US2038401A

US2038401A - Acoustic diaphragm

Info

Publication number: US2038401A
Application number: US452856A
Authority: US
Inventors: Norman E Wunderlich
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1929-06-20
Filing date: 1930-05-16
Publication date: 1936-04-21
Anticipated expiration: 1953-04-21
Also published as: NL28784C; BE369111A; FR692281A

Description

April 21, 1936. N. E. WUNDERLICH ACOUSTIC DIAPHRAGM Original Filed May 16, 1930 Patented Apia 21,1936 I PATENT OFFICE ACOUSTIC DIAPHRAGM Norman E. Wunderlich, West Collingswood, N. 8.,

- assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application May 16, 1930, Serial No. 452,856 In Great Britain June 20, 1929 9 Claims. (Cl. 179-1155) This invention relates to diaphragms for acoustic instruments and particularly to a coil mounting and centering means for conical diaphragms as found in reproducers of the type known in the art as electrodynamic speakers.

The primary object of the invention is to provide an acoustic diaphragmof the character described, which lends itself readily to greater mass production in manufacture, thru the elimination of a plurality of part assembly steps, thereby proportionately reducing the cost of manufacture. The accuracy of the finished product is increased by the further elimination ofvpossible error in positioning and joining a plurality of parts with respect to each other so as to have a common center.

Further in accordance with the invention it is an object to simplify the general practice heretofore in the art, of separately attaching a diaphragm mounting and centering disc or spider and a cylindrical driving coil mounting, to a conical element comprising an acoustic diaphragm, or alternatively, attaching an assembled or integral unit comprising a centering disc and a cylindrical driving coil mounting, to a conical diaphragm as aforesaid.

Further in accordance with the invention, a conical acoustic diaphragm is provided with a cylindrical extension or flange for concentrically locating and supporting a diaphragm driving coil structure and a flat flexible disc is provided for supporting and centering the actuated or driven end of said diaphragm, includingthe centering of said coil, with respect to and in co-operative relation with an electro-magnetic field element, said extension and disc forming an integral part of the conical portion comprising the acoustic diaphragm.

Accordingly, the invention resides in the novel formation of an acoustic diaphragm so as to include a driving coil supporting means and a flat flexible centering means as an integral part of the diaphragm after the formation thereof from a flat sheet of material. 4

While one practical embodiment of the invention has been illustrated and described, it is to be expressly understoodhowever, that the annexed drawing forming a part of this specification, is intended for purposes of illustration only, and-is not to be construed as a definition of the limits of the invention, reference being had to the appended claims for that purpose.

Referring in detail to the annexed drawing wherein like reference characters areemployed to designate corresponding parts,

Fig. 1 is a sectional view of a frusto-conical diaphragm formed in accordance with the preferred form of the invention and assembled in co-operative relation with a fragmentary portion of a field magnet element therefor.

Fig. 2 is a fragmentary sectional plan view of a modified form of the diaphragm centering surface shown in Fig. 1, looking in the direction of the closed end portion of. the conical diaphragm.

Fig. 3 is a view similar to Fig. 2, illustrating a further modification.

Fig. 4 is a fragmentary sectional view similar in part to Fig. 1, illustrating a further modification wherein the driving coil is wound directly on an integral part of the frusto-conical diaphragm.

Referring to the drawing, an electro-dynamic reproducer or loud speaker of the conventional inner core and outer annular ring magnet type, sufliciently complete for the purpose of this invention, is illustrated in Fig. 1, wherein inner and outer pole pieces ill and l I designate the core and ring pole piece of the field magnet respectively, and which together form an annular magnetic field or air gap as indicated at l2.

As usual in-structures of this character, the core I0 is tap screw threaded at the center of its free end for the reception of a suitable screw or the like l3, whereby, in conjunction with suitable washers N, forms a stationary support for the driven end of the conical diaphragm l5, and an actuating coil structure including a mounting or form IS. The coil structure is centralized on the core II), with respect to and in vco-operative relation with the annular air'gap I2.

The opposite or base end of the conical diaphragm I5 is, as usual, mounted over an aperture I! in a baflie plate l8, or on the inner side of the front panel of a cabinet (not shown) by means of a number of arcuate sections 19, for example three, of leather, fabric or the like, having a total 4 length greater than the periphery of the base of the cone. These strips are suitably secured on the one hand to the baiiie plate l8 by means of, a'suitable annulus 20, and on the other, to the base edge of the conical diaphragm in a manner well known to those skilled in the art.

Theadiacent free ends of the arcuate flexible strips or sections l9. are permitted to overlap loosely as indicated at 2|, for example, and there-' fore arenot cemented together. This has been found to be a satisfactory and economical method of securing the base edge of the conical diaphragm.

-More particularly in accordance with the invention, a diaphragm for a reproducer structure 5 the passage therethru I plated.

mation by moulding or pressing a flat sheet of I material preferably buckram, cheesecloth or other suitable fabric, which has been damped j. with any well known sizing material, by means of heated dyes, to deform the flat sheet, of material into conical form.

In this pressing operation, however, the diaphragm is given two additional formations other than conicaL- One of these additional formations consists of a cylindrical coil structure locating and supporting cylindrical flange 22 which is formed during the single pressing operation as an integral part of the conical portion comprising the diaphragm l5, and particularly adapted in this the preferred form, for the attachment thereto of the actuating coil mounting l6 by means of a suit-- able adhesive.

The other one of said additional formations consists of a small area centrally of the diaphragm which remains flat in the said pressing operation and forms a coil centering flexible disc like element 23 disposed in a plane normal to the axis of the conical diaphragm l5, and within the aforesaid supporting flange 22.

In order that the driven end of the conical diaphragm l5 may be attached to the free end of the core ill by means of the screw I 3, it is desirable to form an aperture 24 centrally of the disc like surface 23 of suflicient size to permit of the threaded portion of the screw i3. Accordingly, the said aperture 24 may be blanked out simultaneously with the formation of the conical diaphragm IE, or, it may be formed as a secondary operation after the pressing of the conical diaphragm has been com- Referring particularly to Fig. 2, the flat flexible and imperforate centering surface 23a is modified by providing a plurality of annular corrugations 25 in the said centering surface, or alternatively as shown in Fig. -3, the surface is perforated by means of a'plurality of openings or holes 26 circumferentially disposed radially of the aperture 24 in the centering surface 23b, whereby a greater degree of flexibility is imparted to the said cen- 1 tering surface between its center point of attachment and the periphery thereof. These modified forms impart a greater freedom of longitudinal or axial movement to the diaphragm without unduly reducing the lateral stiffness of the disc, if this is found necessary or desirable.

A further modification is illustrated in Fig. 4,

wherein it will be readly seen that the cylindrical portion 22 described in connection with Fig. 1 is much more pronounced, that is to say, the cylindrical portion projects a greater distance beyond the smaller conical portion of the diaphragm i5 to provide an integral cylindrical member 220 whereon the diaphragm actuating coil 2| may bedirectly wound. This may be accomplished by placing the entire cone i5 upon a suitable mandrel and forming the coil 21 on the freeend portion of thesaid cylindrical member. Accordingly, the usual attachment of a separate cylindrical coil carrying support to a conical diaphragm of the character described is eliminated.

Further withrespect-to Fig. 4, it will also be observed that'the flexible centering surface 230 in this form is disposed within thecylindrical coil support, since the cylindrical projecting member 220 carrying the coil 21 extends inwardly beyond the free end of the inner. pole or core ID to which the centering surface is attached by means of the permit of free longitudinal washers u and I: so that the an :1

- will bedisposed within the air gap i2.

The flexible centering surface 230 is formed within the cylindrical coil support (see Fig. 4) by telescopically reversing the free end portion of the integral cylindrical extension 220 within itself in the moulding or pressing of the diaphragm ii. In telescopically reversing the free end portion of the integral cylindrical extension 220 part way within itself, the wall of the said free end portion is doubled since the wallthickness thereof will then consist of .two thicknesses of the sheet material used for moulding or pressing a conical diaphragm therefrom. This particular operation incidentally enhances the rigidity of the coil receiving portion of the said free end portion for the coil forming operation as aforesaid.

After the diaphragm moulding operation has been completed, the conical diaphragm is preferably subjected to a moisture proofing treatment such as for example with an aluminum paint or the like, thereby rendering the diaphragm substantially non-hygroscopic.

What is claimed is:

1. A unitary sound reproducing diaphragm comprising a frusto-conical surface and a cylindrical surface, the smaller base of said conical surface merging into said cylindrical surface, said cylindrical surface having a corrugated centering disc in a plane normal to the axis of said diaphragm.

2. As an article of manufacture, a frusto-conical diaphragm the apex of which merges into a cylinder having a closedend, the closed end being telescopically reversed into the cylindrical portion to provide a centering disc.

3. The invention defined in claim 2 characterized in that a voice-coil is wound upon the outer surface of the cylinder.

. secured to the small base of said diaphragm,

a corrugated imperforate coil-centering diaphragm-supporting disc of thin flexible material,

and a stationary support for a portion of said disc.

5. A sound-producing device comprising in combination, a frusto-conical diaphragm flexibly supported at its large base, an actuating coil secured to the small base of said diaphragm, a cor-' rugated coil-centering diaphragm supporting disc of thin flexible material, and astationary support for a portion of said disc, the corrugated portion of said disc having suflicient radial length 'to movement thereof without unduly reducing -the lateral stiffness of the same.

6. A sound-producing device comprising in combination, a frusto-conical diaphragm flexibly supported at its base, an actuating coil secured to said diaphragm, a coil-centering diaphragm-supporting disc of thin flexible .material provided with concentric corrugations, and a stationary support for a portion of said disc, the corrugated portion of said disc having suflieient radial length to permit of free longitudinal movement thereof without unduly reducing the lateral stiffness of the same,

'7. In a sound-producing device having a diaphragm flexibly supported at its base and an actuating coil secured thereto, a coil-centering diaphragm-supporting discof thin flexible substantially non-hygroscopic material provided with concentric corrugations, and a stationary support for a portion of said disc, the corrugated portion of said disc having sufiicient' radial'length to permit of free longitudinal movement thereof without unduly reducing the lateral stiffness of the same.

8. A sound-producing device comprising in combination, a cone diaphragm flexibly supported at its base, a magnet having a core and a polepiece, a coil support, an actuating coil carried by said support, said coil being disposed in the air gap between said core and pole-piece and said coil-support being secured to said diaphragm, a thin disc for centering said coil provided with concentric corrugations, said disc being ofthin flexible material and having a portion for receiving said coil support, and a stationary support for another portion of said disc, the corrugated portion of said disc having sufficient radial length to permit of free longitudinal movement thereof without unduly reducing the lateral stiffness of the same. A

9. A sound-producing device comprising in I combination, a cone diaphragm. flexibly supported disposed in the air-gap between said core and pole-piece and the corrugated portion of said disc having suflicient radial length to permit of free longitudinal movement thereof without unduly reducing the lateral stiffness of the same. NORMAN E. WUNDERLICH.