Speaker and speaker system

Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic

Reexamination Certificate

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Details

C381S396000, C181S199000

Reexamination Certificate

active

06754362

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electrically driven speaker and speaker system used in various audio systems, especially a speaker appropriate to be used for mounting in a casing of a small-size equipment and a speaker system to be constituted with a speaker mounted in a casing.
2. Description of the Related Art
An electrically driven speaker is used generally in various audio systems, up to now. An electrically driven speaker has two types according to magnetic circuit structures, i.e., an outer magnet type and an inner magnet type defined by a magnet position in a magnetic circuit. However, respective vibrating member of two-type speakers has almost same structural relation for a magnetic circuit.
An electrically driven speaker, a half-section shown in
FIG. 9
, is provided with an outer-magnet-type magnetic circuit comprising an annular top plate
1
having an opening
1
a
in the center, an annular magnet
2
attached to a bottom surface of the top plate
1
and magnetized in a direction of thickness, and a yoke
3
attached to a bottom surface of the magnet
2
. The yoke
3
is provided with a bottom plate
3
a
, and a center pole
3
b
projecting from the center of the bottom plate
3
a
and forming a gap G between an inner circular surface of the opening
1
a
in the top plate
1
.
In
FIG. 9
, mark
5
shows a frame attached to a top surface of the top plate
1
, mark
6
shows a voice coil supported in the magnetic gap G and vibrating correspondingly to electrical signals, mark
7
shows a cylindrical voice coil bobbin transmitting driving force generated in the voice coil
6
to a vibrating system, mark
8
shows a vibrating member attached to a top edge of the voice coil bobbin
7
, mark
9
shows a damper joined at an inner circular portion thereof to an intermediate position of the voice coil bobbin
7
and joined at an outer circular portion thereof to the frame
5
, and mark
10
shows a roll-shape edge joined at an inner circular portion to an outer circular portion of the vibrating member
8
and joined at an outer circular portion thereof to the frame
5
. The voice coil
6
, the voice coil bobbin
7
, the vibrating member
8
, the damper
9
and the edge
10
constitute a vibration system
12
.
In the speaker by prior art, constituted above, a space A enclosed with the cylindrical voice coil bobbin
7
; describing in detail, a space A formed by a top surface of the center pole
3
b
, an inner circular surface of the voice coil bobbin
7
and a bottom surface of the vibrating member
8
; is ventilated through a thin gap g
1
formed by an outer circular surface of the center pole
3
b
and an inner circular surface of the voice coil bobbin
7
to a space B formed by an outer circular surface of the center pole
3
b
, a top surface of the bottom plate
3
a
, an inner circular surface of the magnet
2
, and a bottom surface of the top plate
1
. Further, the space A is ventilated through a thin gap g
2
formed by an inner circular surface of the top plate
1
and an outer circular surface of the voice coil bobbin
6
, and a ventilating opening
5
a
provided in the air-permeable damper
9
and in the frame
5
to an outside of the frame
5
, i.e. an outside space of the speaker.
When the above structured speaker is inputted with a large power, a large electric current runs in the voice coil
6
so as to be heated. The heat, generated in the voice coil, is transmitted through air of a space between an outer circular surface of the center pole
3
b
and an inner circular surface of the voice coil bobbin
7
to the center pole
3
b
, and transmitted through air of a space between an inner circular surface of the top plate
1
and an outer circular surface of the voice coil
6
to the top plate
1
, and then refrigerated. Furthermore, the heat is also refrigerated by air moving in the thin gap g
2
formed by an inner circular surface of the top plate
1
and an outer circular surface of the voice coil
6
. However, the heat conductivity of air is low and ventilation between the space A and an outside space of the speaker is done through the thin gap g
1
formed by an outer circular surface of the center pole
3
b
and an inner circular surface of the voice coil bobbin
7
so that the ventilation is not enough to refrigerate sufficiently the heat of the voice coil
6
. Therefore, electric resistance of the voice coil
6
increases by heating and electric current goes down then sound pressure corresponding to electric input can not be given.
On driving a speaker, expansion and compression of air in the space A is repeated. When driving a speaker by low frequency range with a large input, insufficient ventilation of air causes increasing expansion/compression coefficient of air so that restraining the amplitude of the speaker reduces playback sound pressure and causes sound distortion by non-linearity of air compliance.
It is proposed on a speaker to provide a throughhole C, as shown in
FIG. 9
, through the center of a center pole
3
b
, extending from a top surface of the center pole
3
b
to a bottom surface of a bottom plate
3
a
, communicating between a space A and an outside of a magnetic circuit, to improve releasing heat generated in a voice coil
6
and transmitted to a center pole
3
b
for reducing temperature rising of the voice coil
6
and increasing allowable input power. According to this proposed speaker structure, ventilation between a space A and an outside of a magnetic circuit is done through the throughhole so that the expansion/compression coefficient of air is decreased and then sound distortion by non-linearity of air compliance is restrained.
In an inner-magnet-type magnetic circuit as shown in
FIG. 10
, a cylindrical magnet
31
is provided on a center of a top surface of a bottom plate
30
a
forming a bottom portion of a bottomed cylindrical yoke
30
and a disk-shaped pole piece
32
forming a magnetic gap G between an inner circular surface of the yoke
30
is joined on the magnet
31
. The inner-magnet-type magnetic circuit is provided with a throughhole C through the pole piece
32
, the magnet
31
and yoke
30
, communicating between a space A and an outside of a magnetic circuit, to improve releasing heat, generated in a voice coil
6
and transmitted to the pole piece
32
, for reducing temperature rising of the voice coil
6
and increasing allowable input power so that the expansion/compression coefficient of air is decreased and then sound distortion by non-linearity of air compliance is restrained.
With popularization of a mobile telephone as a small equipment, miniaturization, weight saving, low pricing and higher performance for a mobile phone are required more and technology development regarding the requirements is a mainstream. Study not only on a speaker itself but also a method for mounting a speaker on a casing are required and then a speaker system constituted with a casing applies a structure shown in FIG.
11
.
A speaker is shown simply with a vibration system and a magnetic circuit in FIG.
11
and mounted to be held between inner surfaces of a casing
20
by facing a surface of the vibration system
4
and a bottom portion of the magnetic circuit
12
respectively to inner surfaces of the casing
20
. Specifically, a sounding surface of the vibration system
4
is placed to abut on an inner surface of a front wall
21
, having a sounding opening
21
a
, of the casing
20
and is pressed by an elastic-material-made pad
23
inserted between an inner surface of a rear wall
22
, parallel to the front wall
21
, of the casing
20
and a bottom surface of the speaker magnetic circuit
12
so that the speaker is mounted and fixed in the casing. In case, pressing the bottom surface of the speaker magnetic circuit
12
directly by the inner surface of the rear wall
22
of the casing
20
, as shown in
FIG. 12
, the speaker is mounted and fixed in the casing.
Objects to be Solved
As mentioned above, a casing for mounting a speaker is miniaturized and a structure which a

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