Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
2001-03-13
2002-10-29
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S419000, C381S422000, C029S594000
Reexamination Certificate
active
06473515
ABSTRACT:
BACKGROUND OF THE INVENTION
Normal magnetic material has a magnetic hysteresis loop characteristic and the relation of magnetizing force and magnetic flux density is nonlinear. As a result, when magnetic flux of a voice coil passes through a center pole and a plate near an air gap, the magnetic reaction in the voice coil results in a distorted output signal from the speaker.
A conventional speaker of the type contemplated by the present invention is illustrated in FIG.
1
. The unit shown in
FIG. 1
has a pole yolk
12
with an inverted T-cross section which has around its bottom an annular magnet
14
that is magnetized in the direction of its thickness. A top plate
18
rests on magnet
14
to form a magnetic gap with the peripheral wall of center pole
16
of pole yolk
12
. A voice coil
28
wound around a bobbin
30
is inserted into the magnetic gap. Bobbin
30
is supported on a frame
26
by a damper
24
that permits vibratory movement of bobbin
30
. A diaphragm
22
with a dust cover
20
is connected to bobbin
30
. The outer periphery of diaphragm
22
is supported by an edge portion
32
that is fixed to frame
26
by a gasket
34
. In order to make effective use of the magnetic flux in the gap, voice coil
28
is wound around bobbin
30
a length in the longitudinal direction of the coil which is greater than the magnetic gap link. Center pole
16
of pole yolk
12
is fitted with a cap
36
provided to reduce the distortion that is introduced into the coil current by the inductance of voice coil
28
. The operation of the speaker shown in
FIG. 1
is as follows. When a current flows through voice coil
28
, either an upward or downward driving force acts on coil
28
depending upon the direction of the current flow. Since voice coil
28
is mobile, the driving force acting on voice coil
28
is transmitted to diaphragm
22
through bobbin
30
. As a result, diaphragm
22
pushes the air in front of it, creating sound waves.
Various methods of eliminating the distortion described above have been attempted, such as covering a center pole with a copper cap as described in
FIG. 1
, and putting a copper ring around the center pole. The copper ring requires a higher level of manufacturing technique and tends to disturb the magnetic flux distribution in the speaker's air gap thus interfering with the output signal. The application of a copper cap covering the center pole of a speaker has been more successful but also has several drawbacks.
The pole/cap configuration and processes used in the prior art for coupling the cap have not resulted in an easily manufactured assembly which performs well, particularly in high volume production environments.
FIG. 2
is directed to one prior art method for coupling the cap described briefly in
FIG. 1
, to a speaker center pole to reduce the distortion introduced into the speakers voice coil due to inductance are shown.
FIGS. 2
a
and
2
b
demonstrate different methods of coupling a distortion reduction cap to center pole
16
of pole yolk
12
. In both methods the cap must be formed on cap die press
40
.
FIG. 2
a
shows the prior art method of coupling distortion reduction cap
46
with adhesives at
42
. Once cap
46
is formed by cap die press
40
, applicator
48
applies an adhesive, such as glue, within cap
46
which in turn is coupled onto center pole
16
of pole yolk
12
to form partial speaker assembly
50
. Use of an adhesive requires additional manufacturing steps to provide the correct amount of adhesive to ensure that center pole
16
receives an even coating to securely couple cap
46
. Distortion reduction cap
46
must also be properly coupled to center pole
16
to ensure no air gaps are formed between cap
46
and center pole
16
. Such gaps reduce the effectiveness of cap
46
.
In order for distortion reduction cap
46
to provide maximum reduction in distortion there must not only be no air gaps between cap
46
and center pole
16
but cap
46
must also remain absolutely stationary. Adhesives used in the prior art are problematic because when subjected to varying temperatures and environmental conditions they can loosen and allow cap
46
to vibrate and move again creating air gaps which effect the distortion reduction performance of cap
46
.
FIG. 2
b
, at
44
, shows an alternate method found in the prior art for coupling a distortion reduction cap to a speaker center pole. The process begins with cap
52
being formed on cap die press
40
. Distortion reduction cap
52
is shown in cross-section and is identical to cap
46
with the exception of an annular inwardly extending lip
54
. Instead of using an adhesive to maintain the coupling between cap
52
and center pole
16
of yolk
12
, the coupling is instead maintained by forcing the lower portion of cap
52
into axial inwardly formed groove
56
within center pole
16
. The portion of cap
52
forced within groove
56
becomes annular inwardly extending lip
54
. This method is inadequate as it does not prevent cap
52
from rotating upon center pole
16
once retained in place, and may result in air gaps between cap
52
and center pole
16
. Vibration from sound waves and due to imperfect road conditions, if the speakers are used in automobiles, may cause such rotation which allows air gaps between cap
52
and center pole
16
to again reduce the effectiveness of distortion reduction cap
52
.
Although not previously discussed, larger conventional type speakers of the type contemplated by the present invention use a center pole which includes a through hole through the center axis of the center pole. Another method for reducing distortion is to keep dust and debris from entering this chamber and affecting the diaphragm. A dust screen is typically attached to the pole yolk with an adhesive. Adhesives used in the prior art are problematic because when subjected to varying temperatures and environmental conditions they can loosen providing gaps around the edges of the screen or disengaging the screen altogether which will allow dust and other contaminants into the speaker affecting the diaphragm and resulting in increased distortion.
Therefore, in light of the foregoing deficiencies in the prior art, the applicant's invention is herein presented.
SUMMARY OF THE INVENTION
The present invention comprises an improved center pole speaker assembly having a distortion reduction cap and an improved method of coupling the cap to a speaker center pole. These and other advantages are provided by a speaker assembly comprising a distortion reduction cap and a cylindrical center pole having a gripping surface formed on an outer cylindrical surface of the center pole and a frustoconical recess on a top surface of the center pole. The distortion reduction cap is coupled to the center pole through the application of pressure on the cap to conform the cap to the center pole and to non-rotatably couple the cap onto the center pole by deforming a portion of the cap against the gripping surface. The distortion reduction cap is coupled to the center pole in a manner forming a corresponding frustoconical portion mating with the frustoconical recess on the top surface of the center pole.
The present invention also provides a method of coupling a distortion reduction cap to a speaker center pole to reduce audio distortion comprising the following steps. Forming a distortion reduction cap. Forming a gripping surface on a center pole having a frustoconical recess on a top surface of the center pole wherein the gripping surface extends radially outwardly from the center pole. Positioning the distortion reduction cap over the center pole. Applying pressure on the distortion reduction cap to conform the distortion reduction cap to the center pole and non-rotatably couple the distortion reduction cap onto the center pole by deforming a portion of the distortion reduction cap against the gripping surface and deforming a portion of the distortion reduction cap forming a corresponding frustoconical portion of the distortion reduction cap mating with the frustoc
Clark Robert J.
Hahn Loeser & Parks LLP
Kuntz Curtis
Ni Suhan
LandOfFree
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