Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
2001-11-09
2004-04-20
Ni, Suhan (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S124000, C381S397000
Reexamination Certificate
active
06724909
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a speaker apparatus for converting an electrical signal into an acoustic signal, and more specifically, toastructure for improving the soundquality.
2. Description of the Related Art
Conventionally, acoustic reproduction is performed by a speaker system
1
having a basic structure as shown in FIG.
7
. In the speaker system
1
, one or a plurality of speaker units
2
are accommodated in an enclosure
3
. The speaker unit
2
, which in many cases assumes a generally conical cross-section, has a vibration plate
4
called “cone.” The speaker unit
2
is also equipped with a magnetic circuit
5
, which has a main magnet
6
, a center pole
7
, and a plate
8
. In a magnetic gap between the center pole
7
and the plate
8
is concentrated magnetic flux generated by the main magnet
6
in high density. A voice coil
9
whose tip is joined to the basal portion of the vibration plate
4
is suspended in the magnetic gap.
When the voice coil
9
is energized, driving force acts on the voice coil
9
in the magnetic gap and the vibration plate
4
is thereby displaced, whereby sound waves are emitted from the vibration plate
4
to the neighboring air. Each speaker unit
2
is accommodated in the enclosure
3
to prevent back-side sound waves (opposite in phase to front-side sound waves) from going around the speaker unit
2
to the front side. Each speaker unit
2
has a frame
10
for use in fixing of the magnetic circuit
5
and for vibratably supporting the vibration plate
4
. The frame
10
is fixed to the enclosure
3
.
Having a structure called “external magnet type,” the magnetic circuit
5
is suitable for a case where a ferrite magnet is used as the main magnet
6
. However, the external magnet type magnetic circuit
5
leaks a large amount of flux to the outside. Where it is used together with a cathode-ray tune (CRT) for acoustic reproduction as part of an audio-visual apparatus such as a TV receiver or a video player or acoustic reproduction for a personal computer or a game machine, there is fear that a color purity error or a distortion may occur and lower the image quality. Countermeasures for decreasing the leakage magnetic flux include attaching a cancellation magnet to the rear side of the magnetic circuit
5
and, in addition, covering the magnetic
11
circuit
5
with a shield cover
12
.
The electromagnetic driving force acting on the voice coil
9
is transmitted to the neighboring air from the vibration plate
4
. The vibration force
4
applies pressure to the neighboring air and receives reactive force therefrom. The reactive force that the vibration plate
4
receives is transmitted to the magnetic circuit
5
through electromagnetic interaction between the voice coil
9
and the magnetic circuit
5
and then transmitted from the magnetic circuit
5
to the enclosure
3
via the frame
10
. Therefore, in the speaker system
1
, when sound is outputted from the vibration plate
4
by driving each speaker unit
2
electrically, the speaker unit
2
itself vibrates and this vibration is transmitted to the enclosure
3
. Sound is also emitted from the surfaces of the enclosure
3
. Being opposite in phase to the sound emitted from the vibration plate
4
, this sound interferes with the sound emitted from the vibration plate
4
. As such, this sound is a factor of deteriorating the quality of sound emitted from the speaker system
1
as a whole. Further, because of reaction to the movement of the vibration plate
4
for emitting sound, the center pole
7
side of the magnetic circuit
4
tends to vibrate. Therefore, the efficiency of energy transmission from the vibration plate
4
to the air is low, which influences the transient characteristic of sound and, in terms of the sound quality, lowers a sense of speed to be given to a listener.
Japanese Unexamined Patent Publications JP-A 5-153680 (1993), JP-A11-146471 (1999), etc. disclose a technique in which in the enclosure each speaker unit is not fixed to the front side of the frame of the speaker unit but to the rear side of the magnetic circuit. By fixing the magnetic circuit to a grounding surface to make vibration hard to be transmitted to the magnetic circuit and to be transmitted from the frame to the enclosure, it is expected that the degree of sound emission from the enclosure will be lowered and the deterioration of sound quality will be decreased.
To strongly support the magnetic circuit portion while accommodating each speaker unit in the enclosure as in the above prior art technique, it is necessary to, for example, make the enclosure of a dividable type and assemble the enclosure after completion of support of each speaker unit. This results in problems that the number of assembling steps of the speaker apparatus increases and the structure of the enclosure becomes complex. There may be cases where the enclosure cannot be divided as exemplified by a speaker that is attached to a vehicle door as the enclosure.
SUMMARY OF THE INVENTION
An object of the invention is to provide a speaker apparatus in which a speaker unit itself can suppress vibration that is caused by reaction to the movement of a vibration plate and which can provide sound quality with a good transient characteristic even in a state that the speaker apparatus is attached to an enclosure.
A first aspect of the invention provides a speaker apparatus comprising a speaker unit including a converter, having a magnetic circuit, for converting an electrical signal into mechanical vibration along an axial line direction of a voice coil, a vibration plate for emitting sound waves to a front side of the converter, and a frame fixed to the converter, for vibratably supporting the vibration plate from its rear side; and a weight heavier than the speaker unit, having a boss formed so as to project to a front side from a central portion of the weight along the axial line of the voice coil, a cross section of the boss taken perpendicularly to the axial line being smaller than that of the magnetic circuit, a tip of the boss being fixed to a rear side of the magnetic circuit.
This speaker apparatus that converts an electrical signal into an acoustic signal and emits the latter to the front side has the speaker unit and the weight. The speaker unit has the converter for converting an electrical signal into mechanical vibration, the vibration plate provided on the front side of the converter, for emitting sound waves, and the frame that is fixed to the converter and vibratably supports the vibration plate from the rear side. Mechanical vibration that is produced from an electrical signal is emitted, as sound waves, from the vibration plate to the neighboring air. Reactive force that acts on the vibration plate from the air is returned to the converter and vibrates the converter. However, the weight that is heavier than the speaker unit and is fixed to the rear side of the converter serves as a virtual ground and hence suppresses the vibration of the converter. Since the vibration of the converter is suppressed, even if the front portion of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be decreased and the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
In this speaker apparatus, mechanical vibration produced from an electrical signal by the converter is emitted, as sound waves, from the vibration plate to the neighboring air. Reactive force that acts on the vibration plate from the air is returned to the converter and vibrates the converter. However, the weight that is heavier than the speaker unit and is fixed to the rear side of the converter serves as a virtual ground and hence suppresses the vibration of the converter. Since the vibration of the converter is suppressed, even if the front portion of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be decreased and
Kowaki Hiroshi
Nishikawa Akira
Tsumori Katsuhiko
Yoshii Hiroyuki
Fujitsu Ten Limited
Ni Suhan
Wenderoth , Lind & Ponack, L.L.P.
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