US2251204A - Sound reproduction - Google Patents

Description

July 29, 1941.

J. D. REID 2,251,204

SOUND REPRODUCTION Filed April 14, 1941 s Sheets-Sheet 1 IINVENTORH JOH D. Rcm

July 29, 1941;

J. D. REID SOUND REPRODUCTION Filed April 14, 1941 3 Sheets-Sheet 2 M-T I 12-- ELCC. OUTPUT D.B. OUTPUT 8-- ACOUSTIC RADIA'HON 0.3. souuo LCVCL 8 FORCE REQUIRED FOR TRACKWIG OUNCQS PRESSURE 'rw RAmus MlLs 'I'NVENTOR. B JOHN D. REID @g @A/Lz/ TORNEY July 29, 1941. J. D. Rab 2,251,204

, scum) REPRODUCTIQN I iFiled April 14, 1 941 =3 Spams-Sheet 3 INVENTOR.

- I JOHN mm 7 AT RNEX Patented July 29, .1941

UNITED- STATES PATENT OFFICE" sounn nnraonub'rion John n. and, Mount Heaithmbhio, ass; or to,

ation, Cincinnati, o, a

The Orosley CIIOI corporation of Ohio Application April 14, 1941, Serial 1:10. 388,355 13 Claims. (c1. 274-38 This invention relates to sound reproduction apparatus and pick-up mechanisms and is more particularly. concerned with reproducing styli. Specifically the invention has to do with rep ro-' ducing. styli adapted for use in effecting reproduction from. records of the laterally cut type wherein the desired sound track is formed in a groov which is displaced laterally according to the modulations required to give the. desired sound.

With sound records of the foregoing type it is common practiceto cut the sound track according to-standard specifications as to width, wail angle and tip radius.

'6 mils, or .006 ofan inch, at the surface of'the The standard width is 1' record,.andafV-shaped cut is made, the walls of which are at an 88 degree angle with each other.

Thisis termed the wall angle. The bottom of ,the, groove is designed to be cut on a radius of 2.3 mils, and this rounded surface is tangent to the walls.

These specifications govern the groove .depth bisecting the '88 'degree wall angle. Slight'variations in the type and shape of the cutter, the weight imposed-thereon and other factors and conditions o'frecording often cause departures from the foregoing standards but the'same fairly represent the average desired 'or maintained by most manufacturers. I

In producing a modulated groove the cutter,

which haslan edge somewhat resembling a chisel,

necessarily moves from side to side as the record rotates thereby producing a sinuous track the width of'which is uniform in a direction along any radius of the record, but is non-uniformxin directions normal to the sides of groove. This results in a groove of varying width which often depth and push away the taiiings. This causes the lower part of the groove to become irregular and imperfect, and this result is accentuated after the tip of the cutter becomes dulled due to there n. Accordingly a reprothe bottom part of the the excess wear ducing stylus foliowin roove-must follow these irregularities, resulting in a loss of electrical resp'onse to the desired modulation, in increased ,response to undesired modulation and, what is more important, in

increased distortion.

It has heretofore been thought desirable, if not necessary, that reproducing styli for effective reproduction must fit well within the groove of the record. Several types of styli have been used for this purpose, siich as steel and chromium plated needles, or styli made from gems or semi-'preciousistones such as, sapphires or diawhich should be 2.1 mils at, a vertical center line monds. With the exception of steel needles, all these had a small rounded p int having a radius of about 2.3 mils. Top quality styli were kept within plus or minus .1 mil or about 4% of 2.3 mils. Styli having radii over 2.4 mils were classified as seconds, and if the radii exceeded 2.! or 2.8 mils, or about 20% of 2.3 mils they were discarded asvirtuaily useless since they caused an increase in directly radiated sound,

.a large increase in wear and because they had other serious disadvantages.

I have found that by increasing the radius of the stylus tip or point by 55 to 120%, or from about three to six times-the increase heretofore thought to be permissible, certain unexpaited and highly desirable .results are secured. I have found that with such an increased radius I can obtain tracking with only one-half the pressure previously required. a three-fold increase in.

pinches thereproduclngstylus and tends to force it to move upwardly. The relatively great force excessive wear.

I .have found that other factors that afle'ct the shape. and nature of the groove, particularly thebottom portion thereoLare the conditions inherent inth-e cutting operation. The surface of the record, which in the case of records manuthus exerted on the stylus and the record causes factured for quantity distribution is initially made of a waxy composition, is harder than the interior, due probably to the surface tension of the composition and to temperature conditions. Thus a cleaner cut is made at the top. At

the lower part of the groove, however, the composition is mor plastic, doesnot out so cleanly. andgreater pressure is required to cut the full eiectricaloutput, a two-fold reduction in acoustic radiation, surprisingly less undesirable noise (with respect to noise caused by manufacturing 'defects in the record as well as with respect to noise caused by defects due to wear) a four-fold increase in life, both with respect to styli and records and an astounding improvement in the quality of sound reproduction. Objects of the invention include the achieve ment of these salutary results and the eliminain the use of the art.

, The

small radius styli of the prior novel features that I considercharacteristic of-myinvention are set forth in the .appended claims. The invention itself, however,.

both as to its specific construction and its adaptation together with additional objects and adtion of many of the undesirable factors involved vantages thereof will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawings, in which:

Figure 1 is an enlarged section through 8. record groove showing various stylus points or tips and their relationship to the groove.

.Figure 2 is a fragmentary and enlarged plan view of the groove with a stylus therein shown in section.

Figures 3, 4 and 5 are graphs showing the effect of various tip radii on electrical output, acoustic radiation and on force required for tracking.

Figure 6 is a fragmentary and enlarged section similar to Fig. 1, showing a modified form of stylus constructed according to the principles of the invention. 7

Figure 7 is a plan view of Fig. 6 taken from the same position as Fig. 2.

Figure 8 is a section along line 8-8 of Fig. '7.

Figure 0 is a side elevation of a stylus constructed as shown in Figs. 6, '1 and 8, showing how the shank may be provided with means for ensuring proper positioning when it is mounted in the reproducing head.

In Fig. 1, I have shown a record fl having a groove ii of standard dimensions. The tip I2 of a stylus constructed according to" the present invention has a radius l2r which-in the instance illustrated is 4 mils and has a total contact surface adjacent the top side walls of the groove represented by the distances A+A. It will be noted that the distance or area of effective contact A+A' will always occur within the upper onethird of the side walls.

A stylus H, such as a conventional chromeplated needle, having a 2.75 mils radius llr contacts the groove over an area represented by the distances C+C' which is only about one-half of A+A'. The radius 1' is close to the maximum permissible in accordance with the prior art.

The tip ity of a standard 2.3 mils stylus having a radius Ilr contacts the groove only at the bottom thereof over a distance represented by B. It must be explained that while the distance B appears to be considerably greater than the total distances A+A'., this is not in practice the fact for the reason that the bottom portion of the groove is highly irregular as has previously been stated, and the practical result is that a stylus of the radius llr actually contacts the groove only at limited areas thereof the total of which is of the order of the total contact area C+C', and less than A+A'.

In Fig. 2 the outer contour of the side wallsof the groove is indicated at I! and Ila, the same being in the form of a sine wave varying at a rate of 7680 cycles per second at the inside of a standard 78 R. P. M. disc record. The adjacent periphery of the stylus tip I! follows, as nearly as it can, the wave form shown, although the full amplitude cannot be attained with the stylus shown. Due, however, to the fact that the small prior art styli follow the rough and irregular lower portions of the groove and are much more subject to the stresses imposed by their having to ride up and down in the groove the output obtained by the large radius stylus shown in Figs. 1 and 2 is many times greater than that obtainable with the small radius type as will hereinafter appear, and this great increase occurs despite the apparent failure to obtain full amplitude that one might expect from the structure illustrated in Fig. 2. The actual movement of the stylus is illustrated by the wave form H.

The surprising differences in electrical outputs obtained from a set of styli identical except for tip radius, and used in a conventional crystal cartridge are shown in Fig. 3, in which various tip radii are plotted against electrical output in db. The curves 20 were taken by using a record having constant modulation cuts at a frequency of 5170 cycles. It will be observed that the output rose steadily with increasing radius to about 4 mils, at which the output was maximum, and thereafter fell off with increased radius. It will be noted that the output at 4 mils is approximately three times that obtained at 2.3 mils for curve 20.

The results of tests madeof the sound radiated directly from the record surface are shown in Fig. 4, where curve 30 represents a groove cut with a steady note of 200 cycles and the curve 40 represents a groove cut with a steady note of 7000 cycles, tip radius being plotted against intensity of directly radiated sound in db. It will be noted that for each frequency directly radiated sound reaches a minimum when the tip radius is about 2.5 mils, and rises as the tip radius is increased to a little over 3 mils. After this, however,'the directly radiated sound drops rapidly until it reaches a minimum at 4 mils, which corresponds to the optimum radius for maximum electrical output as developed from Fig. 3. After reaching the minimumthe curves 0 and 40 rise rapidly again as the radius is increased toward a size equal to the top groove width. It will be noted that for the higher modulation illustrated by curve 40 the minimum obtained with a 4 mil radius shows a two-fold reduction in acoustic radiation over the minimum occurring with a 2 5 mil radius. Curve 40 for 7000 cycles shows a final deflection which occurs as the stylus radius becomes considerably greater than the wavelength of the modulated groove.

It will be readily understood that it is highly desirable to reduce this directly radiated sound from the stylus tip as this conflicts seriously with the desired sound from the loud speaker, particularly at the low levels of reproduction encountered in the home.

In Fig. 5 I have shown curve 50 in which tip radius is plotted against the downward pressure required for tracking. It will be seen that a greater pressure is required with radii above and below 4 mils, and at 2 mils twice as much pressure is required. Increased pressure is undesirable since it results in increased wear on both the stylus and the record. Since I can reduce the required pressure by one half, and as previously explained, can increase the effective contact area with the groove by approximately two to one, I can reduce the pressure per unit area to approximately one quarter of that required with prior art styli. Thus I obtain a decrease in wear and an increase in record life of four or more times.

The small radius stylus often rattles around, so to speak, in the groove, thus causing increased directly radiated noise and distortion of the desired modulation.

' explained, likely to become pinched or jammed in the groove by reason of the fact that the width of the groove varies in a direction normal to the sides thereof. When this occurs a greatly increased pressure is exerted on the stylus tending to force or cam it upwardly and a relatively great pressure per unit area of contact is exerted on the groove walls. The forces thus exerted are Moreover it is, as previouslyv such as enormously to increase the rate of wear, both upon the stylus and the record.

These excessive and destructive forces are not present with the large radiusstylus of the present invention since the stylus rides-along the top of the groove and is little affected by this pinching effect. In other words, for a large radius stylus a given change in groove width produces a much smaller vertical movement of the stylus and thus reduces wear. With a large radius sapphire I have found that records may be played continuously on a record changing phonograph for 500 times with little perceptibl wear, either visually or aurally, whereas records played with a 2:5 mils r sapphire for the same number 'of times were covered'with a fine powder'scraped from the groove, and were so badly eroded as to be practically worthless. Not until the record played with a large radius stylus made in "accordance with the invention reached 20.00 playings did the record attain the same apparentstate oferosion.

More than this, the contrast between the performance of my stylus and a small radius stylus is distinctly perceptible to the ear, for there is not only appreciably less distortion but there is a marked decrease in stray noise both electrical and directly radiated. An old.and worni'record may by reasonof the presentinvention by played with remarkable clarity and iidelit'yiand with startling reduction in the undesirable noise caused by the worn partsyof the record. I attribute this to the fact that'my new stylus contacts the upper portionsof'the groove which are cleanly formed compared to thelower parts of the groove as previously explainedand have not been roughened or scraped by wear.

since this dimension is one which effectively illustrates the principles and advantages of the invention. Instead of merging the arc of the tip into the sides of the stylus as shown in full lines in Fig. 1 it may be desirable to terminate the are at or slightly above the surface of the record and run the sides vertically upwardly as at 64 until'they meet thetapered sides 61 of the stylus, as shown.

In Fig. 7 I have illustrated an enlarged plan view of a; groove 60, the sides of which are modified in a sine wave form tlwhich in this example represents a frequency of 7680 cycles at the inside of a standard 78 R. P. M. record. The stylus 62 is not of circular cross; section but may have a cross section as shown, governed by the radii and extent of the lateral edges which in the instance illustrated is .5 mil. The cross sectional diameter in a direction parallel to the center or the groove is not critical but, as shown in Fig.7, this diameter is smaller than the diameter between -the lateral edge portionsand derives its shape by reason of the widely diverging sides 65- which are tangent to the circles delineated by the 1 1.5 mil radii previously mentioned. The precise It might be here noted that the bottom portions of the groove constitute those portions -which, due to the method of manufacture, are 7 most likely to be defective. Records are formed by the use of a stamper by which a mass of mold able record material is pressed into the final form.

The raised portionson the stamper are thosewhich correspond with the bottoms of the groove and it is these raised portions which receive most wear during the manufacturing process and which are most subject to being marred or scratchedduring processing. Consequently every imperfection present upon the exposed surfaces of the stamper appearsin exact replica at the bottom of the grooves and thus addfurther to the inherent irregularity of the bottom or the groove. As has been indicated, the stylus of the present invention does not ride upon these irregular and-imperfect portions and the undesirable effects thereof are not present in the ouput of the reproducing device. I I In order to avoid shouldering that is, the formation of a shoulder which contacts the top. surface of the recordas afre sult of wear, I may make the tip of. the styliis" cylindrical as indicated at it f in Fig. 1. -.Th'e cylindrical portion may be: conveniently extended a distance equal to about onehalflthe'groovefdepth and the termination thereof may merge with the sides it"of thestylusas' shown. The diameter of theflcylindrical portion ,should be equal to'or slightly less than the width of the groove at the surface of the record. This increases the useful. life of the stylus. V

In Fig. 6 a section similar to but modified from that shown in Fig. 1 is shown'and it will be obcontour of the cross section of the stylus is also determined by the particular type of material used and the requirements of strength, but it is desirable if not essential to have the lateral edge portions ofa sufllciently small size so that they may follow the undulations formed in the sides of the groove even though the waves delineated by theseundulations are short and their amplitude high. In this manner the effective movement of the stylus closely approaches the full amplitude of the wave as shown bythe central diagram which shows'the of the stylus.

It will be understood that theshank of the stylus of Figs. 6-8 should be and preferably is flattened and the socket'therefor arranged so that the stylus fits therein only in a position which'maintains the lateral edges 83 in proper position crosswise ofthe groove. In Fig. 9 I have shown how the butt-end flattened. as at positioned in the type of pick-up.

10 so that'it may be properly mounting of the crystal or other The contour of the stylus shown by the longitudinal section in Fig; 8 is not at all critical. In.

this figure-the 1391 1203 edge portions are showngenerally at 6 8 andtfor the purposes of illustra--v tion are rounded. The radius of curvature in this plane may be. variedwithin wide limits since the lower part of thestylus does not contact the groove. The intermediate portions leading :upto the shank are indicated at 64.1.

h 'lobse fations will now be madein' order fully and completely .to describe and explain the inyention. It

with large radii aremore easily manufactured and their points arenot so subject to fracture'as are those which must be finely ground to radii of the'order 0132.3 mils. Moreover, accidental droppin'g -"of that reproducing head during use served that in this plane the radius 6213.01 the tip 82 is relatively large in the same sense'as that described in connection with the stylus l2 in Fig.-

'1. In Fig. 6 the radius 521 is shownas 4 milsoften ca tiscs' the point of the; stylus to fracture and' since stylii niade in accordance with the present-invention ;-are made with as much as unuchstronger; Since the-strengthdepends upon .the cross sectional area; and the area varies with the square of the radius it will be observed that path 86 of the center til of thestylus may be will be noted that styli doublefthera'dius ofthe prior art styli they are happensthat the reproducing head is I .pear to persons crossing the grooves.

In the foregoing discussion it has been assumed that the turntable is rotating at a speed of 7-8 B. P. M. It will be apparent that the invention is applicable for use with records revolving at a speed of 33%, R. P. M. with increased advantages, most important of which is that the increased output, such as is illustrated in Fig. 3, occurs at a lower frequency. For example, in Fig. 3, curve 20 indicates the improvement in output obtained with the 4 mil radius at a frequency of 5,000 cycles, whereas this same improvement will be noted at 33% R. P. M. at a frequency in the neighborhood of 2130 cycles. Thus I am able to obtain adequate response at slower speeds with records having a minimum diameter of one-half that heretofore required forthis speed of recording.

While I have stated that the foregoing advantages accrue by increasing the radius of the point three to six times more than has heretofore been thought permissible, optimum results are obtained when I use a radius of about 4.2 mils. should be understood, however, that this precise dimension is not itself critical but that I may use somewhat higher and slightly lower radii with concommitant advantage. Variations below 4.2 to the extent of about 15% permit the main fea tures of the invention to be utilized with minor sacrifices. I may on the other hand increase the radius as much as 20% and still attain the desirable results that I have outlined.

Modifications of the invention will readily apskilled in the art without departing from the principles herein outlined. For instance, the invention is applicable for use with grooves cut with different wall angles such as the '75 degree wall angle sometimes used in foreign countries. With such an angle I have found that a tip radius of 4 to 4.2 does not produce optimum results but that a smaller size is required for this purpose, since such smaller size ensures contactof the stylus over an appreciable distance adjacent the top of the side walls or in the area generally indicated at A+A' in Fig. 1.

Having described my inventioml claim:

1. A reproducing stylus for'the reproduction of sound from laterally cutrecords having modulated grooves, comprising a shank having means thereon to ensure the predetermined positioning of said shank in a mounting, said stylus having a tip which is elongated in a direction substantially normal to the sides of the rec'n'rdgroove, said tip modulation in said modulatedgroove and having an are at the lower end thereof of a radius sufficient so that said modulated tip contacts the side walls of said groove adjacent the top por tions only of said modulated groove.

2. A reproducing stylus for the reproduction of sound from laterally cut records having modulated grooves, comprising a shank having means of said shank in elongated in a direction substan-v a mounting, said stylus having a tip which is tially normal said tip having to the sides of the record groove, its sides rounded for cooperation with the modulation in said modulatedgroove lo the reproducing head, and less vertical motion in and having an arc at the lower end thereof of a radius sufficient so tacts the side walls of said groove within the upper one third only of said modulated groove.

3. A reproducing stylus for the reproduction of sound from laterally cut records having modulated grooves, comprising a shank, a tip at the end of said shank, said tip being flattened laterally to form lateral edges, said edges being rounded on a radius of the order of .5 mils, the bottom edge of said laterally flattened tip having a radius sufiiciently large in the said lateral direction that when said stylus is inserted within having its'sides rounded for cooperation with the the tip co a modulated record groove with its lateral edges adjacent the modulation thereof it contacts the side walls thereof adjacent the top only of said modulated groove.

4. A reproducing stylus having a rounded tip the radius of which is the order of 4.2 mils and which contacts with the sides of a laterally cut modulated record groove adjacent the top only of the side walls of said modulated groove, said stylus being sufficiently large that the bottom portion thereof is maintained out of contact with the bottom of said modulated groove.

5. A reproducing stylus having a shank adapted to be secured in a mounting and having a rounded tip the radius of which is of the order of 4.2 mils and which contacts with the side walls of a laterally cut modulated record grooveadjacent the top only of the side walls of said modulated groove, said stylus being suftlciently large that the bottom portion thereof is maintained out of contact with the bottom of said modulated groove.

6. A reproducing stylus for the reproduction of sound from laterally cut records having modulated' grooves, said stylus having a, cylindrical tip the cross sectional diameter of which at the surface of the record is substantially equal to the groove width at such surface, and the end radius of which is appreciably greater than one half said groove width in one direction and appreciably less than one-half said groove width in a direction at right angles thereto.

'1. A reproducing stylus having a cylindrical tip the diameter of which is substantially 6 mils., and the end radius of which is on the order of 4.2 mils in one direction and on the order of .5 mil in a direction at right angles thereto.

8. A reproducing stylus for reproducing sound from laterally-cut grooved records having modulated grooves, said stylus having a tip rounded on an arc the radius of which is large with respect to the modulated record groove and of such dimension that the tip contacts the side walls of said modulated grooves within the upper third only of the side walls of the said modulated groove.

9. A reproducing stylus for reproduction of laterally out sound records having modulated grooves, said stylus having a tip rounded on an arc the radius of which is sufficiently large that ntacts the side walls of said modulated 'grooves within the upper third only of the side thereon to ensure the predetermined positioning wallsof said modulated groove.

10. A reproducing stylus for reproduction of standard laterally cut sound records having grooves 6 mils wide at the top thereof, said stylus having a rounded tip the radius of which that said modulated tip con is of the order of 4.2 mils and which contacts the side walls of said modulated grooves adjacent the top only of the side walls of said modulated grooves.

11. A reproducing stylus for the reproduction of sound from laterally cut records having a groove with upwardly-diverging modulated side walls, said stylus having a groove engaging tip. terminating in a rounded portion having a radius in a plane through the axis of the stylus and extending across said groove which prevents the tip from engaging the bottom of the groove and the lower portions of the modulated side walls of the groove and provides contact between the tip and the side walls of the groove adjacent the top only of the modulated side walls of the groove.

12. A reproducing stylus for the reproduction of sound from laterally cut records provided with a modulated groove having a bottom radius .of approximately 2.3 mils, a depth of approxi- .mately 2.1 mils, and upwardly diverging modulated side walls providing a width at the top or the groove of approximately 6 mils, said stylus having a groove engaging tip comprising a rounded end portion having a radius in a plane through the axis or the stylus and extending across said groove between approximately 15% less than and 20% more than 4.2 mils, said portion contacting said modulated side walls of the groove adjacent the top only of said modulated side walls.

13. The method of reproducing sound from a laterally cut record provided with a, groove having opposed upwardly diverging modulated side walls, which comprises bringing the tip of a reproducing stylus into contact with the upper portions only of the opposed modulated side walls of said groove adjacent the top of said modulated side walls, preventing contact of said tip with the bottom or said groove and with the lower portions of the modulated side walls of said groove. and moving said record relative to said stylus to vibrate the stylus in accordance with the modulation of the upper portion of Said modulated side walls.

. JOHN D. REID.

CERTIFICATE OF CORRECTION.. Patent No. 2,251,20LL, July 29, 19in.

Joan-D. REID.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1+, first column, line 69, ol a iml, strike out the word "modulated" before "tip" and insert the same before "groove" in line 70, same claim; and second column, line7, claim-2, strike out-"modulated" before' tip" and'insert the same before "groove" in line 8, same claim; and'thet the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 50th day of September, A. D. 191;.1.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

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