Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
2000-05-24
2002-06-11
Le, Huyen (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S421000, C381S431000
Reexamination Certificate
active
06404896
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric-acoustic transducer having dual voice coil drivers, and more particularly to an improved electric-acoustic transducer, which can achieve a reproduction of a broad frequency band with high power and high efficiency, even with an ultra slim or small dimension, proper for small electronic appliances such as a notebook computer, by employing dual voice coil drivers and auxiliary magnetic circuits.
2. Description of the Related Art
In general, a sound reproducer is classified into a horn speaker, a system speaker used in an audio-system of high-fidelity such as a component system and including a woofer, a midrange and a tweeter respectively covering a predetermined frequency band, a general speaker covering the entire frequency band by a single unit, a micro-speaker having an ultra-light and ultra-slim construction to be used in a micro-camcorder, a walkman, etc., a receiver used in a mobile communication terminal, an ear-phone having a construction partly inserted in a user's ear, and a buzzer receiving only a specific frequency band.
In a conventional general speaker, a bobbin around which a voice coil is wound is placed in a magnetic gap of a magnetic circuit which comprises a single magnet disposed in a yoke and a top plate mounted on the magnet. Further, the top of the bobbin is fixed to a vibrating diaphragm with a damper, whose center is perforated in a circular shape and whose periphery is fixed to upper and lower portions of the frame. A center cap or a dust cap is assembled at the center of the vibrating diaphragm to cover the center hole of the bobbin.
In the meantime, a micro-speaker employed in a cellular phone, a camcorder, a notebook computer, a micro-cassette, etc., has an electrodynamic construction in which the height of the frame is lowered by omitting the damper, so as to achieve ultra slim and ultra small construction corresponding to the size decrease of the system employing the micro-speaker.
In such an electrodynamic speaker, as shown in
FIG. 1
a
, a protector
1
covers over a frame having a configuration of a recess, and a terminal plate
9
is fixed to the rear surface of the bottom of the frame
2
. A magnetic circuit is formed by a yoke
8
fixed to a middle portion of the bottom of the frame, and a fixed magnet
6
and a plate
7
fixed in the yoke
8
. The edge of the vibrational diaphragm
3
is so fixed to the stepped portion of the frame
2
that a moving coil
5
fixed to the vibrational diaphragm
3
is movably placed in the air gap between the yoke
8
and the plate
7
. In
FIG. 1
a
, numerals
10
and
11
respectively designate a hole and a coil.
The electrodynamic type speaker as above is of a structure in which the attraction and repulsion caused due to a reaction of a non-alternating (a direct current) magnetic flux generated in a fixed magnetic circuit upon an alternating (an alternating current) rotation magnetic flux generated in a moving coil movable in an upward and downward direction vibrate both the vibrational diaphragm and the moving coil upwardly and downwardly to produce sound. That is, the electrodynamic type speaker is a speaker in which the permanent magnet is fixed and the moving coil is moved, so that sound is generated.
However, the electrodynamic type speaker shown in
FIG. 1
a
has disadvantages that in the case where it is manufactured in a micro form in order to apply to a notebook computer, a mini-cassette tape player, and a mobile communication terminal, etc., it is impossible to reproduce an expansion of the ranges of a low-pitched sound and a high-pitched sound necessary for portable electronic appliances in terms of a structure of a speaker.
Furthermore, although a coil wire
11
for supplying electric energy to the moving coil
5
vibrating upwardly and downwardly is fixed by applying a firm adhesive on the opposite ends thereof and a soft adhesive on the middle portion thereof as shown in
FIGS. 1
a
and
1
b
, a breaking of the coil may happen when an excessive input is applied.
Moreover, especially when the vertical height of the speaker is not more than four millimeters, it is disadvantageous in working efficiency due to the construction to connect the flexible wire and the coil
5
with the top of the bobbin on which the coil shorter than the above four millimeters is wound. In this case, the breaking of the coil happens when the vertical height fails to accommodate the width of the vibration of the coil at a high input.
In the case that the input is limited in consideration of the danger of the coil breaking, it is impossible to achieve a high output. Moreover, it is difficult to secure a sufficient space for the vertical vibration for the high output in the speaker.
For reference, in a micro-speaker currently on the market, a rated input of a product is 0.01 (W) to 0.1 (W) when its diameter is less than 20 mm, 0.2 (W) to 0.5 (W) when its diameter is 36 mm, and 0.5 (W) to 1 (W) when 50 to 57 mm.
In the meantime, an appliance such as a notebook computer having a display monitor employs a slim-type speaker mounted near the screen or in a housing of a personal computer. This type of speaker has an oval construction whose dimensions are in a range from 28 by 40 mm to 16 by 35 mm as its minimum. In the case of the speaker having the dimensions of 16 by 35 mm, it exhibits a reproduction band of 480 Hz to 16 KHz when the minimum height is 4.5 mm, and an output of 73 dB under 1 M/1 W.
As the decrease of the dimensions of the speaker which produces a variety of restrictions, the low band resonance frequency f
0
is increased, and the efficiency and the output are decreased.
Meanwhile, in a practical use, the electrodynamic speaker based on the conventional electric-acoustic transducing principle is now utilized as a buzzer capable of reproducing only a single tone signal of a highly narrow one or two KHz.
Owing to the above reasons, there is a need in the art for a micro-speaker that can reproduce a sound of a broad band, receive a high input, and can be automatically embedded in a PCB of a set in all directions of 360 degrees without a soldering process in order to realize a multipurpose mini personal information processing terminal in the near future.
There is required a micro-speaker having the following characteristics and dimensions as a terminal for processing information: a reproduction frequency band of 200 Hz to 16 KHz; a longer axis of 13 mm, a shorter axis of 50 mm, and a height of 4.1 mm; a rated power of two watt; an output sound pressure level of 80 dB at a distance of one meter by an input of one watt; and a good assembling characteristic without using assembling screws.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide an improved electric-acoustic transducer, which can achieve a reproduction characteristic of a broad frequency band with high power and high efficiency, even with ultra slim or small dimensions, proper for a small electronic appliance such as a notebook computer, by employing dual voice coil drivers and auxiliary magnetic circuits.
Another object of the invention is to provide an improved micro-speaker including a plurality of voice coil drivers which enable a high power and a high efficiency and prevent unbalanced vibrations which may happen due to the longer axis of the single driver of the prior art, thereby realizing a clear and clean reproduction of high quality sound.
It is still another object of the invention to provide an improved micro-speaker which has a function of a broad band frequency reproduction capable of performing functions of various portable electronic appliances such as a buzzer, a receiver, a micro-speaker, etc., by a single unit of mini-size.
It is still another object of the invention to provide an improved micro-speaker, in which not only the above-mentioned functions are implemented but automatic mounting/coupling
Kim Kyung Ho
Yoo Dong Ok
Le Huyen
Microtech Corporation
Ni Suhan
Rosenberg , Klein & Lee
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