Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
2001-11-19
2004-06-29
Ni, Suhan (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S423000, C381S424000, C181S174000
Reexamination Certificate
active
06757404
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a loud speaker for high frequency sound that reproduces sound signals and to a diaphragm used for such a loud speaker as well as to a process for a diaphragm.
2. Discussion of the Related Art
In recent years, as music sources to be reproduced are digitized, a loud speaker with more excellent characteristics has been in demand by audio related industries as a sound output apparatus. As for the characteristics of a loud speaker, improvements in a conventional loud speaker such as higher output sound level, lower distortion and flatter frequency response are required. In particular, gaining a diaphragm of a loud speaker for reproducing high frequency sound (also referred to as a tweeter) which greatly affects the quality of sound and establishing a making process therefore have grown in importance. In a conventional loud speaker for reproducing high frequency sound, a dome shaped diaphragm utilizing a polymer film or a resin in a sheet form is used. Here, the dome shaped diaphragm is manufactured by heating and molding the polymer film, or the resin in a sheet form, in a metallic mold.
FIG. 1
is a cross section view, showing an example of a structure of a loud speaker using a polymer film according to a prior art, which shows the right half of the loud speaker from the central axis. As shown in this figure, a dome shaped diaphragm
1
is a diaphragm formed by heating and applying pressure to a polymer film or to a resin material in a sheet form, wherein a dome part
2
, a dome central part
3
, a voice coil junction part
4
, surrounds
5
a
and a frame pasting part
5
b
are formed. Here, the surrounds
5
a
and the frame pasting part
5
b
are referred to as a peripheral part
5
. The frame pasting part
5
b
is defined as the part which is adhered to the attachment surface of a frame
13
. The surrounds
5
a
are defined as the part of the peripheral part
5
which elastically changes through the vibration of the diaphragm
1
. Such surrounds are referred to as a plane edge. In addition, the dome central part
3
is defined as the top part of the dome part
2
while the voice coil junction part
4
is defined as the lower part of the dome part
2
.
A voice coil bobbin
6
is a cylindrical member formed of an aluminum foil, of a thin high polymer foil, of a sheet of paper, or the like. The top edge thereof is bonded to the voice coil junction part
4
by means of adhesive
7
. A voice coil
7
, which generates an electromagnetic driving force, is wound around the lower part of the voice coil bobbin
6
. A top plate
8
in a circular form is arranged inside of the voice coil bobbin
6
while a yoke
9
in a cup form is arranged outside of the voice coil bobbin
6
. In addition, a magnet
10
is arranged between the bottom surface of the top plate
8
and the flat plane surface of the yoke
9
. The top plate
8
, the magnet
10
and the yoke
9
form a magnetic circuit
11
. Then the gap between the external periphery side of the top plate
8
and the internal periphery side of the yoke
9
becomes an annular magnetic gap
12
.
The peripheral part
5
is formed in an annular plate and is attached to the frame
13
with the frame pasting part
5
b
intervened. The voice coil
7
is arranged in the annular magnetic gap
12
and allows the voice coil bobbin
6
to vibrate in a pistonic motion when a driving current corresponding to the audio signal is supplied so as to cause an electromagnetic driving force in the direction parallel to the central axis of the voice coil bobbin
6
. This pistonic motion is conveyed to the voice coil junction part
4
so as to allow the diaphragm
1
to vibrate in the direction of the central axis. In the case that the rigidity of the diaphragm
1
is large and the equivalent mass thereof is small, the dome part
2
vibrates integrally when the dome central part
3
is included. At this time, the surrounds
5
a
are elastically transformed. In this manner, the phase of the sound radiated from the diaphragm
1
becomes uniform so that the volume velocity becomes equal to the audio signal.
A conventional making process for such a dome shaped diaphragm is concretely described in the following.
FIG. 2
is a cross section view showing the structure of the main components of the metallic mold used for the production of the dome shaped diaphragm. This type of dome shaped diaphragm is conventionally used as a diaphragm of a tweeter for reproducing a high frequency range of sound. Then, as for the material thereof, in general, a resin material
20
in a sheet form is used. The thickness of the sheet is, for example, 50 &mgr;m.
FIG. 3
is a cross section view showing the structure of a dome shaped diaphragm
22
in the case that it is manufactured by using a metallic mold
21
of FIG.
2
. This diaphragm
22
is partially different from the one shown in FIG.
1
and has a dome part
23
, dome central part
24
, voice coil junction part
25
, cone part
26
, roll-surrounds
27
and frame pasting part
28
. However, the making process for dome shaped diaphragm
1
of FIG.
1
and the making process for dome shaped diaphragm
22
of
FIG. 3
are essentially the same.
The metallic mold
21
shown in
FIG. 2
is formed of heat pressure metallic mold
29
, which is a male metallic mold, and a heat pressure metallic mold
30
, which is a female metallic mold. The molding sides of the heat mold assembly
29
and the heat mold assembly
30
have approximately the same form and heaters for heating,
29
a
and
30
a
, are built in to the respective metallic molds. Each metallic mold has a molding side for the dome part, a molding side for the voice coil junction part, a molding side for the cone part, a molding side for the roll-surrounds and a molding side for the frame pasting part. The heat mold assembly
29
is attached to a shank
29
b
so as to be able to shift between the pressure position and the release position relative to the heat mold assembly
30
, which is stationary.
In order to manufacturer a diaphragm
22
, a resin material
20
in a sheet form is positioned on the pressure surface of the heat mold assembly
30
and electricity is turned on to the heaters for heating
29
a
,
30
a
of the respective metallic molds so as to heat the respective metallic molds to a predetermined temperature. Then, by pressuring the heat mold assembly
29
, which is a male mold, via the shank
29
b
, the pressure between the two metallic molds is maintained at a predetermined value. Thereby, the resin material
20
is softened and melted so as to be plastically transformed into the shape of the molding size of the metallic mold
21
.
The diaphragm
22
gained in such a manner has a dome form as shown in FIG.
3
and the thickness thereof varies depending on location. The frame pasting part
28
and the middle part of the dome part
23
become 50 &mgr;m, which is the thickness of the material before molding, while there is a tendency of thinning such that the dome central part
24
becomes 20 &mgr;m, the voice coil junction part
25
becomes 35 &mgr;m and the roll-surrounds
27
become 40 &mgr;m.
In this type of dome shaped diaphragm, though it is ideally desirable to secure the same thickness throughout the entirety, in many cases the pressure between the heat mold assemblies
29
,
30
does not spread uniformly throughout the entirety of the diaphragm. Therefore, the thickness varies depending on respective locations within diaphragm
22
. In particular, the thickness of the middle part of the dome part
23
differs greatly from the thickness of the dome central part
24
and the voice coil junction part
25
. This is because the resin material
20
receives pressure which varies locally in strength when it contacts convex surface parts of the heat mold assemblies
29
,
30
at the time of press molding so that the stretched portion expands its area and the thickness of each location varies so as to have uneven values. In particular, the parts essentially require rigidity for high freq
Doi Teruo
Ikeda Kiyoshi
Iwasa Mikio
Koura Satoshi
Kuze Mitsukazu
Matsushita Electric Industrial Co., LTD.
Ni Suhan
Smith Patent Office
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