Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
2001-12-29
2003-10-28
Tran, Sinh (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S419000
Reexamination Certificate
active
06639993
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a loudspeaker for audio and video applications, and more particularly, to a loudspeaker having a specially structured pole piece for improving performance of the loudspeaker including low distortion and high output power.
BACKGROUND OF THE INVENTION
Loudspeakers, or speakers, are well known in the art and are commonly used in a variety of applications, such as in home theater stereo systems, car audio systems, indoor and outdoor concert halls, and the like. A loudspeaker typically includes an acoustic transducer comprised of an electromechanical device which converts an electrical signal into acoustical energy in the form of sound waves and an enclosure for directing the sound waves produced upon application of the electrical signal.
A loudspeaker comprises a coil of wire, typically referred to as a voice coil, which is suspended between a pole piece and a permanent magnet. In operation, an alternating current from an amplifier flows through the voice coil which produces a changing magnetic field around the voice coil. The changing magnetic field around the voice coil interacts with the magnetic field produced by the permanent magnet to produce reciprocal forces on the voice coil representing the current in the voice coil.
The voice coil is disposed within the loudspeaker so that it can oscillate in accordance with the reciprocal forces along the pole piece. The voice coil is attached to a cone shaped diaphragm which vibrates in response to the oscillation (reciprocal movement) of the voice coil. The vibration of the diaphragm produces acoustic energy in the air, i.e., a sound wave.
An example of structure in the conventional loudspeaker is shown in FIG.
1
. The loudspeaker
11
includes a speaker cone
13
forming a diaphragm
17
, a coil bobbin
25
, and a dust cap
15
. The diaphragm
17
, the dust cap
15
and the coil bobbin
25
are attached to one another by, for example, an adhesive. Typically, the coil bobbin
25
is made of a high temperature resistant material such as glass fiber or aluminum around which an electrical winding or a voice coil
27
is attached such as by an adhesive. The voice coil
27
is connected to suitable leads (not shown) to receive an electrical input signal through the electrical terminals (not shown) noted above.
The diaphragm
17
is provided with an upper half roll
21
at its peripheral made of flexible material such as an urethane foam, butyl rubber and the like. The diaphragm
17
is connected to the speaker frame
19
at the upper half roll
21
by means of, for example, an adhesive. At about the middle of the speaker frame
19
, the intersection of the diaphragm
17
and the coil bobbin
25
is connected to the speaker frame
19
through a spider (inner suspension)
23
made of a flexible material such as cotton with phenolic resin and the like. The upper half roll
21
and the spider
23
allow the flexible vertical movements of the diaphragm
17
as well as limit or damp the amplitudes (movable distance in an axial direction) of the diaphragm
17
when it is vibrated in response to the electrical input signal.
The loudspeaker
11
also comprises a magnetic assembly (magnetic circuit) formed of an air gap
41
and annular members including a pole piece
37
, a permanent magnet
33
, and an upper (top) plate
35
. In this example, the pole piece
37
has a back plate
38
integrally formed at its bottom. The pole piece
37
has a central opening (air passage)
40
in the axial direction for dissipating heat generated by the voice coil
27
.
The permanent magnet
33
is disposed between the upper plate
35
and the back plate
38
of the pole piece
37
. The upper plate
35
and the pole piece
37
are constructed from a material capable of carrying magnetic flux, such as steel. Therefore, a magnetic path is created through the pole piece
37
, the upper plate
35
, the permanent magnet
33
and the back plate
38
through which the magnetic flux is running.
The air gap
41
is created between the pole piece
37
and the upper plate
35
in which the voice coil
27
and the coil bobbin
25
are inserted in the manner shown in FIG.
1
. Thus, when the electrical input signal is applied to the voice coil
27
, the current flowing in the voice coil
27
and the magnetic flux (flux density) interact with one another. This interaction produces a force on the voice coil
27
which is proportional to the product of the current and the flux density. This force activates the reciprocal movement of the voice coil
27
on the coil bobbin
25
, which vibrates the diaphragm
17
, thereby producing the sound waves.
In the audio sound reproduction involving such a loudspeaker, it is required that the loudspeaker is capable of producing a high output power with low distortion in the sound waves. It is known in the art that a loudspeaker is more nonlinear and generates more distortion in lower frequencies which require large displacement of the diaphragm. This invention is to improve the performance of the loudspeaker with use of a specifically designed pole piece in the magnetic assembly.
In the conventional technology, there is an example of magnetic assembly in which a cross sectional shape of the pole piece is inclined or curved to improve the speaker performance. This conventional example is disclosed in Japanese Utility Model Publication No.
6-2896
, which is reproduced in
FIGS. 2A and 2B
. The magnetic assembly of
FIGS. 2A and 2B
is configured by a top plate
54
, a pole piece
52
having a back plate
51
, and a permanent magnet
53
sandwiched between the top plate
54
and the back plate
51
. The pole piece
52
has a through hole
55
for air passage. An air gap
56
is created between the pole piece
52
and the top plate
54
for allowing reciprocal movements of the voice coil in the vertical direction of
FIGS. 2A and 2B
.
The inner wall of the pole piece
52
is inclined upwardly in a manner of straight line in
FIG. 2A
so that the inner diameter of the through hole
55
increases toward the top end. Similarly, the inner wall of the pole piece
52
is inclined upwardly in a manner of curved line in
FIG. 2B
so that the inner diameter of the through hole
55
increases toward the top end. According to the description in the publication No. 6-2896, such a conical shape of the upper portion of the pole piece
55
is effective in decreasing the resistance (fluid resistance of air) against the movement of the diaphragm even when the diameter of the through hole
55
is small. However, this conventional technology does not appear to function for reducing the magnetic distortion or increasing the output power of the loudspeaker.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a loudspeaker having an improved acoustic performance which is achieved by low distortion and high output power.
It is another object of the present invention to provide a loudspeaker having an improved acoustic performance which is achieved by a unique structure of the pole piece having a curved inner surface.
The loudspeaker of the present invention has an improved acoustic performance achieved by low distortion and high output power. The loudspeaker includes a speaker frame, a diaphragm connected to the speaker frame, a voice coil which is formed on a voice coil bobbin and is connected to the diaphragm for vibrating the diaphragm, a permanent magnet having a central opening, and a pole piece disposed coaxially within the central opening of the permanent magnet to form an air gap into which the voice coil is disposed. The top area of the through hole of the pole piece is curved with an S-shape in cross section and an inner diameter of the through hole is increased toward the inner top thereof.
Preferably, an inner end of the pole piece is projected toward a direction of the diaphragm substantially higher than an upper surface of an upper plate. The S-shape of the top area of the pole piece is formed of a first curve which is projected in one transversal direction and a seco
Guarin Eric Douglas
Kemmerer Jason
Alpine Electronics, Inc
Muramatsu & Associates
Tran Sinh
LandOfFree
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