US2133815A - Phonograph reproducer - Google Patents

Description

Oct. 18, 1938. H, ARR N 2,133,815

INVENTOR H. C. HA RR/SON- ATTORNEY Patented Oct. 18, 1938 UNITED v STATES PHONOGRAPH REPRODUCER v Henry C/Harrison, Port Washington, N. Y. as- I signor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New 7 York Application September 16, 1936, Serial No. 101,039

2 Claims? 01. 179-10041) This invention relates to phonograph reproducers and the object of the invention is a-high quality reproducer of the universal type which will operate at satisfactory efficiency on either 5 hill and dale or lateral cut records.-

Universal reproducers of various types have been proposed heretofore. Some of these involved switching or some other operation in changing from one type of record to the other and other 10 previous types required a moving system which was not symmetrical with respect to the vertical axis.

In accordance with the general features of this invention a stylus is rigidly and coaxially connected to a circular coil positioned in an air-gap at one side of the coil and mounted to respond to either vertical or lateral stylus vibrations without requiring any special attention on the part of the operator as to the type of record being played.

In one embodiment the air-gap is defined by an outer pole-piece surrounding the coil and a central pole-piece within the coil shaded on one side to provide a gap of the required configuration and in an alternate construction the gap is defined by a circular central pole-piece and an outer polepiece presenting a pole face to only one side of the coil.

The coil and stylus assembly is preferably supported by spaced parallel cantilever springs of the type shown in Patent 2,027,168, granted to me January 7, 1926. One of the springs is free to deflect both vertically and laterally and the other spring is free to deflect both vertically and torsionally but not laterally so that either vertical or lateral vibrations of the stylus will vibrate the active portion of the coil vertically in the air-gap.

In such a structure with the coil rigidly attached to the stylus the coil velocity is always equal to that of the stylus for vertical vibrations thereby fixing the efficiency of the device for vertical records. The lateral efficiency will vary, however, with the relative magnitude of the distances from the stylus point and the active side 5 of the coil to the horizontal axis of rotation. When the reproducer is required to have the same efiiciency on both types of record these distances should be equal but it will be understood that the lateral efliciency may be made greater 50 or less than the vertical efficiency by proper proportioning of the moving system.

In the drawing, Fig. 1 is a reproducer according to the invention with a shaded central pole-piece, and 5 Fig. 2 is an alternate construction having a solid center pole and an outer pole with a semicircular pole face.

In Fig. 1 the coil II is wound on a shallow cup member 12 to which the stylus I3 is Srigidly 'se-' curedon the vertical axis of the coil. .ThisJassembly is resiliently mounted by meansxofthe spaced parallel springs 14 and l5. .which. are clamped to a portion (not shown) of'the stationary structure of the reproducer. The permanent magnet l6rhas apole-piece ll surrounding b the coil I l and a central pole-piece l8 within the coil and magnetically connected to the other pole of the magnet by the member I 9. The central pole-piece I8 is cylindrical in form but is shaded or cut away in its lower portion to form an end 15 piece 20 of semi-circular cross-section.

These two pole-pieces therefore define a semicircular gap Zl in the magnetic circuit on the right side of the cell but substantially no fiux fiows across the left side of the coil from the face 20 22 of the pole-piece I8. The member 26 is composed of brass or other non-magnetic material and serves merely as a spacer for the adjacent portions of the magnetic circuit.

In Fig. 2 the moving system-is identical with 25 that of Fig. 1. The central piece 23, however, is cylindrical throughout its length and the outer pole-piece 24 extends only half way around the coil H to form a semi-circular air-gap 25 at the right side of the coil as in Fig. 1. 30

When the stylus is vibrated vertically by a hill and dale record, the whole assembly moves vertically as a unit and the right half of the coil in either construction cuts the flux in the air-gap and generates voltages corresponding to the stylus 35 vibrations. When the stylus is vibrated laterally, the spring l4 also deflects laterally but the spring l5, being rigid in a lateral sense, deflects torsionally and a rocking motion is imparted to the coil. For the small amplitudes at which the stylus is 40 vibrated the motion of the right side of the coil in the air-gap will be substantially vertical as in the case when the stylus is driven by a hill and dale record.

As stated above the response or efiiciency of the reproducer on hill and dale records is determined by the design of the magnetic circuit and coil structure and is substantially independent of the relative lengths of the vertical and horizontal lever arms '0 and h (Fig. 2) since the stylus is rigidly connected to the coil. The velocity of the coil in the gap when the reproducer is operating on lateral records, however, will be directly dependent on the ratio .of these two arm lengths and the difference between the hill and dale response and the lateral response in decibels is therefore 20 log In the device shown the radius (h) of the coil 1 l is about .135 inch and the distance v from the tip of the stylus l3 to the upper spring I5 is about .215 inch. The ratio is therefore 1.59 which corresponds to about 4 decibels better response on hill and dale than on lateral records. If v=h, the reproducer obviously will be equally efiicient on either type record and if for example h' =.342 inch and v is .215 inch then Substituting this valve in the above equation 20 log .63=-4 lateral emciency is obtainable only at the expense of greater wear on the records and in most cases it is preferable to design the device for slightly lower response on lateral than on vertical records.

. While the invention has been described for purposes of illustration with reference to particular embodiments it is intended to be limited only by the scope of the following claims.

What is claimed is:

1. Ina universal reproducer, a moving system comprising a circular coil, a stylus, and means for holding the coil and stylus in spaced coaxial relation, a magnet system having an outer polepiece surrounding the coil and an inner polepiece shaded to form a semi-circular gap at one side of the coil, and a vertically and torsionally resilient spring supporting the system with one side of the coil within the gap.

2. In a universal reproducer, a moving system comprising a circular coil, a stylus, and means for holding the coil in spaced coaxial relation, a magnet system having pole-pieces defining a semi-circular air-gap at one side only of the coil, and a vertically and torsionally resilient supporting spring attached to said moving system at a distance from the'tip of the stylus which is of the same order of magnitude as the radius of the coil.

HENRY C. HARRISON.

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