US 3570626 A
Description (OCR text may contain errors)
United States Patent 13,570,626
 Inventors Yasunnri Mochida; [51 Int. Cl G 10k 13/00,
' lkuji Kurokawa; Kazukiyo Ishimura, 0 0 Hamamam hi, Ja  Field of Search t. 181/31, 32
21 A l. N 871 684 E22; Fii d 0 Nov: 18, 1969 [561 References CM  Patented Mar. 16, 1971 UNITED STATES PATENTS  Assignee Nippon Gakki Seizo Kabushiki Kaisha 1,292,858 1/1919 Northrop 181/32 Nakazawa-Cho, Hamamatsu-shi, Shizuoka- 3,247,925 4/1966 Warnaka 181/31 Japan 3,291,251 12/ 1 966 Zemrowski 181/31 3; Pnomy g 1966 Primary ExaminerStephen J. Tomsky 1 32: Attorney-Holman & Stern Continuation of application Ser. No. 584,825, Oct. 6, 1966, now abandoned.
I  LOUDSPEAKER WITH ASYMMETRICALLY ABSTRACT: A vibrating diaphragm having a planar shape which is an asymmetric geometric figure, the concept being improved by modifying the contour configuration of the vibrating diaphragm, for example by forming the contour of said diaphragm so that the opposite sides are not parallel or said contour has an irregular curvature.
SHAPED DIAPHRAGM 4 Claims, 19 Drawing Figs.
 U.S.Cl 181/32 PATENTED HAR 1 6 I97! SHEET 2 OF 4 PRIOR ART FIG. 6(B) PATENTEIJ HARI e |97I SHEET 3 IIF 4 FIG FIG. 9
LGUDSlPEAliiEld Wll'ilnl AYMMETRECALLY SHAPED EJKAFHRAGM This application is a continuation of our copending application, Ser. No. 584,825 filed Oct. 6, l966, now abandoned.
This invention relates to loudspeakers and more particularly to improvements in the shape of the diaphragm in loudspeakers which have a diaphragm in the form of a substantially flat plate and the term flat speaker will be employed to define a loudspeaker having a diaphragm of a substantially flat plate.
l-leretofore, a flat speaker, in general, has had a diaphragm of symmetrical planar shape, the most common shape being a rectangle. Such a shape gives rise to the undesirable occurrence of abrupt and extreme peaks and dips in the output sound pressure versus frequency characteristic curve of the loudspeaker as described fully hereinafter.
It is an object of the present invention to provide, in a flat speaker, new and improved diaphragms which do not give rise to the occurrence of the above stated peaks and dips.
Specific objects of the invention as set forth hereinafter.
According to the present invention, briefly stated, there is provided a loudspeaker having a flat-plate diaphragm wherein the diaphragm is clamped or nonflexibly supported at its periphery so that the flexural movement thereof be utilized, said loudspeaker being characterized in that the planar shape of the diaphragm is an asymmetric geometric figure. The term asymmetric geometric figure as used herein means a figure, or a planar shape, that does not have an axis of symmetry or a point of symmetry.
According to the present invention there are provided diaphragms of the above stated character which are of various shapes including figures produced by removing fractional parts from rectangles, polygons without any mutually parallel sides, closed figures of distorted curvilinear form, and closed figures of substantially elliptical or oval form having, at one or more peripheral parts thereof, reverse curvature whereby one or more concave inward depressions are formed.
The nature, principle, and details of the invention will be more clearly apparent from the following detailed description when read in conjunction with the accompanying drawings, in which like parts are designated by like reference numerals and characters.
In the drawings:
HO. HA is a planar view showing the diaphragm and the frame of a flat speaker of known type;
FlG. HE is a perspective view of a speaker provided with the diaphragm shown in H0. lA;
FlG. it: is a sectional view of the speaker provided with the diaphragm shown in FIG. llA;
MG. 2 is a planar view indicating the third-order mode of vibration of the diaphragm shown in FIG. 1A;
H6. 3 is a graphical representation indicating the sound pressure versus frequency characteristic of the diaphragm shown in lFlG. lA;
FIG. 4 is a planar view indicating wave propagations which result in standing waves;
FIG. 5 is a graphical representation indicating the frequency characteristic of the diaphragm affected by the standing waves as indicated in FIG. 4;
FIG. 6A is a planar view showing a fundamental form of a loudspeaker diaphragm according to the invention;
F 16. as is a perspective view of a speaker provided with the diaphragm shown in FIG. 6A;
FIG. 7 is a planar view indicating the third-order vibration mode of the diaphragm shown in FIG. 6A;
FlG. h is a graphical representation indicating the sound pressure versus frequency characteristic of the diaphragm shown in HG. 6A;
H68. 9 through l4, inclusive, are planar views respectively showing other embodiments of the invention and indicating their third-order vibration modes; and
H68. 25 and 16 are planar views respectively showing examples of curvilinear shape embodying the invention.
As conducive to a full understanding of the nature and utility of the present invention, the following consideration of a conventional flat speaker is first presented.
in such a loudspeaker, as shown in M65. 1(A), MB) and 1((1), there is provided a diaphragm l of rectangular shape which is supported elastically or nonelastically at its peripheral edge by a frame 2 and is driven at its central part 0, whereby an acoustical output is obtained. ln FlG. 1C, the numeral 7 shows a driver unit (magnet). A flat speaker of this type has an output sound pressure versus frequency characteristic which includes too big fluctuations (peaks and dips). Among the various causes of this characteristic, the most influential cause is the establishment of standing waves on the diaphragm. This phenomenon may be explained in two ways, the first being that regarding the third-order vibration mode appearing in the low-frequency range, and the second being that regarding higher order vibration modes appearing in the medium-frequency range.
The third-order vibration mode is affected principally by the plan shape of the diaphragm, and the mode is established in a manner to divide the plan shape into three portions. One example of this mode establishment is illustrated with nodal lines in FIG. 2. While the frequency at which the third-order mode is established differs with the mass, size, thickness, Youngs modulus, manner of support, and other factors relating tothe diaphragm, it is ordinarily in the neighborhood of 200 cycles per second (as, for example, in the case of a diaphragm of foamed polystyrene of a density of 0.03 gramme/cm., planar dimensions of 900 mm. by 600 mm., and a thickness of l 1 mm. with its periphery clamped).
At this frequency, resonance and antiresonance occur, and the effective driven mass of the diaphragm varies widely, whereby the sound radiation efficiency becomes poor. Furthermore, because of the relationship between the phases of the vibrating portions of the mode, the directivity becomes poor, that is, the radiated sound pressure differs greatly depending on the direction.
This effect is conspicuous when the planar form of the diaphragm is such that it can be divided regularly into three portions. A rectangular form can be divided into three portions in an extremely regular manner as shown in FIG. 2. At the above-mentioned frequency, a remarkably deep dip 3 appears in the output sound pressure versus frequency curve as indicated in H6. 3.
Vibration modes of higher order depend principally on the manner in which the various sides of the diaphragm periphery face each other. in the case of a rectangular diaphragm, standing waves 4, 5, and s as indicated in H6. 4 are established as a result of vibration reciprocating over the diaphragm l between the frame members. The frequencies of these standing waves are higher than those in the case of the above-mentioned third-order mode and are ordinarily above 500 c/s. in this case, also, the frequencies depend on the mass, size, thickness, Young's modulus, manner of support and other factors relating to the diaphragm.
As a result, in this case, also, the sound radiation efficiency is lowered, and the directivity also becomes poor similarly as in the aforedescribed case of the third-order vibration mode. Then, as indicated in H6. 5, big dips and peaks are produced in the curve of output sound pressure versus frequency at the above-mentioned frequencies.
The specific objects of the present invention are as follows:
i. to eliminate the occurrence of big dips and peaks in the frequency characteristic in a flat speaker of the type wherein the periphery of the diaphragm is clamped (this means not in a state of free-edge support) so that ilexural movement of the diaphragm is utilized;
2. to prevent the establishment of conspicuous standing waves at specific frequencies on the diaphragm and, at the same time, to cause the establishment of complex vibration modes (not excessively conspicuous modes, however) at various frequencies;
3. to suppress the establishment of a third-order vibration mode on the diaphragm and to cause, in an intentional and positive manner, differences in the shapes of mode portions;
4. to provide a diaphragm shape which is asymmetric, that is, a diaphragm shape which has no axis of symmetry or point of symmetry;
5. to suppress the establishment of standing waves on the diaphragm due to the reciprocation of vibration between the opposed sides of the diaphragm and to suppress the establishment of higher order vibration modes;
6. to provide a diaphragm shape conforming to distorted curves so that no parts on mutually opposite sides of the diaphragm periphery will be parallelly facing each other; and
7. to provide a diaphragm divided into two parts, a part contributing principally to vibrations of low-frequency sound and a part contributing principally to vibrations of medium and high frequency sound, in order to increase the radiation efficiency for medium and high sound.
The above stated objects have been achieved by the present invention, the nature and details of which will be apparent from the following description with respect to preferred embodiments thereof, beginning first with a consideration of suppression of the third-order mode.
Referring to FIG. 6A and 68, there is shown a loudspeaker having a diaphragm ll of quadrilateral shape produced by cutting off a right-angled triangle along its hypotenuse from one end of a rectangle, the resulting end side of the diaphragm thereby being oblique disposed. The diaphragm ii is clamped around its periphery to a frame l2 whose periphery has no thinner or reduced portions or corrugations and is driven at a point ii in the vicinity of the center of its geometric configuration.
Accordingly, the state of vibration in this case is similar to that of the conventional case in that, first, a vibration mode of the first order appears at low frequencies to become the lowest resonance frequency of this loudspeaker. Then, since the driving point is in the vicinity of the center of the diaphragm, a second-order vibration mode does not appear, whereby a dip in the characteristic curve is not evident at the frequencies thereof.
However, since the third-order vibration mode assumes a distorted shape as indicated in FIG. 7, the vibration mode is not clearly established, and particularly since the mode portions X and Y assume different shapes, resonance and antiresonance at the frequencies thereof decrease remarkably. Consequently, the frequency characteristic curve in this case, differing from that in the conventional case as indicated in FIG. 3, assumes the form shown in FIG. 8 wherein only a very small dip 3,, appears even at the frequencies corresponding to the third-order mode.
As an experiment on the diaphragm shape shown in FIG. 6, a diaphragm made of foamed polystyrene of a thickness of I 1 mm. and a density of 0.03 gramme/cm. and having a shape resulting by cutting off a 300-mm. 600-mm. right-angled triangle from a 900-mm X 600-mm. rectangle was clamped around its periphery to a frame and driven at approximately the center of its geometric figure. As a result, it was found that the dip in the characteristic curve at the frequencies corresponding to the third-order vibration mode decreased remarkably in comparison with that in the case of the conventional rectangular shape of the diaphragm.
FIGS. 9 through 14, inclusive, show respectively different embodiments of the invention of various shapes of the diaphragm l1 and positions of the driving point 0, and in each case the outline of the third-order vibration mode is indicated. More specifically, FIG. 9 shows a shape which results when a fraction is cut off from a rectangle along a curvilinear line; FIG. ill shows a quadrilateral shape produced by cutting of a triangle from a lengthwise side of a rectangle; FlG. ll shows a shape produced by cutting off a corner of a rectangle along a curvilinear line; H6. 12 shows a scalene right-angled triangle; and FIG. 13 shows a trapezoid with unequal legs.
While the above-mentioned shapes for the diaphragm ll are those resulting from deformations of a rectangle, the diaphragm shape according to the invention need not be limited thereto, of course, being selectable from a broad range of shapes as, for example, shapes resulting from deformations of parts of a square, quadrilaterals with unequal sides and/or unequal angles (although such a shape may cause some difficulty in fabrication) as shown in H6. 14, polygons in general with unequal sides and/or unequal angles, and shapes with curvilinear peripheries as will be described hereinafter.
The quadrilateral shown in FIG. 14 has no parallel opposite sides and, therefore, has the same effectiveness as the curvilinear shapes to be described hereinafter, that is, the advantageous effectiveness of eliminating the disadvantage hereinbefore described with reference to and as indicated by FIGS. 4 and 5.
In addition to the above-mentioned improvement with respect to the third-order vibration mode, the present invention provides further improvement in the medium and high frequency range where higher-order vibration modes exist.
In one example embodying the invention as illustrated in FIG. 15, a diaphragm 21 of a principally elliptical or oval shape having an inward depression 27 which is a concave part formed by a reversal of curvature of the peripheral curve and,
as a result, forming an asymmetric shape and is clamped at its entire periphery to a frame (not shown) and is driven at a point 0 in the vicinity of the center of the geometric figure.
It will be apparent from the description presented hereinbcfore with respect to various examples that it is extremely difficult for a third-order vibration mode to be clearly established in the diaphragm 21 shown in FIG. 15. It will be further ap parent that it is difficult for high-order vibration modes also to be established. The reason for this is that, since the geometric figure of this diaphragm is defined by an irregular curve and does not have mutually parallel opposite sides, standing waves as indicated in FIG. 4 are not established.
Furthermore, this geometric figure has the following advantage. When this diaphragm 2ll is driven at the driving point 0, it vibrates mostly in the part a of the diaphragm at low frequencies, while vibration modes appear in part a and part b at frequencies of medium sounds and high sounds. While the part b is remote from the driving point ll, its actual mass is small since its vibration area is small, and its periphery is clamped, whereby the efiiciency of radiation of medium and high sounds is high.
in another embodiment as shown in FIG. iii, the shape of the diaphragm has been improved on the basis of the same principle as that of the example illustrated in FIG. 15. The shape of the diaphragm shown in FIG. 16 is basically an ellipse but has been deformed with inward depressions 37 which are concave parts being formed at three parts of the peripheral curve by respective reversals of curvature. The deformation prevents all of the propagating waves on the diaphragm reflected at the periphery from gathering at certain points such as the foci of the original ellipse, thereby disturbing the establishment of clear vibration modes. This diaphragm M is fixed at its periphery to a frame (not shown) and is driven at a point 0 in the vicinity of the center of the geometric figure.
The operational functioning and effectiveness of this diaphragm 31 are similar to those of the diaphragm 21 shown in FIG. 115, it being difficult for the third-order vibration mode to be established and'also for high-order vibration modes to be established. At low frequencies, vibration occurs mostly in the part c, and with respect to medium and high frequencies, vibration occurs at remainder parts, whereby the radiation efficiency is increased.
In order to indicate still more fully the nature and utility of the present invention, the following examples of actual practice are set forth, it being understood that these examples are presented as illustrative only, and that they are not intended to limit the scope of the invention.
In one instance, fiat speakers with diaphragms of the geometric shape shown in it]. 15 and of the following dimensions were made and tested.
A 900 mm.
B 600 mm.
C 650 mm.
D from 350 to 400 mm.
in another instance, loudspeakers with diaphragms of the geometric shape shown in FIG. 16 and of the following dimensions were made and tested.
A 900 mm.
B, from 650 to700 mrn.
C from 200 to 250 mm.
D from 550 to 600 mm.
E= from 50 to 60 mm.
F= from 50 to 80 mm.
G= from 50 to 80 mm.
H 650 mm. I
In both of the above instances, satisfactory results were obtained. The above dimensions are set forth merely as examples and will, of course, differ depending on factors such as the material of the diaphragm, its thickness, and the intended lowest resonance frequency.
As described above, by the practice of the present invention, particularly conspicuous vibration modes do not appear at any certain frequencies, and big peaks and dips do not appear in the frequency characteristic curve of the diaphragm. The vibration modes are not excessively clear, that is, they appear by small degrees at various frequencies, and a large number of small peaks and dips appear in the frequency characteristic curve. Peaks and dips of suitable degree are rather desirable, particularly in loudspeakers for musical instruments (that is, they add unique tone colors to the tones).
It should be understood, of course, that the foregoing disclosure relates to only preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.
1. In a loudspeaker of the type having a frame and a substantially flat plate diaphragm, theimprovement comprising a diaphragm of planar shape having an effective peripheral configuration defining an asymmetric geometric figure, means fixedly clamping said efiective peripheral configuration to such frame, said diaphragm being of substantially elliptical shape having, in at least one peripheral part thereof, reverse curvature whereby a concave inward depression is formed, and on the basis of its length or maximum dimension of value A, the width or dimension perpendicular to said maximum dimension isof a value of approximately (650/900) A, and the concave inward depression is situated at a peripheral part thereof at a distance of approximately (600/900) A from one longitudinal end of the diaphragm and a distance of approximately from (350/900) A to (400/900) A from one longitudinal side of the diaphragm.
2. In a loudspeaker of the type having a frame and a substantially flat plate diaphragm, the improvement comprising a diaphragm of planar shape having an effective peripheral configuration defining an asymmetric geometric figure, means fixedly clamping said effective peripheral configuration to such frame, said configuration being of substantially elliptical shape having in at least one peripheral portion thereof, a concave curvilinear depression and in which on the basis of a maximum dimension of value A, the maximum dimension in a direction perpendicular to said first-mentioned maximum direction is of a value of approximately (650/900) A and said depression being located at a distance of from between (600/900) A from one end of said diaphragm adjacent one end of the maximum dimension A.
3. In a loudspeaker of the type having a frame and a substantially flat plate diaphragm, the improvement comprising a diaphragm of planar shape having an effective peripheral configuration defining an asymmetric geometric figure, means fixedly clamping said effective peripheral configuration to such frame, the planar shape being of a distorted curvilinear closed figure and said diaphragm being provided with a substantially oval shape having, in at least one peripheral part thereo