US3358088A

US3358088A - Electromechanical transducer

Info

Publication number: US3358088A
Application number: US373024A
Authority: US
Inventors: Robert A Gault
Original assignee: CTS Corp
Current assignee: CTS Corp
Priority date: 1964-06-05
Filing date: 1964-06-05
Publication date: 1967-12-12
Anticipated expiration: 1984-12-12
Also published as: GB1111293A

Description

Dec. 12, 1967 R. A. GAULT 3,358,088

ELECTRQMECHANICAL TRANSDUCER Filed June 5, 1964 m i /2 k/Z L INVENTOR ROBERT A. GAULT FIGURE 3. W 9

ATTORNEY United States Patent 3,358,088 ELECTROMECHANICAL TRANSDUCER Robert A. Gault, Paducah, Ky., assignor to CTS Corporation, Elkhart, Ind., a corporation of Indiana Filed June 5, 1964, Ser. No. 373,024 7 Claims. (Cl. 179-1155) ABSTRACT OF THE DISCLOSURE An electromechanical transducer having a thermally conductive material bonded in close thermal proximity to the winding of the voice coil for increasing the rate of heat dissipation from the voice coil during operation. With increased dissipation of heat from the voice coil the wattage rating of the transducer may be appreciably increased.

The present invention relates to transducers, and, more particularly, to an electromechanical transducer of the type commonly employed in radios, television sets, hig fidelity and stereo sets, and the like.

During the past decade the wattage rating of amplifiers for equipment such as high fidelity and stereo sets has increased considerably. Consequently, it has been necessary to supply electromechanical transducers capable of handling the high output wattage of the amplifiers. In most designs, the size of the diaphragm of the transducer remains the same, and only the size of the magnetic structure and the voice coil associated therewith for operating the diaphragm is increased to withstand the higher wattage delivered by the amplifier. It would, therefore, be desirable to provide an electromechanical transducer with means for increasing the wattage rating without increasing the size of the magnetic structure or thevoice coil.

Generally one of the wattage rating limitations of an electromechanical transducer is the thermal dissipation of the voice coil and the assembly. By improving the dissipation factor of the voice coil, the transducer not only can be rated at a higher wattage but the transducer can also be subjected to a higher current overload. Generally,

the damage to an electromechanical transducer from a current overload is the result of the voice coil being unable to dissipate the excessive heat generated by the increased wattage carried by the coil. It has been suggested to make the bobbin of the voice coil of a metallic material having a sufiicient thickness so as to be self-supporting. Considerable difliculty has been experienced, however, in adhesion of the turns of the magnet wire forming the winding of the voice coil to the metallic material. Further, the possibility of shorting of the turns forming the winding is also increased when the winding is bonded directly to the metallic material. In the past, various experiments have also revealed that the heat may be dissipated more rapidly by attaching fins or other suitable heat dissipating means to the voice coil. Such heat dissipating means have, however, been virtually ineffective inasmuch as they also substantially increase the mass of the voice coil. Moreover, the increased mass increases the inertia of the diaphragm attached to the voice coil, the increase in inertia being especial-1y detrimental at higher frequencies thereby decreasing the efliciency of the transducer.

In some electromechanical transducers, such as loudspeakers, the efliciency of the loudspeaker at high frequency response has been somewhat improved by mounting a ring of aluminum in spaced relationship to the voice coil. The attachment of the ring to the voice coil is effected through a resilient coupling, e.g., rubber bands. Thus, at high frequencies, the voice coil has little effect in causing the diaphragm to vibrate, and the diaphragm "ice is vibrated primarily by the ring of aluminum which receives the high frequency current by induction from the energized winding of the voice coil. Further details of a similar construction are shown in Barker Patent No. 2,164,374, dated July 4, 1939. Although such loudspeaker designs are eflicient at both the high and low frequencies, the wattage rating of the voice coil is still limited especially at low frequencies inasmuch as the heat generated in the voice coil is not rapidly dissipated by the ring of aluminum resiliently secured by the thermally nonconducting means to the voice coil. It would, therefore, be desirable to provide a loudspeaker with a voice coil having a thermally conductive means in close proximity to the voice coil for rapidly dissipating the heat generated by the voice coil.

Accordingly, it is an object of the present invention to provide an improved electromechanical transducer having the desirable features set forth above.

Another object of the present invention is to provide an electromechanical transducer with a voice coil having a thermally conductive foil bonded in close thermal proximity therewith.

A further object of the present invention is to provide an electromechanical transducer with a bobbin of laminated material, one of the laminations of the bobbin being of electrically nonconductive material for supporting and insulating the turns of the magnet wire forming the winding of the voice coil and the other lamination being of a thermally conductive material for rapidly dissipating the heat generated by the voice coil thereby increasing the wattage rating of the transducer.

Still another object of the present invention is to provide an electromechanical transducer with a cylindrical voice coil having a bobbin disposed in the air gap of the magnetic structure with turns of magnet wire forming a winding on one side of a bobbin and an aluminum foil on the other side of the bobbin bonded to the bobbin for rapidly dissipating the heat generated by the voice coil when subjected to a sustained current overload.

Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Briefly, the present invention is concerned with an electromechanical transducer, e.g., a loudspeaker, having a thermally conductive material bonded and in close thermal proximity to the winding of the voice coil for increasing the heat dissipation of the voice coil in order that the wattage rating of the transducer may be increased.

For a better understanding of the present invention, reference may be had to the accompanying drawings wherein the same reference numerals have been applied to like parts and wherein:

FIGURE 1 is a sectional view of an electromechanical transducer built in accord with the present invention;

FIGURE 2 is an enlarged fragmentary section of FIG- URE 1 showing the voice coil and pole structure; and

FIGURE 3 is a sectional view taken along line III-III of FIGURE 1, assuming that FIGURE 1 is shown in full.

Referring now to the drawings, there is illustrated an electromechanical transducer, e.g., a loudspeaker, generally designated at 10, comprising a dish-like supporting frame 11 having secured thereto a stationary magnetic structure 20.

Considering first the stationary magnetic structure 20, it comprises a permanent magnet 21, a yoke 22, and

pole pieces

23 and 24 secured together by welding or the like. The stationary magnetic structure 20 is fixedly secured to the base portion 12 of the supporting frame 11 by suitable means such as screws. The stationary magnetic structure 20 has an E cross-section as shown in FIGURE 1 of the drawings. The yoke 22 and the

pole pieces

23 and 24 are preferably of iron or other suitable soft magnetizable material. As best seen in FIGURE 3 of the drawings, the

pole pieces

23 and 24 actually are one pole as shown in FIGURE 3 and the other pole 26 encircled by the

pole pieces

23 and 24 defines an annular air gap for the stationary magnetic structure.

For the purpose of transforming electrical energy into acoustical energy, the transducer 1% is provided with a diaphragm 3t) and a voice coil 4t), the outer edge 31 of the diaphragm 3%) being corrugated so as to offer slight resistance to movement of the diaphragm in the axial direction but to provide sufiicient resistance to transverse movement of the diaphragm. The outermost peripheral edge 32 of the diaphragm is fixedly secured with a suitable adhesive to the outer edge 13 of the supporting frame 11. It is to be understood, however, that the outer edge 31 of the diaphragm need not be corrugated and fixedly secured to the frame 11. One end of the voice coil 40 is fixedly secured to the apex 33 of the diaphragm and the other end of the voice coil is disposed in the air gap 25. Generally, proper suspension of the voice coil 46 in the air gap is maintained by a spider 34 extending outwardly of the voice coil and having its inner edge fixedly secured thereto, the outer edge of the spider 34 being fixedly secured to the supporting frame. The spider 34 is preferably of a suitably impregnated cloth or paper formed with annular corrugations to provide a high degree of flexibility in an axial direction and substantial stiifness in the radial direction transverse thereto. A dome shaped dust cover 35 is adhesively secured to the inner cone portion of the diaphragm for maintaining the voice coil 49 and the air gap 25 free of foreign particles.

In order to vibrate or move the diaphragm 30 and the voice coil 49 in response to changes in electrical energy, e.g., by changing the current, the voice coil comprises a winding 41 of magnet wire having a pair of not-shown leads connected to the output of an amplifier. Thus a changing current in the winding 41 associated with a magnetic field in the air gap 25 functions in such a manner so as to force the voice coil axially of the air gap 25 causing the diaphragm 3i) attached to the voice coil 40 through the apex 33 to develop acoustical energy.

Considering specifically the voice coil 40, it comprises a bobbin 42 preferably of an electrically insulating material such as paper or plastic, supporting the winding 41. In accord the present invention, a thermlly conductive material 43, e.g., an aluminum foil, or a material having a high density of metal particles, is adhesively secured or bonded preferably to the entire inner surface of the bobbin 42. It is to be understood, however, that the thermally conductive material 43 could be adhesively secured to only a portion of the inner surface or to the outer surface of the bobbin provided that sufficient insulating means is provided to prevent the magnet Wire from shorting the adjacent turns of the winding 41. Inasmuch as most thermally conductive materials such as aluminum foil have sufiicient structural strength, it is possible to reduce the thickness of the material forming the bobbin to maintain the total mass at a minimum and not effect the combined inertia of the diaphragm 30 and the voice coil 49. Moreover, the thermally conductive material improves the dimensional stability of the bobbin since such materials do not absorb moisture and the like.

The thickness of the aluminum foil 43 and the material forming the bobbin vary depending upon the size of the transducer. For example, in a device built in accord with the present invention, the total thickness of the aluminum foil 43 and the paper of a bobbin of an eight inch loudspeaker was .006 inch, the aluminum foil preferably being much thinner than the electrically insulating material and approximately .801 inch in thickness. Other thermally conductive materials such as copper foil may also be used but aluminum is preferable due to its lightness. Magnetically conductive materials should not be employed for thermally conductive materials since they would affect the performance of the voice coil in the air gap. It has been found that best results are obtained by laminating the thermally conductive material to the paper in a suitable manner before the bobbin is formed into a tube or the like. Satisfactory results have, however, been obtained by bonding an aluminum foil to a formed bobbin.

From the above description, it will be apparent that the same size transducer employing the improved voice coil of the present invention can be rated at a higher wattage since any heat generated by the voice coil is rapidly dissipated by the thermally conductive material 43, e.g., the aluminum foil, forming a part of the bobbin carrying the voice coil.

The present invention will readily be understood in view of the detailed description included above, and no further discussion regarding the operation of the electromechanical transducer is included herewith. It will be appreciated that the voice coil of the transducer of the present invention can also be subjected to a substantially greater current overload than heretofore without damaging the voice coil to any extent because the heat generated by the overload current is rapidly dissipated through the aluminum foil.

While there has been illustrated and described what is at present considered to be a preferred embodiment of the present invention, it will be appreciated that numerous changes and modifications are likely to occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In an electromechanical transducer; the combination of a supporting means; a magnetic structure carried by the supporting means; a voice coil operably associated with the magnetic structure, the voice coil comprising a bobbin of electrically insulating material having a predetermined thickness, a winding disposed on the outer surface of the bobbin, and a lamination of thermally conductive material fixedly bonded to the inner surface of the bobbin adjacent to the winding for dissipating the heat generated by the winding, said lamination of thermally conductive material having a thickness less than said predetermined thickness; and means operably connected to the voice coil for developing acoustical energy upon energization of the winding of the voice coil.

2. An electromechanical transducer comprising a dishlike supporting frame, a stationary magnetic structure fixedly secured to the frame having a generally E shaped cross-section and including a magnet projecting a field between the inner arm of the E serving as one pole and the outer arms serving as the other pole, a diaphragm having an apex and a corrugated outer edge secured to the frame, a cylindrical laminated bobbin circumposing the one pole and attached to the apex of the diaphragm, one lamination of the bobbin being of a thermally conductive material and the other lamination of the bobbin being of an electrically insulating material, said thermally conductive material having a thickness less than the thickness of said electrically insulating material, and a winding carried by the laminated bobbin for carrying a changing current associated with a changing magnetic field, the magnetic field cooperating with movement of the bobbin attached to the diaphragm through the apex.

3. In an electromechanical transducer the combination of a supporting frame, a stationary magnetic structure fixedly secured to the frame and having an E shaped crosssection including a magnet projecting a field between the inner arm of the E serving as one pole and the outer arms serving as the other pole to define an air gap therebetween, a diaphragm having an apex and a corrugated outer edge fixedly secured to the supporting frame, a bobbin of electrically nonconductive material disposed in the air gap and secured to the apex of the diaphragm, a winding of magnet wire attached to one side of the electrically nonconductive bobbin for carrying a changing current associated with a magnetic field of the magnetic structure, and a thermally conductive material fixedly attached to the other side of the bobbin and in close proximity with the winding for providing a continuous and uninterrupted path for conducting heat away from said voice coil thereby to rapidly dissipate the heat generated by the winding during operation, said thermally conductive material having a thickness less than the thickness of the electrically insulating material and the magnetic field cooperating with movement of the bobbin attached to the diaphragm through the apex.

4. In an electromechanical transducer, the combination of a supporting frame, a stationary magnetic structure fixedly secured to the supporting frame, a bobbin disposed in the air gap of the stationary magnetic structure, a diaphragm having an apex fixedly secured to the bobbin, a winding attached to one side of the bobbin for carrying a changing current associated with a magnetic field of the stationary magnetic structure, said bobbin consisting of an electrically nonconductive material, and a thermally conductive material fixedly bonded thereto in close proximity to the winding whereby upon energizing the winding the heat generated by the winding is rapidly dissipated by the thermally conductive material.

5. In an electromechanical transducer having a stationary magnetic structure, a voice coil operably associated with the stationary magnetic structure, said voice coil comprising a winding for energization during operation, and a diaphragm secured to the voice coil the improvement in said transducer comprising, a bobbin for supporting the winding, said bobbin consisting of a first lamination of thermally conductive material and a lamination of electrically nonconductive material fixedly bonded to said first lamination, said winding Wound on said bobbin in close proximity to said first lamination whereby during operation the heat generated by the winding is rapidly dissipated by the first lamination.

6. The electromechanical transducer of claim 5, wherein the lamination of thermally conductive material is substantially thinner than the thickness of the lamination of electrically non-conductive material and said nonconductive material is paper.

7. The electromechanical transducer of claim 5, wherein the lamination of thermally conductive material is substantially thinner than the thickness of the lamination of electrically nonconductive material and said nonconductive material is plastic.

References Cited UNITED STATES PATENTS 2,485,745 10/1949 Koonz 336-61 2,769,942 11/1956 Hassan 179115.5 3,160,716 12/1964 Luth 179115.5

KATHLEEN H. CLAFFY, Primary Examiner.

A. A. MCGILL, Assistant Examiner.

Claims

5. IN AN ELECTROMECHANICAL TRANSDUCER HAVING A STATIONARY MAGNETIC STRUCTURE, A VOICE COIL OPERABLY ASSOCIATED WITH THE STATIONARY MAGNETIC STRUCTURE, SAID VOICE COIL COMPRISING A WINDING FOR ENERGIZATION DURING OPERATION, AND A DIAPHRAGM SECURED TO THE VOICE COIL THE IMPROVEMENT IN SAID TRANSDUCER COMPRISING, A BOBBIN FOR SUPPORTING THE WINDING, SAID BOBBIN CONSISTING OF A FIRST LAMINATION OF THERMALLY CONDUCTIVE MATERIAL AND A LAMINATION OF ELECTRICALLY NONCONDUCTIVE MATERIAL FIXEDLY BONDED TO SAID FIRST LAMINATION, SAID WINDING WOUND ON SAID BOBBIN IN CLOSE PROXIMITY TO SAID FIRST LAMINATION WHEREBY DURING OPERATION THE HEAT GENERATED BY THE WINDING IS RAPIDLY DISSIPATED BY THE FIRT LAMINATION.