US2325807A - Phonograph mounting - Google Patents

Description

Aug. '3, 1943.

l. l.. STEPHAN PHONOGRAPH MOUNTING y Filed April 23, 1'941 'A 2 sheets-sheet 1 Aug. 3, 1943.

PHONOGRAPH MOUNT ING Filed April 23, 1941 2 Sheets-Sheet 2 L. STEPHAN 2,325,807

Patented Aug. 3, 1943 PHON OGRAPH MOUNTING Ingo L. Stephan, Delanco, N. J., assignor to Philco Radio and Television Corporation, Philadelphia, Pa., a corporation of Delaware Application April 23, 1941, Serial No. 389,988

2 Claims.

This invention relates to improvements in electric phonographs, and has particular reference to that type of instrument in which a radio, a phonograph connected therethrough, and a loudspeaker common to both, are mounted in a single cabinet.

Still more particularly, the invention relates to an improved phonograph mounting means which is especially useful in that type ofA phonograph reproducer utilizing only a small driving force to eiect lateral motion of the stylus, as for example the photo-electric reproducer described in the copending application of -E. O. Thompson, No. 357,322, led September 18, 1940, in which the motor, turntable and a sound pickup of the photo-electric type are mounted as a unit. Devices of this character are highly sensitive and are at times subject to serious micropbonic vibrations, due to the fact that the phonograph sound pickup and the loudspeaker are both supported by common cabinet Walls which form a mechanical path or circuit tending to transmit vibrations from the loudspeaker to the pickup.

The result is objectionable microphonic feedback from the loudspeaker through the pickup and back to the amplifier. 'Ihis objectionable action has presented a special problem in modern constructions, since the amplifiers and sound repro-V ducers are particularly sensitive, and many of the objectionable mechanical vibrations have a frequency within the audio .frequency band.

It has been proposed heretofore to employ rubber blocks or common coil springs to resiliently mount the motor, turntable, and pickup as a unit, but such constructions, while helpful, have not resulted incomplete isolation of the pickup from objectionable vibrations. For example, the photoelectric pickup of the above-mentioned copending application utilizes a mirror mounted for limited rotational movement about a vertical axis, and therefore it must be damped particularly against vibrations of the pickup supporting plate in a horizontal sense. The action of this mirror need not be fully described here, as it forms no part of the present invention, per se. However, it should be pointed out that undesirable vibrations, especially in a horizontal sense, interfere (ci. 17g-100.12)

a novel mounting for the plate which carries the turntable, motor and pickup, which .mounting re'- siliently supports the vertically imposed weight of the above elements, while at the same time allowing a high degree of flexibility for base plate movements in the horizontal sense.

Another object of the invention resides in the provision of a weight-carrying base plate support system, the natural frequency of which is substantially below the lowest frequencies which could be picked up and amplified.

A still further object of the invention is the provision of a base plate of the above vtype which is supported in a xed transverse portion of the cabinet by means of conical spiral springs of such construction that, although allowing nexibility of the kind described, they are of'relatively small overall height.

It is also an object of the invention to provide a base plate mounting spring which may be very readily mounted in the machine, and which is particularly well adapted to meet the conditions encountered during shipment of the phonograph.

The manner in which the above objects and advantages are realized will be best understood by a consideration of the following description, taken together with the accompanying drawings which illustrate the preferred embodiment of the .invention In the drawings: y

Fig. 1 is a view, partly sectional and partly elevational, showing the invention applied to a radiophonograph combination; Y

Fig. 2 is a perspective viewvof the main cabinet support member, which is adapted to support the weight carrying base plate;

Fig. 3 is an enlarged sectional view of one of the base plate mounting units shown in Fig. 1;

Fig. 4 is an enlarged elevational view of one of the mounting springs; and

Fig. 5 is a face view of the blank from which the spring is made. 1

Referring particularly to Fig. 1, the cabinet is generally indicated by the reference numeral/2, and has a radio reeciver 3, a phonograph 4, and a loudspeaker 5 mounted therein. The phonograph pickup is preferably connected to the audio amplifier of the receiver for amplification and reproduction of the recorded sound, as will be well understood. The phonograph is preferably of the type disclosed in the above-mentioned application and comprises a. photo-electric pickup embodying an oscillating mirror.

The cabinet is provided with a. supporting shelf 6, upon which base plate 1 is resiliently carried by a plurality of supporting springs 8. Preferably four springs are provided, one at each corner of the base plate, but any suitable number may be employed. Y The resiliently mounted base plate provides a resilient unitary mounting for the motor 9, turntable I 0, and tone arm II.

Referring to Figs. 2 and 3, the supporting shelf 6, has a plurality of apertures I2 therein forming countersunk spring-supporting seats, and a tapped sleeve or bushing I3 with-a retaining flange thereon is mounted in each aperture in axial alignment with the spring 8.

As shown in Figs. 3 to 5,the spring metal is of relatively high and narrow rectangular section. Although it is preferred to employ carbon steel, the springs may be made of any material having a high degree of strength andresilience, as long as the cross sectional shape is in substantial accordance with the illustrated embodiment. I

As clearly illustrated in. Fig. 5, each spring is preferably formed from, a preformed blank of sheet metal, and the end portions of the blank are so configured that the lower edge of the bottom coil and the upper edge of the top coil will each lie in a plane perpendicular to the spring axis when the blank is coiled. This avoids any tendency of the spring to cock sideways in its countersunk recess. Moreover, it can be seen that the Width of the blank tapers toward that end of the blank which forms the upper coils, thus insuring suillcient flexibility in the vertical direction.

Each spring ts snugly into its countersunk hole I2, and carries the base plate I on its upper edge. In order to securely position the base plate with respect to each mounting spring, a hole is provided in the base plate through which bolt I4 extends and is firmly gripped by the upper spring coil. This firm cooperation also avoids accidental displacement of the bolt.`

In connection with this positioning bolt, it will be noted that it may be depressed and its threads engaged with the cooperating thread formed interiorly of the sleeve I3, thus depressing the spring until the base plate 1 is in firm contact with the foundation coil of the spring. During shipment of the machine it is desirable to have' vibrations which can be transmitted from the cabinet structure to the pickup, are below the lowest frequencies that will affect the pickup.

Moreover, this spring is simple to mount,-Well adapted to cooperate with the securing-position- V ing bolt, and its cross section has the additional advantage of providing a rigid seat for Ythe base plate when it is depressed during shipment.

It will be understood, of course, that the invention is not limited to the specific embodiment illustrated but is capable of other embodiments and modifications. Further, it will be apparent that the invention is not limited to a radiophonograph combination but is applicable to any phonographic apparatus.

I claim: E

l. In a phonographic sound reproducing apparatus of the cabinet type, having a motor, turntable, sound pickup, loudspeaker and an amplifier mounted within the cabinet; a device for minimizing microphonic feedback from the loudspeaker to the pickup, comprising a floating base member adapted to carry the motor, turntable and pickup, a' foundation member within the cabinet, a plurality of conical spiral springs xed in said foundation member and adapted to carry said floating base member, each of said springs being of stock substantially rectangular. in crosssection, the height of the cross-section paralleling the longitudinal axis of the spring and being substantially greater than the width thereof, and means coopera-ting with the foundation member to rigidly secure said base member and foundation member together, said means being releasable and serving to position said oating base member with respect to said springs when in the released position.

2. In a phonographic sound reproducing apparatus of the cabinet type, having a motor, turntable, sound pickup, loudspeaker and an amplier mounted Within the cabinet; a device for minimizing microphonic feedback from the loudspeaker to the pickup, comprising a floating base member adapted to carry the motor, turntable and pickup, a foundation member within the cabinet having aplurality'of countersunk recesses therein, a plurality of conical spiral springs Vseated respectively in said recesses and supporting said base member, each of said springs comprising a coiled strip of sheet material whose sides are substantially parallel with the axis of the spring, a plurality of tapped sleeves carried by said foundation member in axial alignment with the respective springs, and a bolt extendingfrom said -base member axially through each spring and engageable with the associated sleeve to secure the base member to the foundation member.

INGo L STEPHAN.

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