Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
2000-09-11
2004-05-11
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S420000, C381S404000
Reexamination Certificate
active
06735322
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a speaker whose voice coil bobbin is supported by a plurality of dampers.
FIG. 5
is a cross sectional view showing a conventional speaker whose voice coil bobbin is supported by a plurality of dampers. In the speaker
1
shown in
FIG. 5
, a voice coil bobbin
3
is coaxially disposed within a casing
2
. The voice coil bobbin is supported at the fore end (the upper end in the drawing) and at the mid position by a couple of dampers
4
A and
4
B such that the voice coil bobbin
3
is vibratory in the axial direction. Those dampers are located between the voice coil bobbin and the casing
2
.
A voice coil
5
is put on the rear end (the lower end in the drawing) of the voice coil bobbin
3
. A disc-like plate
6
is made of iron and has a center hole.
The plate
6
is coaxially disposed around the voice coil
5
. A slight gap is present between the plate and the circumferential outer surface of the voice coil
5
. The plate
6
is fastened to the casing
2
.
A magnet
7
having a center hole is bonded to the rear side surface (the lower side surface in the drawing) of the disc-like plate
6
in a state that the magnet
7
and the disc-like plate
6
are coaxially disposed. A disc-like yoke
8
made of iron is bonded to the rear side surface of the magnet
7
. A center pole
8
A is integrally formed at the central part of the front side surface (the upper side in the drawing) of the disc-like yoke
8
. The center pole
8
A is inserted into the voice coil bobbin
3
from its rear end, and located therewithin in a state that the former is slidable relative to the latter.
This conventional speaker is arranged such that the voice coil bobbin
3
is supported by use of the two dampers
4
A and
4
B so as to hold a linearity of a vibration of the voice coil bobbin
3
when it axially vibrates by current of an acoustic reproducing signal flowing through the voice coil
5
in a magnetic field, which is developed, by the magnet
7
, among the disc-like plate
6
, disc-like yoke
8
and center pole
8
A.
The conventional speaker
1
fails to perfectly hold the linearity of the vibration of the voice coil bobbin
3
, however. The reason for this is as follows: The dampers
4
A and
4
B are located closer to the fore end of the voice coil bobbin
3
with respect to the magnetic circuit formed by the voice coil
5
, disc-like plate
6
and center pole
8
A. Therefore, the supporting positions of the voice coil bobbin
3
are disposed asymmetrically with respect to the magnetic circuit.
Therefore, when the voice coil bobbin
3
vibrates at a low resonance frequency f
0
and its vibration amplitude increases, the voice coil bobbin
3
rolls or unintentionally moves. In this state, there is a danger that the voice coil
5
comes in contact with the disc-like plate
6
. Particularly in the speaker for reproducing low frequencies, operation of the speaker for reproducing sounds at large output power levels is difficult.
In the structure of the speaker
1
, the iron yoke
8
forming the magnetic circuit develops a magnetic field around the voice coil
5
. Therefore, the size of the yoke
8
is large relative to the size of the whole speaker
1
. Accordingly, the speaker
1
is heavy.
FIG. 6
is a cross sectional view showing another conventional speaker in which a voice coil bobbin is supported by a plurality of dampers. A speaker
10
of
FIG. 6
is of the called inside magnet type, while the speaker
1
of
FIG. 5
is of the called outside magnetic type in which the magnet is located outside the voice coil bobbin.
The speaker
10
is constructed such that a magnet
11
is located within a voice coil bobbin
12
, and the rear end surface (the lower end surface in the drawing) of the magnet
11
is bonded to a yoke
13
. The yoke
13
is formed with a disc-like bottom plate
13
A and an outside center plate
13
B located outside the magnet
11
. The circumferential inner surface of the fore end of the outside center plate
13
B is confronted with the circumferential outer surface of an inside center plate
14
, which is bonded to the fore end surface (the upper end surface in the drawing) of the magnet
11
in a state that a voice coil
15
is interposed therebetween. In the thus constructed speaker, the voice coil develops a magnetic field.
The voice coil bobbin
12
is supported by a damper
17
A and a damper
17
B such that it is vibratory in the axial direction. The damper
17
A is located between the fore end thereof (the upper end in the drawing) and a casing
16
. The damper
17
B is located between the rear end (the lower end in the drawing) and the outside center plate
13
B.
In the speaker
10
, the supporting positions of the dampers
17
A and
17
B are located symmetrically with respect to the voice coil
15
. Therefore, a linearity of the vibration of the voice coil bobbin
12
is more reliably secured.
As seen from the figure, in the structure of the speaker
10
, the damper
17
B for supporting the rear end of the voice coil bobbin
12
is disposed inside the outside center plate
13
B. Therefore, the diameter of the damper
17
B is limited by the damper
17
B.
For this reason, where the outside center plate
13
B is small in diameter, the diameter of the damper
17
B is correspondingly small. In this case, the vibration characteristic of the voice coil bobbin
12
is impaired. Where the diameter of the outside center plate
13
B is excessively increased to increase the diameter of the damper
17
B, the speaker
10
increases in size and weight.
SUMMARY OF THE INVENTION
The present invention has been made to solve the problems of the conventional speaker in which the voice coil bobbin is supported by a plurality of dampers. An object of the present invention is to provide a speaker in which the voice coil bobbin is supported by a plurality of dampers, which the speaker can produce sounds at high output power levels, and is reduced in size and weight.
A speaker defined in item
1
comprises: a first magnet disposed at a mid position of a voice coil bobbin while surrounding the circumferential outer surface of the voice coil bobbin mounted on a vibrating plate; a first voice coil wound on the circumferential outer surface of the voice coil bobbin at a position where the voice coil bobbin faces one end of the first magnet with a predetermined gap being interposed therebetween; a second voice coil wound on the circumferential outer surface of the voice coil bobbin at a position where the voice coil bobbin faces the other end of the first magnet with a predetermined gap being interposed therebetween; a center pole, disposed within the voice coil bobbin, for developing two magnetic fields in a state that the first and second voice coils are located between the one and other ends of the first magnet; and at least one couple of dampers for supporting the voice coil bobbin at position's such that the voice coil bobbin is axially vibratory, the positions being located on both sides of and symmetrical with respect to those portions of the voice coil bobbin which are respectively wound with the first and second voice coils.
In the speaker, two magnetic fields are developed between the one end of the other end of the first magnet and the center pole by the first magnet in a state that the first and second voice coils are interposed therebetween.
When current is fed to the first and second voice coils located in those magnetic fields, the voice coil bobbin axially vibrates in accordance with an amplitude of the current.
The voice coil bobbin is supported at least one couple of dampers for supporting the voice coil bobbin at positions which are located on both sides of and symmetrical with respect to those portions of the voice coil bobbin which are respectively wound with the first and second voice coils. Therefore, even when the amplitude of the vibration of the voice coil bobbin is large, a linearity of the vibration is perfectly secured. There is no chance that the voice coil bobbin rolls or unintentionally moves.
A stable vib
Dabney P.
Kuntz Curtis
Pioneer Corporation
Sughrue & Mion, PLLC
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