US2749393A - Molded sound reproducer and method of making the same - Google Patents

Description

June 5, 1956 H. o. FUCHS 2,749,393

MOLDED SOUND REPRODUCER AND METHOD OF MAKING THE SAME Filed May 1, 1951 IN V EN TOR.

BMW/6m;

United States Patent MOLDED SOUND REPRODUCER AND METHOD OF MAKING THE SAME Harold 0. Fuchs, Carle Place, N. Y., assignor to Pickering Associates, Inc., Oceanside, N. Y., a corporation of New York Application May 1, 1951, Serial No. 224,029

6 Claims. (Cl. 179100.41)

This invention relates to a molded construction for a 2,749,393 Ce Patented June 5,1956

' netic material fixedly and rigidly mounted near the free end of a channel-shaped cantilever spring 17 and projecting downwardly through the gap between the ends of the pole pieces 11 and through the center of the spool 14 and the coil 15. The cantilever spring 17 is secured'to the center of the bar magnet 12 which in turn is a part of the sound reproducer for phonographs and more particularly to a sound reproducer cast in a resin.

It is an object of this invention to provide a sound reproducer, particularly a magnetic sound reproducer, in which all of the parts are cast in a solid mass of resin having only a stylus and contact prongs protruding.

It is a further object of this invention to provide a method of assembly of a magnetic sound reproducer and easing the same in a solid body of resin which is easy and inexpensive.

These and other objects of this invention will become more apparent upon consideration of the following description taken together with the accompanying drawings in which:

Fig. 1 is a plan view of the magnetic sound reproducer of the type which may be used in this invention, positioned in a mold;

Fig. 2 is a longitudinal, vertical section of the magnetic sound reproducer of this invention in a mold;

Fig. 3 is a vertical, transverse section of the armature in the mold taken on line 33 of Fig. 2;

Fig. 4 is a longitudinal, vertical section of the finished magnetic sound reproducer of this invention, and

Fig. 5 is a bottom perspective view of the magnetic sound reproducer of this invention.

This invention provides a sound reproducer assembly cast within a solid mass and incorporating a core of viscous fluid material which permits reciprocation of the pickup armature and at the same time dampens the vibrations of the armature.

My invention is illustrated in connection with a magnetic sound reproducer of the general type disclosed in the co-pending application of Norman C. Pickering, Serial No. 681,800, filed July 8, 1946. This magnetic type of sound reproducer comprises a moving system and also a fixed portion embodying a generating system or coil. An assembly of the fixed and moving parts of this type of sound reproducer'is shown in the drawings. Referring to Fig. l, the fixed portion of the sound reproducer assembly comprises a frame made up of a pair of pole pieces 11 of magnetic material positioned at the opposite ends of a bar magnet 12. The pole pieces 11 on the opposite sides of the frame 10 project inwardly toward each other. The pole pieces 11 taper toward their inner ends and terminate a short distance from each other leaving a small gap in the magnetic circuit in which the armature 13 is disposed as shown in Figs. 2 and 3. When the unit is assembled, the poles of the magnet 12 engaging the pole pieces 11 makes them respectively north and south poles.

. As seen in Fig. 3, the pole pieces 11 extending inwardly are provided'with upper and lower fingers. Between these fingers is supported a spool 14 composed of insulating material. Wound on the core 16 of the spool 14 is the current generating element in the form of a coil 15. The central opening of the wound coil and the rigid frame 10 together with the pole pieces 11.

In order to produce a relatively light but stiff armature, the armature 13 is of tubular construction wherein the ratio of stiffness to mass is relatively high. Thus, it will be seen that the vertical armature 13, as viewed in Figs. 2, 3 and 4, which extends downwardly through the center of the coil 15 and the gap between the ends of the pole pieces, is of tubular form. Integrally secured to the lower end of the tubular portion is a jewel stylus 18 mounted in the tubular end in a well-known manner.

1 or the other of the pole pieces causing corresponding movement of the armature 13 around the longitudinal axis of the spring 17. This, in turn, causes a flux in the armature which cuts through the field of the coil and causes electrical impulses or voltages therein. The coil is connected to a sound amplifying system through leads 19 and contact prongs 20.

It has been discovered that the operation of a sound reproducer can be improved by a damping action on the movements of the stylus carrying armature. It has also been discovered that unctuous substances having the viscosity of petrolatum or a viscous lubricating oil having a Saybolt viscosity of over 199 are satisfactory damping media in a sound reproducer of the nature described herein. In other sound reproducers, other unctuous substances with greater viscosity, such as medium lubricating oil with a Saybolt viscosity of between and 200 may be satisfactory. According to this invention, the damping substance employed may be selected in accordance with the characteristics of the sound reproducer parts incorporated in the cast cartridge. A desirable damping action may also be obtained with certain solid compounds which have a stifi viscous action, such as audiod and viscoloid. In the following description, viscosity refers to the property of internal fluid friction in fluids and soft solids which is caused by a slight resistance to. change of form arising from the molecular attraction between the moiecules of the substance. The term viscous is used to indicate a substance having a degree of viscosity which will provide a satisfactory damping action to the armature with which it is employed.

The sound reproducer described above is representative of the type of sound reproducer which may be used in my invention. In this invention the sound reproducer is made by casting a resin around the reproducer as- I sembly in a mold. In Fig. l the lower half 21 of a mold and an upper half of the mold ,26. The upper half of the mold 26 is seated on the lower half 21 and is joined thereto by a dovetail joint 27. The upper half of the mold is provided with sprues 28 through which the casting material is introduced into the cavity 25.

In one mode of carrying out this invention, the reproducer parts are first assembled. The pole pieces 11 are fastened to their respective ends of the bar magnet 12 by a suitable adhesive or other means. The spool 14 with its coil 15 wound thereon is placed between the fingers of the pole pieces 11 with the leads 19 extending therefrom. At the end of the leads 19, the contact prongs are attached. The armature 13 carrying its stylus 18 is mounted on one end of the spring 17 and the other end of the spring 17 in turn is mounted at the center of the upper surface of the bar magnet 12 with the stylus extending downward through the core 16 and the coil 15. The assembled reproducer parts are then inserted in the lower half 21 of the mold opened by the removal of the upper half 26. The armature 13 is inserted in the hollow mandrel 24 while the core 16 of the spool is slid over the outside of the mandrel 24 so that the mandrel 24 fits in the annular area between the armature 13 and the core 16. The pole pieces 11 rest on the upper surface of the platform 22. The pole pieces, thus supported off the floor of the lower half 21 of the mold, hold the reproducer assembly in this position while the assembly is maintained vertical by the spool 14 and armature 13 on the mandrel 24. With the assembly thus held in position in the lower half 21 of the mold, a viscous grease is applied to the upper side of the reproducer assembly in the vicinity and around the moving parts. As shown in Figs. 2, 3 and 4, this viscous grease envelops the free end of the spring 17 and armature 13. Additional viscous grease is placed around the armature by insertion through a lower open end 29 of the hollow mandrel 24. The grease inserted through the open end 29 is forced under pressure along the surface between the armature 13 and the mandrel 24 until it meets and merges with the grease placed around the upper end of the armature 13. This grease may be inserted in the open end 29 by means of a syringe or any other suitable method. The contact prongs 20 are placed in suitable passages through the wall of the mold at the joint 27 between the upper half 26 and the lower half 21. With the reproducer assembly thus in position, the upper half 26 is placed in position on the lower half 21 and the two halves of the mold are clamped together by suitable means.

The surfaces of the cavity are waxed prior to the closing of the mold. The reproducer cartridge of this invention is cast from a resin which is poured into the cavity 25 through one or more sprues 28. The cavity is vented by similar sprues. The cast resin is allowed to solidify or cool to a hard solid. At the completion of the solidification, the mold is open and aided by the waxed cavity walls and the grease layer in the mandrel 24 and the cast cartridge is easily removed from the mold in the form shown in Figs. 4 and 5.

The cast resin may be any resin which will set and cure from a fluid state at a temperature in the molding operation which will not cause the viscous grease to melt and run so as to lose its function as a core. The melt may be either a resin melted to pour into the cavity 25 or dissolved in a suitable solvent to flow into the cavity 25. One suitable resin is a resin or mixture of resins selected from the unsaturated polyester resin.

In the case cartridge, the reproducer assembly is encased in a solid resin with a grease core 31 around the armature 13 and the end of the spring 17. Except for the parts encased in the grease core 31, the reproducer parts are firmly embedded in solid resin. To complete the assembly of a cartridge 30, additional viscous grease may be injected around the armature 13 in the core 16. Then a small rubber dust shield 32 is inserted over the armature 13 and into a recess 33 formed in the bottom of the cast cartridge by the raised platform 22. This dust shield seals the core 16 around the armature 13. A

ring 34 of a cast phenolic or a metal is snapped in place in the recess 33 over the dust shield 32.

The cast cartridge 36 is then complete in the form shown in Figs. 4 and 5. The armature 13 is free to move freely at the end of spring 17. The viscous grease of core 31 serves as a damping medium for the motion of the armature and the free end of the spring 17. At the same time, the grease of the core 31 provides a core around the moving parts of the cast cartridge 30 to allow these parts motion while the remainder of the parts are securely held in the cast resin. In this way the sound reproducer is converted into a single, integral, unitary member and the freedom of motion of the moving parts is not impaired while the action of a damping substance is simultaneously incorporated into the cast cartridge 30. The viscous grease of the core 31 may be any suitable inert viscous compound of satisfactory consistency. As the casting temperature is not intended to be greater than F, most heavy petroleum greases will be satisfactory. In those cases where less damping action is sought, a lighter or less viscous grease may be employed with corresponding adjustments in the casting temperature if necessary. A viscous grease may be prepared from a mixture of silicone oil and diatomaceous earth to have a consistency of heavy cold cream. This silicone diatomaceous earth compound will stand up as a core during casting with a resin having a melting point of 150 F. and it will also have a viscosity providing desirable damping qualities.

Among the many advantages of this invention are the light weight of the completed cast cartridge and the solidity of its unitary construction. Also, the parts of the reproducer assembly are completely protected from atmospheric action. In sound reproducers any avoidance of resonance or spurious noises caused by loose parts is desirable. Encasing the assembly parts in a solid body to hold them permanently and securely with relation to each other insures the reduction, if not complete elimination of undesirable interference or operation of the parts.

In addition, the permanent and unvarying damping action of the sealed-in grease core material is advantageous. Other advantages are the economy of manufacture both in materials and in the assemblying operation. Also, the easy adaptation of the reproducer of this invention into a variety of reproducer arms is an advantage. It will thus be seen that by means of this invention an improved reproducer assembly is provided in a relatively simple and inexpensive manner and a novel and advantageous method of producing the reproducer is provided.

Modifications may be made in the illustrated and described embodiments of this invention without departure from the spirit of the invention. In the above description, the cast material has been described as a cast resin. Specifically, this refers to the polyester synthetic resin. This resin is selected for the example for its compatibility with the light grease employed as damping compound and core material in the example. The spirit of this invention is the adaptation of the viscous fluid material and the cast material to combine in the method of this invention to provide the product of this invention. The polyester resin referred to in the specific embodiment above melts and solidifies at a temperature which is close to the melting point of the viscous damping compound and core material. Other cast materials may likewise be selected for casting within the temperature limitation of the melting point of the viscous compound. These other cast materials may include both synthetic and natural plastic materials without departure from the spirit of this invention.

In another possible modification the casting may be carried on at a" lowered temperature which would also lower the melting point of the viscous grease. Thus, a grease with a lower melting point may be employed as the damping medium without losing its function as a core in the casting operation.

A feature of this invention is the dielectric properties of the casting material. Likewise, the viscous compound may be varied in physical properties according to the degree of damping desired in the cast cartridge. In application to this invention where the damping compound is changed, the cast material may be correspondingly changed in substance Without departure from this invention. For this reason, this invention is limited by the scope of the accompanying claims.

I claim:

1. A method of forming a unitary sound reproducer cartridge having parts for sound reproduction including moving parts comprising the steps of mounting the sound reproducing parts in a mold, inserting a hollow shaft of said mold within the coil of said sound reproducing parts, immersing at least part of the moving parts of said sound reproducer in a core of a grease substance having a Saybolt viscosity of 100 or more, casting a resin in said mold at a temperature below 150 F. substantially completely enclosing said reproducer parts and said core in said one piece resin casting and removing said casting and said enclosed core and parts from said mold and removing said hollow shaft from said coil and said one piece resin casting to provide a small access passage from said reproducer parts through said casting.

In a magnetic sound reproducer the combination of a core of a grease having a Saybolt viscosity of 100 or more, a reproducer assembly associated with said core, moving parts of said reproducer assembly at least partially immersed in said core, a solid one piece resin casting substantially completely enclosing said core and said reproducer assembly save for a single narrow passage in said resin casting extending outward from said core and an armature of said reproducer assembly extending out of said casting from said core through said narrow passage.

3. In a magnetic sound reproducer a combination of a core of a grease having a Saybolt viscosity of at least 100, a reproducer assembly including in combination a pair of pole pieces, a coil, a bar magnet and an armature supported on the free end of a spring mounted on said bar magnet, said armature and said free end of said spring immersed in said core; a solid one piece resin casting substantially completely enclosing said reproducer assembly and core having said bar magnet, pole pieces and coil embedded therein, a single narrow passage through said resin casting and an end of said armature extending out of said casting through said passage.

4. In a magnetic sound reproducer, the combination of a core of viscous fluid having a Saybolt viscosity of at least 100, a solid one-piece resin casting enclosing said core, a reproducer assembly partially immersed in said viscous fluid and partially embedded in said resin casting including in combination a pair of pole pieces, a coil, a bar magnet and an armature mounted on the free end of a spring mounted on said bar magnet, said bar magnet being embeddedin said casting and said armature and said free end of sai spring being immersed in said core, and said solid one-piece casting substantially completely encompassing said reproducer assembly and said core save for a single, narrow passage through said casting and an end of said armature extending out of said casting through said passage.

5. A magnetic sound reproducer as claimed in claim 4 having said coil and said pole pieces and terminal leads embedded in said resin casting and contact prongs partially embedded in said resin casting and extending therefrom.

6. A method of forming a unitary sound reproducer cartridge having parts for sound reproduction including moving parts comprising mounting the sound reproducing parts in a mold, immersing a portion of said moving parts of said sound reproducer in a viscous substance having a Saybolt viscosity of or more, casting a resin in said mold, embedding a portion of said reproducer parts in said resin and enclosing said core and said moving parts in said resin casting, providing a small access passage through said resin casting, removing said casting and said enclosed core and parts from said mold to provide said unitary sound reproducer with a substantially completely enclosing solid one-piece resin casting formed around said reproducer parts and said core.

References Cited in the file of this patent UNITED STATES PATENTS 1,333,004 Vaughn Mar. 9, 1920 2,037,255 Miller Apr. 14, 1936 2,400,662 Roberton May 21, 1946 2,471,592 Thomson May 31, 1949 2,519,185 Harris Aug. 15, 1950 2,538,164 Pickering Jan. 16, 1951 2,543,127 Pickering Feb. 27, 1951 2,548,353 Cunningham Apr. 10, 1951 2.5 948 Lynch Apr. 29, 1952

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