Loudspeaker

In a loudspeaker, a diaphragm is equally divided circumferentially into a plurality of regions which have the same shape with each other. Each of the divided regions is formed by a hyperbolic paraboloid. The hyperbolic paraboloid is obtained by moving a straight line connecting between two segments along these two segments. The hyperbolic paraboloid is large in strength and can suppress generation of the dividing vibration of the diaphragm.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a loudspeaker for use in, for example, an 
audio system and, in particular, to a diaphragm of the loudspeaker. 
2. Description of the Prior Art 
As shown in FIG. 18, a loudspeaker includes a cone-type diaphragm 11. At a 
base end side (small-diameter side) of the diaphragm 11, a voice coil 12 
is provided. By changing a magnetic field around the voice coil 12 
depending on a sound signal, a magnetic force between a magnet (not shown) 
and the voice coil 12 is changed so as to vibrate the diaphragm 11 forward 
and backward, that is, along a center axis of the diaphragm 11. The 
diaphragm 11 is normally made of paper and formed into a conical shape. A 
large-diameter side opening edge (outer peripheral edge) 13 of the 
diaphragm 11 is held by an elastic ring (not shown) so that the diaphragm 
11 can vibrate forward and backward. Since the vibration state of the 
diaphragm 11 controls a regenerative frequency characteristic, a 
high-frequency distortion frequency characteristic and the like, the 
performance of the loudspeaker is essentially determined by the diaphragm 
11. 
The ideal vibration is such that the diaphragm 11 makes forward and 
backward motions while maintaining its original conical shape. However, in 
practice, the diaphragm 11 presents behavior deviated from the ideal 
vibration. Recently, since the observation technique and the computer 
processing for the vibration state have been advanced, the actual 
vibration state has been largely elucidated. It has been known that, as 
shown in FIG. 19A, the diaphragm 11 may be twisted to cause corrugation of 
the large-diameter side opening edge 13, or, as shown in FIG. 19B, the 
circumference of the diaphragm 11 is corrugated to form nodes of the 
vibration while keeping axial symmetry. This behavior is called dividing 
vibration. 
The reason for the behavior is considered as follows: 
For example, immediately upon backward displacement of the diaphragm 11, 
since the large-diameter side opening edge 13 thereof tries to stay at the 
position due to inertia, it is resultantly contracted toward the center 
axis of the diaphragm 11. Thus, as shown in FIG. 20, compressive forces 
are generated at any circumferential portions of the diaphragm 11. In 
contrast with this, immediately upon forward displacement of the diaphragm 
11, tensile forces are generated at any circumferential portions of the 
diaphragm 11. 
Accordingly, as described above, the ideal behavior is not accomplished to 
thereby degrade the sound quality. The conventional loudspeaker has the 
basic problem as noted above, which thus causes the following problems: 
For ensuring sufficient sound pressures at a low-frequency region, the 
diaphragm 11, which is thick and large, is required. Thus, the diaphragm 
11 becomes heavy to increase its moment of inertia. The dividing vibration 
becomes greater as the moment of inertia becomes greater or the vibration 
frequency becomes greater (as the frequency of occurrences of crests and 
troughs on the circumference of the diaphragm 11 becomes greater). 
Eventually, the loudspeaker incorporating such a diaphragm 11 can be only 
used at the low-frequency region. 
On the other hand, for using the diaphragm 11 at a high-frequency region, 
since an influence of the dividing vibration is large, the moment of 
inertia is required to be small. Thus, the diaphragm 11, which is small in 
thickness and large in strength, is required. Even if the diaphragm 11 is 
thin, the sufficient sound pressures can be ensured at the high-frequency 
region. However, in this case, the loudspeaker incorporating such a 
diaphragm 11 can not be used at the low-frequency region, and further, it 
is necessary to use titanium, beryllium or the like, which is expensive, 
as a material of the diaphragm 11. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a 
loudspeaker which can suppress the dividing vibration and thus accomplish 
the good quality of sound. 
According to one aspect of the present invention, there is provided a 
loudspeaker comprising a diaphragm, wherein the diaphragm is formed by a 
hyperbolic paraboloid which is obtained by moving a straight line 
connecting between two segments along the two segments. 
According to another aspect of the present invention, there is provided a 
loudspeaker comprising a diaphragm which is circumferentially divided into 
a plurality of regions each having a first segment forming a peripheral 
edge thereof, wherein each of the divided regions is formed by a 
hyperbolic paraboloid which is obtained by moving a straight line 
connecting between the first segment and a second segment located inward 
of the first segment and not located in the same plane with respect to the 
first segment, along the first and second segments. 
According to another aspect of the present invention, there is provided a 
loudspeaker comprising a diaphragm which is circumferentially divided into 
a plurality of regions each having a first segment forming a peripheral 
edge thereof, wherein each of the divided regions is formed by a pair of 
hyperbolic paraboloids which are obtained by moving a straight line 
connecting between the first segment and a second segment located in a 
plane including a middle point of the first segment and a center axis of 
the diaphragm and not located in the same plane with respect to the first 
segment, from the middle point of the first segment to both ends of the 
first segment and from one end of the second segment to the other end 
thereof. 
It may be arranged that the second segment corresponds to the center axis 
of the diaphragm. 
It may be arranged that the second segment extends outward from the center 
axis of the diaphragm. 
It may be arranged that the number of the divided regions of the diaphragm 
is set to an odd number. 
The present invention covers a case wherein the diaphragm is formed by a 
portion or portions of the hyperbolic paraboloid(s). Further, in the 
present invention, the hyperbolic paraboloid includes not only a perfect 
hyperbolic paraboloid, but also such a curved surface that is approximate 
to the perfect hyperbolic paraboloid. Moreover, the word "segment" 
represents a segment of a straight line or a chord of a curved line.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Now, preferred embodiments of the present invention will be described 
hereinbelow with reference to the accompanying drawings. Throughout the 
specification and claims, the word "segment" represents a segment of a 
straight line or a chord of a curved line. 
FIG. 1 is a perspective view showing a diaphragm 2 incorporated in a 
loudspeaker according to the first preferred embodiment of the present 
invention. The diaphragm 2 does not have the conical shape as in the prior 
art, but is formed by hyperbolic paraboloids. When the diaphragm 2 is 
equally divided into four regions in a circumferential direction 
(circumferentially) thereof and S1 to S4 are assigned to the four regions, 
respectively, S1 to S4 have the same shape. A large-diameter side opening 
edge 21 has a circular shape. Accordingly, if the opening edge 21 is taken 
as a circular line (circle), a peripheral edge of each of S1 to S4 is 
formed by an arcuate segment (chord) corresponding to a quarter of the 
circle. 
Since the divided regions S1 to S4 have the same shape, a structure of S1 
will be described hereinbelow. As shown in FIG. 2A, on connecting between 
A or C and P2) are formed alternately with each other in the 
circumferential direction. Then, as shown in FIG. 3, the foregoing 
hyperbolic paraboloids are penetrated by a cylindrical member 3 whose 
center axis is the center axis L and whose radius is, for example, about a 
quarter of a radius of the circle 21. The surfaces extending from the 
circumference of the cylindrical member 3 to the circle 21 form the shape 
of the diaphragm 2 shown in FIG. 1. 
FIG. 4 is a diagram for explaining the shape of the diaphragm 2 and 
includes a sectional view of the divided region S1 as seen from the side 
of the center axis L and a top view of the whole diaphragm 2 as seen from 
above. Seeing from the side of the center axis L, a small-diameter side 
opening edge (inner peripheral edge) 22 has the shape of a mountain (abc). 
The diaphragm 2 having the foregoing shape is designed, for example, by 
computer graphics and made of paper, carbon, metal or the like. 
FIG. 5 shows the whole structure of a loudspeaker incorporating the 
foregoing diaphragm 2. In this embodiment, a new feature resides in 
structure of the diaphragm 2, and the conventional structures can be 
applied to the other portions of the loudspeaker as they are. In FIG. 5, 
numeral 4 denotes a frame, and the large-diameter side opening edge 21 is 
attached to the frame 4 at its forward end via an elastic roll edge 41. On 
the other hand, the small-diameter side opening edge 22 of the diaphragm 2 
is fixed onto the circumference of a cylindrical member 42 (corresponding 
to the foregoing cylindrical member 3). 
A voice coil 43 is wound around the circumference of the cylindrical member 
42 at its base end side. Further, a yoke 5 is provided so as to confront 
the voice coil 43. Numeral 51 denotes a magnet, 52 a center pole, 53 a 
damper and 54 a cap. The shown loudspeaker is of an inside driving type, 
wherein a magnetic field around the voice coil 43 is changed according to 
a sound signal so that a magnetic force between the voice coil 43 and the 
yoke 5 is changed to vibrate the diaphragm 2 forward and backward. 
On the hyperbolic paraboloids forming the diaphragm 2, compressive and 
tensile forces are well balanced, and the surface areas thereof are 
theoretically equal to each other on both sides thereof. Accordingly, the 
hyperbolic paraboloids are used in building constructions as providing 
very strong structures, and hence, the diaphragm 2 is reluctant to 
deformation so that the dividing vibration can be suppressed. Now, 
consideration is given to stresses which are generated upon vibration of 
the diaphragm 2. When the diaphragm 2 is forced out forward from a 
backward (retreated) position, the small-diameter side opening edge 22 of 
the diaphragm 2 is pushed via the cylindrical member 42. At this time, 
since the large-diameter side opening edge 21 tries to stay at the 
position due to inertia, the opening edge 21 is subjected to a relatively 
backward force. In this case, if the diaphragm 2 has the conventional 
conical shape, tensile stresses are generated at any portions of the 
diaphragm 2 as described before. On the other hand, in the diaphragm 2 
according to this embodiment, compressive stresses and tensile stresses 
are exerted simultaneously. 
FIG. 6 shows the state of it, wherein a half of one of the foregoing 
divided regions S1 to S4 (for example, a region from A to B in FIG. 2A) is 
illustrated. Since the surface forming the diaphragm 2 is gradually 
distorted as going inward (backward) from the arcuate segment AB, when the 
opening edge 21 is subjected to the relatively backward force, the tensile 
stresses are generated at a region of the surface near a front edge (crest 
portion) 61 while the compressive stresses are generated at a region of 
the surface near a rear edge (trough portion) 62. Specifically, as 
described above, on the whole, the crests and the troughs are arranged 
alternately in the circumferential direction on the surfaces of the 
diaphragm 2, and hence, the tensile stresses and the compressive stresses 
are generated alternately with each other. Further, since the surfaces are 
distorted, the directions of vibration are not uniform at respective 
positions. Accordingly, the deformation of the diaphragm 2 is suppressed 
so that the dividing vibration is not likely to occur. 
Further consideration is given to the case wherein, as shown in FIG. 7, the 
diaphragm 2 is cut by a plane Q orthogonal to the center axis L of the 
diaphragm 2. In case of the conventional diaphragm having the conical 
shape, distances from the peripheral edge of the diaphragm in section to 
the center axis L are equal to each other at any positions on the 
peripheral edge. Thus, as in the prior art explained with reference to 
FIG. 19B, the nodes of vibration are generated. On the other hand, in this 
embodiment, since each of the surfaces of the diaphragm 2 is distorted, 
that is, since, microscopically, the adjacent straight lines forming the 
surface are located at distorted positions relative to each other, 
distances from the peripheral edge of the diaphragm 2 in section to the 
center axis L are different from each other at the respective positions on 
the peripheral edge in section. Thus, no nodes are generated. 
As appreciated from the foregoing description, if the diaphragm 2 is formed 
by the hyperbolic paraboloids, the generation of the dividing vibration 
can be suppressed so that the good sound quality can be accomplished. 
Since the diaphragm 2 is reluctant to the generation of dividing vibration, 
even if the diaphragm 2 is thick and large for ensuring the sufficient 
sound pressures at the low-frequency region, the generation of dividing 
vibration can be suppressed even at the high-frequency region. As a 
result, the loudspeaker incorporating the diaphragm 2 can be used over the 
wide frequency band. Further, since the degree of freedom for selection of 
a material of the diaphragm 2 is enlarged, the diaphragm 2 can be produced 
with less cost as compared with the prior art. 
FIG. 8 shows a diaphragm of a loudspeaker according to the second preferred 
embodiment of the present invention. In this embodiment, the diaphragm 2 
is of a so-called flat type having no depth. Specifically, the straight 
segment P1P2 shown in FIG. 2A is raised until P1 reaches the center O of 
the circle 21, and further, the diaphragm 2 is not truncated by the 
cylindrical member 3 so that the surfaces of the diaphragm 2 extend from 
the circle 21 to the center axis L. Accordingly, the crest portions (lines 
connecting between B and P1) of the surfaces forming the diaphragm 2 exist 
in the plane including the circle 21. Although FIG. 8 shows only a quarter 
region of the diaphragm 2 with the straight lines, the other three quarter 
regions have the same structure. 
FIG. 9 shows a diaphragm of a loudspeaker according to the third preferred 
embodiment of the present invention. In the foregoing first and second 
preferred embodiments, the diaphragm 2 is equally divided into four 
regions for the formation of the hyperbolic paraboloids. However, it is 
not limited to the four regions. In this embodiment, the diaphragm 2 is 
equally divided into three regions in the circumferential direction, and 
the hyperbolic paraboloids are formed per region in the same manner as in 
the second preferred embodiment (FIG. 8). In FIG. 9, an arcuate segment AC 
is obtained by trisecting a circle 21. Also in this embodiment, regions 
connecting between A and P2 and between C and P2 correspond to the 
troughs, while regions connecting between B and P1 correspond to the 
crests. FIG. 10 shows a loudspeaker of an inside driving type 
incorporating the diaphragm 2 shown in FIG. 9. 
FIG. 11 shows a diaphragm of a loudspeaker according to the fourth 
preferred embodiment of the present invention. In this embodiment, the 
diaphragm 2 is equally divided into two regions in the circumferential 
direction, and the hyperbolic paraboloids are formed per region in the 
same manner as in the second preferred embodiment (FIG. 8). In FIG. 11, an 
arcuate segment AC is obtained by bisecting a circle 21. It is assumed 
that the diaphragm shown in FIG. 8 is called a four-division type, the 
diaphragm shown in FIG. 9 is called a three-division type, and the 
diaphragm shown in FIG. 11 is called a two-division type. When forming a 
diaphragm of an n-division type, if n is set to an odd number, the shapes 
of the surfaces arranged in a diameter direction of the diaphragm differ 
from each other so that the strength of the diaphragm is increased as 
compared with a diaphragm of an even number-division type. Further, since 
the states of distortion of the surfaces arranged in the diameter 
direction differ from each other, the resonance noise can be suppressed. 
Since the weight of the diaphragm can be reduced as a value of n is set to 
be smaller, it is preferable that the value of n is set to 10 or less. On 
the other hand, the diaphragms shown in FIGS. 8, 9 and 11 may also be used 
as being reversed. Further, as shown in FIG. 12, the hyperbolic 
paraboloids may be formed such that the straight segment P1P2 is divided 
at the ratio of 1:1/2:1:1/2 in length and a hyperbolic paraboloid is 
formed between each of the divided regions of the straight segment P1P2 
and each of quadrisected regions of the arcuate segment AB. Specifically, 
the divided region of "1" of the straight segment P1P2 is further divided 
equally into k regions, the quadrisected region of the arcuate segment AB 
is further divided equally into k regions, and the corresponding equally 
divided points are connected by straight lines so as to form a hyperbolic 
paraboloid. Similarly, the divided region of "1/2" of the straight segment 
P1P2 is further divided equally into k regions so as to form a hyperbolic 
paraboloid in the same manner. In the diaphragm thus formed, boundary 
lines between the adjacent hyperbolic paraboloids, that is, boundary lines 
indicated by circles in FIG. 12, become crests. 
FIGS. 13A to 13C show a diaphragm of a loudspeaker according to the fifth 
preferred embodiment of the present invention, wherein FIG. 13A is a 
perspective view, FIG. 13B is a side view and FIG. 13C is a plan view. In 
this embodiment, three straight lines located at positions higher (forward 
side) than a plane including a circle 21 and extending radially from the 
center axis L at 120 degrees relative to each other along a plane parallel 
to the plane including the circle 21 are given as X1, X2 and X3, and inner 
and outer ends of each of the straight lines X1, X2 and X3 are given as P1 
and P2, respectively. By moving a straight line connecting between A and 
P1 along an arcuate segment AB and along the straight segment P1P2 and 
moving a straight line connecting between C and P1 along an arcuate 
segment CB and along the straight segment P1P2, hyperbolic paraboloids are 
formed. Specifically, for example, by equally dividing AB into k regions, 
equally dividing P1P2 into k regions and connecting between the 
corresponding equally divided points by straight lines, a hyperbolic 
paraboloid is formed. In FIG. 13A, AC is a trisected arcuate segment of 
the circle 21, and B is the middle point of AC. Seeing from above, each of 
X1 to X3 and B are located on a straight line as shown in FIG. 13C. 
FIGS. 14A and 14B show a diaphragm of a loudspeaker according to the sixth 
preferred embodiment of the present invention, wherein FIG. 14A is a 
perspective view and FIG. 14B is a side view. In the fifth preferred 
embodiment, P1 and P2 of each of X1 to X3 are set at the same height 
relative to the circle 21. On the other hand, P2 may be located upward or 
downward relative to P1 so as to change a characteristic of the diaphragm. 
In the sixth preferred embodiment, as shown in FIGS. 14A and 14B, the 
outer ends P2 of X1 to X3 are set higher than the inner ends P1 in the 
diaphragm shown in FIGS. 13A to 13C. The diaphragms shown in FIGS. 13A-13C 
and 14A-14B may be used as being reversed, that is, either in forward 
orientation (shown in the figures) or in backward orientation. 
FIG. 15 shows a loudspeaker of an outside driving type incorporating the 
diaphragm 2 shown in FIGS. 13A to 13C. The diaphragm 2 is provided at one 
end of a cylindrical member 81 working as a coil bobbin. A voice coil 82 
is wound around the cylindrical member 81, and a pole piece 83 is disposed 
at the other end side of the cylindrical member 81. A magnet 84 is in the 
form of a ring surrounding the voice coil 82. Numeral 85 is a corrugated 
damper, and the diaphragm 2 is supported to a support portion 86 via the 
damper 85. The lightweight diaphragm 2 may be easily produced through 
press working. In this case, it may be arranged that the diaphragm 2 and 
the bobbin 81 are formed integral with each other using, for example, a 
titanium metal plate. 
FIG. 16 shows a diaphragm of a loudspeaker according to the seventh 
preferred embodiment of the present invention. The shapes of the 
hyperbolic paraboloids are not limited to the foregoing examples. For 
example, a conoid hyperbolic paraboloid may be formed between an arcuate 
segment (chord) and a straight line parallel thereto. FIG. 16 shows the 
diaphragm having such conoid hyperbolic paraboloids. Specifically, a 
circle (large-diameter side opening edge) 21 is equally divided into, for 
example, four regions and, using a square 7 having a common center axis 
with the circle 21, a straight line 70 is moved along a quadrisected 
arcuate segment DE of the circle 21 and along a side de of the square 7 
parallel to the arcuate segment DE so as to form a hyperbolic paraboloid 
between the arcuate segment DE of the circle 21 and the side de of the 
square 7. Similarly, hyperbolic paraboloids are formed with respect to the 
other three quarter arcuate segments of the circle 21. Also in this 
embodiment, the strength of the hyperbolic paraboloids is large and, when 
cut by a plane orthogonal to the center axis of the circle 21, distances 
from the peripheral edge of the diaphragm in section to the center axis 
are different from each other at the respective positions on the 
peripheral edge in section. Thus, the dividing vibration can be 
suppressed. 
The shape of the large-diameter side opening edge 21 of the diaphragm is 
not limited to circular, but may be polygonal, such as triangular or 
quadrilateral. In this case, for example, a small-diameter side opening 
edge may have a circular shape so as to form conoid hyperbolic paraboloids 
in a manner similar to FIG. 16. 
Relationships between sound pressures and frequencies were examined with 
respect to the conventional loudspeaker shown in FIG. 18 and the 
loudspeaker shown in FIGS. 9 and 10. The results are shown in FIGS. 17A 
and 17B, wherein the axis of ordinate represents the scale of a recorder 
and corresponds to the sound pressure although not directly representing 
dB. FIG. 17A shows the results about the conventional loudspeaker, while 
FIG. 17B shows the results about the loudspeaker shown in FIGS. 9 and 10. 
In each of the loudspeakers, carbon fiber was used as a material of a 
diaphragm. In the conventional loudspeaker, a diameter and a depth of the 
diaphragm were set to 320 mm and 65 mm, respectively. On the other hand, 
in the loudspeaker shown in FIGS. 9 and 10, a diameter of the circle 21 of 
the diaphragm was set to 320 mm while a depth of the diaphragm was set to 
55 mm. As seen from the results, the change of the sound pressures 
relative to the change of the frequencies is more gradual in the 
loudspeaker shown in FIGS. 9 and 10 as compared with the conventional 
loudspeaker so that the good sound quality can be achieved. 
As described above, according to the loudspeaker of each of the foregoing 
preferred embodiments, since the diaphragm is formed by the hyperbolic 
paraboloids, the dividing vibration can be suppressed. 
While the present invention has been described in terms of the preferred 
embodiments, the invention is not to be limited thereto, but can be 
embodied in various ways without departing from the principle of the 
invention as defined in the appended claims.