US2474993A - Phonographic transducer device - Google Patents

Description

y 1949. e. c. TIBBETTS 2,474,993

PHONOGRAPHIC TRANSDUCER DEVICE Filed Nov. 29, 1945' 05y v We;

Patented July 5, 1949 UNITED PHGNOGRAPHIC TRANSDUCER DEVICE George C. Tibbetts, Camden, Maine, assignor t0 Tibbetts Laboratories, a corporation of Maine Application 4 Claims.

In some phonograph apparatus the movement of the needle is predominantly in the direction of the vertical dimension or depth of the groove but usually the movement is back and forth in the direction of the crosswise dimension of the groove. In either case only the vibration in one direction should be transmitted to the transducer. For example if the recording is of the type in which the movement is intended to be in the direction corresponding to the width of the groove, transmission to the transducer of movement in the other dimension of the groove introduces distortions.

Objects of the present invention are to produce a phonographic device, which confines the effective movement of the needle substantially to one of the aforesaid dimensions of the groove, which is light and compact, which can be manuiactured easily and economically, which minimizes harmonic distortion and surface noise, which affords a high order of fidelity, which permits easy regulation of frequency response, and which is generally superior to phonographic devices of the prior art.

According to the present invention the device comprises a needle support which transmits to the transducer movement along one dimension of the groove without permitting substantial transmission to the transducer of movement in the other dimension, in combination with a transducer movable back and forth and means interconnecting the support and transducer for movement back and forth in unison. Preferably the support has a flexible portion on one or both sides of the needle axis which permits swinging movement of the needle. In the preferred embodiment the needle support permits movement transversely of the record groove but is relatively immovable in a direction perpendicular to the surface of the record. The support may be made more flexible in one dimension than the other by making it thinner in one dimension. In the specific embodiment hereinafter described the support comprises a flat bar and means for rigidly supporting the bar at each end, the bar having a flexible portion between the needle and each of the supporting means and each flexible portion having a dimension lengthwise of the needle which is greater than its dimension crosswise of the needle, whereby back and forth movement of the needle produces torsional or twisting movement of the support or vice versa.

For the purpose of illustration typical embodiments of the invention are shown in the accompanying drawings in which November 29, 1945, Serial No..631,681

Fig. 1 is a top plan view of one embodiment;

Fig. 2 is a section on line 2-2 of Fig. 1;

Fig. 3 isa top plan view of another embodiment; and

Fig. 4 is a section on line 1-4 of Fi 3;

The particular embodiment of the invention shown in Figs.1 and 2 comprises a casing l which is preferably formed of Bakelite or other similar insulating material, a phonographic transducer 2, which may be like that disclosed in my copending application Serial No. 570,361 filed December 29, 1944, now Patent No. 2,403,692, issued July 9, 1946, and a support 3 for the needle 4. The transducer 2 is mounted in the casing by means of resilient blocks 6 of rubber or other yielding material. The blocks are cemented or otherwise secured to the bottom of the transducer and they are also preferably cemented to the bottom of the casing l. The needle support 3 comprises an elongate bar having a thickcentral portion andrelatively thin ends which are secured to the casing by means of bolts 7. Intermediate the thick central portion and the thin left end is a socket 8 having its axis inclined at the usual angle to which phonograph needles are inclined. While the needle 4 may be mounted in the socket in any suitable way, as illustrated in the drawings it is mounted by means of two plugs 9 and ll! of rubber or other suitable material which are preferably under radial compression. Intermediate the socket 8 and the sidewall of the casing I is another block ll of rubber or other yielding material adapted to damp the vibrations of the bar 3, the block I! being cemented to the outer surface of the socket or to the inner surface of the casing or to both. Extending laterally from the bar 3 is a short arm I 2 which is connected to the transducer through the medium of a vertical rod is which may be cemented or otherwise secured to the arm and to the transducer. While the rod i2 is preferably rigid it may be formed of rubber so as to be somewhat yielding. The casing I has vertical openings 5 to receive bolts or other fastening means for mounting the device on the tone arm of the phonograph or the like. When mounting the needle in the semi-permanent manner of Figs. 1 and 2, the needle preferably has a sapphire or other durable point. The rod l3 may be flattened so that its cross-sectional dimension lengthwise of the bar 3 is greater than its dimension crosswise of the bar 2.

The modification shown in Figs. 3 and 4 is similar to the embodiment of Figs. 1 and 2 except in that the needle I4 is removably mounted plate 24 is preferably mounted on the bottom of the casing to limit the movement of the needle in case the projecting end of the needle is struck accidentally. The plates have openings wide enough; to-p er-mit normal vibration of the needles without contact between the; two.

In each embodiment leads and 26 are con nected to the terminals of the transducer for the purpose of connecting the device *in cirtlit.

In following a groove which moves the needle sidewise, the supporting bar istwi'stedback iand" 51 forth in the thin portions at each"en'd,threby causing the arm l2 to move'up-anddown? .Tliis up and down movement is transmitted through the rod l3 to the transducer 2 which causesthe" transducer to vary the current in its circuit in 2 the usualway; Variatibns of 1 current thi'ough the transducer 2 -moves the rodl3'up ahd 1iown and inturn this causes theneedle to swinglaterally because of the torsional movement of the supporting means and each thin portion having flexibility which is greater crosswise of the needle than lengthwise of the needle.

2. A device of the character referred to comprising a needle adapted to trace a record groove, a needle support which permits movement transversely of said groove but which is relatively immovable in a direction perpendicular to the surfaceof the record, a transducer capable of back and forth movement, and means interconnecting said support and transducer so that one of said movements produces the other movement, said supportcompris'ing a bar and means for rigidly supporting the bar at each end, the bar having a flexible' portion between the needle and each of said supporting means and each flexible portion having a dimension lengthwise of the needle which is greater than its dimension crosswise of th'e'needle.

3. A device of the character referred to comprising-'a'needleadapted to trace a record groove, aneedle support which permits movement transversely'of said groove-butwhich'is relatively immovable in a direction*perpendicularto the surbars -3 and 23. Up amnesia-movement offthe 25 face-of'the're'cordfa tranSducer'capable of back needle has" little if 'any efit on the transducer because of the rubber'plugs9 and lfl a'nd because of the relatively-= large-vertioal 'dimensionof the bar' 3* and I4? By mo'unting th'e "plug'sB '-*and'- l 0 under radial' compression' the radial rnovement of the needle re1ati'vel-y' to the 'bar 'isrninimized without correspondingly reducing the freedom-of movement -of the 1 needle -length'tvlse of" its axis. Thus the device function's 'with'minimilm harmonic distortions and 1 minimum 1 surfacenoise, 335

The peak fre'tluen'oy ofthe devic-maybepredeterminedby the mass of the needle support, the mass of the-needle, the'modulus of' elasticity of the'material -frorn whiclr the needle' support is 40 made, the le'ngth' -of the" thin portions" of the needle support, the thicknes s and 3 width" of i the thin portions of the needle support; andthe characteristics of I the" transducer 2, its supporting'pads'B; an'd theiia'inpifig-=bl ock ll.

It should be understood that 'the present dis closure is for the purpose of illustration 'only and that this inventionincludes all modifiation's and equivalents which fall within the scop e' 'of tl'i'e appended claims;-

I claim: I

1. A device of r the character'- referred to-com prising-a needle adapted to tracea record groove, aneedle, support which permits movement trans versely ofsaid-groovebutwhichis' relatively m'--' movable in a adirection perpendicularlto the sin" face of'the record, a transducercapablewf-back and forth movement; and-means interconnecting said support-and transducer so'that one oi said movements produces the'other movementi said support comprising a bar' and -mean's 'for rigidly supporting the bar at each-end; the bar lraying-a thin portion-betweenthe needle and each of -said and- 'iorthmovem'ent} and means interconnecting said'su'pportand transducerso that one'of said movements producestheother movement, said supp'ort comprising a" flat bar and means for mountingthe needle-with its axis extendingedgewise orthe* bar; said means comprising elastic material which permits'mov'ement of the needle relatively to the bar endwiseof'the-needle.

4'; A device'of' the='charactr'referred to com- "prisinga needleadaptedto trace a record groove,

aneedlesupport Whichpermits movement transversely of said groove-but which is relatively immovable ina direction" perpendicular to the surface of th'e'recordya'transducercapable of back and forth movement, and means interconnecting said support'anwtransducerso that one of said movementsproduces the" other'movement, said support comprising a flat bar andmean's for mounting the needle with" its axis extending edgewise ofthe-b'ar; said means comprising elastic material whichpermitsmovem'ent of theneedle"relatively"to"the bar endwise of the'needle, said material being: compressed radially 'of the needle to'min'imize radial movement of the needle relative'lyto the bar;

GEORGE C. TIBBETTS.

REFERENGES CITED The follorwingrreferenlces are "of record in I the file of "this-patent:

UNITED STATES PATENTS

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