Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
2000-05-24
2002-05-07
Tran, Sinh (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S420000, C381S409000
Reexamination Certificate
active
06385328
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electro-acoustic micro-transducer having a three-mode reproduction feature, and more particularly to an electro-acoustic micro-transducer having a high power, high efficiency acoustic transducing feature and a three-mode broad band frequency reproduction feature on a micro-scale basis in a compact electronic appliance, in which part of a yoke is cut out and simultaneously a soft material is used as edges of the incised yoke so that a moving coil assembly can be sufficiently vibrated up and down.
BACKGROUND ART
In general, an acoustic reproduction apparatus is classified into a horn type speaker, a system speaker which is used for a hifi audio system such as a component system, including a woofer, mid-ranger and tweeter covering a respectively particular frequency band, a general speaker covering all frequency bands via a single unit, a micro-speaker having an ultra-light and ultra-slim structure which is used in a compact electronic appliance such as a ultra-compact camcorder and walkman, a receiver used for a mobile communications terminal, an earphone having a structure whose part is inserted into the ear, and a buzzer for reproducing only a frequency of a particular band.
In a conventional general speaker, a bobbin around which voice coils are wound is positioned in a magnetic circuit in which a single magnet is installed in a yoke and a top plate is installed on top of the magnet. Also, the upper portion of the bobbin has a structure where the outer circumferential portion thereof is fixed to the upper and lower portion of a frame, the center portion thereof is fixed to a circularly perforated vibration plate and damper, and a center cap called a dust cap for closing the whole of the bobbin is combined in the center portion of the vibration plate.
However, a micro-speaker used in a mobile phone, a camcorder, a notebook PC, an ultra-compact cassette recorder, adopts an electro-dynamic type structure in which a damper is omitted and simultaneously the height of a frame portion is lowered so as to accomplish an ultra-compact and ultra-thin type structure in correspondence to compactness of a set.
In the electro-dynamic speaker as shown in
FIG. 1
a,
a protector
1
is covered on the upper end of a groove type frame
2
, a terminal plate
9
is fixed to one side on the bottom surface of the frame
2
, and a magnetic circuit is formed of a yoke
8
fixed in the center portion of the frame bottom, a permanent magnet
6
and a plate which are coupled in the yoke
8
. A moving coil
5
fixed to a vibration plate
3
is fixed to an edge
4
of the vibration plate
3
formed in the intermediate step portion of the frame
2
, so as to be moved in a magnetic gap G between the yoke
8
and the plate
7
. In
FIG. 1
a,
a reference numeral
10
denotes an air ventilation hole and a reference numeral
11
denotes a signal lead wire.
The electro-dynamic micro-speaker has a structure for generating an acoustic sound in correspondence to a driving signal created by the up-and-down vibration of the vibration plate
3
and the moving coil
5
due to an attractive and repulsive force which is created by an interaction of a non-alternating (direct-current) magnetic flux generated from a fixed magnetic circuit and an alternating (alternating-current) rotating magnetic flux generated from the moving coil
5
which can move up and down in accordance with the Fleming's left-hand rule.
However, in the case of the electro-dynamic micro-speaker shown in
FIG. 1
a,
it is not possible to perform an extensive reproduction of a low level sound and a high level sound which are required in the portable electronic appliance in view of a speaker structure when the electro-dynamic micro-speaker is manufactured into an ultra-micro-speaker for use in a camcorder, a notebook PC, a compact cassette recorder and an information communications portable terminal, for the following reasons.
For example, in the case that a speaker is 4 mm in height and 20 mm in diameter as shown in
FIG. 1
c,
a bobbin
4
is set about 2.3 mm in length l and 9.5 mm in diameter. In this case, the whole length l of the bobbin is constructed so that a connection area a, a coil winding area b and a margin c between the coil
5
and a flexible wire
11
are allocated into 0.9 mm, 1.2 mm and 0.2 mm, respectively.
However, in the case that the flexible wire
11
of 0.8 mm in diameter is soldered with the coil
5
by a soldering lead, a vibration width d which makes a coil assembly
15
vibrate up and down is set 0.3-0.4 mm or so which is a distance between the flexible wire
11
and the upper end of the yoke
8
.
If the coil assembly
15
vibrates with the set vibration width d or wider, the soldering portion
16
of the flexible wire
11
contacts the upper end of the yoke
8
, to thereby cause so we call touch noise generated and lose the value of an acoustic reproduction product.
Thus, although there is a clearance of at least 0.7 mm between the lower end of the bobbin
4
and the bottom of the yoke
8
which can be increased according to the height of a permanent magnet
6
in the conventional art, an extension of a magnetic gap G lowers an efficiency of the speaker greatly. Accordingly, such an extension of the magnetic gap G has not been used.
The vibration width d cannot but limit an allowable input and the size of a magnet used is limited due to the limited vibration width d. As a result, it has not been possible to realize a high power and high efficiency speaker in view of its structure. Further, since a soft material has not been used for an edge of the vibration plate
3
in order to suppress a smooth vibration of the coil assembly
15
, it has been difficult to lower a low band resonance frequency f
0
of the speaker in proportion to the stiffness of the edge.
Further, when the flexible wire
11
is used in order to supply a driving signal to the moving coil
5
from an external source, both ends of the flexible wire
11
is tightly fixed by a solid bonding material
12
and
13
and the intermediate portion of the flexible wire
11
is fixed to a vibration plate
3
by use of a soft bonding material 14 as shown in
FIGS. 1
a
through
1
c.
However, when an excessive input signal is applied, the flexible wire
11
may be cut due to overheat.
For reference, in a commercially available receiver product, a rating input is 0.01-0.1 W in the case of a product having 20 mm or less in diameter, 0.2-0.5 W in the case of a product having 36 mm or so in diameter, and 0.5-1 W in the case of a product having 50-57 mm or less in diameter.
Also, in a high quality of a micro-speaker, a rating input is 0.2-0.3 W and the maximum input is 0.5 W in the case of a product having 20 mm in diameter.
As described above, as the size of the speaker grows smaller, a number of structural restrictions are caused. As a result, a low band resonance frequency f
0
becomes high and its efficiency and output are lowered.
Meanwhile, an electromagnetic speaker made using an electro-acoustic transducing theory and structure uses only a function of a buzzer for reproducing only a monotonous sound signal of 1 or 2 KHz, which is extremely narrow in actual applications.
For the above reasons, an ultra-compact speaker should appear soon in which a high efficiency multifunction of performing a broad band acoustic reproduction and receiving a large-scale input with an ultra-compact design can be integrated into a single unit in order to realize a compact personal information processing terminal where video, audio and office processing functions are integrated.
DISCLOSURE OF THE INVENTION
To solve the above-mentioned problems involved in the conventional electro-acoustic micro-transducer, it is an object of the present invention to provide an electro-acoustic micro-transducer having a three-mode broad band frequency reproduction feature, which can cover all acoustic reproduction functions of a buzzer, a receiver and a micro-speaker for a portable electronic device, with a single unit in which part of a yoke opposin
Kim Kyung Ho
Yoo Dong Ok
Microtech Corporation
Tran Sinh
LandOfFree
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