US1866361A - Driving unit for loud-speakers - Google Patents

Description

July 5, 1932. p U H 1,866,361

DRIVING UNIT FOR LOUD SPEAKERS Filed Aug. 14, 1930 a -llll 'ii iilii iiii'ii;

Inventor".

Hans P KuehnL 9 Hi s Aug)? 'r eg,

" the gap to permit the free vibration therein Patented July 5, 1932 j rs ATENT HANS I. KUEHNI, 0F SGHENEGTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW"YORK DRIITING "UNIT FOR LOUD-SPEAKERS Application filed August 14, 1930. Serial No. 475,233.

My invention relates to speech current devices for converting electric oscillation into sound waves or vice versa, particularly to loud speaker devices of the moving coil type, and has for its principal object the provision of an improved driving unit for such devices.

In the use of loud speakers in which 2. diaphragm is driven by a coil moving in an air gap formed by a magnet structure it is clesirable that the gap be short in order to permit the production of a strong magnetic field in the gap by the use of only a comparatively small magnet structure, or in certain cases by the use of a permanent magnet or magnets. But di'fiiculties have been encountered heretofore in the attempt to provide an efficient loud speaker comprising a moving coil and at the same time having a short air gap, due to the comparatively wide space required at of the moving coil system commonly used, comprising a coil or coils of many turns connected directly to a source of current varying in accordance with sound waves and mounted on a stiff supporting member, usually a cylinder rigidly fastened to a cone diaphragm.

In accordance with my invention I have provided an efficient loud speaker which is of the moving coil type but in which the air I gap formed by the magnet structure is Very short. To accomplish this result the speech current source is not connected to a moving coil but to a stationary coal or coils mounted on a core, and the moving coil is replaced by a flat, single turn, short-circuited conducting member in which the currents actuating the diaphragm are induced by transformer action. It is a feature of my invention that by reason of the short air gap characterizing the driving unit for the loud speaker a strong magnetic field may be produced, sufficient for the satisfactory operation of a cone type loud speaker in many uses, by permanent magnets, thereby avoiding the necessity of providing electromagnets for this purpose.

It is a further feature of my invention that the transformer incorporated in this driving unit may replace the transformer usually connected between the power tube of a radio receiver and the loud speaker.

My invention will be better understood from the following descriptionwhen consideredin connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a side elevation of a speech current device embodying my invention; Fig. 2 is an enlarged perspective view of a part of this device; and I Fig. 3 is a sectional view on line 11 of Fig. 1.

In the embodiment of the invention shown in the drawing the speech current device is a loud speaker comprising a cone diaphragm 10 actuated by a driving unit 11 of the moving coil type in' which a magnetic field is produced by a magnetic unit 12 and the moving coil forms part of a speech current transformer 13. In the magnetic unit 12 a frame memberv 14 is provided on which are mounted two oppositely disposed, preferably permanent magnets 15, 16 so arranged that poles of opposite polarity are'dispos edadjacent each other to form two air gaps 17 18. The

transformer 18 comprises a core member 19 having a' leg 20 and two primary coils-2l, 22 at the ends thereof, mounted on the magnetic unit 12 as by studs 23 and so arranged that the magnets 15,16 surround the core.

The core leg 20 is disposed centrally in the I space enclosed by the magnets and at right angles to the plane of the air gaps 17 18. The secondary of transformer, 13 is a shortcircuited winding member 24% constituting the moving coil of the loud speaker driving unit 11. Winding member 2 1 is a thin, flat, rectangular plate of suitable current conducting material such as copper or aluminum arranged to surround the core leg 20.- The central portions of the two opposite sides 25, 26 of the plate are disposed closely adjacent to the coreleg to reduce the leakage reactance and between adjoining ends of the two primary coils 21, 22, and the side portions 27 and 28 are disposed respectively in the air gaps 17 and 18. The side portions 27 and 28 may be as long as orlonger than the side portions 25,26 in order that a relatively large part of member 24; maybe disposed in the air gaps. The plate 24: is maintained in proper position by suspension means which comprise strings 29 connected to the corners of the plate and which may be made adjustable by attaching the strings to adjusting screws 30. The cone 10 is connected to the plate 2d at one side thereof, as by a driving rod 31 fastened to a lug 32 formed at the center of plate side 27.

In the operation of the above described loud speaker device embodying my invention, speech currents from any suitable source (not shown), such as a. radio receiver, are causedto flow in the primary coils 21, 22 of transformer 13. A varying secondary current corresponding to the speech current in these coils is thereby induced in the shortcircuited secondary winding constituted by the'plate 24 surrounding the coreleg of the transformer. This varying secondary current flows in the portions 27, 28 of plate 24 which are suspended in the air gaps 17, 18 and the entire plate, of which these portions form a part, vibrates in the plane of the plate and in the direction of the cone driving rod 31, under the influence of the magnetic field produced in the air gaps by the magnets 15, 16 of the magnetic unit 12, thereby vibrating the rod and the diaphragm attached thereto.

It will be seen that since the flat portions 27, 28 of the single turn secondary winding 24 which constitutes the speech current conductors moving in the magnetic field in air gaps 17, 18 are relatively thin, and since the motion of these conductors is in the plane of the flat surface thereof, therefore, the gap between adjacent poles of the magnet unit extending in opposite directions from said winding substantially at right angles to the plane thereof.

2. A speech current device including a vibratable member, a short-circuited flat rectangular winding connected thereto, a speech current transformer comprising a core member and said winding, a magnet structure arranged to surround said core member and having two oppositely disposed magnets forming a pair of air gaps, said winding being arranged to. surround said core member and having oppositely disposed portions is of such length only as to provide for the insertion of a thin plate between the poles and for the small clearance space required for ed ewise movement of the plate in the gap. t will be seen further that by reason of the fact that it is thus possible to maintain the air gaps 17, 18 extremely short, a high field intensity may be provided by a magnet unit 12 comprising permanent magnets.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A speech current device including a vibratable member, a short-circuited flat winding connected thereto, a speech current transformercomprising a core member and said winding, a magnet structure arranged to surround said core member and having two oppositely disposed magnets forming a pair of air gaps, said winding being arranged to surround said core member andhaving oppositely disposed portions each arranged to move in the same direction in a different one of said air gaps, and means to suspend said fiat winding comprising pairs of flex-

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