Acoustics – Diaphragm – Mounting or suspension means
Reexamination Certificate
1999-05-07
2001-10-23
Nappi, Robert E. (Department: 2837)
Acoustics
Diaphragm
Mounting or suspension means
C181S171000, C181S166000
Reexamination Certificate
active
06305491
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a speaker with an edge having advantageous characteristics, which is suitable for reproducing an audio signal of a large input.
2. Description of the Related Art
In recent years, a small size sound reproduction device which does not require a large space has been provided for a stereo system or a personal computer to be used at home. A speaker used for such sound reproduction device typically has a diaphragm of a small diameter (hereinafter, referred to as diaphragm diameter).
FIG. 9A
is a cross-sectional view of an exemplary structure of a conventional speaker having a small diaphragm diameter.
FIG. 9B
is an enlarged cross-sectional view illustrating an edge
9
and the vicinity thereof in FIG.
9
A. In
FIG. 9A
, an annular magnetic circuit including a center pole
2
, a magnet
3
and a top plate
4
is formed at a lower end of an annular frame
1
.
A magnetic flux of a high density is generated in an annular gap
5
formed between an outer periphery of an upper portion of the center pole
2
and an inner periphery of the top plate
4
. A voice coil bobbin
6
is retained in the gap
5
in such a way that the voice coil bobbin
6
can vibrate freely in upward and downward directions. A voice coil
10
is wound around the periphery of the voice coil bobbin
6
at a lower portion thereof. When a driving current corresponding to an audio signal is applied to the voice coil
10
, an electromagnetic force is generated in the voice coil
10
, resulting in a piston-like vibration of the voice coil bobbin
6
in the electric field generated in the gap
5
.
A diaphragm
8
is fixed at an upper end of the voice coil bobbin
6
, and a damper (also referred to as a suspension)
7
is connected in vicinity of the upper end of the voice coil bobbin
6
. The diaphragm
8
is attached to the frame
1
via the edge
9
, while the damper
7
is attached to the frame
1
directly. The diaphragm
8
is retained directly by the edge
9
and indirectly by the damper
7
, in such a manner that the diaphragm
8
is permitted to vibrate freely.
In the speaker thus structured, when a driving current proportional to the audio signal is applied to the voice coil
10
, an electromagnetic force of the voice coil
10
and a magnetic flux of the gap
5
interact with each other, thereby generating a driving force in the voice coil
10
, which in turn vibrates the voice coil
10
. As the voice coil
10
vibrates, the diaphragm
8
retained by the damper
7
and the edge
9
is vibrated in upward and downward directions, so as to output a sound from the speaker.
As the edge
9
of the speaker, the edge shown in
FIGS. 9A and 9B
is most commonly used. The edge
9
is referred to as a roll edge since its cross-sectional configuration shows a shape of a semi-circular roll, and the edge
9
is disposed at the outer periphery of and concentrically with the diaphragm
8
. As the material of the edge
9
, a cloth impregnated with resin, a urethane foam sheet, a rubber sheet orthelike can be used. The roll-shapededge
9
and the wave-shaped (also referred to as a corrugation) damper
7
constitute a supporting system of the diaphragm
8
of the speaker, assuring a large vibration amplitude of the diaphragm
8
.
However, a diameter of the diaphragm
8
in the conventional small speaker as shown in
FIG. 9A
is too small to generate a large sound pressure. In other words, in order to acquire a particular magnitude of sound pressure, the vibration amplitude of the diaphragm
8
needs to be increased in an inverse proportional manner with respect to an area of the diaphragm and the square of a frequency of audio signal.
The highest amplitude of the diaphragm is proportional to a size of the roll of the edge
9
. There is no significant difference between the size of the roll in a speaker with a small diaphragm diameter and that of the roll in a speaker with a large diaphragm diameter. Therefore, obtaining a sufficiently large amplitude in a speaker with a small diaphragm diameter is difficult, and thus a problem remains that a reproduced sound deteriorates especially in a low frequency range.
FIG. 10
is a schematic cross-sectional view illustrating a displacement of the roll structure of the edge
9
. In
FIG. 10
, a dashed line shows a state of the edge
9
where a driving current is not applied to the voice coil
10
and the diaphragm
8
is at a neutral position. In contrast, a solid line shows a state of the edge
9
where a large driving current of a low frequency is applied to the voice coil
10
and the diaphragm
8
is displaced along the Z axis in a (+) direction. As is clear from
FIG. 10
, when a large driving current of a low frequency is applied to the voice coil
10
, the edge
9
is extended to be stretched completely.
FIG. 11
illustrates a displacement of the edge
9
, measured by a laser Doppler displacement analyzer, in one cycle during which a driving current corresponding to a sound of a drum being attacked is applied to the voice coil
10
and the diaphragm
8
is vibrated at an amplitude within a range of ±10 mm along Z axis. As is clear from
FIG. 11
, while the edge
9
shows a roll shape when the diaphragm
8
is at a neutral position, the edge
9
is displaced into a straight shape and stretched when the diaphragm
8
vibrates at the amplitude of ±10 mm.
When a large driving current of a low frequency is applied to the voice coil
10
, the edge
9
is stretched, and an unusual sound is produced from the edge
9
so as to remarkably deteriorate the quality of a reproduced sound. The unusual sound is the same as a sound generated when a thin sheet of rubber, a cloth, a sheet of paper or the like Is suddenly stretched from a loose state (stretching sound).
SUMMARY OF THE INVENTION
A speaker of this invention includes a diaphragm, a frame accommodating the diaphragm and an edge attached to an outer periphery of the diaphragm as well as to an inner periphery of the frame so as to retain the diaphragm within an interior of the frame, wherein the edge has a thickness, which is smallest at substantially a central portion between the diaphragm and the frame and the vicinity thereof, and increases toward the diaphragm and the frame.
According to the present invention, the edge is formed thin at substantially a central portion thereof and thicker toward the diaphragm and the frame, i.e., an inner and outer peripheries thereof. Thus, a stiffness of the edge is low in the vicinity of the center and is high in the vicinities of the inner and outer peripheries. As a result of the low stiffness, the edge is easily deformed in the vicinity of the center, and a linearity of the displacement of the diaphragm in response to a driving current applied to a voice coil is retained, as long as a vibration amplitude of the diaphragm is kept within a particular range. In addition, when a large stretching force is applied to the edge at a high amplitude of the diaphragm, the stretching force is dispersed by the inner and outer peripheral portions of a high stiffness, thereby preventing the edge from being suddenly stretched completely and preventing a stretching sound due to such sudden stretching from being generated.
In one embodiment of the invention, the edge has a roll shaped cross-section. In other words, the present invention can be applied to the most commonly used edge in which a cross-section thereof is of a roll shape.
In one embodiment of the invention, the edge is formed of a foam material so as to have a structure in which the surface layers are dense, while the interior is coarse. In such a case, the edge is formed to have a sandwich structure in which the surface layers are dense and stiff, while the interior is coarse and light-weight, thereby enabling an acquisition of a light-weight, but thick, edge having an appropriate stiffness and viscoelasticity as a supporting system of a diaphragm. In addition, as compared to an edge made of a foam material having a uniform quality from a surface to a
Hasegawa Mitsuhiro
Iwasa Mikio
Sato Kazue
Takewa Hiroyuki
Martin Edgardo San
Matsushita Electric - Industrial Co., Ltd.
Nappi Robert E.
Ratner & Prestia
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