US2777902A - Phonograph cabinet - Google Patents

Description

F. C. GOLDMARK PHONOGRAPH CABINET Filed Aug. 19,

FIG.

Jan. 15, 1957 f J, u my G /m C V 4 L f a JH I D/ W F L U EWE ||s wm G 1u- F Im @fr :Vwvnrwy VJMgvU/A ,Un .uwtwww UMH/uv@ EYS United States Patent 'i PHONOGRAPH CABINET Peter C. Goldmark, New Canaan, Conn., assigner to Columbia Broadcasting System, Inc., New York, N. Y., a corporation of New York Application August 19, 1952, Serial No. 305,246 6 Claims. (Cl. 179-100.4)

This invention relates to phonographs, and particularly to a compact electric phonograph of relatively small volume capable of high fidelity reproduction.

There is a considerable demand for relatively small, compact, high fidelity phonographs. Among other factors, high fidelity reproduction requires a frequency range extending from low bass frequencies to high treble frequencies. While the exact range depends upon the degree of perfection sought, a range extending from 50 to 10,000 cycles per second, with reasonable smoothness of response within this range, is commonly considered adequate. Of course, factors other than frequency range are important in securing true high fidelity, such as low harmonic distortion, good transient response, adequate loudspeaker damping, etc.

yIn the medium and high frequency ranges there is little difficulty in obtaining adequate fidelity of reproduction even in a phonograph of relatively small volume, provided good engineering practice is followed. However, good reproduction of low frequencies, particularly those below about l() cycles per second, is commonly obtained only by housing the loudspeakers in cabinets of relatively large volume. Although so-called table models have been available for a long time, they are commonly deficient in bass response due to the small cabinet volumes available.

It is a primary object of the present invention to provide a compact phonograph of the table model type in which full utilization of the entire available cabinet volume is made in order to improve the bass response.

In accordance with the invention a cabinet is provided having a hinged cover which, in the closed position, makes a tight lit with the lower box portion of the cabinet. A record player is mounted in the box portion and one or more loudspeakers with an associated amplifier are mounted beneath the record player, suitable openings being provided in the sides of the box for the loudspeakers. It is preferred to employ two loudspeakers on opposite sides of the cabinet to obtain a spacial distribution of sound which materially increases the realistic quality of the music. Except for the loudspeaker openings -the cabinet is substantially imperforate, and these openings are covered by the diaphragms of the speakers.

In the heretofore common practice, the record playing mechanism consisting of a turntable, pickup etc., is'mounted on a base plate which in turn is resiliently mountedon a supporting plate which extends from wall to wall of the cabinet. In contra-distinction to this arrangement, in accordance to the present invention the base plate is supported on brackets which extend around only a portion of the periphery of the cabinet, and an open space is provided between the base plate and adjacent side walls to allow sound waves to pass freely therearound. Advantageously the brackets do not extend along the portions of the side walls where the speakers are mounted. The brackets themselves are made narrow and the base plate vertically spaced therefrom so that even in these regions sound waves can pass readily 2,777,902 Patented Jan. 15, 1957 from beneath the record player in this manner, and by providing a tight t between the cover and box sections of the cabinet, the volume above the base plate is made available to form, together with the volume below thc plate, ya closed resonant chamber which improves the bass response and increases the acoustic damping of the loudspeakers.

The invention will be more fully understood by reference to the following description of a specific embodiment thereof, taken in conjunction with the drawings in which:

Fig. 1 is a plan view of the phonograph with the cover closed;

Fig. 2 is a side elevation of the phonograph;

Fig. 3 is a plan view of the phonograph with the cover open;

Fig. 4 is a cross section taken along the line 4-*4 of Fig. 3;

Fig. 5 is a cross section taken along the line 5 5 of Fig. 4; and

Fig. 6 is a detail relating to the base plate suspension.

Referring to Figs. 1 and 2, a cabinet is shown having a lower box section 10 and a cover section 11 hinged thereto at 12. A grille 13 is provided for a loudspeaker in one side of the cabinet. The limited size of the cabinet requires that relatively small loudspeakers be employed, and it has been found advantageous to employ two loudspeakers in order to obtain adequate volume at low frequencies. Further, in order to obtain a spacial distribution of sound, the two Speakers are mounted on opposite sides of the cabinet. Sound from these two oppositely-directed sources is rellected from dilferent Walls of a room and reaches the ears of a listener from different directions and with different phase relations. This greatly improves the realistic quality of the reproduction over that obtained from a single source.

Accordingly, the loudspeakers are mounted one on each side of the cabinet, and a grille similar to 13 is provided on the opposite side of the cabinet from that shown in Fig. 2. Each grille, here shown as rectangular, extends only part way through the side wall and is backed by a panel having a circular cut-out which corresponds to the diameter of the speaker. Suitable control knobs 14 are provided, one of which may be the conventional on-otf switch combined with a volume control, and the other a tone control.

As shown in Fig. 3, the hinge l2 is of the piano-hinge type extending entirely across the rear of the cabinet. A layer of felt 15 may be provided on the upper edges of the sides of the box section so that when thc cover 1l is closed a tight lit is ensured. The felt may be placed on the corresponding edges `of the cover rather than on the box, or on both if desired. With Sulliciently accurate construction of the box and cover sections, the felt may be dispensed with.

The cabinet is preferably of fairly heavy construction, one-half inch plywood being suitable. The joints should follow good cabinet practice so that the entire cabinet is strong and rigid. Side rails 16, 16' are advantageously employed along the upper edges of the sides of the cabinet for re-enforcenlent. A hinged stop 17 may be provided to limit the angle through which the cover can move, and to hold it in raised position for changing records.

Referring to Fig. 3, a record player is provided comprising a base plate 2l on which is mounted a turntable 22 and pickup arm 23. An electromechanical pickup cartridge, such as a crystal or variable reluctance cartridge, is mounted in the free end 23 of the arm. An automatic record changer is here depicted and an arm 24 is provided to hold the records in proper position for successive dropping. A suitable motor and driving mech- 3. anism is located-below-the baseplateZ-l: A/controlknob 1s provided so that different rotational speeds may be selected. Advantageously, the pickup arm 23 is provided with a dual-stylus cartridge sc'that both co1ive,ntio11" 1l78V R. i?. M. coarse-groove records and long-playing 331/3 R. P; M. hue-groove recordsmay be reproduced. An open space 26 isf providedbetween the base'plate 2l and the adjacent walls of the'cabinet extending entirely around the periphery-ot thebase plate.

Referring to Figs. 4 6, the base plate 2l. is resiliently supported on narrow brackets 27, 27' which are afiixed to the walls ofthe lower box section. Conveniently the brackets are made o'bwood and supporting blocks 28, 2S' are provided for rigidity. rEhe brackets are counters'unk at 3l toreceive corresponding' springs 32' by means of which the base plate 2l is resiliently` supported in a horizontal position.

Loudspeakers 33 and id'are mounted on opposite sides of the cabinet and an electronic amplifier is located in the section indicated by the rectangle 35". i are ol' the electroacoustic direct-radiating type with diaphragme generaliy conical form. They are registered with grilles It?) so that the. iront radiation passesdirectly into the surrounding room. ln order to permit as large diameter speaker as possibie in the limited available space, recesses are provided in the side rails i6, 16' to accommodate the upper rim portions thereof. in the embodiment shown, substantially the entire, radiating area of the diaphragme is below the level of the upper surface of base plate 2.1. Tous the back radiation from the speakers is directly into the volume below the base plate. Since,

however, the construction described herein makesthe entire cabinet volume available as a single acoustic chamber, a portion of the diaphragms can extendA above the base plate 2l it desired.

From Fig. 5 it will be noted that the.supportingbrackets 27, 27 extend around only a portion of the periphery of the side walls of the cabinet, slightly less than 50% of the periphery with the specific dimensions'illustrated. Furthermore, the relatively narrow brackets permit free passage ot sound waves from beneath the base plate through the space 26 between base plate and'side walls to the volume above the base plate `as indicated by the arrow 3d in Fig. 6. Thus sound waves can pass freely around the base plate at all points ofits periphery.

part of the volume below the base plate, acoustically speaking, so that tie entire inner volume of the cabinet (except for the portions physically occupied by apparatus) is `availal'lle as a resonant chamber for the loudspeakers. This greatly improves the bass response and enables overall reproduction of excellent fidelity to be obtained.

While the exact extent and location of the brackets can depart from that illustrated, it is particularly advantageous not to have them extend across those portions of the side walls where the speakers are mounted. Thus `the back radiation can freely pass into the upper space through the adjacent portions `or passage 26.

As an aid to the ready practice of the invention the following detailed dimensions and other data are given of a specic construction which has given excellent performance, it being understood that the invention is not confined thereto. The cabinet was strongly made of 1A. in plywood and was l5' inches wide inside. The inside height was 8% inches, the box being 6 inches deep andthe cover 2% inches deep. The depth of the cabinet was 121/3. inches at the center and lll/2 inches at the sides. The side rails i6, le' had a horizontal thickness of 3/4 inches and a vertical width of 1% inches. The base plate 21 was l31/s inches wide and 11% inches deep, and was mounted with the upper surface thereof il@ inches below the top of the box section. This provides a clearance of at least 3/inch around `the entirel periphery of the base plate, with a somewhat greater clearance at the front.

The loudspeakersinV this manner the volume above the base plate is made "a The speakers were fairlyv inexpensive 6 inch speakers: The overall amplitude-frequency characteristic of the pickup and ampliier was designed to provide considerable bass boost, the input to the speakers at 60 cycles being of the order of 20 db higher than at 1000 cycles. This electrical bass boost in itself is'not adequate to produce the desired uniformity in acoustic response. As is well known, adequate-reproduction' of lowfrequencies requires not only adequate electrical input but alsoproper acoustic loading of the loudspeakers and proper damping thereof. The latter is provided by the construction described=-here inbefore which enables the entire cabinet volumeto serve `as an acoustic chamber.

A phonograph constructed with the foregoing specifications was found to give an essential constant acoustic output from 60 cycles to 10,000 cycles. Substantial acoustic output was obtained below 60 cycles, extendingas low'as 30 cycles.. This'is believed' to be quiteV outstanding for a cabinet ofl'e'ss than one cubic foot volume. The importance of the cabinet-construction and thev mounting of the base plate described hereinbefore was readily' apparent by merely raisingv the cover. Just a slight opening of the cover markedly reduced the bass response, andthe dicerence was readily apparent with deep organ' music'.

Many modifications and departures from the specific.

example' given above maybe made within `the scope of the invention. With a well made cabinet it has been found that the layer ot' felt around the edge of the cover suiced to insure an adequately tight closure, and may. even be dispensed with. However, more elaborate means.

maybe employed to secure a tight closure if desired. The brackets described hereinbefore have been found. satisfactory and are relatively inexpensive. lf.desired,.how ever, individual narrow metal brackets may be provided for cachot" the coil springs 32, thereby leaving. even greater freedom `for sound waves topass from below the base plate to the volume thereabove. These and other modifications will occur to those skilled in the art within the spiritand scope of the invention.

l claim:

l.` A phonograph comprising a lower box section having a. bottom and side walls, an upper coversection hinged to said box section and formingv a tight t therewith in they closed position, the cover section being in its closedV position .during normal phonograph operation, a= record' turntable and an associated electromechanical pickup mounted ona supporting base plate, supportingbrackets extending. around a portion only of the inner 'perihery' of said side walls, said base platebeing mounted substantially horizontally on said brackets, an electro-acoustic loudspeaker mounted in said box section'with at least the major portion thereof below the plane of. said base plate, and an open space between said baseplate and` the adjacent-sidewalls around substantiallythe entireperiphery thereof whereby the volumes both above and belowsaid base plate forma closed acoustic chamber' for said loudspeaker, said box and cover sections beingv unitary and substantially imperforate tothe exteriorfexcept for an opening registered with the front ofa loudspeaker.

2. A phonograph which comprises 'alower box section having' `a bottoml and side walls, an uppercover section hinged to said box section and forming a--tight lit therewith in the closed position, the cover section being.- in its closed position during normal-.phonograph operaed on one of said side walls with at least a major por-- tion thereof below theplane or' vsaid base plate, said brackets. not extending along the portion of said base` plate adjacent said loudspeaker, and an open space between said base plate and the adjacent side walls around substantially the entire periphery thereof whereby the volumes both above and below said base plate form a closed acoustic chamber for said loudspeaker, said box and cover sections being unitary and substantially imperforate to the exterior except for an opening registered with the front of a loudspeaker.

3. A phonograph which comprises a lower box section having a bottom and side walls, an upper cover section hinged to said box section and forming a tight t therewith in the closed position, the cover section being in its closed position during normal phonograph operation, a record turntable and associated electromechanical pickup mounted on a supporting base plate, narrow supporting brackets extending around a portion only of the inner periphery of said side walls, said base plate being mounted substantially horizontally on said brackets with clearance therebetween, an electroacoustic direct-radiating loudspeaker mounted on one of said side walls with at least -a major portion thereof below the plane of said base plate, said brackets not extending along the portion of said base plate adjacent said loudspeaker, an electronic amplifier mounted in said box section below said base plate and connected between said pickup and said loudspeaker, fand an open space between said base plate and side walls around substantially the entire periphery thereof whereby the volumes both above and below said base plate form a closed acoustic chamber for the back radiation of said loudspeaker, said box and cover sections being unitary and substantially imperforate to the exterior except for an opening registered with the front of a loudspeaker.

4. A phonograph which comprises a lower box section having a bottom and side walls, an upper cover section hinged to said box section and forming a tight t therewith in the closed position, the cover section being in its closed position during normal phonograph operation, a record turntable and associated electromechanical pickup mounted on a supporting base plate, supporting brackets extending around a portion only of the inner periphery of said side walls, said base plate being mounted substantially horizontally on said supporting brackets, a plurality of electroacoustic direct-radiating loudspeakers mounted on opposite side walls of said box section with at least a major portion thereof below the plane of said base plate, and an open space between said base plate and the adjacent side walls around substantially the entire periphery thereof whereby the volumes both above and below said base plate form a closed acoustic chamber for said loudspeaker, said box land cover sections being unitary and substantially imperforate to the exterior except for openings registered with the fronts of said loudspeakers.

5. A compact high delity phonograph which comprises a lower box section having a bottom and side walls, an upper cover section hinged to said box section and forming a tight iit therewith in the closed position, the cover section being in its closed position during normal phonograph operation, a record turntable and associated electromechanical pickup mounted on a supporting base plate, narrow supporting brackets extending around a portion only of the inner periphery of said side walls, resilient mounting means supporting said base plate substantially horizontally on said supporting brackets with clearance therebetween, a plurality of electroacoustic direct-radiating loudspeakers mounted on opposite side walls of said box section with at least a major portion thereof below the plane of said base plate, said brackets not extending along the portions lof said base plate adjacent `said loudspeakers, an electronic amplier mounted -in said box section below said base plate and connected between said pickup and said loudspeakers, and an open space between said base plate land side Walls around sub* stantially the entire periphery thereof whereby the volurnes both above and below said base plate form a closed acoustic chamber for the back radiation of said loudspeakers, said box and cover sections being unitary and substantially imperforate to the exterior except for openings registered with the fronts of said loudspeakers.

6. A compact high delity phonograph which comprises a lower box section having a bottom and side walls, an upper cover section hinged to said box section and forming a tight tit therewith in the closed position, the cover section being in its closed position during normal phonograph operation, a record turntable and associated electromechanical pickup mounted on a supporting base plate, narrow supporting brackets aixed to the side walls of said box section and extending along not more than about percent of the periphery thereof, resilient mounting means supporting said base plate substantially horizontally on said supporting brackets with vertical cle-arance therebetween, a plurality of electroacoustic direct-radiating loudspeakers mounted on opposite side walls of said box section with at least a major portion thereof below the plane of said base plate, said brackets not extending along the portions of said base plate adjacent said loudspeakers, an electronic amplier mounted in said box section below said base plate and connected between said pickup and said loudspeakers, and an open space between said b-ase plate and side walls around substantially the entire periphery thereof whereby the volumes both above and below said bas-e plate form a closed acoustic chamber for the back radiation of said loudspeakers, said box and cover sections being unitary and substantially imperforate to the exterior except for openings registered with the fronts of said loudspeakers.

References Cited in the tile of this patent UNITED STATES PATENTS 1,705,017 rakosky May 12, 1929 2,108,846 Brown Feb. 22, 1938 2,174,107 Kenney Sept. 26, 1939 2,610,694 De Boer Sept. 16, 1952 FOREIGN PATENTS 709,411 France May 18, 1931 782,095 France May 27, 1935

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