dynamic, cone type loud-

speaker, and more particularly to a loudspeaker with

suspension means for supporting the cone from a frame.

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 sus-

pension 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 semi-

circular 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 butadien rubber or isobutyl-

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70,575 /74 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 peri-

pheral deformation be larger than the radial deformation.

An edge formed of cotton cloth has the following dis-

advantages: 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. More-

over, sounds are generated from the edge.

An edge formed of the vulcanized mixture of the above-

mentioned rubber with carbonic fine grains has the follow-

ing disadvantages: The thickness of the edge should be

relatively large for the required stiffness. Therefore,

the sound conversion efficiency is lowered with the in-

crease 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 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 stiff-

ness.

However, the conventional damper cannot be deformed

486.5 52

575/74 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 elec- trical resonance are increased and so.the quality of the reproduced sounds is worsened.

SUMMARY OF THE INVENTION

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70.57 5/74

The present invention provides a loudspeaker

comprising a diaphragm with a voice coil, a frame surround-

ing said diaphragm, and a suspension means for suspending

said diaphragm from said frame, which is characterized

in that said suspension means is formed of a mixture of'

elastic materi alImpregatded wxh carbo fibers/-ACM

The above, and oth r preferred features and advan-

tages 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

Figure 1 is a schematic cross-sectional view of a

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70,575 /74 loudspeaker of one preferred embodiment of this invention;

Figure 2 is a plan view of a first suspension means in Figure 1;

Figure 3 is an enlarged plan view of a part of the first suspension means shown in Figure 2;

Figure 4 is a cross-sectional view taken along the line IV-IV of Figure 31

Figure 5 is a cross-sectional view of a metal mold employed for the manufacture of the first suspension

means shown on Figure 2;

Figure 6 is a rio view of a second suspension means in Figure 1;

Figure 7 is an enlarged plan view of a part of the second suspension means shown in Figure 6; Figure 8 is a cross-sectional view taken along the line VIII-VIII of Figure 7;

Figure 9 is a'graph showing a frequency-response characteristic; and

Figure 10 is a graph showing a frequency-impedance characteristic.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figure 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 yokel: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

6 486, 552

575 /74 diaphragm 9 fixed on the upper end of the bobbin 5. The

first annular suspension means 20 is bonded to the upper

end of a 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 dia-

phragm 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 edge or first suspension means 20 will now be

described in detail with reference to Figures 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 Figure 3.

The upper end of the diaphragm 9 is fixed on the

inclined portion 20b of the first suspension means

and the upper end of the frame 7 is fixed to the horizon-

tal circumferential portion 20c of the first suspension

means

7 486.552

70.575 /74 The method for manufacturing the edge 20 will be

described with reference to Figure

1 to 40 aron fibers, with Young's modulus 2 20000 kg/mm diameter 8-C 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 0 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 therone metal mold 23, heated up to the

said required temperature. The mixture 22 is put between

the metal molds 23 bnd 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 Figure 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 0 a temperature over 140 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 Figure

2 and Figure 4.

In the manufacturing process, since the mixture 22

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70575 /74 is spread out directionally, the carbon fibers 21 con- tained 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 (Figure 3).

With such a dispersion of the carbon fibers 21, the

deformability of the first suspension means 20 is im-

proved 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 26 can be reduced.

According tbXie ivention, the second suspension

means 28 is also formed of the mixture of elastic

material with the carbonfibers.

Referring to Figure 6 to Figure 8, a second sus-

pension means 28 has a plurality of concentric curved

portions 28a with a semicircular cross section projecting

upward. It also has concentric 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 sus-

pension means 20 with the carbon fibers. As shown in

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70,575 /74 .Figure 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 31 be more than

20000 kg/mm 22 and that the diameter of the carbon fiber 31

is smaller than the Jength of the carbon fiber, for example,

about 1 to 40c, aron 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 sus- pension means 28 can be manufactured in the same manner

as the first suspension means 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 dis-

persed 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 sus- pension means 28 can be reduced.

Figure 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 for a speaker using cotton cloth, the

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70.575 /74 response fluctuates in frequencies above 500.-Hz, where

peaks or dips occur. Therefore, the quality of tone is

deteriorated. 4w In aqlj for a speaker using the

first suspension means according to this invention, no

peak or dip occurs in the higher frequencies. The re-

sponse lowers abruptly in the frequencies above a higher threshold frequency 1500 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 im-

proved due to the reduction of the weight.

Figure 10 shows frequency-impedance characteristics.

Curve is for a conventional loudspeaker using a damper

formed of cotton cloth impregnated with phenol resin,

where the resonant frequency f is 78 Hz, the maximum

impedance Z o 100f and the minimum impedance RE 6Jl. The

sharpness QM of the mechanical resonance is represented fo by an equation f2- 0M where fl and f 2 are Q r2 1 Z 1 frequencies for an impedance Z From a.curve

fl 67 Hz and f2 88 Hz are apparent. Therefore,

3.71 for the curve The sharpness 88-67 Q of the electrical resonance is represented by an RE 6 equation Qo QM x Qo 3.71 x 0.223 0o for the curve b.

The values of.Q M and Qo are large for the conventional is damper, as above described and so the damping effect low for the lower frequency range. Therefore, it will be

understood that the tone quality is inferior. The frequency characteristic is remarkably improved

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70,575 /74 by using the second suspension means 28 according to this

invention, as shown by a curve on Figure 10, where the

resonant frequency.f is 84 Hz, the maximum impedance

Zo 242 and the minimum impedance RE 6AI. The frequencies 84 f and f2 are 50 Hz and 143 Hz for an impedance Z

Therefore, the sharpness QM of the mechanical resonance

is 84 0.9. And the sharpness Q of the 143-50 6 electrical resonance is 0.9 x 0.18. 24 +6 It will be understood that QM and Qo can be remark-

ably 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.

486,552

Claims (1)

1. 70.575 /74 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

   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, which

   is characterized in that said suspension means is formed

   of a mixture of elastic material impregnated with carbon

   fibers,, a ;1 dU1 A 2. A loudspeaker according to claim 1, wherein said

   elastic material is rubber.

   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 intermedi-

   ate 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 inter-

   mediate portion having a wave-like cross section. A loudspeaker according to claim 1, wherein

   said ela tic material is ak

   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, which is characterized in

   that at least one of said suspension is being formed of

   a mixture of elastic material impregnated with carbon

   am fiber a dad2m,4 01

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   70.575/74 7. A loudspeaker according to claim 6, wherein' said

   elastic material is rubber.

   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.

   A loudspeaker according to any one of claims 1

   to 5 wherein said mixture of elastic material impregnated

   with carbon fibers is 1 to 40% by weight carbon fibers.

   11. A loudspeaker according to any one of claims

   6 to 9 wherein said mixture of elastic material impregnated

   with carbon fiber is 1 to 40% by weight carbon fibers.

   12. Loudspeaker substantially as hereinbefore

   described with reference' to the accompanying drawings.

   DATED this 4th day of July, 1977.

   SONY CORPORATION

   By its Patent Attorneys:

   CLEMENT HACK CO.

   Fellows Institute of Patent Attorneys of Australia.

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