Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1998-03-27
2001-01-16
Kuntz, Curtis A. (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S401000, C381S405000, C381S410000
Reexamination Certificate
active
06175637
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an acoustic transducer of electromagnetic coupling type (electromagnetic induction type), i.e. a transducer such as a speaker or a headphone for converting an electrical signal into acoustic sounds and a transducer such as a microphone for converting acoustic sounds into an electrical signal.
2. Description of the Related Art
In the case of an external magnet type, for example, an acoustic transducer of an electromagnetic coupling type comprises a magnetic circuit having a magnetic gap formed between a plate and a center pole across a magnet composed of the plate, a yoke with the center pole attached thereto and in which a first coil is fixed to the plate or the center pole within the magnetic gap of the magnetic circuit and an insulated second coil is fixed to a diaphragm in an opposing relation to the first coil within the magnetic gap of the magnetic circuit.
In an acoustic transducer such as a speaker or a headphone, when a first coil is used as a drive coil (primary coil) and a signal current is supplied to this drive coil, a secondary current corresponding to the signal current is induced in a second coil serving as a secondary coil by an electromagnetic coupling. Then, owing to the Fleming's left-hand rule, a drive force corresponding to a signal current is generated in the second coil, and the diaphragm to which the second coil is fixed is vibrated to generate a sound pressure corresponding to the signal current.
FIGS. 14 and 15
show examples of electromagnetic coupling type speakers according to the related art, respectively.
FIG. 14
shows the example of the electromagnetic coupling type speaker in which a drive coil is attached to a plate.
FIG. 15
shows the example of the electromagnetic coupling type speaker in which a drive coil is attached to a center pole.
Specifically, in the electromagnetic coupling type speaker shown in
FIG. 14
, a center pole
11
is unitarily formed at the center portion of the upper surface of a flange-like yoke
10
. A magnet
20
is attached to the upper surface of the circumferential portion of the yoke
10
. An annular plate
30
is attached to the upper surface of the magnet
20
. A magnetic circuit
6
is formed so as to have a magnetic gap
5
formed between an outer peripheral surface of a tip end portion of the center pole
11
and an inner peripheral surface of the plate
30
, and a drive coil
1
is attached to the inner peripheral end surface of the plate
30
.
The yoke
10
has a hole
12
defined at its bottom portion and also has a terminal assembly
4
with an input terminal
3
attached to its lower surface. A lead wire
2
of the drive coil
1
is inserted into the hole
12
and connected to the input terminal
3
by soldering. The lead wire
2
is each attached to the start of the winding and the end of the winding of the drive coil
1
, and each connected to a separate input terminal.
A secondary coil
7
is inserted into the magnetic gap
5
. The secondary coil
7
is either an insulated cylinder of one turn made of a nonmagnetic conductive material such as aluminum or an insulated winding having a plurality of turns.
A lower portion of a frame
40
is attached to the upper surface of the plate
30
. An outer peripheral portion of an upper end of a diaphragm
50
such as a cone is attached through an edge
51
and a gasket
45
to an upper inner peripheral end portion of the frame
40
. An outer peripheral portion of a damper
47
is attached to the frame
40
, and a lower end portion of the diaphragm
50
and an inner peripheral portion of the damper
47
are attached to the secondary coil
7
. A center cap
49
is attached to a lower end portion of the diaphragm
50
or an upper end portion of the secondary coil
7
.
In the electromagnetic coupling type speaker shown in
FIG. 15
, a recess is formed around the outer peripheral surface of the upper end portion of the center pole
11
, and the drive coil
1
is attached to the center pole
11
by means of this recess. A rest of elements and parts in
FIG. 15
is similar to that of the electromagnetic coupling type speaker shown in FIG.
14
.
In the electromagnetic coupling type speaker shown in
FIG. 14
or
15
, when a signal current is supplied to the drive coil
1
, a secondary current corresponding to the signal current is induced in the secondary coil
7
due to an electromagnetic coupling. Then, owing to the Fleming's left-hand rule, a drive force corresponding to the signal current is generated in the secondary coil
7
, and the diaphragm
50
with the secondary coil
7
attached thereto is vibrated in the upper and lower direction, thereby resulting in a sound pressure corresponding to the signal current being generated.
However, in the related-art electromagnetic coupling type speaker shown in
FIG. 14
or
15
, since the drive coil
1
is disposed within the magnetic gap
5
of the magnetic circuit
6
, the width (length of the direction perpendicular to the axis of the speaker) of the magnetic gap
5
cannot be reduced by the thickness of the drive coil
1
so that a magnetic force of the magnetic gap
5
is reduced, thereby resulting in a sensitivity of the speaker being lowered. If a large magnet is used as the magnet
20
in order to increase the magnetic force of the magnetic gap
5
and to increase the sensitivity of the speaker, then the speaker becomes large in size and cannot be produced inexpensively.
In addition, if the number of turns of the drive coil increases in order to increase the inductance of the drive coil
1
, then the width of the magnetic gap
5
increases so that the sensitivity of the speaker is lowered. Hence, the inductance of the drive coil
1
cannot increase. As a result, an electromagnetic coupling force between the drive coil
1
and the secondary coil
7
is too lowered in a low band range of less than 2 kHz to reproduce low-frequency signals of large amplitude. Hence, the electromagnetic coupling speaker according to the related art can be used only to reproduce high-frequency signals.
Furthermore, while the outer or inner circumferential surface of the drive coil
1
contacts with the plate
30
or the center pole
11
, its contact area is small so that heat cannot be radiated from the drive coil
1
instantly. As a consequence, not only a thick wire material cannot be used as the drive coil
1
but also a large current cannot be quickly flowed to the drive coil
1
with the result that an allowable input signal level cannot be increased.
While the case in which the electromagnetic coupling type transducer is applied to the speaker has been described so far, this is also true in other transducer such as the headphone. The transducer such as the microphone has a similar arrangement except only that the input and output are reversed.
SUMMARY OF THE INVENTION
In view of the aforesaid aspect of the present invention, it is an object of the present invention to provide an electromagnetic induction type acoustic transducer apparatus in which a sensitivity can be increased without making the acoustic transducer large in size and without making the acoustic transducer expensive.
It is another object of the present invention to provide an electromagnetic induction type acoustic transducer apparatus in which sounds of low tone can be reproduced or picked up, thereby making it possible to realize a transducer of whole band range type or a transducer specialized in reproducing low-frequency signals of large amplitude.
It is a further object of the present invention to provide an electromagnetic induction type acoustic transducer apparatus in which an allowable input level of a transducer can be increased from a standpoint of a head-radiation of a first coil.
According to an aspect of the present invention, there is provided an electromagnetic induction type acoustic transducer apparatus which is comprised of a magnetic gap formed between a plate and a pole piece serving as an assembly of a magnetic circuit, a conductive ring attached
Fujihira Masao
Kishigami Jun
Muraguchi Takahiro
Shinohara Ikuo
Tokushige Kenji
Harvey Dionne N.
Kuntz Curtis A.
Maioli Jay H.
Sony Corporation
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