Information
-
Patent Grant
-
6724909
-
Patent Number
6,724,909
-
Date Filed
Friday, November 9, 200122 years ago
-
Date Issued
Tuesday, April 20, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Wenderoth, Lind & Ponack, L.L.P.
-
CPC
-
US Classifications
Field of Search
US
- 381 337
- 381 338
- 381 182
- 381 161
- 381 162
- 381 285
- 381 386
- 381 387
- 381 388
- 381 390
- 381 395
- 381 397
- 381 412
- 381 124
- 181 175
- 181 179
- 181 199
-
International Classifications
-
Abstract
A weight is attached to the rear side of a magnetic circuit of a speaker unit. The tip of a boss that projects to the front side from the weight is joined to the rear side of a center pole of the magnetic circuit with a bolt. Even if reactive force that is generated when an electrical signal is converted into mechanical vibration by the magnetic circuit and a voice coil and sound waves are emitted from a vibration plate is transmitted to the magnetic circuit, the vibration of the magnetic circuit is suppressed by the weight. In this manner, sound quality with a good transient characteristic can be obtained.
Description
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 the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
Since the tip of the boss projecting from the weight is attached to the rear side of the external magnet type magnetic circuit in such a manner that the boss extends along the axial line of the voice coil, the area of junction between the magnetic circuit and the weight can be made small. As the junction area becomes larger, it becomes more difficult to join the weight to the rear side of the magnetic circuit uniformly over the entire junction surface and hence abnormal sound becomes more prone to occur due to vibration-induced closing and opening of a slight gap. However, in this speaker apparatus, since only the tip of the boss projecting from the weight is joined to the rear side of the magnetic circuit, sufficient junction uniformity can easily be secured. Where the weight is made of a ferromagnetic material such as iron, there is fear that magnetic flux may escape from the magnetic gap. However, in this speaker apparatus, since the weight is joined to the magnetic circuit only in the neighborhood of the axial line, even if the weight is made of a ferromagnetic material, its influence on the magnetic flux generated by the magnetic circuit can be minimized.
Since the tip of the boss projecting from the weight is attached to the rear side of the external magnet type magnetic circuit in such a manner that the boss extends along the axial line of the voice coil, the area of junction between the magnetic circuit and the weight can be made small. Since only the tip of the boss projecting from the weight is joined to the rear side of the magnetic circuit, sufficient junction uniformity can easily be secured. Further, since the weight is joined to the magnetic circuit only in the neighborhood of the axial line, even if the weight is made of a ferromagnetic material, its influence on the magnetic flux generated by the magnetic circuit can be minimized, whereby the electro-acoustic conversion efficiency of the speaker apparatus can be prevented from being reduced.
The magnetic circuit may be of an external magnet type and have an annular cancellation permanent magnet for decreasing leakage magnetic flux on the rear side of an annular main permanent magnet for generating magnetic flux for driving the voice coil. The boss of the weight may penetrate through a hollow portion of the cancellation permanent magnet and be fixed to the rear side of a center pole of the magnetic circuit.
With this configuration, although the cancellation permanent magnet for decreasing leakage magnetic flux is provided on the rear side of the magnetic circuit, since the boss of the weight can be joined to the magnetic circuit at a position close to the rear side of the main permanent magnet while penetrating through the hollow portion of the annular cancellation permanent magnet, vibration of the magnetic circuit can be suppressed by directly adding a weight to the magnetic circuit that receives reactive force from the voice coil.
Although the cancellation permanent magnet for decreasing leakage magnetic flux is provided on the rear side of the magnetic circuit, this configuration makes it possible to suppress vibration of the magnetic circuit by directly adding a weight to the magnetic circuit that receives reactive force from the voice coil.
A second aspect of the invention provides a speaker apparatus comprising a speaker unit including a main converter for converting an electrical signal into mechanical vibration, a vibration plate for emitting sound waves to the front side of the main converter, and a frame fixed to the converter, for vibratably supporting the vibration plate from a rear side thereof; a compensation converter for converting an electrical signal to mechanical vibration, the compensation converter being fixed to a rear side of the main converter and smaller and lighter than the main converter; and a compensation mass body lighter than the vibration plate, for serving as a load of mechanical vibration of the compensation converter.
With this configuration, the compensation converter that is smaller and lighter than the converter of the speaker unit is fixed to the rear side of the speaker unit, and the compensation mass body that is lighter than the vibration system of the speaker unit serves as a load of mechanical vibration of the compensation converter. The compensation converter is electrically driven so that the compensation mass body is given approximately the same momentum as the vibration system of the speaker unit is given when the converter of the speaker unit is driven, whereby the reactive force received by the converter of the speaker unit is made opposite in direction to that receivedby the compensation converter and the two reactive forces cancel out each other, as a result of which vibration can be suppressed. Since the vibration of the converters is suppressed, even if the front side of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be made small. Therefore, the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
With this configuration, the compensation converter that is smaller and lighter than the converter of the speaker unit is fixed to the rear side of the speaker unit, and the compensation mass body that is lighter than the vibration system of the speaker unit serves as a load of mechanical vibration of the compensation converter. However, since the compensation converter is electrically driven so that the compensation mass body is given approximately the same momentum as the vibration system of the speaker unit is given when the converter of the speaker unit is driven, the reactive force received by the converter of the speaker unit is made opposite in direction to that received by the compensation converter and the two reactive forces cancel out each other, as a result of which vibration can be suppressed. Since the vibration of the converters is suppressed, even if the front side of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be made small. Therefore, the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained. Since the compensation converter and the compensation mass body are made smaller and lighter, the weight of the speaker apparatus is not much increased.
A third aspect of the invention provides an acoustic signal output apparatus comprising a speaker unit including a main converter for converting an electrical signal into mechanical vibration, the main converter having a first movable portion capable of moving along a predetermined axial line, a vibration plate attached to the first movable portion, for emitting sound waves to a front side of the main converter, and a frame fixed to the main converter, for vibratably supporting the vibration plate from the rear side thereof; a compensation converter for converting an electrical signal to mechanical vibration, the compensation converter being fixed to a rear side of the main converter and having a second movable portion capable of moving along the predetermined axial line; a compensation mass body attached to the second movable portion, for serving as a load of mechanical vibration of the compensation converter; a signal source for generating an electrical signal corresponding to an acoustic signal to be outputted; and a signal processing circuit for receiving an output of the signal source, amplifying or attenuating the output, and supplying the main converter and the compensation converter with respective electrical signals having such phases that the first movable portion and the second movable portion move in opposite directions.
With this configuration, an electrical signal that is outputted from the signal source is supplied to the main converter and the compensation converter via the signal processing circuit, whereby the vibration plate of the speaker unit is driven and an acoustic signal is outputted. The main converter and the compensation converter are supplied with such electrical signals that the first movable portion and the second movable portion move in opposite directions. Therefore, reactive force received by the main converter and that received by the compensation converter have the same phase and act in opposite directions and hence cancel out each other, whereby vibration can be suppressed. This prevents adverse effects on an output acoustic signal and hence prevents deterioration in sound quality.
The signal processing circuit may comprise a first amplification circuit for amplifying a signal to be supplied to the main converter and a second amplification circuit for amplifying a signal to be supplied to the compensation converter, amplification factors of the first and second amplification circuits being determined in accordance with loads of mechanical vibration of the main converter and the compensation converter, respectively.
With this configuration, an electrical signal that is outputted from the signal source is amplified by the first amplification circuit and then supplied to the main converter, and is also amplified by the second amplification circuit and then supplied to the compensation converter. The amplification factors of the first and second amplification circuits are determined in accordance with the loads of mechanical vibration of the main converter and the compensation converter, respectively. For example, if the loads are the same, the amplification factors are set at the same value. If the loads are different from each other, the amplification factor of one amplification circuit corresponding to a converter having a smaller load is set larger than that of the other amplification circuit. With this configuration, even if the loads of the main converter and the compensation converter are different from each other, the two converters amplification factors of the drive currents, that is, electrical signals applied to the two converters, can be set correctly in accordance with, for example, a similarity ratio between the two converters.
The signal processing circuit may comprise an amplification circuit for amplifying a signal to be supplied to the main converter and the compensation circuit and an attenuation circuit for attenuating an output of the amplification circuit and supplying an attenuated signal to the main converter, an attenuation factor of the attenuation circuit being determined in accordance with loads of mechanical vibration of the main converter and the compensation converter.
With this configuration, an electrical signal that is outputted from the signal source is amplified by the amplification circuit. An output of the amplification circuit is on one hand supplied to the compensation converter as it is, and on the other hand attenuated by the attenuation circuit and then supplied to the main converter. The attenuation factor of the attenuation circuit is determined in accordance with the loads of mechanical vibration of the main converter and the compensation converter. With this configuration, With this configuration, the two converters amplification factors of the drive currents, that is, electrical signals applied to the two converters, can be set correctly in accordance with, for example, a similarity ratio between the two converters.
The invention further provides a speaker apparatus which converts an electrical signal into an acoustic signal and emits the acoustic signal to the front side, comprising a speaker unit including a converter for converting an electrical signal into mechanical vibration, a vibration plate provided on the front side of the converter, for emitting sound waves, and a frame fixed to the converter, for vibratably supporting the vibration plate from the rear side; a compensation converter fixed to a rear side of the converter of the speaker unit, for converting an electrical signal to mechanical vibration in the same manner as the converter of the speaker unit does; and a compensation vibrator for serving as a load of mechanical vibration of the compensation converter, the compensation vibrator being approximately as heavy as a vibration system of the speaker unit.
With this configuration, the compensation converter that is equivalent to the converter of the speaker unit is fixed to the rear side of the speaker unit, and the compensation vibrator approximately as heavy as the vibration system of the speaker unit serves as a load of mechanical vibration of the compensation converter. An electrical signal equivalent to an electrical signal for driving the converter of the speaker unit is applied to the compensation converter so that reactive force received by the converter of the speaker unit is opposite in direction to that received by the compensation converter, whereby the two reactive forces cancel out each other and vibration can be suppressed. Since the vibration of the converters is suppressed, even if the front side of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be made small. Therefore, the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
This configuration makes it possible to suppress vibration of the converters by generating, on the rear side of converter of the speaker unit, vibration that is equivalent to vibration occurring in the converter of the speaker unit and causing the two kinds of vibration to cancel out each other. Since the vibration of the converters is suppressed, even if the front side of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be made small. Therefore, the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
Other and further objects, features, and advantages of the invention will be more explicit from the following detailed description taken with reference to the drawings wherein:
FIG. 1
is a partially sectional side view shows a schematic configuration of a speaker apparatus according to an embodiment of the invention;
FIG. 2
is a partially sectional side view of a speaker system using the speaker apparatus of
FIG. 1
;
FIG. 3
is a partially sectional side view shows a schematic configuration of a speaker apparatus according to another embodiment of the invention;
FIG. 4
is a partially sectional side view shows a schematic configuration of a speaker apparatus according to a further embodiment of the invention;
FIG. 5
is a block diagram showing, in a simplified manner, the electrical configuration of an acoustic signal output apparatus according to another embodiment of the invention;
FIG. 6
is a block diagram showing, in a simplified manner, the electrical configuration of an acoustic signal output apparatus according to another embodiment of the invention; and
FIG. 7
is a side sectional view of a conventional speaker system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now referring to the drawings, preferred embodiments of the invention are described below.
FIG. 1
shows a schematic configuration of a speaker apparatus
21
according to an embodiment of the invention. The upper half of
FIG. 1
is a side sectional view and its lower half is a sectional view. That is, the speaker apparatus
21
is a rotary body formed by rotating the upper half section of
FIG. 1
about an axial line
29
a
. The speaker apparatus
21
has a speaker unit
22
and a weight
23
. The speaker unit
22
, which is basically the same as the conventional speaker unit
2
as shown in
FIG. 7
, emits sound through vibration of a vibration plate
24
. The vibration plate
24
is driven by utilizing a magnetic field that is generated by a magnetic circuit
25
. Being of an external magnet type, the magnetic circuit
25
generates a magnetic field by means of an annular main magnet
26
, a center pole
27
, and a plate
28
. The center pole
27
is composed of a disk
27
a
and a projection
27
b
protruding from the central portion thereof in the form of a right circular cylinder. Strong magnetic field is generated in a magnetic gap between the outer peripheral surface of the top portion of the projection
27
b
of the center pole
27
and the inner peripheral surface of the plate
28
and a voice coil
29
is suspended in the magnetic gap. The voice coil
29
includes a cylindrical bobbin
29
b
and a wire
29
c
wound on the basal portion of the bobbin
29
b
. When an electrical signal is applied to the voice coil
29
, electromagnetically generated force acts on the voice coil
29
along an axial line
29
a
of the voice coil
29
and drives the vibration plate
24
in the axial direction
29
a
. The vibration plate
24
is supported by a frame
30
so as to be vibratable along the axial line
29
a.
To suppress leakage of magnetic flux to the outside, the magnetic circuit
25
of the speaker unit
22
according to this embodiment has a cancellation magnet
31
and a shield cover
32
. The cancellation magnet
31
is magnetized in the opposite direction to the magnetization direction of the main magnet
26
. For example, if the main magnet
26
is magnetized in such a manner that the N pole and the S pole are located on the front side (i.e. the left-hand side of
FIG. 1
) andthe rear side (i.e. the right-hand side of FIG.
1
), respectively, in a state that the main magnet
26
is set in the speaker unit
22
, the cancellation magnet
31
is magnetized in such a manner that the N pole and the S pole are located on the rear side and the front side, respectively. Each of the main magnet
26
and the cancellation magnet
31
is a ferrite-type permanent magnet. The center pole
27
, the plate
28
, and the shield cover
32
are made of a ferromagnetic material such as iron. In the magnetic circuit
25
, the inner surface, i.e. the left-hand surface as observed in
FIG. 1
, of the shield cover
32
, the cancellation magnet
31
, the disk
27
a
of the center pole
27
, the main magnet
26
, and the plate
28
make intimate contact with one another along the axial direction
29
a
of the voice coil
29
.
The vibration plate
24
is supported to as to be able to vibrate relative to the frame
30
along the axial line
29
a
by means of an edge
33
that is attached to the front-side outer peripheral surface of the vibration plate
24
and a damper
34
that is attached to the basal portion of the vibration plate
24
and has a vibration damping function. The basal portion of the vibration plate
24
is joined to the front portion of the bobbin
29
b
of the voice coil
29
. A wire
29
c
is wound on the basal portion of the bobbin
29
b
of the voice coil
29
, whereby the voice coil
29
receives force that results from the electromagnetic interaction with a magnetic field in the magnetic gap G. The front-side opening of the voice coil
29
is closed by a dust cap
35
to prevent dust or the like from entering the magnetic gap. A gasket
36
is attached to the outer peripheral surface of the edge
33
to prevent the edge
33
from being crushed when the speaker unit
22
is attached to a cabinet.
The weight
23
is provided on the rear side of the magnetic circuit
25
of the speaker unit
22
. The weight
23
is heavier than the entire speaker unit
22
. For example, the weight
23
is made of iron and 1.5 times heavier than the entire speaker unit
22
. The weight
23
generally assumes a cannonball-like shape having a flat end face on the front side and a streamline curved surface on the rear side. The cross section of the weight as taken perpendicularly to the axial line
29
a
is smaller than that of the magnetic circuit
25
. A boss
37
projects from the center of the front end face of the weight
23
. Only the tip of the boss
37
of the weight
23
is joined to the rear side of center pole
27
of the speaker unit
22
. In this embodiment, the weight
23
is formed, along its center line, with a through-hole that goes from the rear end of the weight
23
to the tip of the boss
37
. A bolt
38
is inserted into the through-hole from the rear side and joined to the center pole
27
in such a manner as to be engaged with threads that are formed in the center pole
27
along its center line. A flat washer
39
and a spring washer
40
are provided on the side of the head of the bolt
38
to prevent loosening of the bolt
38
. Alternatively, the bolt
38
may be integrated with the weight
23
in such a manner that the weight
23
is formed with a threaded projection.
In this embodiment, in the speaker apparatus
21
for converting an electrical signal into an acoustic signal and emits the latter to the front side, the magnetic circuit
25
and the voice coil
29
form a converter
20
for converting an electrical signal into mechanical vibration. And the speaker unit
22
is provided with the vibration plate
24
for emitting sound waves to the front side of the converter
20
and the frame
30
that vibratably supports the vibration plate
24
from the rear side and that is fixed to the converter
20
. The weight
23
is fixed to the rear side of the converter
20
and is heavier than the speaker unit
22
.
Mechanical vibration that is produced from an electrical signal by the converter
20
is emitted, as sound waves, from the vibration plate
24
to the neighboring air. Reactive force that acts on the vibration plate
24
from the air is returned to the converter
20
and vibrates the converter
20
. However, the weight
23
that is heavier than the speaker unit
22
is fixed to the rear side of the converter
20
. Because of the resultant inertia, the weight
23
serves as a virtual ground, and hence the vibration of the converter
20
is suppressed.
The converter
20
of the speaker unit
22
according to this embodiment has the magnetic circuit
25
and converts an electrical signal into vibration along the axial direction
29
a
of the voice coil
29
(electromotive type). The weight
23
is provided in such a manner that its center line coincides with the axial line
29
a
of the voice coil
29
. The cross section of the weight
23
taken perpendicularly to the axial line
29
a
is smaller than that of the magnetic circuit
25
. The boss
37
projects from the center of the weight
23
to the front side along the axial line
29
a
, and the tip of the boss
37
is fixed to the rear side of the magnetic circuit
25
of the converter
20
. Since the tip of the boss
37
projecting from the weight
23
is attached to the rear side of the external magnet type magnetic circuit
25
in such a manner that the boss
37
extends along the axial line
29
a
of the voice coil
29
, the area of junction between the magnetic circuit
29
and the weight
23
can be made small. As the junction area becomes larger, it becomes more difficult to join the weight
23
to the rear side of the magnetic circuit
25
uniformly over the entire junction surface and hence abnormal sound becomes more prone to occur due to vibration-induced closing and opening of a slight gap. In the embodiment, since only the tip of the boss
37
projecting from the weight
23
is joined to the rear side of the magnetic circuit
25
, sufficient junction uniformity can easily be secured. Where the weight
23
is made of a ferromagnetic material such as iron, magnetic flux escapes from the magnetic gap to weaken the magnetic field there. In the embodiment, since the weight
23
is joined to the magnetic circuit
25
only in the neighborhood of the axial line
29
a
, although the weight
23
is made of a ferromagnetic material, its influence on the magnetic flux generated by the magnetic circuit
25
can be minimized.
Being of an external magnet type, the magnetic circuit
25
is provided with the cancellation magnet
31
as the annular cancellation permanent magnet for decreasing leakage magnetic flux on the rear side of the main magnet
26
as the annular main permanent magnet for generating magnetic flux for driving the voice coil
29
. The boss
37
of the weight
23
penetrates through an opening portion formed on the central portion of the shield cover
32
and the hollow portion of the cancellation magnet
31
and is fixed to the rear side of the center pole
27
of the magnetic circuit
25
. Although the cancellation magnet
31
for decreasing leakage magnetic flux is provided on the rear side of the magnetic circuit
25
, since the boss
37
of the weight
23
can be joined to magnetic circuit
25
at a position close to the rear side of the main magnet
26
while penetrating through the hollow portion of the annular cancellation magnet
31
, vibration of the magnetic circuit
25
can be suppressed by directly adding a weight to the magnetic circuit
25
that receives reactive force from the voice coil
29
.
FIG. 2
shows, in a simplified manner, a speaker system
41
using the speaker apparatus
21
of FIG.
1
.
FIG. 2
is a side sectional view except for the speaker apparatus
21
which is shown as a side view. Like the conventional speaker unit
2
as shown in
FIG. 7
, the speaker unit
22
of the speaker apparatus
21
, specifically, the front portion of its frame
30
, is fixed to an enclosure
43
having an opening
42
. Since vibration of the converter of the speaker unit
22
is suppressed by the weight
23
, even if the front portion of the frame
30
is fixed to the enclosure
43
, vibration that is transmitted to the enclosure
43
via the frame
30
can be made small. Therefore, the emission of undesired sound from the enclosure
43
can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
Conventionally, a very large number of structures are available as the structure for attaching the speaker unit
22
to the enclosure
43
and as the structure of the enclosure
43
.
FIG. 2
shows a simplest combination of those structures. Where the weight
23
is heavy, it may directly be supported by a certain means in the enclosure
43
. Since the vibration-suppressed portion is supported, only a small amount of vibration is transmitted from the supported portion to the enclosure
43
and hence deterioration of the sound quality can be avoided.
FIG. 3
shows a schematic configuration of a speaker apparatus
51
according to another embodiment of the invention. Likewise as
FIG. 1
, the upper half of
FIG. 3
is a side sectional view and its lower half is a sectional view. That is, the speaker apparatus
51
is a rotary body formed by rotating the upper half section of
FIG. 3
about an axial line
29
a
. Components in
FIG. 3
having the corresponding components in
FIG. 1
are given the same reference numerals as the latter and redundant descriptions will be omitted. In the speaker apparatus
51
according to this embodiment, a compensation unit
52
is attached to the rear side of the speaker unit
22
. The compensation unit
52
has a magnetic circuit
85
and a voice coil
89
that have basically the same structure as the magnetic circuit
25
and the voice coil
29
of the speaker unit
22
, respectively. The voice coil
89
of the compensation unit
52
is supported so as to be vibratable along the axial line
29
a
by a damper
84
that has basically the same structure as the damper
34
of the speaker unit
22
. However, where the compliance of the edge
33
of the speaker unit
22
is not much larger than that of the dampers
34
,
84
, the compliance of the edge
33
also contributes to the vibration of the vibration plate
24
. Therefore, in such a case, the damper
34
of the compensation unit
52
is replaced by a damper that is smaller in compliance than the dampers
34
,
84
. The mass of the vibration system including the vibration plate
24
and the dust cap
35
of the speaker unit
22
and the air around the vibration plate
24
is attached to the bobbin
89
b
of the voice coil
89
of the compensation unit
52
rather than the weight
53
. The magnetic circuits
25
,
85
of the speaker unit
22
and the compensation unit
52
are provided back to back and joined to each other with a bolt
58
. The center poles
27
,
87
of each magnetic circuits
25
,
85
is formed with a female screw to engage the bolt
58
. The damper
84
of the compensation unit
52
is supported by a partial frame
60
.
In this embodiment, the speaker apparatus
51
for converting an electrical signal into an acoustic signal and emitting the latter to the front side has the speaker unit
22
and the compensation unit
52
. The speaker unit
22
is provided with the magnetic circuit
25
and the voice coil
29
that constitute the main converter
20
for converting an electrical signal into mechanical vibration, the vibration plate
24
for emitting sound waves to the front side of the main converter
20
, and the frame
30
that vibratably supports the vibration plate
24
from the rear side and that is fixed to the main converter
20
. The compensation unit
52
has a compensation converter
80
that is fixed to the rear side of the main converter
20
of the speaker unit
22
and converts an electrical signal into mechanical vibration like the main converter
20
of the speaker unit
22
does and a weight
53
, as a compensation mass body, that is approximately as heavy as the vibration system of the speaker unit
22
and serves as a load of mechanical vibration of the compensation converter
80
.
More specifically, being of an external magnet type, the magnetic circuit
85
of the compensation converter
80
generates a magnetic field by means of an annular main magnet
86
, a center pole
87
, and a plate
88
. The center pole
87
is composed of a disk
87
a
and a projection
87
b
protruding from the central portion thereof in the form of a right circular cylinder. Strong magnetic field is generated in a magnetic gap between the outer peripheral surface of the top portion of the projection
87
b
of the center pole
87
and the inner peripheral surface of the plate
88
and a voice coil
89
is suspended in the magnetic gap. The voice coil
89
includes a cylindrical bobbin
89
b
and a wire
89
c
wound on the basal portion of the bobbin
89
b
. When an electrical signal is applied to the voice coil
89
, electromagnetically generated force acts on the voice coil
89
along an axial line
29
a
, whereby the voice coil
89
moves in the axial direction
29
a.
To suppress leakage of magnetic flux to the outside, the magnetic circuit
85
of the compensation converter
80
has a cancellation magnet
91
and a shield cover
92
. The cancellation magnet
91
is magnetized in the opposite direction to the magnetization direction of the main magnet
86
. For example, if the main magnet
86
is magnetized in such a manner that the S pole and the N pole are located on the front side (i.e. the left-hand side of
FIG. 3
) and the rear side (i.e. the right-hand side of FIG.
3
), respectively, the cancellation magnet
91
is magnetized in such a manner that the N pole and the S pole are located on the front side and the rear side, respectively. Each of the main magnet
86
and the cancellation magnet
91
is a ferrite-type permanent magnet. The center pole
87
, the plate
88
, and the shield cover
92
are made of a ferromagnetic material such as iron. In the magnetic circuit
85
, the inner surface, i.e. the right-hand surface as observed in
FIG. 3
, of the shield cover
92
, the cancellation magnet
91
, the disk
87
a
of the center pole
87
, the mainmagnet
86
, and the plate
88
make intimate contact with one another along the axial direction
29
a
of the voice coil
89
. The shield cover
32
of the main converter
20
of the speaker unit
22
and the shield cover
92
of the compensation converter
80
of the compensation unit
52
are tightly fixed to each other with a bolt
58
.
An electrical signal equivalent to an electrical signal for driving the converter
20
of the speaker unit
22
is applied to the converter
80
of the compensation unit
52
so that reactive force received by the converter
20
of the speaker unit
22
is opposite in direction to that received by the converter
80
of the compensation unit
52
, whereby the two reactive forces cancel out each other and vibration can be suppressed. Since the vibration of the converters
20
,
80
is suppressed, even if the front side of the frame
30
is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame
30
can be made small. Therefore, the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
FIG. 4
shows a schematic configuration of a speaker apparatus
61
according to a further embodiment of the invention. Likewise as
FIGS. 1 and 3
, the upper half of
FIG. 4
is a side sectional view and its lower half is a sectional view. That is, the speaker apparatus
61
is a rotary body formed by rotating the upper half section of
FIG. 4
about an axial line
29
a
. Components in
FIG. 4
having the corresponding components in
FIG. 1
or
3
are given the same reference numerals as the latter and redundant descriptions will be omitted. In this embodiment, as in the embodiment of
FIG. 3
, a compensation unit
62
is attached to the rear side of the speaker unit
22
. However, in the compensation unit
62
according to this embodiment, a damper
64
and a magnetic circuit
65
are different from the damper
34
and the magnetic circuit
25
of the speaker unit
22
. In particular, the magnetic circuit
65
is made smaller and lighter than the magnetic circuit
25
by using a smaller main magnet
66
than the main magnet
26
of the magnetic circuit
25
. In accordance with the size reduction of the main magnet
66
, a center pole
67
, a plate
68
, a voice coil
69
, a cancellation magnet
71
, and a shield cover
72
are changed from the counterparts in
FIG. 3. A
weight
73
is also made lighter than the weight
53
in FIG.
3
.
More specifically, in the speaker apparatus
61
according to this embodiment, a compensation unit
62
is attached to the rear side of the speaker unit
22
. The compensation unit
62
has a magnetic circuit
65
and a voice coil
69
that have basically the same configuration as the magnetic circuit
25
and the voice coil
29
of the speaker unit
22
, respectively. The voice coil
69
is supported so as to be vibratable along the axial line
29
a
by a damper
64
that has basically the same configuration as the damper
34
of the speaker unit
22
. However, where the compliance of the edge
33
of the speaker unit
22
is not much larger than that of the dampers
34
,
64
, the compliance of the edge
33
also contributes to the vibration of the vibration plate
24
. Therefore, in such a case, a damper that is smaller in compliance than the dampers
34
,
64
is used. Themass of the vibration system including the vibration plate
24
and the dust cap
35
of the speaker unit
22
and the air around the vibration plate
24
is attached to the bobbin
69
b
of the voice coil
69
of the compensation unit
62
rather than the weight
73
. The magnetic circuits
25
,
65
of the speaker unit
22
and the compensation unit
62
are provided back to back and joined to each other with a bolt
58
. The center poles
27
,
67
of each magnetic circuits
25
,
65
is formed with a female screw to engage the bolt
58
. The damper
64
of the compensation unit
62
is supported by a partial frame
60
.
In this embodiment, the speaker apparatus
61
for converting an electrical signal into an acoustic signal and emitting the latter to the front side has the speaker unit
22
and the compensation unit
62
. The speaker unit
22
is provided with the magnetic circuit
25
and the voice coil
29
that constitute the main converter
20
for converting an electrical signal into mechanical vibration, the vibration plate
24
for emitting sound waves to the front side of the main converter
20
, and the frame
30
that vibratably supports the vibration plate
24
from the rear side and that is fixed to the main converter
20
. The compensation unit
62
has a compensation converter
75
that is fixed to the rear side of the main converter
20
of the speaker unit
22
and converts an electrical signal into mechanical vibration, the compensation converter
75
being smaller and lighter than the main converter
20
of the speaker unit
22
, and a weight
73
, as a compensation mass body, that is lighter than the vibration system of the speaker unit
22
, for example, the vibration plate
24
, and serves as a load of mechanical vibration of the compensation converter
75
.
More specifically, being of an external magnet type, the magnetic circuit
65
of the compensation converter
75
generates a magnetic field by means of an annular main magnet
66
, a center pole
67
, and a plate
68
. The center pole
67
is composed of a disk
67
a
and a projection
67
b
protruding from the central portion thereof in the form of a right circular cylinder. Strong magnetic field is generated in a magnetic gap between the outer peripheral surface of the top portion of the projection
67
b
of the center pole
67
and the inner peripheral surface of the plate
68
and a voice coil
69
is suspended in the magnetic gap. The voice coil
69
includes a cylindrical bobbin
69
b
and a wire
69
c
wound on the basal portion of the bobbin
69
b
. When an electrical signal is applied to the voice coil
69
, electromagnetically generated force acts on the voice coil
69
along an axial line
29
a
, whereby the voice coil
69
moves in the axial direction
29
a.
To suppress leakage of magnetic flux to the outside, the magnetic circuit
65
of the compensation converter
75
has a cancellation magnet
71
and a shield cover
72
. The cancellation magnet
71
is magnetized in the opposite direction to the magnetization direction of the main magnet
66
. For example, if the main magnet
66
is magnetized in such a manner that the S pole and the N pole are located on the front side (i.e. the left-hand side of
FIG. 4
) and the rear side (i.e. the right-hand side of FIG.
4
), respectively, the cancellation magnet
71
is magnetized in such a manner that the N pole and the S pole are located on the front side and the rear side, respectively. Each of the main magnet
66
and the cancellation magnet
71
is a ferrite-type permanent magnet. The center pole
67
, the plate
68
, and the shield cover
72
are made of a ferromagnetic material such as iron. In the magnetic circuit
65
, the inner surface, i.e. the right-hand surface as observed in
FIG. 4
, of the shield cover
72
, the cancellation magnet
71
, the disk
67
a
of the center pole
67
, the main magnet
66
, and the plate
68
make intimate contact with one another along the axial direction
29
a
of the voice coil
69
. The shield cover
32
of the main converter
20
of the speaker unit
22
and the shield cover
72
of the compensation converter
75
of the compensation unit
62
are tightly fixed to each other with a bolt
58
.
The components
66
-
68
,
71
, and
72
of the magnetic circuit
65
of a compensation converter
75
are similar, in shape, to the respective components
26
-
28
,
31
, and
32
of the magnetic circuit
25
of the main converter
20
, and the components
66
-
68
,
71
, and
72
are versions reduced at a predetermined ratio of the components
26
-
28
,
31
, and
32
. The damper
64
of the compensation unit
62
is similar, in shape, to the damper
34
of the speaker unit
22
, and the former is a version reduced at a predetermined ratio of the latter. In this manner, the compensation unit
62
is reduced in size and weight. A projection
27
b
of the center pole
27
of the main converter
20
may have the same size as a projection
67
b
of the center pole
67
of the compensation converter
75
. The voice coil
29
of the main converter
20
may have the same size as the voice coil
69
of the compensation converter
75
.
In this embodiment, the magnetic circuit
65
that is smaller and lighter than the magnetic circuit
25
of the main converter
20
of the speaker unit
22
is fixed to the rear side of the speaker unit
22
. In the main converter
20
of the speaker unit
22
, the mass of the magnetic circuit
25
accounts for most of the mass of the converter. The converter of the compensation unit
62
has the smaller and lighter magnetic circuit
65
. Therefore, the entire converter of the compensation unit
62
is smaller and lighter than the converter of the speaker unit
22
. The compensation unit
62
has a weight
73
, as a compensation mass body, that is lighter than the vibration system of the speaker unit
22
. The weight
73
serves as a load of mechanical vibration of the converter
75
of the compensation unit
62
. The compensation unit
62
is driven in phase by a higher power so that the vibration system of the compensation unit
62
is given the same momentum as the vibration system of the speaker unit
22
is given when the converter of the speaker unit
22
is driven, whereby the reactive force received by the main converter
20
of the speaker unit
22
is made opposite in direction to that received by the compensation converter
75
of the compensation unit
62
and the two reactive forces cancel out each other, as a result of which vibration can be suppressed. Since the vibration of the converters
20
and
75
is suppressed, even if the front side of the frame
30
is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame
30
can be made small. Therefore, the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
FIG. 5
is a block diagram showing, in a simplified manner, the electrical configuration of an acoustic signal output apparatus
100
according to another embodiment of the invention. The acoustic signal output apparatus
100
has one of the speaker apparatuses
51
and
61
as shown in
FIGS. 3 and 4
, a signal source
101
, and a signal processing circuit
102
. First, a description will be made of the case where the speaker apparatus
51
of
FIG. 3
is used.
As shown in
FIG. 3
, the speaker apparatus
51
has the speaker unit
22
, the compensation converter
80
, and the weight
53
as a compensation mass body. The speaker unit
22
is provided with the main converter
20
that has the voice coil
29
as a first movable portion capable of moving along the axial line
29
a
and converts an electrical signal into mechanical vibration, the vibration plate
24
that is attached to the voice coil
29
and emits sound waves to the front side of the main converter
20
, and the frame
30
that is fixed to the main converter
20
and vibratably supports the vibration plate
24
from its rear side. Fixed to the rear side of the main converter
20
and having the voice coil
89
as a second movable portion capable of moving along the axial line
29
a
, the compensation converter
80
converts an electrical signal into mechanical vibration. The weight
53
is attached to the voice coil
89
and serves as a load of mechanical vibration of the compensation converter
80
.
The signal source
101
generates an electrical signal corresponding to an acoustic signal to be outputted. The signal processing circuit
102
has a first amplification circuit
103
and a second amplification circuit
104
that are electrically connected to the signal source
101
in parallel. The first amplification circuit
103
amplifies a signal to be supplied to the main converter
20
, and the second amplification circuit
104
amplifies a signal to be supplied to the compensation converter
80
. To the first amplification circuit
103
and the second amplification circuit
104
is inputted an output of the signal source
101
in the same phase. The signal processing circuit
102
amplifies the outputs of the signal source
101
, and supplies the main converter
20
and the compensation converter
80
with electrical signals having such phases that the voice coils
29
and
89
move in opposite directions.
The first amplification circuit
103
is electrically connected to the voice coil
29
of the main converter
20
. The second amplification circuit
104
is electrically connected to the voice coil
89
of the compensation converter
80
. The amplification factors of the first amplification circuit
103
and the second amplification circuit
104
are represented by G
1
and G
2
, respectively.
An electrical signal from the signal source
101
, corresponding to an acoustic signal to be outputted is inputted to the first amplification circuit
103
andthe second amplification circuit
104
in the same phase. One of the electrical signals outputted from the signal source
101
is amplified at the amplification factor G
1
by the first amplification circuit
103
and then supplied to the voice coil
29
. The other electrical signal is amplified at the amplification factor G
2
by the second amplification circuit
104
and then supplied to the voice coil
89
. Electrical signals outputted from the first amplification circuit
103
and the second amplification circuit
104
are supplied to the respective voice coils
29
and
89
in the same phase.
The amplification factors G
1
and G
2
of the first amplification circuit
103
and the second amplification circuit
104
are determined in accordance with the loads of mechanical vibration of the main converter
20
and the compensation converter
80
, respectively. In the speaker apparatus
51
according to an embodiment of the invention, the main converter
20
and the compensation converter
80
are identical and the weight
53
is as heavy as the vibration system of the speaker unit
22
. Therefore, the amplification factors G
1
and G
2
are set equal to each other.
In this manner, outputs of the signal source
101
are amplified by the respective signal processing circuits
103
and
104
of the signal processing circuit
102
and the same electrical signals (having the same phase) are supplied to the respective voice coils
29
and
89
. Therefore, reactive force received by the main converter
20
and that received by the compensation converter
80
have the same phase and act in opposite directions and hence cancel out each other, whereby vibration can be suppressed.
Next, a description will be made of the case where the speaker apparatus
61
as shown in
FIG. 4
is used.
As shown in
FIG. 4
, the speaker apparatus
61
has the speaker unit
22
, the compensation converter
75
, and the weight
73
as a compensation mass body. The speaker unit
22
is provided with the main converter
20
that has the voice coil
29
as a first movable portion capable of moving along the axial line
29
a
and converts an electrical signal into mechanical vibration, the vibration plate
24
that is attached to the voice coil
29
and emits sound waves to the front side of the main converter
20
, and the frame
30
that is fixed to the main converter
20
and vibratably supports the vibration plate
24
from its rear side. Fixed to the rear side of the main converter
20
and having the voice coil
69
as a second movable portion capable of moving along the axial line
29
a
, the compensation converter
75
converts an electrical signal into mechanical vibration. The weight
73
is attached to the voice coil
69
and serves as a load of mechanical vibration of the compensation converter
75
.
The signal source
101
generates an electrical signal corresponding to an acoustic signal to be outputted. The signal processing circuit
102
has a first amplification circuit
103
and a second amplification circuit
104
that are electrically connected to the signal source
101
in parallel. The first amplification circuit
103
amplifies a signal to be supplied to the main converter
20
, and the second amplification circuit
104
amplifies a signal to be supplied to the compensation converter
75
. To the first amplification circuit
103
and the second amplification circuit
104
is inputted an output of the signal source
101
in the same phase. The signal processing circuit
102
amplifies the outputs of the signal source
101
, and supplies the main converter
20
and the compensation converter
75
with electrical signals having such phases that the voice coils
29
and
69
move in opposite directions.
The first amplification circuit
103
is electrically connected to the voice coil
29
of the main converter
20
. The second amplification circuit
104
is electrically connected to the voice coil
69
of the compensation converter
75
. The amplification factors of the first amplification circuit
103
and the second amplification circuit
104
are represented by G
1
and G
2
, respectively.
An electrical signal from the signal source, corresponding to an acoustic signal to be outputted, is inputted to the first amplification circuit
103
and the second amplification circuit
104
in the same phase. One of the electrical signals outputted from the signal source
101
is amplified at the amplification factor G
1
by the first amplification circuit
103
and then supplied to the voice coil
29
. The other electrical signal is amplified at the amplification factor G
2
by the second amplification circuit
104
and then supplied to the voice coil
69
. Electrical signals outputted from the first amplification circuit
103
and the second amplification circuit
104
are supplied to the respective voice coils
29
and
69
in the same phase.
The amplification factors G
1
and G
2
of the first amplification circuit
103
and the second amplification circuit
104
are determined in accordance with the loads of mechanical vibration of the main converter
20
and the compensation converter
75
, respectively. In the speaker apparatus
61
according to an embodiment of the invention, the compensation converter
75
is smaller and lighter than the main converter
20
and the weight
73
is lighter than the vibration system of the speaker unit
22
. Therefore, the amplification factor G
2
of the second amplification circuit
104
is set larger than the amplification factor G
1
of the first amplification circuit
103
so that the vibration systems of the speaker unit
22
and the compensation unit
62
are given the same momentum.
In this manner, outputs of the signal source
101
are amplified by the respective signal processing circuits
103
and
104
of the signal processing circuit
102
and electrical signals amplified at the amplification factors G
1
and G
2
are supplied to the respective voice coils
29
and
69
in the same phase. Therefore, reactive force received by the main converter
20
and that received by the compensation converter
75
have the same phase and act in opposite directions and hence cancel out each other, whereby vibration can be suppressed. Further, since an electrical signal to be supplied to the main converter
20
is amplified by the first amplification circuit
103
and an electrical signal to be supplied to the compensation converter
75
is amplified by the second amplification circuit
104
, the two converters
20
,
75
amplification factors of the drive currents, that is, electrical signals applied to the two converters, can be set correctly in accordance with, for example, a similarity ratio between the two converters
20
,
75
.
FIG. 6
is a block diagram showing, in a simplified manner, the electrical configuration of an acoustic signal output apparatus
110
according to another embodiment of the invention. Components in
FIG. 6
having the corresponding components in
FIG. 5
are given the same reference symbols as the latter and will not be described below. The acoustic signal output apparatus
110
according to this embodiment is similar, in configuration, to the acoustic signal output apparatus
100
of FIG.
5
. Attention should be paid to the facts that the acoustic signal output apparatus
110
is suitable for use with the speaker apparatus
61
, and that a signal processing circuit
112
receives an output of the signal source
101
, attenuates it, and supplies the main converter
20
and the compensation converter
75
with electrical signals having such phases that the voice coils
29
and
69
move in opposite directions.
The signal processing circuit
112
has an amplification circuit
113
and an attenuation circuit
114
. The amplification circuit
113
amplifies a signal that is supplied to the main converter
20
and the compensation converter
75
. The attenuation circuit
114
attenuates an output of the amplification circuit
113
and supplies an attenuated signal to the main converter
20
. For example, the attenuation circuit
114
is a variable resistor circuit. The amplification factor of the amplification circuit
113
is set at a predetermined value G
3
. The attenuation factor of the attenuation circuit
114
is determined in accordance with the loads of mechanical vibration of the main converter
20
and the compensation converter
75
. That is, the attenuation factor is so set that the vibration systems of the speaker unit
22
and the compensation unit
62
are given the same momentum.
An electrical signal from the signal source
101
, corresponding to an acoustic signal to be outputted, is amplified at the amplification factor G
3
by the amplification circuit
113
. The amplified electrical signal is on one hand supplied to voice coil
69
of the compensation converter
75
as it is, and on the other hand attenuated by the attenuation circuit
114
and then supplied to voice coil
29
the main converter
20
. The electrical signals supplied to the converters
20
and
75
have the same phase.
As described above, an output of the signal source
101
is amplified by the amplification circuit
113
of the signal processing circuit
112
, and the amplified electrical signal is on one hand supplied to the voice coil
69
as it is and on the other hand attenuated by the attenuation circuit
114
and then supplied to the voice coil
29
(the electrical signals having the same phase are supplied to the voice coils
29
and
69
). Further, an electrical signal to be supplied to the compensation converter
75
is amplified by the amplification circuit
113
, and an electrical signal to be supplied to the main converter
20
is amplified by the amplification circuit
113
and then attenuated by the attenuation circuit
114
. Therefore, the ratio between drive currents, that is, electrical signals applied to the converters
20
and
75
, can be set correctly in accordance with a similarity ratio between the converters
20
and
75
. In particular, Where a variable resistor circuit is used as the attenuation circuit
114
, a drive current to be applied to the main converter
20
can be adjusted easily without deviating the phase.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and the range of equivalency of the claims are therefore intended to be embraced therein.
Claims
- 1. 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 a rear side thereof; 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.
- 2. The speaker apparatus of claim 1, wherein the magnetic circuit is of an external magnet type and has an annular cancellation permanent magnet for decreasing leakage magnetic flux on a rear side of an annular main permanent magnet for generating magnetic flux for driving the voice coil, and wherein the boss of the weight penetrates through a hollow portion of the cancellation permanent magnet and is fixed to a rear side of a center pole of the magnetic circuit.
Priority Claims (1)
Number |
Date |
Country |
Kind |
P2000-344214 |
Nov 2000 |
JP |
|
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
977616 |
Gottschalk |
Dec 1910 |
A |
4230907 |
Hasselbach et al. |
Oct 1980 |
A |
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