US2821578A

US2821578A - Phonograph tone arm for pseudo-stereophonic sound reproduction

Info

Publication number: US2821578A
Application number: US463947A
Authority: US
Inventors: Jr George Arthur Morrell
Original assignee: Astatic Corp
Current assignee: Astatic Corp
Priority date: 1954-10-22
Filing date: 1954-10-22
Publication date: 1958-01-28
Anticipated expiration: 1975-01-28

Description

Jan. 28, 1958 G. A. MORRELL, JR I 2,821,578

PHONOGRAPH TONE ARM FOR PSEUDO-STEREOPHONIC SOUND REPRODUCTION Filed Oct. 22, 1954 2 Sheets-Sheet 1 2a I I 21 I T I I5 g i 231,2 zzlBfiAm g 1 INVENTOR ozone: ARTHJR new, JR.

BY MW I ATTORNEY Jan. 28, 1958 G A.- MORRELL, JR 2,821,578 PHONOGRAPH TONE ARM FOR PSEUDO-STEREQPHONIC SOUND R RODUCTION EP Filed Oct. 22, 1954 r 2 Sheets-Sheet 2 United States Patent PHONOGRAPH TONE ARM FOR PSEUDO-STEREO- PHONIC SOUND REPRODUCTION George Arthur Morrell, Jr., Conneaut, Ohio, assignor to The Astatic Corporation, Conneaut, Ohio, :1 corporation of Ohio Application October 22, 1954, Serial No. 463,947 Claims. (Cl. 179-100.41)

The present invention relates to phonograph apparatus, and more particularly to a novel and improved tone arm assembly for incorporation with conventional phonograph turntable apparatus whereby the sameis adapted to obtain a plurality of separate pick-up responses from a conventional recording having but a single sound track or groove.

In so-called biuaural or stereophonic sound systems it is common practice to employ a plurality of separate sound channels each including separate control means and separate speaker outlets, the latter being located in spaced relation within a room or theater, for example, whereby different sounds emanate from ditferent points in the room. The location of the various speakers preferably corresponds approximately with the location of the microphones or other devices used in the recording of the sound tracks so that a realistic three dimensional effect is obtained during reproduction of the sound. The present invention, however, contemplates the use of but a single sound track, with the employment of a novel means for obtaining a plurality of time-displaced re-- spouses from such sound track, which responses may be separately processed and amplified and reproduced by means of separate spaced speaker outlet devices whereby to obtain an ingenious and highly realistic pseudo-stereophonic sound effect. In general, this eifect is obtained by so processing the separate time-displaced responses that high frequency tones are reproduced at one point while low frequency tones are reproduced at another point. Thus, in reproducing orchestral recordings, for example, the violins and other high-toned instruments will appear to be in one area of the rooms, while the bass instruments will appear to be in another area, all of which creates a unique spatial effect to the listener.

As an overall object, the present invention seeks to provide a novel tone arm assembly for use with a conventional phonograph turntable wherein are incorporated a plurality of separate record engaging styli and pick-up cartridge assemblies arranged in a novel manner so that the plurality of styli may follow the same sound track or groove in the recording, the styli being spaced a predetermined distance, however, so that a desired timedisplaced relationship is obtained in the stimuli taken from the recording.

In the preferred form of my invention two spaced styli and pick-up cartridges are employed to obtain two separate signals or stimuli, and I have found it desirable to displace these signals by approximately A of a second. Thus, it will be readily understood that in reproducing from a standard or 78 R. P. M. recording it will be necessary that the styli be spaced to a greater extent than is required for reproduction from micro-groove 45 or 33% R. P. M. recordings. Accordingly, it is another and more specific object of the invention to provide a novel tone arm assembly incorporating a plurality of pickup cartridge units wherein the assembly may be readily adapted during manufacture for use in either standard or micro-groove recording systems, substantially the whole of the assembly being of standard manufacture.

A further object of the invention resides in the provision of a novel dual stylus tone arm assembly for pseudostereophonic sound reproduction wherein novel arrangements are provided for mounting separate pick-up cartridge units in the tone arm so that the separate styli of the separate units may properly track or follow a single groove in the recording, regardless of the position of the tone arm on the recording.

Yet another object of the invention is the provision of a tone arm assembly constructed in accordance with the above stated object wherein novel means are provided for insuring that both of a pair of separate styli will engage the same sound track or groove when the tone arm is moved into operative position over a record disc.

The above and other objects and advantages of the invention will become apparent upon full consideration of the following detailed specification and accompanying drawing wherein are disclosed certain preferred embodiments of my invention.

In the drawing:

Figure 1 is a fragmentary longitudinal section view ofteachings" Figures 4 and 5 are fragmentary longitudinal section and bottom plan views respectively of a second embodiment of the tone arm of my invention; and

Figure 6 is an illustrative representation of the improved tone arm assembly of my invention, showing the manner in which a plurality of separately mounted recorded engaging styli track a single sound groove across the face of a recording disc.

Referring now to the drawing, and initially to Figures 1-3 thereof, the numeral 10 designates a tone arm member of generally conventional construction, in the outer free end of which is mounted a tandem pick-up cartridge assembly 12, the latter being mounted by means or screws 14 which engage threaded bosses 11 on the tone arm. in accordance with the preferred teachings of the invention the tandem pick-up cartridge assembly 12 comprises a fiat metal mounting plate 13 which is secured directly to the tone arm 10 and which mounts at its forward end portion a first pick-up cartridge 15. the latter being secured in spaced relation to the mounting plate 13" by means of suitable screws 16 and spacing washers 17, substantially as shown in Figure 1. The cartridge 15, in

the illustrated apparatus, is reversely disposed with re-l spect to the tone arm 10; that is, the stylus member 25 of the cartridge assembly extends rearwardly from the rearward end of the cartridge. Thus, the extreme forward tip of the stylus member 25 is provided with an acute bend so that it engages the surface of a forwardly moving recording disc in the proper manner. As shown in Figure 2 the mounting plate 13 extends rearwardly considerably beyond the first pick-up cartridge 15. And extending downwardly from the rearwardmost portion of the plate 13 is a stud or pivot 18 which is threaded at its lower end to receive a nut 21. Supported on the pivot member 18 is a forwardly extending auxiliary supporting arm 19, which is provided with a bear ing portion 19'- which engages the pivot 18 and is supported thereon by means of a friction-reducing washer;

20 and the nut 21.

At the outer or forward end of the cartridge supporting arm 19 is mounted, ,byirneans of bolts 23, a second pick:

up cartridge 22. The second cartridge 22 faces forwardly in the main arm and is provided with a conventional forwardly extending stylus member 26. In the illustrated arrangement the tandem cartridge assembly is conditioned for use in the microgroove recording systems, and the

styli

25 and 26 are spaced about three-eighths of an inch apart so that when both styli track the same record groove the response of the second stylus 26 will be advanced in time by approximately second with respect to the response of the first or forward stylus 25, it being understood that in normal operation the surface of a record disc will be moving from right to left with respect to the arm shown in Figure 1.

In accordance with the teachings of the invention the auxiliary cartridge supporting arm 19 is offset downwardly at its forward end portion so that the two cartridge assemblies and 22 are positioned on approximately the same level. Preferably, however, the second cartridge 26 should normally hang slightly lower than the first cartridge 15 so that when the complete tandem assembly is positioned in record engaging position the forward cartridge 15 supports little if any of, the weight of the second cartridge.22.

Of course, the

cartridges

15 and 22 are of conventional design, and are therefore intended to support the Weight of the tone arm, so that a certain predetermined stylus pressure is afforded. In the illustrated apparatus the stylus 25 of the forward cartridge supports substantially the entire weight of the tone arm, in accordance with the thus stated conventional practice. Accordingly, there is secured to the upper surface of the auxiliary cartridge supporting arm 19 a small lead weight 24 which serves to apply a predetermined pressure to the second stylus 26, to simulate the weight of a normal tone arm. It will be understood, of course, that this weight does not substantially affect the operating characteristics of the forward stylus 15 because of self-supporting nature of the second 7 cartridge assembly.

provided with output terminals 15 and 22' respectively which are separately connected to

dual conductor cables

27 and 28 respectively. The separate output responses thus obtained from the

cartridges

15 and 22 are preferably separately'amplified and processed and directed to spaced outlet speakers so that a unique stereophonic or binaural sound effect is obtained. Usually it will be desirable to separately filter the separate responses so that a first frequency band is amplified and, reproduced in one system while another frequency band is amplified and reproduced in a separate system.

Referring now to Figure 6, there is shown a conventional single-track recording disc 31 which, in the illustration, is of the slow speed or micro-groove type. The disc 31 is centered upon a suitable turntable, not shown, by means of a center spindle S1. Adjacent the turntable is a fixed universal pivot device 50 which supports the tone arm 10 for both up-and-down and side-to-side movements, in the conventional manner. In accordance with the preferred practice followed in the art the pivot point 50 is so positioned, and the arm 10 so arranged that the stylus or styli may track the record groove substantially tangentially across the entire face of the record. It will be observed, however, that as the radius of the record groove decreases toward the center of the disc the relation of the groove and the direct line (indicated at 32) between the outer or fixed stylus 25 continually changes. That is, with the stylus engaging the groove adjacent the outer edge of the record there is a relatively wide angle between groove and the direct line 32 between the stylus 25 and pivot 50, while at the inner or center portion of the record the direct line 32 is almost tangent to the groove. Thus, in order for the second stylus 26 to properly follow the groove it must move progressively .closer to the direct line-32 as the tone. arm moves inardly." Of course, as the line 32 is fixed in its relation to the tone arm 10 the stylus 26 must move with respect to the arm 10 in the direction of the center of the record disc. In the apparatus of my present invention this is provided for by the pivoted mounting or support for the cartridge 22, all as heretofore described.

Of course, since the relation of the floating cartridge 22 to the fixed cartridge 15 will depend upon the radius of the groove at the point of tracking, there will necessarily be a variance in the initial relation of the cartridges for record discs of different sizes; and since recording discs are conventionally manufactured in several different sizes I have found it necessary to provide means for adjustably locating the floating cartridge 22 in an initial position so that when the tone arm 10 is lowered into playing position at the outer edge of a recording disc both

styli

25 and 26 will automatically engage with the same convolution of the sound track or groove. To this end I provide that the pivot stud 18 for the floating cartridge 22 be tilted or canted in the manner shown in Figure 3 so that the action of gravity upon the floating cartridge 22' urges the same toward the outer side of the tone arm 10, or away from the line 32 shown in Figure 6. In accord= ance with the teachings of the invention there is provided on the outer wall of the tone arm 10 a threaded here which receives an adjustable thumb screw 29. Theinner end of the thumb screw 29 projects into the interior of the tone arm toward the floating cartridge 22 and defines a stop to limit the extent of pivoting movement of the cartridge 22 in a direction toward the outer wall of the tone arm. A lock nut 30 is also provided so that the thumb screw may be securely locked in any of its adjusted positions. Of course, once the tone arm is lowered into playing position and the

styli

25 and 26 begin to track a sound groove the floating cartridge will move progressively away from the thumb screw 29 as is clearly indicated in Figure 6.

Referring again to Figure 1, I have illustrated therein an arrangement wherein the stylus 25 carried by the fixed cartridge is replaced by a reversely disposedthat' is, forwardly extending-stylus member 25. The arrangement is such that the distance between the stylus tips is considerably greater than in the first described apparatus,

so that when the recording disc is revolving at an increased speed, for example the standard speed of 78 revolutions per minute, the desired time-displaced relationship of the separate pick-up responses is maintained substantially constant. Of course, while I prefer that the second pick-up response be delayed by approximately of a in U. S. Patent No. 2,575,999, to Cordes, are employed' In the latter embodiment the cartridge assemblies 15" and 22" are of tall, narrow physical outline, whereas in the first described embodiment the cartridge assemblies are of small vertical but relatively large transverse andlongitudinal dimensions. Thus, in the embodiment of Figures 4 and 5 the mounting plate 13 is of a slightly different form, and the stylus loading weight 24 is mounted at the side of the floating cartridge 22'. In other respects the embodiments are the same or equivalent.

It should thus be apparent that I have accomplished the several objects initially set forth. The subject invention represents a substantial advance in the phonographic art whereby it is'now possible and practical for home users of phonographic apparatus to obtain a unique and pleasing pseudo-stereophonic sound effect while employing conventional single track records. The heart of the invention resides in the provision of a practical unitary tone arm assembly incorporating a pair of pick-up cartridge units in such manner that the separate styli of the units may track a single sound groove in time delayed relation across the entire face of a record, notwithstanding that the radius of the groove continually varies, as does the orientation of the tone arm with respect to the recording disc.

Various specific features of importance are the provision of a novel floating support for one of the tandem cartridges whereby the stylus tip loading may be properly realized, the provision of means for permitting relative movement between the cartridges as required in properly tracking a sound groove, and the provision of readily adjustable means for automatically orienting the cartridges in proper initial relation so that when the tone arm is lowered into operative engagement with a recording disc the several styli will engage the same convolution of the sound groove.

Where it is desired to employ a single stylus, for conventional reproduction, the floating cartridge assembly may be removed or otherwise rendered inoperative; and to this end a skilled mechanic may provide, within the teachings of the invention, suitable means for locking the floating cartridge assembly in raised or retracted relation.

It should thus be clearly understood that the embodiments herein specifically shown and described are intended to be illustrative only, as many alterations may be made therein without departing from the spirit and scope of the invention. For example, the teachings of this invention are clearly applicable to arrangements employing more than two pick-up units. It is therefore recommended that reference be had to the following appended claims.

I claim:

1. A tandem cartridge phonograph tone arm assembly for pseudo-sterophonic sound reproduction comprising in combination a tone arm, a first pick-up cartridge assembly mounted in fixed relation to said tone arm, and a second pick-up cartridge mounted in floating relation to said tone arm, said cartridge assemblies having separate spaced stylus members arranged to track the same convolution of a recording disc sound groove in time-displaced relation whereby one of said separate spaced stylus members is movable a predetermined distance from the other during tracking across the record disc.

2. Apparatus according to claim 1 further including means incorporated with said second pick-up cartridge to increase the weight thereof whereby to simulate the weight of the unsupported free end of a tone arm.

3. Apparatus according to claim 1 further including means causing said second cartridge assembly to be urged into a predetermined initial relation with respect to said tone arm.

4. A tandem cartridge phonograph tone arm assembly for pseudo-stereophonic sound reproduction comprising in combination a tone arm, a first pick-up cartridge assembly mounted in said tone arm, and a second pick-up cartridge mounted in said tone arm in floating relation to said first cartridge assembly, said cartridge assemblies having separate spaced stylus members arranged to track the same convolution of a recording disc sound groove in time-displaced relation whereby one of said separate spaced stylus members is movable a predetermined disfiance from the other during tracking across the record 5. A tandem cartridge phonograph tone arm assembly for pseudo-stereophonic sound reproduction comprising in combination a tone arm, cartridge mounting means secured in said tone arm, a first pick-up cartridge mounted in fixed relation to said cartridge mounting means, an auxiliary cartridge supporting member pivotally mounted 6 on said mounting means, and a second pick-up cartridge fixedly mounted on said auxiliary supporting member, said cartridge assemblies having separate spaced stylus members arranged to track the same convolution of a recording disc sound groove in time-displaced relation whereby one of said separate spaced stylus members is movable a predetermined distance from the other during tracking across the record disc.

6. Apparatus according to claim 5 further including means carried by said auxiliary supporting member to add additional weight thereto.

7. A tandem cartridge phonograph tone arm assembly for pseudo-stereophonic sound reproduction comprising in combination a tone arm, a first pick-up cartridge assembly mounted in fixed relation to said tone arm, a second pick-up cartridge mounted in floating relation to said tone arm, said cartridge assemblies having separate spaced stylus members arranged to track the same convolution of a recording disc sound groove in time-displaced relation, means incorporated with said second pick-up cartridge to increase the weight thereof whereby to simulate the weight of the unsupported free end of the tone arm, means causing said second cartridge assembly to be urged into a predetermined initial relation with respect to said tone arm, and adjustable limit means determining said initial relation.

8. A tandem cartridge phonograph tone arm assembly for pseudo-stereophonic sound reproduction comprising in combination a tone arm, a first pick-up cartridge assembly mounted in fixed relation to said tone arm, a second pick-up cartridge mounted in floating relation to said tone arm, said cartridge assemblies having separate spaced stylus members arranged to track the same convolution of a recording disc sound groove in time-displaced relation, means incorporated with said second pick-up cartridge to increase the weight thereof whereby to simulate the weight of the unsupported free end of a tone arm, means causing said second cartridge assembly to be urged into a predetermined initial relation with respect to said tone arm, and said means tending to urge comprises a canted but substantially vertical pivot means for said second cartridge whereby said cartridge tends to pivot in a first direction by the action of gravity.

9. Apparatus according to claim 8 further including an adjustable abutment member positioned at one side of said tone arm to limit the pivotal movement of said second cartridge in said first direction.

10. A tandem cartridge phonograph tone arm assembly for pseudo-stereophonic sound reproduction comprising in combination a tone arm, cartridge mounting means secured in said tone arm, a first pick-up cartridge mounted in fixed relation to said cartridge mounting means, an auxiliary cartridge supporting member pivotally mounted on said mounting means, a second pick-up cartridge fixedly mounted on said auxiliary supporting member, said cartridge assemblies having separate spaced stylus members arranged to track the same convolution of a recording disc sound groove in time-displaced relation, said auxiliary supporting member having a bent-around end portion defining spaced bearing portions, and a member depending from said cartridge mounting means and engaging said spaced bearing portions.

References Cited in the file of this patent UNITED STATES PATENTS 1,811,841 Benjamin June 30, 1931 1,992,893 Thomas Feb. 26, 1935 2,079,959 Fear May 11, 1937 2,105,318 Goldsmith Ian. 11, 1938 FOREIGN PATENTS 737,328 Germany July 10, 1943