US 3711659 A
An improvement in the method and manner of constructing a loud speaker voice coil, such improvement consisting of utilizing conductive metal foil as the wound element for supported positioning and reciprocal movement within an associated magnetic air gap; such a metallic foil coil may consist of one or more turns of either superimposed or alternately off-set foil windings.
Description (OCR text may contain errors)
United States Patent 1 Bremseth LOUDSPEAKER VOICE COILS  Inventor: Gerald B. Brernseth, 5700 NW.
67th St., Oklahoma City, Okla. 73|32 Filed: Jan. 20, 1971 Appl. No.: 107,994
US. Cl. ..l79/ll5.5 VC, 336/223 Int. Cl. ..I-I04r 9/04 Field of Search.....l79/I-l5.5 R, 115.5 DV, I 15.5
 References Cited UNITED STATES PATENTS 2,445,276 Massa .1 ..l79/l 15.5 vc
[4 1 Jan. 16, 1973 FOREIGN PATENTS OR APPLICATIONS 383,664 ll/l932 Great Britain ..I79/l 15.5 VC
Primary Examiner-Kathleen H. Claffy Assistant Examiner-Douglas W. Olms Attorney-Dunlap, Laney, Hessin & Dougherty  ABSTRACT An improvement in the method and manner of con structing a loud speaker voice coil, such improvement consisting of utilizing conductive metal foil as the wound element for supported positioning and reciprocal movement within an associated magnetic air gap; such a metallic foil coil may consist of one or more turns of either superimposed or alternately off-set foil windings.
2 Claims, 5 Drawing Figures volume-efficiency.
BACKGROUND OF THE INVENTION 1. Field of the Invention v The invention relates generally to the art of audible sound reproduction and, more particularly, but not by way of limitation, it relates to improved voice coil apparatus for use in loudspeaker assemblies.
2. Description of the Prior Art The prior art includes no teaching as to a similar type of voice coil structure as formed by wound metallic foil. The use of foil has been known in constructing certain transformer and radio frequency coil structures, and particularly in such applications wherein the inherent characteristics and structural capabilities of foil lend themselves to particular applications. There are no known teachings heretofore which extend in any way into the sound reproduction art.
SUMMARY OF THE INVENTION The present invention contemplates an improved transducer drive coil wherein the drive coil assembly is constructed of one or more windings of a metallic foil of selected thickness and width. The wound foil coil may be varied in any of foil thickness, foil width, type and configuration of foil overlap per winding, etc., to vary accordingly the inductance characteristics of the coil for particular applications.
Therefore, it is an object of the present invention to provide an improved acoustic energy transducer drive coil which offers the advantages of increased strength, simplicity, heat-dissipation capability, and high It is also an object of the invention to provide a transducer drive coil having higher power handling capability per unit size of structure.
It is still further an object of the present invention to provide a loudspeaker voice coil of high efficiency which can be constructed with decreased thickness and volume as compared to prior art forms of voice coil.
Finally, it is an object of the present invention to provide a loudspeaker or microphone voice coil which is inherently stronger than like units formed with prior construction techniques and materials, and which foil voice coil exhibits increased exposure surface while allowing less dead space within the magnetic gap volume.
Other objects and advantages of the invention will be evident from the following detailed description when read in conjunction with the accompanying drawing which illustrates the invention.
BRIEF DESCRIPTION OF THE DRAWING FIG. I is a vertical section through a loudspeaker structure which utilizes a voice coil constructed in accordance with the present invention;
FIG. 2 is a side elevation of a coil former and voice coil constructed in accordance with the invention;
FIG. 3 is a partial vertical section showing one form of coil former and voice coil relationship; 7
FIG. 4 is a partial vertical section showing an alternative form of coil former and and I FIG. 5 is a vertical section'through a typical form of dome diaphragm utilizing a foil coil constructed in accordance with the invention.
voice coil configuration;
DETAILED DESCRIPTION OF THE INVENTION While the teachings of the invention are applicable to any of various types of electromagnetic transducing assembly, the description proceeds relative to an exemplary application in an acoustic energy generating device. Thus, referring now to FIG. 1, a conventional form of loudspeaker assembly 10 consists of a frame element 12 supporting a diaphragm l4 and driver assembly 16. The frame element 12 consists of an outer ring frame 18 and such as a clamping ring 20 suitably fastened therebeneath to receive and hold an outer peripheral edge 22 of diaphragm 14. Diaphragm 14 is of the usual construction having such as molded concentric ridges 24 adjacent the outer supporting point or peripheral edge 22.
An inner circumferal edge 26 of diaphragm 14 is formed as a cylindrical sleeve and secured as by bonding with suitable epoxy or the like to the outside of one end of a coil former 28, i.e., usually a cylindrical tube section formed of phenolic plastic or the like and secured to diaphragm 14 in axial alignment therewith. Centering of the diaphragm l4 and coil former 28 is effected in usual manner by a resilient spider 30 which is suitable bonded at the point of juncture of diaphragm l4 and coil former 28 to extend radially outward for circumferal affixure to the speaker frame, shown schematically as dash-line 32. Thus, the frame portion 32 provides secure structure from the outer frame ring 18 rearward to support and align the various operating elements of the loudspeaker 10, this structure being wellknown and conventional in design.
The magnet assembly 16 is rigidly supported by frame portion 32 so that it is maintained in magnetically interactive relationship with coil former 28 and voice coil 34. The voice coil 34 is comprised of one or more turns of a selected foil material as wound circuitously around the lower end 36 of coil former 28 to be moveably supported within a symmetrically shaped air gap 38 as formed by magnet assembly 16. The voice coil 34 may be wound from any of selected metallic foil materials; however, operation has been achieved to excellent advantage using aluminum foil of thickness 0.001 inch. Any of various metal foils or alloy foils may be used. The thickness too is a matter of choice depending upon the type of speaker performance and the characteristics to be stressed.
The magnetic assembly 16 is of conventional design having a cylindrical magnet 40 and a center pole portion 41, and an annular ring portion 42'is secured by a brace portion 44 to maintain the proper circular air gap 38. The type and configuration of magnetic assembly I6 may also be varied so long as a sufficient size of air gap 38 is provided to receive the voice coil 34.
FIG. 2 illustrates the manner in which voice coil 34 is connected to respective take-down leads 46 and 48, shown in FIG. I as connected through diaphragm 14 to signal supply leads 50. As can be noted in FIG. 2, the wound foil voice coil enables a further advantage of utilizing folded extensions of the coil foil as the take down leads 46 and 48. This is proven to be a superior method of take-down lead construction due to the fact that the foil is extremely thin and can be folded at right angles and led out of the coil configuration without the need for a special tolerance in the magnetic structure.
Thus, a speaker with a foil coil need not suffer an efficiency loss due to the necessity to provide a clearance for the take-down lead as has been a chronic problem in conventional loudspeaker designs of single layer coil construction. Each of the take-down leads 46 and 48 is made by folding a simple 90 bend in the foil ends so that the ends (leads 46 and 48) extend along the coil former 28 for suitable connection to the external energizing voltage input. Such energizing voltage may be applied by any of various well-known connection methods; however, as shown in FIG. l,'connection may be by suitable solder joint or other affixure through the diaphragm 14 to voltage supply leads 50.
The foil coil winding may be arranged in any of various cross-sectional configurations. Thus, as shown in FIG. 3, the foil coil 34 is wound about the lower end of coil former 28 which each successive foil overlay placed in exact superposition over prior wrapped layers. The coil 34 may consist of as many overlays 54 as are needed in establishing the requisite inductive characteristics; and also, the choice of foil width, thickness, metal type, etc. are subject to similar selection and adjustment.
FIG. 4 illustrates an alternative form of foil coil 56 which is wound with alternate foil overlays 58 off-set by a pre-determined distance denoted by arrows 60, such configuration enabling much increased external exposure surface to each individual foil overlay 58. Thus, in certain applications where dead space may not be critical, and heat dissipation may become a primary consideration, the cross-sectional configuration such as that of foil coil 56 may be desirable. It should be understood that various cross-sectional configurations and foil overlay patterns different from those shown may find use in certain special applications. It is also contemplated that it may be advantageous to vary the foil thickness or width along its length to further alter the concentration of inductive material about the coil.
In operation, the speaker assembly functions in generally the same manner utilizing foil coil 34 as does the conventional speaker assembly utilizing a wound wire coil. The only differences in operation are in the improvements of certain physical characteristics as enabled by the foil coil. Thus, the foil voice coil has served to overcome some persistent problems in speaker manufacture such as coil concentricity. This is an especial problem with construction of the larger voice coil sizes, and coils formed in accordance with the foil coil method have proven to be much more resistant to warping than are conventional wire wound coils. In the usual practice, the curing of a very thin epoxy bonding agent in and around the combination of many layers of thin foil forms a monolithic block which is inherently stronger than conventional voice coil structures. Another common failing of conventional voice coils is the loosening of the end turns of the coil in response to certain stress movements, which loosening quickly weakens and lessens dependability of the coil structure. In the case of the foil coil there are no end turns to loosen as the entire surface of each foil layer is firmly bonded or attached to the next foil layer above (as well as'below) with the result that the entire coil package is extremely sturdy and exhibiting a high affinity for coil concentricity. I
The method of foil coil construction also has an increased advantage in simplicity. Thus, acoil winding machine needs no complex traverse mechanism, no gears, no cams, etc. The coil is easily positioned accurately on the-coil former, and thereafter it is easily inspected and handled in further assembly. In construc; tion, the designer has the advantage of knowing the precise measurement of the axial length of the coil since this is the width of the foil itself. There are so many variables in normal wire coil construction practice that it has been usual to design the speaker to operate with a rather large tolerance in the axial length of the voice coil. This practice then contributesto a wasting or a failure to utilize all or an appreciable majority of the available magnetic flux across the associated air gap.
FIG. 5 illustrates a foil coil as constructed in accordance with the invention and utilized in a highpowered compression driver horn application. Thus, FIG. 5 illustrates a dome diaphragm 70,-as is commonly utilized in a driver unit of a horn assembly. The dome diaphragm consists of a dome portion 72 and cylindrical side wall 74 which is formed integrally with a radially extending spider portion 76 to be suitably retained in annular clamping assemblies 78 and 80, as is well-known. A coil former 82 of cylindrical form is axially aligned with the cylindrical side wall 74 of diaphragm 70 and securely affixed thereto by suitable bonding, e.g., by epoxy cement or the like. A foil coil 84 is then wound around the lower end of coil former 82, such foil coil 84 being suitably bonded in the manner as previously set forth. The take-down leads from foil coil 84 may be led out in any of various ways; however, it may prove advantageous in many applications to lead the foil strip take-down leads 86 (shown in dash-lines) outward along the under side of spider portion 76 of dome diaphragm 70. Such practice will result in no unnecessary drag or unbalancing of the spider element to hamper operation of the driver assembly. lt is also foreseen that some applications will allow elimination of the coil former member altogether.
The foregoing describes a novel voice coil which has many inherent advantages. The invention is superior to all other types of voice coil construction in its ability to dissipate heat. Thus, a multi-layer foil voice coil may be made such that each turn has two edges exposed for heat dissipation. The fact that there are no trapped turns, as are found in conventional square or round wire coils, also allows the coil to heat evenly with no hot spots. This enables the voice coil to make maximum use of the available magnetic flux within the air gap of the magnet assembly, there being no dead air space. The ability to increase the cross-sectional area of the conductor within the flux gap serves to increase the volume-efficiency of the voice coil. That is, the efficiency ofa loud speaker varies as the square of the magnetic flux density times the square of the length of wire within the air gap. Since the length of wire with a given cross-sectional area and a given resistance is fixed, and the magnetic flux density increases with reduction of the magnetic gap volume, the volume-efficiency of the coil will be the controlling factor in the ef ficiency of a speaker with a given magnet structure.
The use of the foil coil and advanced insulation and bonding measures of an extremely thin coating contribute to the lessening of the dead space in the center of the magnetic gap and therefore, this effects an increase in the volume-efficiency of the coil. Such increase enables the best use of the magnetic flux available in the given magnetic gap thereby to convert more of the electrical energy to acoustic energy than would be possible with a conventional speaker utilizing a wire wound voice coil. This, in turn, will result in less of the electrical energy being converted to heat, and the combination of the features brings into being the possibility of construction of loud speakers with higher efficiency and higher power-handling capability than any yet designed.
It should be understood too that the employ of single and multi-layer foil coil energizing units is by no means limited to loudspeaker assemblies. Various other forms of electromagnetic transducer, such as the numerous types of microphone and many accelerometer devices including high-powered shake table transducers, should gain functional advantage with utilization of the foil coil teachings.
Changes may be made in the combination and arrangement of elements as heretofore set forth in the specification and shown in the drawing; it being understood that changes may be made in the embodiments disclosed without departing from the spirit and scope of the invention as defined in the following claims.
What is claimed is: l. in an electromagnetic transducer assembly of the type having a frame member supporting a diaphragm in contact with the surrounding air, and a magnet assembly secured in place by said frame member to define an air gap having magnetic flux present thereaeross, the coil structure comprising:
coil former means securely affixed to said diaphragm and disposed to be supported within said air gap;
coil means formed from metallic foil wound in circuitous form, said coil means being wound upon said coil former means within said air gap with each alternate winding of said metallic foil in an off-set relationship relative to a mid-position within said air gap;
means providing insulation between any one part of said metallic foil and another part of said metallic foil; and
conduction means providing electrical connection to each one of the opposite ends of said metallic foil.
2. A transducer assembly as set forth in claim 1 wherein said strip of metallic foil is formed into a coil with successive windings displaced from superposition by predetermined amounts which vary the inductive characteristics in pre-set manner,