US3484730A - Tunable high frequency electrodynamic driver - Google Patents

Description

Dec. 16, 1969 J. F. MCCORMICK 3,484,730

TUNABLE HIGH FREQUENCY ELECTRODYNAMIC DRIVER Filed March 7, 1968 2 Sheets-Sheet 1 INVENTOR. Josfifiv/ I. Ma tam/wk MJM Age/v7 Dec. 16, 1969 .J F. M CORMICK 3,484,730

TUNABLE HIGH FREQUENCY ELECTRODYNAMIC DRIVER Filed March 7, 1968 2 SheetsSheet 2 I v 5 '4 I INVENTOR. J056PH i Ma (@fiM/CK BY 4;; d gfg United States Patent 3,484,730 TUNABLE HIGH FREQUENCY ELECTRO- DYNAMIC DRIVER Joseph F. McCormick, Hingham, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Mar. 7, 1968, Ser. No. 711,383 Int. Cl. HOlf 7/08; H04r 9/00, 9/06 U.S. Cl. 335222 Claims ABSTRACT OF THE DISCLOSURE An electrodynamie driver having a cylindrical movable coil assembly of low mass radially supported by several equiangularly-spaced spring rods gripped by adjustable split bushings releasably clamped by the rigid support portion of the driver assembly.

BACKGROUND OF THE INVENTION This invention pertains to the art of electrodynamic drivers.

SUMMARY OF THE INVENTION The invention concerns suspending the moving coil assembly on several radial pring rods and split bushings on each spring rod adjustable to establish the spring rod length for the desired tuning and matching.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of an electrodynamic driver, exclusive of holder and magnets;

FIG. 2 is a section taken on line 22 of FIG. 1, wherein part of the ring is broken away, and

FIG. 3 is a sectional view on an enlarged scale taken on line 3-3 of FIG. 1.

Similar numerals refer to similar parts throughout the several views.

The disclosed embodiment of the invention includes a circular rigid support plate 10 having a central bore 12. The plate 10 is formed with a circular recess 14 in one face. The bottom of the recess is formed with a uniworm width circular channel 16 at the perimeter of the recess. The smaller diameter wall 18 of the recess is parallel to the axis of the bore. A ring 20 of lesser width than the width of channel 16 is seated against the bottom of the channel 16 and against the smaller diameter wall 18 and is secured in place by press fit. A companion ring 22 of essentially the same dimensions as the ring 20 is secured coaxially to ring 20 in face-to-face relationship by means of eight machine screws 24. The 0pposed faces of the rings are formed with matched V-shaped radial grooves 26 spaced ninety degrees apart around the rings. Two machine screws 24 bracket each matched pair of grooves. Two radial grooves 28 bracket a pair of the machine screws and serve as passageways for connecting leads 30.

A moving coil assembly 32 is adjustably supported by the rings 20 and 22 for axial oscillation. The coil assembly includes a thin-walled coil form 34 supporting a helically wound conductor 36. A spider 3 8 having a circular rim 40 of approximately the same outside diameter as the coil form is reduced in diameter at one end and press fitted into the coil form. The spider has four legs 42 that merge into axial junction 44 that is threaded axially. Four thin spring rods 46 are secured in coplanar relationship by being pressed into the legs 42 of the spider and project radially outward of the spider by equal amounts. The distance from top-to-top of diametrically aligned rods is slightly less than the diameter of the recess 14- in plate 10. A split bushing 48, square in cross- 3,484,730 Patented Dec. 16, 1969 p CC section, and wherein the split is a cut through one edge. and about 25% longer than the width of the rings, is mounted on each of the projections. The split bushings are nested in the V-shaped grooves with the cut in the bushing between the rings to permit clamping. Each bushing is clamped and unclamped by the corresponding pair of bracketing screws. Conducting leads 30 that extend through grooves 28 connected to the ends, not shown, of the helical coil 36 and are cemented to the rim of the spider. The other ends of leads 30 are connected to posts 50 that are secured in counterbores 52 in the plate.

The spacing between the outer perimeter of the rings and the circular wall of the recess is approximately equal to the spacing between the inner perimeter of the rings and the spider rim. The bushings 48 may be provided with markings to facilitate adjustment of the four bushings for a desired frequency response of the moving coil assembly. When the clamping screws are loosened a thin tool can be used to adjust each bushing radially.

One end of the helical coil is approximately coplanar with the recessed face of plate 10. Any constant field magnet means 54 conventional for interaction with driver coils is secured against the face of the plate 10 that is recessed. The magnets are sandwiched between the plate 10 and a holder 62.

A rod, not shown, is threaded into the center of the spider for connection to a speaker cone, a low mass valve means of a hydroacoustic amplifier, or other similar device.

This invention provides an adjustable low mass high modulus, high spring rate assembly that permits matching and tuning. The spring rate and thus the natural frequency of the assembly are tunable by adjustment of the split bushings.

It will be understood that various changes in details, materials, and arrangements of parts (and steps), which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

Iclaim:

1. An electrodynamic driver comprising a hollow circular cylindrical coil form carrying a helically wound conductor on its outer surface,

a circular member affixed coaxially to one end of said coil form,

a plurality of coplanar thin spring rods secured to said circular member to extend radially outward therefrom and spaced equiangularly about the axis coil form and circular member,

a split bushing carried by each spring rod and adjustable along the spring rod, and

means for clamping each bushing into gripping engagement with the respective spring rod and at a selected position along the rod, and operable to selectively unclamp each bushing to permit independent adjustment of each bushing along the respective spring rod, for suspending said coil form and circular member with equal lengths of spring rod between the coil form and the split bushings.

2. An electrodynamic driver as defined in claim 1,

wherein said circular member includes an integral spider of several equiangular spaced radial legs extending from the circular portion to an axial junction of the legs.

3. An electrodynamic driver as defined in claim 2,

wherein said radial legs number four and said spring rods number four and said spring rods are aligned with and are seated in said radial legs.

4. An electrodynamic driver as defined in claim 3, means formed with a circular step onwhich one of wherein said rings is press fitted. 7

said split bushings are essentially square in cross-section and the split is radial and extends through one References Cited of the four edges, 5 UNITED STATES PATENTS said means for clam in includes two rin s of e ual inside and outside di ameters and whici has s ub- 2221068 11/1940 Alons' stantially less radial thickness than the length f 2263819 11/1941 Ray 335 222 the bushings, each ring having four radial equiangu- 2556816 6/1951 Lukacs 335-222 larly spaced V-shaped grooves for seating the 'bushm G. HARRIS, Primary Examiner ings, and four pairs of clamping screws coupling the two rings, each pair of clamping screws bracketing U.S. C1.X.R. aligned grooves in the two rings. 179-.1l5.5

5. An electrodynamic driver as defined in claim 4,

further including 7 15

Images