US2494918A - Inductively energized electro-dynamic loud-speaker - Google Patents

Description

Fan, W, W5@

W. K. VOLKERS INDUCTIVELY ENERGIZED ELECTRODYNAMIC LOUDSPEAKER Filed Sept. 17, 1946 Inventor WAL T'ER If. VOL KERS By Wm (12),

Niamey of the voice coil.

Patented Jan. 17, 1950 "UNITED STATES 'PATEN'T 7O"'F5'FICE.

INDUQTIVELY ENERGIZED ELECTRO- DYNAMIC LOUD-SPEAKER Walter K. Volkers,

to Volkers & Schafie New York Schenectady, N: Y., assign'or r, 'IncJ, acorporationor Application September 17, 1946, Serial No. 697,588

' 1 Claim.

" The present invention covers a new type of dynamic loudspeaker which has a stationary voice coil instead'of the moving voice coil, which is being customarilyused in dynamic speakers today. The principal advantages of a stationary voice coil when compared to a moving voice coil are the following:

be matched directly with the output tubes, whereby theoutput transformers, now customarily used','-can beomitted. This greatly reduces the manufacturing costs of sound amplifiers, radio receiversand-similar electronic "equipment using the new type of loud speaker.

3. Stationary voice coils are less delicate and require less skill in manufacturing than moving coils and therefore reduce the amount of labor required for producing the new speaker.

4. The total weight of the active parts attached to the speaker cone is smaller in case of the new design as compared with an ordinary moving coil speaker, giving the new speaker improved frequency response and better sensitivity.

5. A stationary voice coil permits the elimination of the pig-tail connections to the voice coil.

While the structures to be described herein are especially useful for loud speaker purposes, they have other uses as will be explained more fully hereinafter. Broadly, my invention is useful in the field of electro-mechanical transducers for translating mechanical vibrations into electrical vibrations or, conversely, translating electrical vibrations into mechanical vibrations. My improved transducer involves a vibratory armature formed of thin sheet-like magnetic material mounted for vibration in its own plane and includes a magnetic system (either permanent magnet or electro-magnetic) for establishing an exciting magnetic field through the armature normal to the plane thereof, and a coil arranged in inductive relation to the armature with the turns thereof at right angles to both the direcr tion of vibration of the armature and the direction of the biasing field. When the coil is energized by a signal current, the interaction between the field of the coil and the exciting field establishes mechanical forces on the armature to move or vibrate'the'same in accordance'with the well known three-finger rule in determining electrodynamic action. Conversely, if the armature is vibrated, corresponding voltages are induced'in the coil.

' My invention is illustrated and compared to previous standard designs in'the. accompanying drawing in which Figure 1 showsa cross-section of the electromagnetic 'driving's'ystem of an ordinary movingcoil type speakerj and Figure 2 is a" cross-section of the new stationary-coil ty e speaker.

The conventional'dynamic loudspeaker shown in Figure lhas a moving coil I wound on a cardboard cylinder 2 which is fastened to the speaki'ers cone The magnetic system for supplying "the exciting 'field'consists of a soft iron core 4, i a ring -typepermanent magnet 5, a yoke plate 6 "and apole-ring 1. "The magnetic lines of force which penetrate radially the active air gap between the core 4 and the pole-ring 1 are illustrated by the arrows 8 and 9. Electrodynamic action between the flux produced by current passing through the wires of coil l and the magnetic lines of force 8 and 9 creates a mechanical upward or downward pulling action as indicated by arrows l0 and II. This force causes the moving coil l to move up and down which makes the speaker cone 3 vibrate and produce sound.

The preferred form of new speaker according to the present invention is shown in Figure 2. It also has a paper cone 2| which produces sound. However, instead of a moving coil, there are attached to the cone twoconcentric rings 22 and 23 which are made of soft iron, preferably low-loss sheet material. They are held in spaced relation by alightweight ring 24 made of cardboard, wood or some plastic material. Between the tworings 22 and 23 there is placed thevoice coil 25 which is stationary and can, therefore, be attached to any stationary part of the loudspeaker, for instance, itsiron core 26. A supportingring 21 made of plastic material such as phenolic resin or any equivalent insulation material may be used for this purpose. The other parts of the loudspeaker closely resemble those of the standard speaker shown in Figure 1. Again a permanent ring-type magnet 28 is being used, also ayoke disc 29 and apole ring 30. The magnetic lines of force forming the exciting field are again radial as illustrated by arrows 3| and 32 and again they produce mechanical raising or lowering forces as indicated byarrows 33 and 34. In this case, however, there are no direct active magnetic forces between the stationary magnetic parts represented by thecore 26 and the pole ring 3| and the moving parts represented by the twothin iron rings 22 and 23 which are attached to the loudspeaker. Instead, the actual internal dynamic action takes place between the stationary coil and the thin iron parts emitting and absorbing the flux surrounding it. In other words, the actual driving effect is caused by thestationary coil 25 and the twothin iron rings 22 and 23. Since the flux passes through them only transversely, they can be madeextremely thin and light.

From the foregoing description it will be seen that in my invention the vibratory armature is formed of relatively thin sheet-like magnetic material mounted for vibration in its own plane.

While thearmatures 22 and 23 described above are of cylindrical form, it will be understood that they may assume other forms such as a flat .vane. It will also be noted that the exciting field established bymagnet 28 passes through the magnetic armature normal tothe plane thereof, and the turns of thecoil 25 are arranged .at right angles to both the direction of the exciting field and the direction of vibration of the armature."

It goes without saying that the. present invention is not limited to the permanent-magnettype speaker shown in the drawings forproducingthe exciting field. It can be applied to speakers having any other type of magnetic excitation. A simple bar-type magnet. can be used instead of the ring magnet, or any other magnet exciting device may be used. Bell-shaped, horseshoe-type, laminated types, and many other .forms of permanent magnets canbe'used, also electromagnetic excitation by means of exciting coils. To show all possible types of'sp'eakers incorporating my invention would exceed the available space for drawings accompanying this patent specification.

Like the ordinary dynamic loud speaker, my invention is capable of being used for translation of acoustic vibrations, or mechanical vibrations, into corresponding electric currents. For example, structures involving the principles outlined above may be used as microphones, phonograph pickup elements and recording heads. Also, while I have described my invention as applied especially to loudspeakers, it is obvious that the same type of structure may be used in telephone receivers of the head-set type and bone-conduction type.

I claim:

An electro-mechanical transducer comprising, in combination, a magnetic structure including an annular pole piece surrounding a central core and providing an annular air gap surrounding said core and including means for establishing a radial exciting field in said gap, an annular coil mounted in fixed position within said air gap and in spaced relation with both gap-forming. members to provide concentric component air gaps of annular form on radially opposite sides of said coil, and a vibratory armature comprising a-pair of concentric magnetic cylindrical members positioned within said component air gaps and mounted for vibration parallel with the axis of said coil. 1

WALTER K. VOLKERS.

REFERENCES CITED The following references are of record in'the file of this patent:

UNITED STATES PATENTS Messick J an. -7, 1936

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