US2832844A

US2832844A - Speaker driver

Info

Publication number: US2832844A
Application number: US655557A
Authority: US
Inventors: Matsuoka Earl
Original assignee: LOUDSPEAKERS Inc, University of
Current assignee: LOUDSPEAKERS Inc, University of; UNIVERSITY LOUDSPEAKERS Inc
Priority date: 1957-04-29
Filing date: 1957-04-29
Publication date: 1958-04-29
Anticipated expiration: 1975-04-29

Description

April 29, 1958 E. MATSUOKA SPEAKER DRIVER 2 Sheets-Sheet 1 Filed April 29. 1957 INVENTOR.

lrroEA/Ey tates Patent SPEAKER DRIVER Earl Matsuoka, Thornwood, N. Y., assignor to University Loudspeakers, lne, White Plains, N. Y., a corporation of New York Application April 29, 1957, Serial No. 655,557

12 Claims. (Cl. 179-1155) This invention relates to loudspeakers, and more particularly to a horn driver unit having a simplified acoustic transformer or coupler utilizing radial slots.

A primary object of the invention is the provision of an improved horn type dynamic loudspeaker having a greatly expanded high frequency range; an over-all acoustic elficiency as high as 50%; high power capacity; and a low frequency range dependent principally upon the horn with which it is used. c

It is well known in the art that to obtain high efficiency over this range the acoustic impedance of the air in front of the diaphragm must be matched with the mechanical impedance of the diaphragm. An impedance matching device or acoustic coupler or transformer is ordinarily used between the diaphragm andthe throat of the horn. This consists basically of an extremely narrow chamber next to the diaphragm in which the latter moves, and an arrangement of ducts leading from this chamber to the throat of the horn. These ducts are designed to be substantially uniform in aggregate, cross-section, from the air chamber to the throat. There is a theoretical limit upon the maximum distance from any point on the diaphragm to the.nearest duct opening, which is that it must not exceed one-quarter wave length of the highest sound wave which it is desired to reproduce efiiciently.

Mostduct arrangements in common use utilize segments of annular slots. The use of one slot imposes the limitation on the size of the diaphragm described above, which in turn limits power capacity. Two concentric slots require a plurality of separate, concentrically assembled mechanical parts, which are less economical than the structure of the instant invention.

An acoustically preferred arrangement of ducts for use with a relatively large diaphragm is a plurality of radial slots, since such slots can communicate with every portion: of the surface. The concave rather than the convex side of a non-planar diaphragm should be juxtaposed to such ducts in order that the mean length of path from any point on the diaphragm to the horn throat may be substantially uniform.

, In the past the fabrication of such radial slots has required the individual machining of a large number of deep, narrow grooves and the assembly of the member containing these grooves in accurate alignment with other machined pieces.

It is a second primary object of this invention to provide an acoustic coupler, adapted to be economically 'die cast or molded in one piece without machining any grooves, which eliminates limitations on the upper frequency range which previously were intrinsic in the use of annular slots.

For use in dusty locations, especially where magnetic particles are present, it is essential that the magnetic air gap be sealed from the horn throat where such particles can enter. In devices constructed according to the prior art in which radial slots were juxtaposed to the concave side of a diaphragm, it was possible for magnetic and 2 a other dirt to be attracted through the horn and throat and into the air gap.

It is a third primary object of this invention to provide a dust excluding assembly.

Another object of this invention is to provide an an nular seat for the diaphragm asvan integral part of the acoustic coupler.

Another object is to provide means for centering the diaphragm driving coil in the magnetic air gap as an integral part of the acoustic coupler.

Other objects and features of the invention will appear when the following description is considered in connection with the annexed drawings, in which:

Fig. 1 is a front elevational view of the loudspeaker of this invention;

Fig. 2 is a vertical, cross-sectional view of the loudspeaker of Fig. l, the section being taken on the lines. 2-2 of Fig. 1;

Fig. 3 is an enlarged detail view in cross-section of a portion of Fig. 2, showing the upper part of the dia' phragm and the surrounding elements;

Fig. 4 is an enlarged, partial front elevational view of the acoustic coupler shown in the sectional view of Fig. 2;-

Fig. 5 is a horizontal, cross-sectional view of the acoustic coupler shown in Fig. 4, taken on the lines 55;'

Fig. 6 is an enlarged rear elevational view of the acoustic coupler shown in Figs. 1, 2, 4, and 5.

Referring to the drawings, particularly Fig. 2, the speaker driver unit comprises the magnet 10, the yoke 11, the inner circular pole piece 15, the outer annular pole piece 16, the arc-shaped, nonmagnetic member 17, which disposes the inner pole piece with respect to the outerpole piece and establishes the air gap 18 (see Fig. 3), an acoustic coupler 22, a diaphragm 24, and an outer housing 14.

Referring to Fig. 3, the diaphgram, generally indicated at 24, is shown as having a substantially cylindrical portion 28 extending from the periphery of the convex side, and a generally fiat, radially extending rim portion 29. The latter is affixed to a shelf 23 on the acoustic coupler 22. Pressure of'the shelf 23 on the diaphragm rim 29 is assured by relieving the'diaphragm-rim contacting surface at an angle 20, as indicated in Fig. 5. This insures a tight, acousticalseal. shown. It may be seen that the acoustic coupler is'so contoured as to afford uniformly spaced relationship to the diaphragm, radially inward of the edge of the shelf 23. The diaphragm assembly includes the voice coil form 21 and the voice coil 27 aifixed to the inside surface of the cylindrical portion 28. One or more beads as at 25 may be formed on the diaphragm for stiffening purposes.

The acoustic coupler 22 is shown separately in Figs. 4, 5, and 6. A plurality of slots 36 is formed between the solid portions 37. These radial slots provide acoustic communication between the dome side 30 and the frustum" of the cone 35. The coupler has a generally flat annular portion 22. The portions 42 of the slots 36 disposed generally in the plane of this portion 22 may be considered tobe apertures in this portion. It may be seen, that, first, these apertures are so arranged as to provide. no more than a predetermined spacing between any;

point in the air chamber juxtaposed to the diaphragm,

such as the point 40, and the edge of the nearest slot 36," and, second, the channels leading outwardly from these slots are so shaped as to have a predetermined taper from, the diaphragm side to the throat side,.which in this em-.

bodiment has zero value, i. e., the channels are of uniform cross-section. On the annular portion 22 surrounding the f dome 30, there may be seen the shelf 23 onwhich thediaphragm 24 seats, the oflfset annulus 33 for clearing-the rim of the diaphragm, and the annular step 34 for clear- A resilient gasket 2a is ing the cylindrical step 28 in the diaphragm and forming thereby a narrow acoustic chamber between the dome 30 and the bowl portion of the diaphragm. It may be seen that the area of the diaphragm which is actually used for driving the air in the throat, includes the rim portion 29. The conical surface 38 on the acoustic coupler 22 is so shaped as to fit within a corresponding conical seat in the housing 14.

The voice coil leads are brought out on opposite sides of the voice coil 27 and connected to terminals afiixed to one of the outer housing portions in a manner well known in the art. A projection 39 is formed integrally on the conical side of the coupler. This fits into a corresponding depression in the housing 14 in order to orient the coupler in the housing. Any such irregular portion may be arranged for mating with a conjugal portion. This is used for so phasing the leads of the voice coil that they will be the same in every unit, relative to the outside terminals. This is necessary when connecting a plurality of loudspeakers in one array in order to avoid sound cancellation effects.

The invention has been described as embodied in a loudspeaker, though it is to be understood that the same construction is usable as a sound pickup device.

The drawings and description are to be taken generally as illustrative rather than restrictive on the broad in vention. Various changes may be made in manufacture, such as different locations of the casting parting surfaces, and the like.

In the claims the term transducer is used to indicate a sound-translating device, usable either as loudspeaker or microphone.

I claim:

1. A transducer comprising a diaphragm with a bowlshaped portion having a convex side, a substantially cylindrical portion extending from the periphery of said convex side, a generally fiat rim extending radially therefrom, a voice coil form ailixed to the inner surface of said cylindrical portion, and a voice coil mounted on said form, a magnetic system having an air gap associated with said voice coil, and a housing having a throat for conducting sound; a mechanical acoustic body having a base from which a fluted conoidal front portion extends and having a generally flat annular portion adjoining the base of said conoidal portion, the rear surface of said body having a central portion with a convex shape similar to that of the bowl-shaped portion of the diaphragm, and flat annular means cooperating with said annular portion, supporting the rim, defining a narrow acoustic chamber between the diaphragm and the body, the surface of said conoidal portion having a plurality of ridges defining therebetween an equal number of radial slots, each slot extending longitudinally through the conoid and having formed contiguously therewith an aperture bounded by the walls of the slot and by a portion of said generally flat annular portion; said slots and apertures forming channels, said channels cooperating with the wall of the sound-conducting throat in said housing to form a plurality of sound-conducting ducts having predetermined aggregate crosssectional area relationships and communicating between closely spaced portions of the diaphragm and the irustum of said conoidal portion; said voice coil disposed on the side of the diaphragm opposite to said throat in the housing to seal said air gap against the entry of contaminating matter.

2. A transducer as described in claim 1, characterized by a concentric periphery on said magnetic system and centering means therefor comprising said cylindrical portion on the rear side of said diaphragm, said cylindrical portion being concentric with the axis of said diaphragm.

3. A transducer as described in claim 1, characterized by an outer housing and means for making connections between said voice coil and external terminals comprising a keying protrusion and aconjugal depression for de- 4 termining the angular position of said mechanical acoustic body relative to said outer housing.

4. A transducer as described in claim 1, characterized by the aggregate area of said apertures being a predetermined proportion of the area of the bowl shaped portion of said diaphragm, and the aggregate area of said slots adjacent to the apertures being similar thereto and having a predetermined rate of flare from the apertures to the frusturn of said conoidal portion.

5. A transducer as described in claim 1, characterized by the radial dimension of each slot being much greater than the peripheral dimension.

6. A transducer comprising a diaphragm with a bowlshaped portion having a convex side, a substantially cylindrical portion extending from the periphery of said convex side, a generally flat rim, a voice coil form aflixed to the inner surface of said cylindrical portion, a voice coil on said form; a magnetic system associated with said voice coil; a mechanical acoustic body having a base from which a fluted conoidal front portion extends and a generally fiat annular portion adjoining said base, the rear surface of said body having a central portion with a convex shape similar to that of the bowl-shaped portion of said diaphragm and fiat annular means cooperating with said flat annular portion, for supporting said rim, delining a narrow acoustic chamber between said diaphragm and said body, the surface of said conoidal portion having a plurality of ridges defining therebetween an equal number of radial slots, each slot extending longitudinally through said conoidal portion and having formed contiguously therewith an aperture bounded by the walls of said slot and by a portion of said generally fiat annular portion, forming a plurality of sound ducts communicating between closely-spaced portions of said diaphragm and the frustum of said conoidal portion and wherein the voice coil is aifixed to said diaphragm on the side thereof opposite to said conoidal portion said voice coil and magnetic system sealed against the entry of contaminating matter through the slots.

7. A mechanical acoustic body having a base from which a fluted conoidal front portion extends and a generally flat annular portion adjoining said base, said conoidal portion having a rear surface, the surface of the conoidal portion having a plurality of longitudinal ridges and an equal number of radial slots formed therebetween, each slot having formed contiguously therewith an aperture bounded by the walls of the slot and by a portion of said generally flat annular portion, said rear surface having a central convex portion opposite to the base of the conoidal portion and a generally flat annular surface surrounding said convex portion.

8. A mechanical acoustic body as described in claim 7, characterized by an annular ofl-set on said rear surface surrounding said flat portion with a cylindrical surface concentric 'with the axis of said convex portion.

9. A transducer comprising a diaphragm with a. bowlshaped portion symmetrical about a central axis, said bowl-shaped portion having a convex side and a concave side, a substantially cylindrical portion extending from the periphery of the convex side of said diaphragm, a generally flat annular rim extending therefrom, a voice coil form affixed to the inner surface of said cylindrical portion, and a voice coil on said form; a magnetic system having an annular air gap associated with said voice coil; and a housing having a throat disposed on the concave side of the diaphragm for conducting sound to a horn whereby the diaphragm is interposed between the horn and the magnetic air gap and thus seals said air gap against the entry of contaminating matter; a unitary mechanical acoustic body formed with a convex rear surface having substantially the same radius of curvature as that of said diaphragm, a substantially flat annular portion formed integrally therewith, and a concentric annular cylindrical flange extending therefrom, said con.- vex portion cooperating with said bowl-shaped portion of said diaphragm to form a narrow acoustic chamber, the diaphragm rim aligned by said flat annular portion; said cylindrical portion of the diaphragm spaced from a cylindrical portion of said magnetic system to dispose it concentrically around said voice coil; said body having a plurality of radial apertures extending longitudinally from said acoustic chamber through at least part of the housing throat, said body and said housing cooperating to define a plurality of radial slots having predetermined aggregate cross-sectional area relationships which communicate between closely spaced portions of said dia phragm and said throat.

10. A transducer comprising a diaphragm with a bowlshaped portion having a convex side and a concave side, a substantially cylindrical portion extending from the periphery of the convex side of said diaphragm, a generally fiat annular rim extending therefrom, a voice coil form affixed to the inside surface of said cylindrical portion, and a voice coil form on said form; a magnetic system having an annular air gap associated with the voice coil; and a housing having a throat disposed on the concave side of the diaphragm for conducting sound to a horn said diaphragm interposed between the horn and the magnetic air gap sealing the air gap against the entry of contaminating matter; a unitary, mechanical acoustic body formed with a convex rear surface having substantially the same radius of curvature as that of said diaphragm and a substantially flat annular portion formed integrally therewith, said convex portion cooperating with said bowl-shaped portion of said diaphragm to form a narrow, acoustic chamber, the diaphragm rim aligned by said annular portion; said body having a plurality of radial apertures extending longitudinally from said acoustic chamber through at least part of the housing throat, said body and said housing cooperating to define a plurality of radial slots having predetermined aggregate cross-sectional area relationships which communicate between closely spaced portions of said diaphragm and said throat.

11. A transducer comprising a diaphragm with a bowlshaped portion having a convex side and a concave side, a substantially cylindrical portion extending from the periphery of the convex side of said diaphragm, a generally fiat annular rim extending therefrom, a voice coil form aiu'xed to the inner surface of the cylindrical portion, and a voice coil on said form; a magnetic system having an annular air gap associated with said voice coil; and a housing having a throat disposed on the concave side of the diaphragm for conducting sound to a horn said diaphragm interposed between said throat and said magnetic air gap sealing said air gap against the entry of contaminating matter; a unitary mechanical acoustic body formed with a convex rear surface having substantially the same radius of curvature as that of said diaphragm and an integral annular supporting portion therefor, defining a narrow acoustic chamber between said diaphragm and said body; said body having a plurality of radial apertures extending longitudinally from said acoustic chamber through at least part of the housing throat, said body and said housing cooperating to define a plurality of radial slots having predetermined aggregate cross-sectional area relationships which communicate between closely spaced portions of said diaphragm and said throat.

12. A diaphragm as described in claim 11, characterized by at least one concentric bead in said bowl-shaped portion.

References Cited in the file of this patent UNITED STATES PATENTS 1,707,544 Thuras Apr. 2, 1929