US2476414A

US2476414A - Phonograph pickup having plastic torsion arm

Info

Publication number: US2476414A
Application number: US595576A
Authority: US
Inventors: William H Hutter
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-05-24
Filing date: 1945-05-24
Publication date: 1949-07-19
Anticipated expiration: 1966-07-19

Description

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L2 INV EN TOR.

" 1 z 3 4 5 e 7 a sex |o BY July 19, 1949. I w. H. HUTTER 2,476,414

PHONOGRAPH PICKUP HAVI'NG PLASTIC TORSION ARM Filed May 24, 1945 50 I50 v 50w 600010.000

FREQUENCY Q 4 d v M v 9 STIFFNESS ml 4 Patented July 19, 1949 UNITED STATES PATENT OFFICE P O GRB PICKUP J 'PASTIQ roRsIoN williarn Hatter, Chicago, Ill. Application May 24, 1945, Serial No. 59Z Qlairng. (Cl. 179-40941) .MY n eh eh rel s te h r veme it phonograph pick-up construction.

A phonograph pickeup comprises, in general, means to convert mechanical vibrations cor; respondingly fluctuating electrical cgrrents, i eh tr th tt he fmeehe t tte h t ib ia tieh hem e eth-s n a i Poi te e r e ep er h meet e ith t-.1 he t h heets h Pe eee d 9 e rh ehereete tet ee ea h s a hi h v lta huttt a e u st el ni m re en r ueh a i en ran e and h ran e sh uld preferably b eoezs eh iv w th the a d b e r n f ee heiee- By uni m he eehe m ant absence of sharp resonance peaks in the @uqtible ran A primary object of this invention is to provide a phonograph pick-up having low mechanical impedance, and non-resonating characteristics. In terms of performance these characteristics eeh ut to higher ve eee ee pet 19w i ee rsi and stylns wear, uniform response anc;1i r ngroved tracking. V

These objects are obtaineg Joy pr ovid -ing yipraeh transmitting ans hav n th e he'exe ter than that required by the Vplum'e o f material re t pro u e t e re is te e iif he I have found that a vibration transmitting member fabricated from thatg cup ,of materials known as plastics and which incliides synthetic resins and various cellulose base plastics, embody the proper degree of stiffness and mass. When such mat ria s ar eed imly htee t m-t a ob e e the m t ih t en t hahi tihe m er th hrie a t' p lifltPS- T i io i qhti e h i he t of th 9 9 h i g ehphlea eh etie .13 e htl hlee Q itober 30, 1944, novy U. S. P aterlt No. 2,551,2 2}, reet Q t t' .2 w th Wh eh htee eeej' fhle e ihr en n t n he eat i it 999: tinuation in part of my cojbending application S al 42 fi ed Am 1 4%. new e hanttehed, whie e ete t Pla 'ti n e le mine principal ernleodimentirrqerrt ior;

h in sh wn and thee; eht ri e a piez 'e e t i ew te wever, it is u sle ee that he t ete e 9i ih eh eh app e h' e Q-R1 l embo i ethe types of conversion mean Another ie h m hv htieh is to pro ide w a ti eh 't eh mtttth mem r o su h char.- eeterietiee h t th eh m mn eene t ereof he t a tte ped nc a th e ratacther qhv r i h me ns-the b e e tt s a direct coupling between the two. tith 5? h dLtt e b e ei h the ee I 2 et 2 eparate em haht eehehhg ele ent we he it etieh t a sm tt n mea s th h theta! is min ted e he vq teee eu ectohtributod objects aretoprovide a vipration trehehh tthe me hhe whi h t i a di tribut e an e eeht el eht .e he et eethr iss pative tej e ehee, the wh. :h; stiett h teti ant e ht eleble e he ie eestill t thle ab e t i5 t9 evide i tet eh transmitting means of integral cons1;ructio rg e the tendehe 0f the ar iee, Sit t the P11 V1011. 4y h ed vth efheier'. t meme 9; le ee mee e a e9 R ee e th sep rate a ts seeh as the erq hex e e e an t9 sehh e e h lle h eie hp h eh- A st l te m-e; ehi et t9 m' it e imm ee teemi hetreeh' 119231 91 t ansmi t n d the ti et te he Yihtetieh thehe hitti ehe hate heel; 9t m ta wh ch h a e eartiye y hi h den ity hd aeemna e ive y h h sti ness'. These characteristics contribute to a high hhne ea h h'ie e era phene ti n to t sa e e met a h ef e ye m s Stiff l-.

The m ttle mat r s el m e re r to he e ee ez etii y 19w a h t and a e m e t Lew etitin ie tem e ed w th m t h n he pie ee vibra n tran m tt ng means hich s m p ise tm tieh a t u h ,lew ti m n heea ee the the m ta ti ra n e sm he members formerly psed. This results in good t?? P T-i g"W- h e er vto abil 9f th s te point tofollow faith f nlly the record groove irre; ee ettv 4 a. tlehe in mp tue n r c "th ee aek h eheteete ie ie ere eb in wi h: em the ee h the i ht on h e e p i t as aaat et e tt i ha e eta n e perfect treeke with only h if prince ressure for all ire-r enemies 1, tin h r he t te thousand, es d terfnine'd by a test record; This performance has teeth eeeh ed e hem z et y l .hieh o ta er het eht ehiie h responseeheh 52 i the eh h e ve t e t ,1; ve 1 s es 9 h e eht e fle tthes w h m etet rer t h h ette e ettteet are ehere tz vby e r e aehr hithhh re p n e o b th Me e teehehs .ehtatn .hy the e o uma d stam in M ieh im edanc and fuhthe eeee ti et s met rackin This nee s: it te th use a a cemp ian c p n b tween the metal vibration transmissicn member and the crystal, whi re ults in decreased volta e outpu in other words with vibration transmitting means, high voltage output is incompatible with good tracking and uniform response.

This incompatibility is in large measure eliminated by following the practices of my invention.

Other objects, features and advantages of this invention will become apparent as the description proceeds.

With reference now to the drawings, in which like reference numerals indicate like parts- Fig. 1 is a sectional elevation through a pickup showing one embodiment of my invention;

Fig. 2 is an elevation of a vibration transmitting means and crystal showing another embodiment of my invention, only a portion of the housing being shown;

Fig. 3 is a top view of the vibration transmitting means and crystal shown in Fig. 2;

Fig. 4 is a graph showing the response advantage obtained from a pick-up embodying my invention; and

Fig. 5 is a diagram showing the stiffness and density of representative types of plastic materials which may be used in accordance with my invention.

The principles of my invention may be applied to a vibration transmitting means in which the needle is separable from the chuck and yoke, as shown in Fig. 1, or it may be applied to a pickup in which the yoke and needle are integral, as shown in Figs. 2 and 3.

In the Fig. 1 form of my invention, the reference numeral ll designates the pick-up housing which may be in two separable parts, in accordance with the usual practice. A crystal I 2 is mounted within the housing by means of gripping pads l3 which engage one end of the crystal. The other end of the crystal is coupled to vlbrae tion transmitting means generallydesignated by the reference numeral I4, which comprises two parts, a longitudinally disposed member [5, and a needle l6. Both of these members are made of an organic plastic material, as will be pointed out hereinafter in greater detail.

The lower end of the needle [6 is provided with a record engaging point. I! which may be of a suitable hard alloy, or which may be a sapphire. The longitudinally disposed member [5 terminates at one end in a yoke l 8 which engages the crystal 12. The other end is provided with a chuck l9 which is adapted to receive the needle IS. The yoke may be cemented to the crystal. The shank of the needle [6 is tapered, and it fits into a correspondinglytapered bore in the chuck [9, the tapering arrangement providing a very secure coupling between the two. A key 20 on the needle fits in a cooperating keyway 2| in the chuck to facilitate proper alignment of the parts. The construction of these parts is pointed out in greater detail in my co-pending application Serial 'No. 561,061, of which this is a continuation in part. The vibration transmitting means is mounted in the housing by means of a rubber journal 22 which surrounds the cylindrically shaped intermediate portion of the longitudinally disposed member l5. A pivot screw '23 extends inwardly from the front wall of the housing I l and engages a suitable bore 24 in the longitudinally disposed member IS. The screw and the bore are aligned with the longitudinal axis of member l5,= and cooperate with rubber'journal 23 to permit oscillation of the vibration transmitting means about said longitudinal axis.

In the form of my inventionshownin Figs. 2 and 3, the vibration transmitting'means 301$ an integral member, and includes a downwardly extending arm portion 3|, and a longitudinally disposed portion 32, the end of which terminates in a yoke 33. The yoke 33 comprises a plurality of pairs of fingers for the purpose of securing a firm grip on the crystal 35 irrespective of any surface irregularities. A rubber journal 34 surrounds the longitudinally disposed portion 32, the rubber journal being adapted to fit within the housing in the usual manner.

The yoke 33 grips one end of crystal 35, and the other end of the crystal is mounted between suitable damping pads 35 in the usual manner.

The lower end of the arm 3| is curved forwardly and carries a suitable record engaging point 31.

The vibration transmitting means E and 3 are composed of a low density, high molecular weight plastic material, such as those known as synthetic resins, or as plastic cellulose products. I prefer to use organic plastic materials having a density of less than two grams per cubic centimeter and having a Youngs modulus of less than 10 10 dynes per square centimeter.

Representative types of plastic materials are listed below under their usually accepted chemical designation and trade names, and the Youngs modulus and density are given for each. These materials are numbered from 1 to 10, and I have found that a vibration transmitting member composed of any one of these ten materials gives the satisfactory results heretofore mentioned. For the purposes of comparison, the corresponding characteristics of certain metals are also 7 given in the following table.

Youngs N0 Chemical Type Trade Names Modulus 1 f g Dyn/cmj gm. cm.

Beetle Plaskonh" 9. 3 l. 48 L ite 3. 8 1.18 3.1 1.13 2. 6 1.36

Styrene 2. 3 1.36 Ethyl Cellulose- 2. 1 1.14 7.- Cellulose Ace- 1.9 1.21

tate Butyrate. 8.. tyrene Polystyrene 1. 5 1.06 9.. Acetate Lumarith Tenite.- 1. 4 1.32 10. Vinylidene. 0. 9 1. 70 43 1. 74 67. 5 2.85 7. 7

1 Times 10 response from a pick-up made accordin to my invention; curve 'B' shows the response of a pickup in which the metal vibration transmitting member isundamped; and curve C shows the response of a typical commercial pick-up in which the metal vibration transmitting member is provided with" damping in order to secure a substantially uniform response,'and very loose coupling in order to secure tracking. The latter type of pick-up is often referred to as a high fidelity pick-up, due to the effort made to secure a uniable sacrifice of voltage output.

A comparati- "1y undamped pick-up, on the other hand, while its voltage output is more satisfactory, is characterized by various resonances which show up as in curve B. The peak at 2500 cycles represents the crystal resonance,

an the su s qu nt peakrepresents needle resonance. The peak at 250 cycles i dicates the h n e over point. or the test record from constant amplitude to constant velocity.

Curve-VA on the other hand, combines the uni.- form response oi curve (1 with the voltage output of curveB. 1 It is the combination of theseEdesirable characteristics that is produced by the practics of my invention The low. voltage output of curve 0 cannot be entirely compensated for by the speaker amplification in order to. give acceptable results. This is i n he reason that due to. abrasives used in the manufacture of the record, there is a constant noise level which Fig. 4. occurs at about 0.1 volt. Therefore the'ratio of noise to signal in a high; fidelity pick-up such as that whose response is shown in curve C, increases to an undesirable extent at frequencies of: from 2000 to 10,000 cycles. This efiect considerabl diminishes the desirability of a so-called high fidelity pick-up. It a will be noted that in curve A, a. comparatively low ratio of noise to signal is maintained out to 10,000 cycles.

The reason for an improved performance of a pick-up embodying my invention are at present not fully understood. Without committing myself to any theory, however, it is believed that plastic materials have a much greater dissipative resistance, or internal resistance, than metals, due

to their molecular structure. This higher interi.

nal resistance apparently is of assistance in damping out resonance peaks; and, in particular, it dispenses with the need of lumped damping.

A further advantage in the use of plastic materials is that it permits a much greater latitude in the mechanical design of the vibration transmitting members. The values listed in the foregoing table are not the sole determinants of the stiffness and mass of the vibration transmitting means; the dimensions of the parts must also be considered. The above table does indicate, how ever, that for a vibration transmitting means of given dimensions, a greatly reduced impedance may be expected if plastic is used instead of metal. plastic vibration transmitting means cannot be determined categorically by reference merely to the resonant frequency of a corresponding me- While the resonance frequency of a tallic vibration transmitting means, I have found that when the dimensions of the plastic vibration transmitting means are sufficient to withstand the net weight of the tone arm, the response curve of the pick-up is relatively absent from resonant peaks.

In general, the stiffness increases as the fifth power of the dimensions, whereas the mass increases as the third power of the dimensions, so that it is evident that a considerable variation in resonant frequency, which in general is proportional to the square root of the effective stillness over the effective mass, may be eifected by comparatively minor structural changes. Thus the resonance frequency may be empirically adjusted after the general design of the pick-up has been determined.

6 A further element of latitude in mechanical design is occasioned by the fact that stiffness may be varied considerably by regulating the amount of plasticizer used. Thus the compliance may be increased,- and the'output impedance regulated to match the input impedance of the crystal. One result of impedance matching, either by change in dimensions, or by'the proper use-of plasticizer is the elimination of the tendenc of "the vibration transmitting means, or'variou'sparts thereof,

"to: resonate separately from the'crystal, or at lower frequencies than the crystal resonance. i

The addition of plasticizer may also be expected to increase the internal or dissipative resistance of the vibration transmitting means.

To sum 'upthe foregoing, the use ofplastic materials for vibration transmitting'means providesdistributed damping, and permits the selection of a. design which is free from resonant peaks, and which. also permits impedance matching;

The designs shown in Figs. lto 3 have been found to give. satisfactory results when fabricated from a diam-inc type of plastic sold under the trade name-cf nylonfl It will be noted that in thesedesigns no separate coupling element is used between the vibration transmitting means and the crystal. This results in more 'eflicient coupling, and hence greatervoltage output. I have also found it desirable to grip the crystal near its edges, thereby subjecting a greater area of the crystal to deformation.

The foregoing description has illustrated my invention as applied to a crystal pick-up em" bodying a twister construction and adapted for use with lateral cut records. It will be evident however, that the principles of my invention may be applied to other types of pick-ups than crystal pick-ups, and also to pick-ups adapted for use in connection with hill and dale cut records. Furthermore, the invention may be applied to bender type pick-ups as well as to twister type.

Furthermore, it is apparent that my invention is applicable also to other plastic substances than those specifically enumerated herein. The foregoing description and the appended drawings are deemed to be illustrative only and the invention is to be limited only by the appended claims.

I claim:

1. In a phonograph pick-up, a crystal, means for transmitting torsional vibrations to said crystal, and. a stylus connected to said vibration transmitting means, said vibration transmitting means being formed entirely from a non-elastomeric organic plastic material having a density of less than 2.0 grams per cubic centimeter and a Youngs modulus of less than 10 10 dynes per square centimeter, and comprising an elongate member having a yoke at one end thereof engaging said crystal and a portion connecting said yoke with said stylus, the thickness and width dimensions of said connecting portion being substantially equal to each other, and said stylus projecting outwardly from said elongate member and away from the axis thereof whereby lateral vibration of said stylus will cause torsional vibration of said vibration transmitting means.

2. A phonograph pick-up as claimed in claim 1 in which said organic plastic material is nylon.

3. In a phonograph picki-up, a crystal, means for transmitting torsional vibrations to said crystal, and a stylus connected to said vibration means being formed entirely from a non-elastomeric organic plastic material having a density of less than 2.0 grams per cubic centimeter and a Youngs modulus of less than 10 l0 dynes per square centimeter, and comprising an elongate member havinga yoke at one end thereof engaging said crystal and a portion connecting said yoke with said stylus, said connecting portion being of substantially uniformcross sectional area and said stylus projecting outwardlyfrom said elongate member and away from the axis thereof whereby lateral vibration of said stylus will cause torsional vibration of said vibration transmitting means.

4. A phonograph pick-up as claimed in claim 3 in which said organic plastic material is nylon.

5. In a phonograph pick-up, a crystal, means for transmitting torsional vibrations to said crystal, a stylus connected to said vibration transmitting means, said vibration transmitting means being formed entirely from a non-elastomeric organic plastic material having a density of less than 2.0 grams per cubic centimeter and a Young's modulus of less than 10 10 dynes per square centimeter, and comprising an elongate member having a yoke at one end thereof engaging said crystal and a portion connecting said yoke with said stylus, and saidstylus projecting outwardly from said elongate member and away from the axis thereof whereby lateral vibration of said stylus will cause torsional vibration of said vibration transmitting means, and means REFERENCES CITED The following references are of record in the me of this patent:

UNITED STATES, PATENTS Number Name Date 1,655,974 Russell Jan. 10, 1928 2,177,239 Bird Oct. 24, 1939 2,267,693 Di Toro Dec. 23, 1941 2,280,763 Hasbrouck Apr. 21, 1942 2,313,129 Dohan Mar. 9, 1943 2,320,572 Dann June 1, 1943 2,328,952 Burt Sept. 7, 1943 2,352,311 Di Toro June 27, 1944 D. 139,584 Jensen Nov. 28, 1944 FOREIGN PATENTS Number Country Date 372,428 Great Britain 'May' 12, 1932 Great Britain July 6, 1933