Loudspeaker

A loudspeaker has two magnets disposed directly with respect to voice coils for generating a repulsion magnetic field at the voice coils, without interposition of yoke but with mutually repulsing magnetic polarities of the magnets, and a diaphragm directly coupled at inner peripheral edge substantially to the center of outer periphery of the voice coils. Driving force is transmitted highly efficiently from the voice coils to the diaphragm, and the loudspeaker can be sufficiently minimized in the thickness and weight.

BACKGROUND OF THE INVENTION 
This invention relates to loudspeakers and, more particularly, to a 
loudspeaker made to be thin and light with a repulsion magnetic field 
utilized. 
DESCRIPTION OF RELATED ART 
For known loudspeaker of the kind referred to, there may be enumerated ones 
described in Japanese Patent Publication No. 40-25922 by S. Morita, 
Japanese Utility Model Publication No. 2-30957 by U. Kawano, and so on, in 
which known loudspeakers a spacer is employed in combination with thin 
disk-shaped or ring-shaped permanent magnets disposed on both surfaces of 
the spacer to oppose their surfaces of the same polarity, so that the 
entire arrangement can be minimized in the thickness and weight. Further, 
a report titled "An Ultralight Loudspeaker With Repulsion Magnetic Field 
Applied" by H. Kumakura et al in JAS Conference '92 Appointed Theses, 
published by Nippon K. K. Kenwood, discloses a technical matter realizing 
the light weight loudspeaker by means of the repulsion magnetic field 
utilized. 
In the loudspeaker of the kind referred to, generally, it has been demanded 
that the thinness and lightness are promoted after achieving high and 
sufficient improvements in the transmission efficiency of the driving 
force from the voice coils to the diaphragm and in the reproduced tone 
quality. At the foregoing known technical level, however, there has been 
shown no technique contributive enough for improving the driving force 
transmission efficiency from the voice coils to the diaphragm but only an 
arrangement in which the voice coils themselves or the voice coils and the 
diaphragm are mutually coupled through a transmission member interposed 
between them, so as to be the cause of a problem rendering transmission 
loss rather remarkable. Further, a supporting structure for the voice 
coils so far employed has been in the form of a so-called rolling 
mechanism, in which the voice coils cannot be supported at their center 
point, and generally the structure has involved a problem in highly 
improving the tone quality. For the field system with respect to the 
diaphragm, further, there has been employed an aspect still employing an 
outer yoke, i.e., a ring yoke, and this has been a restriction imposed on 
the thickness minimization. 
SUMMARY OF THE INVENTION 
Accordingly, a primary object of the present invention is to provide a 
loudspeaker which is capable of remarkably improving the transmission 
efficiency of the driving force from the voice coils to the diaphragm, 
effectively removing any influence of the known rolling mechanism for the 
voice coils, with any outer yoke made omittable while highly improving the 
tone quality, and sufficiently achieving the minimization in the thickness 
and weight. 
According to the present invention, this primary object can be realized by 
means of a loudspeaker in which a pair of permanent magnets are disposed 
to mutually repulse in the magnetic polarity for forming a repulsion 
magnetic field in the center of a frame, voice coils wound on a coil 
bobbin are disposed within this repulsion magnetic field, and the voice 
coils are supported with respect to the frame by a supporting means 
wherein the pair of magnets are disposed directly with respect to the 
voice coils for generating the repulsion magnetic field in a yoke-less 
manner, and a diaphragm is directly coupled at inner peripheral edge 
substantially to the center of outer periphery of the voice coils. 
With the above yoke-less arrangement, the loudspeaker of the present 
invention can be sufficiently contributive to the minimization in the 
thickness and weight, while the direct coupling of the voice coils to the 
diaphragm can remarkably reduce any drive-force transmission loss to 
remarkably improve the transmission efficiency, and the supporting of the 
voice coils at the center of the outer periphery thereof can restrain any 
influence of the rolling mechanism. 
Other objects and advantages of the present invention shall be made clear 
as the description of the invention advances with reference to preferred 
embodiments shown in accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, there is shown an embodiment of the loudspeaker according to the 
present invention, in which a loudspeaker 10 comprises a generally 
dish-shaped frame 11 having in the central part a support mound 11a bulged 
from a bottom flat part, a support step 11b made substantially at an 
intermediate position of peripheral side part, and sound holes 11c made in 
the peripheral side part around the support step 11b, which part being 
slightly sloped towards the axis of the central support mound 11a, and two 
permanent magnets 13 and 14 are stacked on the top of the mound 11a with a 
spacer 12 interposed between them. 
The magnetic 13 and 14 are formed in a disk shape and respectively 
magnetized to have opposite polarities in thickness direction, and are 
opposed to each other at mutually repulsing sides of the same polarity, 
e.g., N-pole sides, as spaced by the spacer 12 preferably of the same disk 
shape, so that a repulsion magnetic field can be provided without any yoke 
interposed between the magnets. While in this case the spacer 12 should 
preferably be prepared by such magnetic material as SS41 or the like, it 
is also possible to prepare the spacer with a non-magnetic material, and, 
when the magnets 13 and 14 are to be held in position by any other 
arrangement, the spacer may be replaced just by an air gap. On the other 
hand, the two magnets 13 and 14 should preferably be prepared by such 
anisotropic sintered magnet as a neodymium magnet. 
Voice coils 15 are disposed within the frame 11 so as to surround the 
stacked magnets 13 and 14, as wound on a coil bobbin 16 axially vibratable 
closely about outer pheripheral edge of the disk-shaped magnets 13 and 14, 
that is, to be disposed within the repulsion magnetic field generated by 
the two magnets 13 and 14. To the center of outer periphery of the voice 
coils 15 on the bobbin 16, a cone-shaped disphragm 17 is directly coupled 
at its inner peripheral edge defining a central opening, while the 
diaphragm 17 is secured at its outer peripheral edge through an edge 
damper 18 to the frame 11 at its portion adjacent to a top outer periphery 
of the frame 11. A sub-cone 19 is also directly coupled at its inner 
peripheral edge to the voice coils 15 at its part adjacent to the inner 
peripheral edge of the diaphragm 17, and a dust-preventing center cap 20 
is fitted to the center of the sub-cone 19 so as to cover the magnets 13 
and 14. 
Further, a supporting damper 21 is secured at its inner peripheral edge to 
the central part on the outer periphery of the coil bobbin 16, and at its 
outer peripheral edge to the support step 11b. 
Now, in the loudspeaker 10, as shown in FIG. 1, the voice coils 15 are 
disposed directly within the repulsion magnetic field generated by the two 
magnets 13 and 14 as shown in FIG. 1, without any yoke interposed, and the 
arrangement can be contributive to the minimization in the thickness and 
weight. Further, the direct coupling of the cone-shaped diaphragm 17 to 
the voice coils 15 is effective to reatrain any transmission loss of the 
drive force from the voice coils 15 to the diaphragm 17 to be the minimum, 
and the vibration of the diaphragm 17 can be made to faithfully rise in 
response to input signals to the voice coils. Further, since the support 
point of the voice coils 15 by the damper 21 is positioned substantially 
in the center of the voice coils 15, any influence of the rolling 
mechanism can be removed, and generally speaking the tone quality can be 
improved at a high degree. 
In another embodiment shown in FIG. 2, the sub-cone 39 is provided integral 
with the coil bobbin 36, in which event the vibration of the coil bobbin 
36 on which the voice coils 35 are directly transmitted to the sub-cone 
39, and the function of this sub-cone 39 can be further improved. 
In the embodiment of FIG. 2, substantially the same constituents as those 
in the embodiment of FIG. 1 are denoted by the same reference numbers as 
those given in FIG. 1 but with "20" added, and other constituents and 
functions than described are the same as those in the embodiment of FIG. 
1. 
In the foregoing embodiments of FIGS. 1 and 2, it is possible to improve 
low frequency range characteristics, by interposing a mechanical filter 
(not shown) between the voice coils 15 or 35 and the diaphragm 17 or 37. 
Referring next to FIG. 3, there is shown a further embodiment of the 
loudspeaker according to the present invention, in which loudspeaker 50 
the frame 51 comprises two frame halves 51A and 51B, a lower positioned 
one 51B of which is formed generally in a flat dish shape, while an upper 
positioned one 51A to be fitted to the lower half 51B is so provided that 
its outer peripheral part is disposed preferably to be substantially in a 
plane symmetry with an outer peripheral part of the lower positioned half 
51B with respect to a horizontal plane including a line Y perpendicular to 
the axial line X of the loudspeaker 50. The coil bobbin 56 on which the 
voice coils 55 are wound is formed to be elongated in the direction of the 
axial line X, and the voice coils 55 are wound in central part of the 
outer periphery of the bobbin 56, and upper and lower dampers 61A and 61B 
are secured at their inner peripheral edges respectively to each of both 
ends of the coil bobbin 56 in the axial line X. 
To the center of the outer periphery of the voice coils 55, an inner 
peripheral edge of the diaphragm 57 of, for example, a flat and honeycomb 
structure is directly secured, the flat diaphragm 57 is expanded on the 
plane including the horizontal line Y, and the outer peripheral edge of 
the diaphragm 57 is secured through an edge damper 62 held between both 
holding edges at outer peripheries of the upper and lower frame halves 51A 
and 51B, while the upper and lower dampers 61A and 61B are secured at 
their outer peripheral edges respectively to the inner peripheral edge of 
the upper frame half 51A and to the support step 51b of the lower frame 
half 51B. Further, the frame halves 51A and 51B include the sound holes 
51c made in areas adjacent to the outer periphery. 
In the present embodiment, in contrast to the foregoing embodiment of FIG. 
1 or 2 employing the cone shaped diaphragm 17, the two magnets 53 and 54, 
upper and lower dampers 61A and 61B and outer peripheral parts of the 
frame halves 51A and 51B are disposed substantially in the plane symmetry 
with respect to the flat diaphragm 57. Thus, in the present embodiment, 
the diaphragm 57 is directly coupled to the operational center point of 
the voice coils 55 and supporting system of the voice coils 55 and 
diaphragm 57 is made to be the plane symmetry with respect to the plane 
including the line Y, so that the influence of the rolling mechanism can 
be removed in a more excellent manner. 
In the embodiment of FIG. 3, substantially equivalent constituents to those 
in the embodiment of FIG. 1 are denoted by the same reference numbers as 
those used in FIG. 1 but with "40" added, and other constituents and 
functions than those referred to above are the same as those in the 
embodiment of FIG. 1. 
As shown next in FIG. 4 in contrast to the embodiment of FIG. 3, the flat 
diaphragm 77 is coupled at the inner peripheral edge through a mechanical 
filter 83 to the center of the voice coils 75, so that the low frequency 
zone characteristics can be made excellent. In this embodiment of FIG. 4, 
too, the equivalent constituents to those in the embodiment of FIG. 1 or 3 
are denoted by the same reference numbers as those used in FIG. 1 or 3 but 
with "60" or "20" added, and other constituents and functions are the same 
as those in FIG. 1 or 3. 
While in the foregoing embodiments the repulsion magnetic field has been 
disclosed to be generated by the disposition of the two disk-shaped 
magnets opposed at their repulsive pole surfaces of the same polarity with 
the spacer interposed between them, this magnetic circuit generating the 
repulsion magnetic field involves such magnetic flux distribution as 
represented by a curve G1 shown in FIG. 5 with respect to the magnetic 
circuit, where a leakage of flux cannot be said less, and it is intended 
to more improve the degree of concentration of the flux, preferably, so as 
to elevate the utilizing efficiency of the magnets. 
Accordingly, in a further embodiment of the present invention shown in FIG. 
6, the voice coils 105 are wound on a short cylindrical magnetic sleeve 
113 fixedly mounted to the central part on the outer periphery of the coil 
bobbin 106, whereby the magnetic flux distribution in the magnetic circuit 
for generating the repulsion magnetic field will be as represented by a 
curve G2, in which the flux concentration is elevated specifically in the 
flux adjacent the magnetic sleeve 113, and the utilizing efficiency of the 
magnetic force of the two magnets 103 and 104 can be elevated. In this 
case, the same operation can be achieved by forming the voice coils 
themselves or the coil bobbin with a magnetic material. 
In the foregoing embodiments of FIGS. 1 to 4, the repulsion magnetic field 
generated by the magnetic circuit of the two magnets 123 and 124 with the 
spacer 122 disposed between them will be as shown in FIG. 7, in which a 
magnetic field portion MF1 generated radially outward between both of the 
two magnets 123 and 124 will be of a higher intensity than that of other 
magnetic field portion MF2 or MF3 divided from the portion MF1 towards 
outer exposed pole surface of the magnet 123 or 124 radially inward. When 
the voice coils are wound for adaption to the radially inward magnetic 
field portions MF2 and MF3, a drive force by means of the radially outward 
magnetic field portion MF1 is not sufficiently generated in the voice 
coils, and it is desired to utilize effectively this magnetic field 
portion MF1. 
In another embodiment of the present invention shown in FIG. 8, therefore, 
the voice coils 125 wound on the coil bobbin 126 comprise three portions, 
that is, a coil portion 125b corresponding to the magnetic field portion 
MF2 of the one magnet 124, an intermediate coil portion 125a corresponding 
to the magnetic field portion MF1 between the two magnets 123 and 124, and 
a coil portion 125c corresponding to the magnetic field portion MF3 of the 
other magnet 124, and the respective coil portions 125a to 125c are made 
different in their winding direction for obtaining high drive forces with 
the respectively corresponding magnetic field portions MF1 to MF3, so that 
a clockwise drive force will be generated in the coil portions 125b and 
125c as viewed in top plan view, for example, while an anti-clockwise 
drive force will be generated in the coil portion 125a between the coil 
portions 125b and 125c. 
With this arrangement, as will be readily appreciated, the reverse 
directional magnetic field portion between the two magnets 123 and 124 can 
be effectively utilized, and a high drive force can be obtained even if 
the thickness and weight are intended to be remarkably minimized. 
According to the present invention, various design modification can be made 
within the scope of appended claims. While, for example, the magnets have 
been described as being formed in the disk shape, the one formed in a ring 
shape will allow substantially the same function to be attained.