US1842770A - Loud speaker - Google Patents

Description

Jan. 26, 1932. R, E, THOMPSON 1,842,770

LOUD SPEAKER Filed Aug. 22. 1930 ATTORN EYS Patented Jan. 26, 1932 PATENT OFFICE ROY E. THOMPSON, OF NYACK, NEW YORK LOUD SPEAKER Application inea August 22, 1930. serial No. 477,089.

This invention relates to electrodynamic sound reproducing elements of the loud speaker7 variety adapted to-convert relatively largeamou-Iits oftelectrical into acoustical en- 8 erg-y.v

primary object of the invention is to provide-a sound reproducingl element of the type specied wherein the diaphragm is caused to vibrate asa unit, piston fashion', substantially 'y free from flexure. at all acoustical frequencies and` amplitudesv of vibration as a result of its mode of actuation rather than toany inherent stiffness ofthe diaphragm. material. M lit has been, recognized that with the usual I* methods of loud speaker operationv wherein the diaphragm is supported` for vibratile actuation at one point or portionV only, the diaphragmis subject during vibration to flcxure "in varying degree throughout its radial extent dependent upon the-frequency and amplituderof vibration, and is accordingly characterizedf by vibration of individual portions thereofi withA respect to other portions.

The object of this invention is accomplished bytheprovision of a sound reproducer of the so-call'e'd dynamic type, having a diaphragm which is maintained` in a uniformly stretched conditionv during the application of the vibrational sound producing forces. Means are provided. whereby these sound producing forces cause the diaphragm to vibrate as a whole substantiall without'flexure, there being1 obtained' there y virtually complete freedom of vibrationof'individual portions ofthei diaphragm with respect `to other portions resulting in vibrational patterns.

The above described diaphragm operation is obtained by the provision of a pair of actuv ating coils bearingy the signal or sound-producing currents, these coils being situated in uniform magnetic fields and attached to the diaphragm, oneat the outer periphery and another knear the center or apex. The diaphragm is `maintained in a uniformly stretchedy condition by the application of steady, .biasing currents tothe actuating coils, the relative directions of the biasing currents being such asfto fonce-theV coils apart axially thereby maintaining the diaphragm at alll wl timesunder-continuous tension. The signal- A feature of the invention consists in the provision of a circuit arrangement for applying the biasing and signaling current to the actuating coils in the manner stated.

Theinvention will be more clearly understood from the following detailed description and reference to the drawings of which:

Figure 1 illustrates in front elevation a cone type sound reproducer in accordance with the present invention.

Figure 2 illustrates a section along'the line 2--2 of Figure 1; and

Figure 3 is a diagram of a wiring arrangement for applying the biasing and signaling currents to the actuating coils affixed to the diaphragm.

Like elements are designated in the several views by the same numbers.

The sound reproducer, or'loud speaker., illustrated in Figures 1 and 2 comprises a diaphragm 10in the form of a conical frustum composed of a; light rvibratile material such as stiff paper, an aluminum alloy or the like. Cylindrical flanges 11 and 12are provided respectivey at thelarger base, or outer periphery, of the cone and" at the smaller base, near the apex. The outer circumference or periphery, is attached to" a supporting ring 18 by means of light flexible supports 14 of soft leather or other material having little or no stiffness, which are fastened to the dia.- phragm by eyelets and to the ringby screws. The ring 13 is mounted in positionupon-a suitable rigid non-magnetic supporting crossmember 14, which may be attachedftoa stand or, if desired, to awall;

An annular electromagnet 16 including an iron or steelcore 17 of U-shaped'cross section, is afxedto the supporting member 15.

The magnet core is provided with circular opposed pole pieces 18 and 19 and is magn netized by steady direct current supplied over leads 21 and 22 to the toroidal magnetizing coil 20. A second electromagnet 23 similar to the first is attached to the central portion oi the supporting member 15, this second magnet comprising an iron cup-shaped core member 2a, provided with a circular pole piece 25 which is attached to the outer circumference of the cup-shaped member. A central pole piece 26 projects from the center of the cup-shaped member, and the face of this pele piece is opposite that of pole piece 25. A toroidal magnet coil 27 serves to polarize the magnet thru the medium of direct current supplied thereto over leads 28 and 29.

Permanent magnets having no magnetizing coils could be used in place of the electromagnets, but the operation is more satisfactory with the use of the electromagnets due to the increased magnetic action obtainable. The cylindrical flanges 11 and 12 of the diaphragm extend within the annular spaces between the opposed pole pieces of magnets 16 and 23 respectively and are symmetrically located with respect to the faces thereof. Signal current coils 30 and 31 for actuating the diaphragm are wound about the langes 11 and 12 respectively, the coils terminating in the pairs of leads 32-33 and 3%-35 for applying the signaling and biasing currents thereto.

For prop-er operation of the sound reproduring element, the relative directions of current flow for the polarizing currents in the magnet coils 2G and 27 as well as 'for the biasing and signaling currents in the actua- ting coils 30 and 31 must be correct. Fig. 3 shows a combination whereby the correct result is obtained together with a suitable circuit arrangement for simultaneously applying the biasing and signaling current in proper relative directions to the actuating coils. In Fig. 3 the electromagnets 2O and 27 are energized' by means not shown in such manner as to make corresponding pole pieces of each magnet of like polarity as indicated.

The actuating coils 30 and 31 are bot-h Y wound in the same sense i. e. in accordance With a left hand spiral, and are serially connected in this manner between the terminals of the secondary winding of an input transformer 36. With such connection it will be apparent that for signaling waves impressed upon the primary winding of the input transformer currents will be set up in a series-aiding sense in the actuating windings 30 and 31 such as to operate them in unison in the same direction axially and thereby to vibrate the diaphragm 10 as a unit.

In order to prevent flexure of the diaphragm vduring such vibration steady biasing currents are applied to the actuating coils in a parallel opposed sense such that the coils are at all times urged apart axially to maintain the diaphragm under continuous tension. ln the specific arrangement of Fig. 3 the biasing currents are supplied from a battery 40 having its negative terminal connected to the junction between the windings 30 and 31 and its positive terminal connected to the variable contact 41 of a potentiometer 39, the fixed resistance of which is connected to opposite terminals of the secondary transformer winding thru choke coils 37 and 3S respectively, the latterl offering a high impedance to the entrance of signaling currents into the shunt path. The directions or' current liow for the biasing currents are correct 'for maintaining the diaphragm under tension.

In the operation of the device the superposition of the liuctuating signaling currents upon the steady biasing currents will at each instant causethe resultant current in one actuating coil to decrease by the same amount that it is increased in the other actuating coil. This correspondingly decreases the force on the one coil urging it axially away from the other and at thel same time increases by the same amount the force on the second coil urging it axially away from the first. There results therefore an unbalanced component of force which operates to move the diaphragm bodily in the direction of the unbalanced force component while it is still maintained under tension by the balanced components of the biasing currents which steadily urge the actuating coils apart.

The design of magnets 20 and 23 should of course be such that normally equal biasing currents in windingsv 30 and 31 will cause each coil to be acted upon by thesame force. The potentiometer 39 is provided, however, in order to compensate for slight discrepancies in this respect as well to adjust the axial position of the diaphragm with reference to the magnet.

Adjustment of the sliding contact 41 in one direction or the other from the median position will increase the biasing current in one vibrating coil and decrease it in the other; in this Way varying oppositely the magnitudes of the electromagnetic forces acting upon the respective coils; This will produce a resultant axial shift of the diaphragm as a whole and thus provides a means of' properly centering the same.

What is claimed is:

1. A sound reproducer comprising a diaphragm, a. pair of coil windings attached to said diaphragm, means for producing a uniform magnetic field around each of said windings, means for impressing sound producing electric waves upon said coils in an additive sense and means for impressing uniform direct current upon said windings in an opposing sense.

2. A sound reproducer comprising a conical shaped diaphragm, a signal current coil attached at the outer circumference of said diaphragm, a signal current coil attached at the inner circumference `of said diaphragm, a uniform magnetic field enveloping said outer coil and a uniform magnetic field enveloping said inner coil, said signal current coils having applied thereto direct biasing currents so polarized with respect to each other and to the polarity of the two magnetic fields that said coils are urged in opposite axial directions whereby said diaphragm is maintained under continuous tensions.

3. A sound reproducer comprising a conical shaped diaphragm, a signal current coil attached at thev outer circumference of said diaphragm, a signal current coil attached at the inner circumference of said diaphragm, a uniform magnetic field enveloping said outer coil and a uniform magnetic field enveloping said inner coil, said signal current coils having applied thereto direct biasing cur rents so polarized with respect to each other and to the polarity of the two magnetic fields that said coils are urged in opposite axial directions whereby said diaphragm is maintained under continuous tensions, and means for simultaneously applying signaling currents to said coils such that they are actuated in the same axial directions thereby whereby said diaphragm is vibrated bodily substantially without flexure in accordance with said signaling currents.

4:. A sound reproducer comprising a diaf phragm in the form of a frustrum of a cone,

said frustrum having an axially extending cylindrical flange affixed at each base, a sound-current coil wound on each flange, a magnet located at each flange, each of said magnets having a circular pole-piece on each side of the associated coil whereby each of said coils is located in an annular magnetic field, said diaphragm being supported in position by flexible means, means for impressing upon said coils direct biasing currents so polarized with respect to each other and to the polarity of said magnets that said coils are repelled from each other in an axial direction thereby maintaining said diaphragm under continuous tension, and means for impressing electric signaling waves upon said coils such that they are simultaneously actuated in the same axial direction whereby said diaphragm is vibrated bodily without flexure.

5. A sound reproducer comprising a diaphragm, a pair of coils and means for producing a pair of uniform magnetic fields, one of said coils being att-ached to said. diaphragm around the outer circumference and Within one of said fields, the other of said coils being attached to said diaphragm around the center and being located within the other of said fields, means Vfor causing uniform direct current'to pass through said coils in such a manner as to urge said coils in opposite directions,

and means for causing alternating currents corresponding to soundwavestopass through saidcoils such that they cooperate in lmoving said diaphragm lin `the same direction.

=6. A sound'reproducer according :to claim -5 `in which the means for ycausing lthe altervDating currents to cooperate in Apassing' 'through said coils a series connection of said vcoils with'the alternating current source, andthe means for causingthesaid direct curpass through said coils comprises a npair of series connected impedsfinces shunted across said alternating current source and a source of direct current connected from a point between said iinpedances to the junction of said coils.

'l'. 3. sound reproducer .comprising a diaphrag n, coil winding attached in proximity to the outer circumference of said diaphragm, a. coil winding attached in proximity to the center of said diaphragm, means for impressing signal currents upon said windings in such relative polarity that said windings are actuated in the same direction to vibrate said diaiilirag;y i, and biasing means for pern enen y adjuk .iig the axial position of said di;y u'agm, said biasing means being solely electrical.

S. A sound reproducer according to claim in which said means for permanently adj listing said diaphragm comprises a source of uniform direct current which flows in opposing directions through said windings and a potentiometer for regulating the flow of direct current through said windings.

9. An electric l sound reproducer comprising a diaph lagm vibratile to sound, signal current acti ting c ils attached adjacent the center and outer periphery thereof respectively, permanent electrical biasing means urging said coils in opposite directions for maintaining said diaphragm under continuous tension, and means for so applying electric signaling Waves to said coils for simultaneonslv actuating them in the same direction to vibrate said diaphragm bodily substantially free from flexure.

l0. An electrical sound reproducer comprising a diaphragm vibratile to sound, flexible means supporting said diaphragm in operative position, signal current actuating coils attached adjacent the center and outer periphery thereof, means producing steady magnetic fields enveloping said coils adapted to produce axially directed reacting forces, means for applying steady polarizing cui rents to said coils adapted to repel the same axially of said diaphragm for maintaining the same under continuous tension, and means for adjusting the relative intensities of said polarizing currents for producing axial ad- `iustment of said diaphragm.

ll. An electrical sound reproducer comprising a diaphragm vibratile to sound, flexible means supporting said diaphragm in opera-tive position, signal current actuating coils attached adjacent the center and outer periphery thereof, means producing steady magnetic fields enveloping said coils adapted to produce axially directed reacting forces, means for applying steady polarizing currents to said coils adapted to repel the same axially of said diaphragm for maintaining the same under continuous tension, means for adjusting the relative intensities of said polarizing' currents for producing axial adjustment of said diaphragm, and means for applying electric Vsignaling Waves to said coils w for similarly and simultaneously actuating same whereby said diaphragm vibrates bodily substantially free from ieXure.

In testimony whereof I aiiX my signature.

`ROY E. THOMPSON.

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