US2730572A - Phonograph transducer - Google Patents

Description

Jan. 10, 1956 J. ANDRES PHONOGRAPH TRANSDUCER Filed Aug. 8, 1952 a. Z, .M 4%

improper operation.

4United States Patent PHDNOGRAPH TRANSDUCER Lloyd J. Andres, Chicago, Ill., assignor to Permo, Incorporated, Chicago, lll., a corporation Application August 8, 1952, Serial No. 303,294

4 Claims. (Cl. 179-100.41)

This invention relates in general to transducers and more particularly to a magnetic phonograph transducer.

Magnetic transducers previous to this invention incorporate armatures adapted to carry replaceable or xed needles. These armatures are movably positioned betweenY pole pieces by means of resilient bearings and/or spring suspensions including built in dampening means. It is well known that an eicient transducer of this character must include an armature and needle having low mass and a relatively high factor of lateral compliance together with predetermined vertical compliance and, to further complicate optimum results, the armature must be provided with a dampening material to minimize self resonance.

A common defect in previous transducers resides in the delicate armature suspension in which the desire for low mass, high compliance, effective dampening and self centering is at best a poor compromise. Armature suspensions of this class are subject to deformation from shock applied to the needle, and often displace the armature from its neutral position between pole pieces resulting in In many transducers adaptable for replaceable needles, damage to the armature often occurs when a needle is replaced unless great care and skill is eX- ercised in so doing.

The present invention overcomes the above objections through the provision of a magnetic transducer in which a conveniently replaceable needle is the armature which inherently provides low mass, effective dampening, predetermined vertical and lateral compliance and sufcient stiifness to maintain its predetermined neutral position between the pole pieces, and constitutes the principal object of the invention.

A further object of the invention is the provision of a magnetic transducer in which a replaceable combination armature needle is secured by one end thereof.

Another object of the invention is the provision of a replaceable needle for a magnetic transducer having a shank portion rnade from a helical convolute of magnetic material with the playing point secured in one end of said shank and the opposite end adapted to be rigidly secured in a transducer.

These and other objects and advantages in one embodiment of the invention are described and shown in the appended specification and drawing in which Fig. l is atop plan view of the transducer.

Fig. 2 is a cross sectional view of the transducer shown in Fig. 1 taken through section line 2 2 Fig. 3.

Y Fig. 3 is a bottom cross sectional view of the transducer shown in Fig. 1 taken through section line 3 3 Fig. 2.

Fig. 4 is a cross sectional end view taken through section line 4 4 Fig. 2.

Fig. 5 is an enlarged cross section of the needle shown in Fig. 2 taken through section line 4 4 with dampening material added.

Fig. 6 is a fragmentary enlarged cross sectional view of an alternate construction of the needle shown in Fig. 5.

Referring to Fig. 1, the upper body 1 of the transducer ICC comprises a non-magnetic frame in which all other components are secured. Tubular rivets 2 2 serve the dual purpose of retaining the principal components in proper relation and the means through which the transducer may be mounted in a tone arm. The two pins 3 3 provide the electric output connections. Screw 4 is threaded into the body for securing one end of the needle in rigid rela-` tion with the body 1. An aperture 5 is provided to facilitate removal of the needle when required.

Referring to Figs. 2, 3 and 4, a bottom cover 6 is retained by rivets 2 to complete the enclosure of the transducer and to retain other components in their respective operating positions. A pair of U-shaped pole pieces 7 8, made of magnetic material, are positioned in the body as shown with a permanent magnet 9 bridging both pole pieces, thus supplying north and south polarity to the pole pieces as shown by the letters N S in Fig. 3. Each of the pole pieces 7 8 are provided with a pair of projecting pole faces 10 10, 11 11, spaced apart from each other providing independent upper and lower air gaps across which two concentrated magnet flux paths are provided by the magnet 9. A coil having predetermined inductance is wound on bobbin 12, which bobbin is secured within the pole pieces 7 8 as shown with its pair of lead wires terminating in pins 3 3, which pins are insulated from the body 1 by insulator 13.

Referring to Fig. 4, a combination armature-needle 14 made of para-magnetic filament of uniform cross section in the form of a coil spring is snugly positioned at its upper end portion in a cylindrical bore 15 in the body 1, and a playing point 16 is secured by cement or solder in the opposite end of needle 14. The inside and outside diameter of a typical needle may be approximately .15 inch and .035 inch respectively. Certain well known alloys of high permeability having magnetic properties suitable for the needle are also mechanically favorable in that they eX- liibit relatively high moduli of elasticity even when annealed. The needle is retained in its normal neutral position between the two pairs of pole faces by said screw 4 threaded into body 1 with a slug 17 of soft material, like copper, between the inner end of the screw and the needle intended to slightly deform under the pressure exerted by the screw to secure the needle lirmly against vibratory forces.

Fig. 5 is a greatly enlarged view of the needle 14 showing the playing point 16 secured in one end and the interstices between turns as well as the entire space within the convolute filled with Visco-elastic dampening material, such as Viscoloid, polyethylene or one of the well known rubber base dampening materials.

Since the dynamic character of the needle may be varied to suit specic conditions, Fig. 6 illustrates an alternate needle 1S in which the convolute is formed from ribbon, of uniform elongated cross section, to achieve greater lateral stilness and lower mass than the round wire convolute shown in Fig. 5.

In operation, it is apparent from the foregoing that when the playing point 16 is engaged in a laterally recorded sound track the needle 14 will be oscillated laterally from its normal neutral position in accordance with the modulations in the sound track. Thus a portion of the magnetic ux, which normally independently bridges the upper and lower pole faces, will alternately be carried through the low reluctance needle in opposite directions through diagonally opposite pole faces 10 11. The coil in bobbin 12 will then be alternately threaded by a portion of this magnetic flux in opposite directions and a corresponding modulated electric current will be generated in the coil and through a circuit connected to said coil in accordance with well known laws.

lt is also apparent that the playing point 16 is vertically resilient with respect to the body 1 to provide proper com- 3. pliance when the playing point encounters well known pinch track conditions in the soundtrack groove.

The well known dampeni'ng materials above mentioned are subject to relatively rapid deterioration, and since: the needle requires replacement asl the inevitable result of wear to the playing pointl the simultaneous replacement of. the dampening material with each needle insures proper performance of the transducer. lt is also-to be noted that noA unusual skill isrequired to replace the needle because ofthe simple manipulation of the set screw 4 and the use ofV the aperture 5'V through which a small' wire or pin may be inserted tc conveniently eject the discarded needle.

Having thus described my invention, I- claim:

1. A magnetic phonograph transducer for energizing a sound, circuit comprising a body, a pair of pole pieces in spaced relation` in said. body, each of said pole pieces having an integral pair of poles in parallel spaced relation, the two said pairof pole pieces spaced from each other forming two air gaps, a permanent magnet bridging said pole pieces for normally providing two zones of magnetic ux across said air gaps, a coil of predetermined inductance symmetrically positioned within a portion of said pole pieces with its axis substantially centered in said air gaps and normal to the said zones of magnetic ux, a needle shank ot magnetic wire material in the shape of a helical convolute with a playing point secured at one end thereof, resilient dampening material substantially filling the space within the said convolute, means in said body for securing said shank by an end portion opposite that of said playing point with said shank extending through said coil substantially midway in said air gaps and intersecting said zones of magnetic dus' whereby the lateral movement of said playing peint will dex said shank in the said air gaps and generate a current in said coil when said coil is connected to a sound circuit.

2. A magnetic phonograph transducer for` energizing a sound circuit comprising a body, a pair of pole pieces in spaced relation in said body, each of said polepieces having an integral pair of poles in parallel spaced relation, the two said pair of pole pieces spaced from each other forming two air gaps, a permanent magnet bridging said pole pieces for normally providing two zones of magnetic ux across said air gaps, a coil of predetermined inductance symmetrically positioned within a portion of said pole pieces with its axis substantially centered in said air gaps and normal to the said zones oE magnetic flux, a needle shank of magnetic wire material in the shape of a helical convolute with a playing point secured at one end thereof, means in said body forsecuring said shank by an end portion opposite that of said. playing point with said shank extending through said coil substantially midway in said air gaps and intersecting said zones of magnetic ilux whereby the lateral movement of said playing point will ilex said shank in the said air gaps and generate a current in said coil when said coil is connected to a sound circuit.

3. A combination armature-needle for a magnetic phonograph transducer comprising an elongated coil spring of predetermined compliance formed of paramagnetic wire of uniform cross section, said spring having one end portion adapted to be secured in a said transducer and having a playing point secured in its opposite end, the space and interstices within said spring substantially filled with a` Visco-elastic dampening material in intimate contact with said spring.

4. A combination armature-needle for a magnetic phonograph transducer comprising an elongated helical convolute or" predetermined compliance formed of paramagnetic ribbon of uniform cross section, said convolute having one end portion adapted to be secured in a said transducer and having a playing point secured in its opposite end, the space and interstices within said convolute substantially, lilled with a viscoelastic dampening material in intimate contact with said convolute.

References Cited in the iile of this patent UNITED STATES PATENTS 375,0543 Watkins Feb. l, 1887 436,512 Weigand Sept. 16, 1890 1,732,029- Round Oct. 15, 1929 2,563,413 Ostrow Aug. 7, 1951

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