US2239717A

US2239717A - Electromechanical-conversion device

Info

Publication number: US2239717A
Application number: US222666A
Authority: US
Inventors: Hunt Frederick Vinton; Pierce John Alvin
Original assignee: Individual
Current assignee: Individual
Priority date: 1938-08-02
Filing date: 1938-08-02
Publication date: 1941-04-29
Anticipated expiration: 1958-04-29

Description

April 29, 1941- F. V. HUNT ETAL 2,239,717

ELECTROMECHANICAL-CONVERS IN DEVICE Filed Aug. 2, 1958 5 sheets-sheet 1 April 29, 1941. F. v. HUNT ETAL ELECTROMECHANICAL-CONVERSION DEVICE Filed Aug. 2, 1938 5 Sheets-Sheet 2 April 29, 1941.l F. v. HUNT ETvAL '2,239,717

ELECTROMECHANICLCONVERSION DEVICE I Filed Aug. 2, 1958 5 sheets-sheet 3 April 29, 1941. F, v. HUNT El-AL 2,239,717

ELECTROMECHANI CAL- CONVERS ION DEVICE Filed Aug. 2, 1938 5 Sheets-Sheet 4 76 77 y"i 2f 77 l S T1 1F11- 7,2 L: L *'74 y y April 29, 1941. F. v. HUNT ETAL l 2,239,717

` ELECTROMECHANIcAL-coNvERsION DEVICE Filed Aug. 2,` 193s 5 sheets-sheet 5 fr@ 53m-gi! Patented Ain. 29, 1941 ELECTROIWECHANICAL- CONVERSION DEVICE Frederick Vinton Hunt, Belmont, and John Alvin Pierce, Cambridge, Mass.

Application August 2, 1938, Serial No. 222,666

53 Claims.

The present invention relates to electromechanical-conversion devices, and more particularly to vibration-translating devices such, for example, as are used for reproducing or recording sound with wax, shellac, lacquer, metal, and similar phonograph-record materials.

It has generally been believed that the nature of the apparatus employed makes it impossible to record on phonograph records frequencies higher than about 6,000 cycles; that, even if they could be recorded, the delicate engravings corresponding to those frequencies would become worn away from the record within the first few reproductions; and that even if such high frequencies could be reproduced, they would be drowned out by the accompanying high noise levels.

An object of the present invention is tofprovide a new and improved phonograph reproducer that shall reproduce phonograph records with great fidelity and with very small wear on the material of which the records are constituted, even athigh frequencies. v

With this end in view, a feature of the invention resides in a rugged phonograph reproducer that shally have low needle-point impedanceqand a total unbalanced weight supported by the stylus which shall be so extremely small that the needie-point pressures exerted upon the record shall l not be in excess of the elastic limit of the material of which the record is constituted. In practice, the said total unbalanced weight may be less than a few grams, which is so small that it becomes feasible to omit the, abrasives heretofore usually employed in the material of which the records are constituted. It is these abrasives, and not the reproducers, that have probably been responsible for the production of the before-mentioned high noise levels.

In order to have as much `output as possible, and yet retain this extremely small weight, substantially all of the mass of the moving system wear on the tip of the stylus is so very small that r it may be constituted of a permanently mounted jewel, such as a sapphire.

As high frequencies are recorded with correspondingly small amplitudes of movement, another object of the invention is to provide a nonpivotal support for the stylus. the necessary movements of the stylus being provided for by rendering the support flexible in suitable directions. f

A further object of the present invention is to provide an electrodynamical structure which shall be reversible so that when electric currents are conducted to the apparatus a desired type of motion can be imparted to a stylus as for the recording of a phonograph record, or to a mirror so mounted that it can deflect a beam of light; these motions are to be obtained in a new and improved manner by a. type of electrodynamical structure which is self-supporting and does not require the use of pivots.

Other and further objects will be explained hereinafter and will-be particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawings, in which Fig. l is a plan of a phonograph reproducer embodying the invention, shown in position upon a phonograph record of the lateral-cut type; Fig. 2 is a section, upon a larger scale.' taken upon the line 2 2 of Fig. 1, looking in the direction of the arrows; Fig. 3 is a plan, upon the same enlarged scale, of the front portion of the tone arm supporting the reproducer mechanism as shown in Fig. l; Fig. f1 is a section, upon vthe same enlarged scale, taken upon the line 4 4 of Fig. 1 or Fig. 3, looking in the direction of the arrows; Figs. 5, 6 and 7 are enlarged sections taken upon the lines 5 5, 6-6 and 1--1, respectively, of Fig. 3, looking in the direction of the arrows; Fig. 8 is a similarly enlarged end view of the reproducer shown in Fig. 1; Fig. 9 is a side elevation of an inductor-loop element embodied in the reproducer; Fig. 10 is a blank from which a modiiied inductor coil may be formed; Fig. 11 is a plan, corresponding to the elevation of Fig. 9, of the modiiied inductor element made from the blank of Fig. 10; Fig. 12 isa fragmentary plan of a preferred modification corresponding to Fig. 1; Fig. 13 is a section taken upon the line |3-I3 of Fig. 12, looking in the direction of the arrows; Fig. 14 is an enlarged section taken upon the line I4-I4 of Fig. 13, looking in the direction of the arrows; Figs. 15 and 16 are sections corresponding to Fig. 14 of modications; Fig, 17 is a diagrammatic fragmentary perspective of a modification of the invention more 'particularly designed for use with records of the hilland-dale type; Figs. 18 and 19 are sections corresponding to Figs. 14, 15 and 16 of further modifications more particularly designed for use with records of the hill-and-dale type; Fig. 20 is a sectional plan view corresponding to Fig. 3; Fig. 2l is a fragmentary perspective of a modification Fig. 22 is a plan of a modification more especially adapted for reversible use as a recorder; Fig. 23 is an elevation corresponding to the plan of Fig. 22; and Figs. 24 and 25 are sectional views taken along the lines 24-24 and 25-25, respectively, of Fig. 23, looking in the direction of the arrows.

A stylus needle 3, the lower end of which is adapted to be disposed in contact with the undulations in the sound track of a phonograph record I of the lateral type, or 2 of the hill-anddale type, is mounted at the front end of a movable tone arm. This reproducer support, comprising the tone arm, is shown comprising two substantially parallel spaced metal tubes 5 held together as a unitary structure at their rear by a transformer-carrying frame 1, and at their front by a permanent magnet, as hereinafter described. A horizontally disposed pivot pin 4 extends through the tubes 5, as shown more particularly in Fig. 2, about which the tone arm is intermediately pivoted to swing freely in an upand-down direction. To this end, the pin 4 is provided with sockets 30 and 32 disposed at the ends of the pin, into which are tted the pointed ends of horizontally disposed sharp-pointed

pivotal screws

26 and 28 that are mounted in opposite vertically disposed side walls of a horizontally disposed box-shaped structure 24. The tone arm is adapted to swing freely also back and forth, or to the right and the left, as viewed in Fig. 2, about sharp-pointed

pivotal screws

6 and 8, that are respectively vertically disposed in upper and lower arms I2 and I4 of a U-shaped frame I6 adjustably carried upon an arm I8, and that extend vertically into sockets 20 and 22, respectively, externally provided upon upper and lower walls of the box-shaped structure 24. A small transformer I is mounted upon the frame 1, at the rear of the stylus support, and constitutes a counterweight for the front part of the tone arm and reproducer mechanism. The frame I is slidable upon the tubes to adjust the position of the counterweight.

According to the embodiment of the invention illustrated in Figs. 1 to 11, the rear ends of two parallelly disposed spaced high-intensity permanent magnet bars 54 are respectively secured in the front open ends of the tubes 5. Though shown cylindrical, the magnet bars 54 may equally well be square or rectangular in cross section. Pole pieces 33 may optionally be provided on the magnet bars, facing each other, as shown in Fig. 7. The magnet bars 54 are held together as a unitary structure. thus holding together the front ends of the tubes 5, by a soft-iron saddle or yoke 64. The non-magnetic saddle 65 is clamped by a pin 9 about the front ends of the magnets 54, and the saddle 64 by a screw and nut II aboutintermediately disposed portions of these magnet bars. A small stationary soft-iron pole piece 'Il is held by the pin 9 in the yoke 65. The two magnet bars 54 may be combined into a single U-shaped form, preferably rectangular in cross-section with the neck of the U at the rear and, if desired, with a cut-out lin the neck for the hereinafter-described inductor element to pass therethrough.

A strong concentrated magnetic eld is provided from the right-hand north pole, marked N, of the upper magnet 54, as viewed in Fig. 3, to the right-hand south pole, marked S, of the lower magnet 54, then to the left-hand north pole, marked N, of the said lower magnet, and the left-hand south pole, marked S, of the said upper magnet, and finally back to the right-hand north pole, marked N, of the said upper magnet.

The portion of the reproducer that more immediately carries the stylus 3, and which is more immediately driven thereby, is mounted at the front of the tone arm in the space between the magnet bars 54. It is constituted of material substantially all of which may be active electromagnetically; in its preferred form, it is constituted of a pivotless-inductor dynamic-type device, preferably in the form of a substantially horizontally disposed single-turn elongated loop I3. The loop is a combined electric circuit and mechanical support, and the customary deadweight of present-day constructions is entirely eliminated. The sides of the loop are disposed transversely in the magnetic eld of the permanent-magnet bars 54. Its rear ends 66 are clamped between

insulating blocks

18 and 80, held together, between the magnet bars 54, by the saddle 64, as shown more particularly in Fig. 6, and they are connected to the transformer I0 by

wires

58 and 60 that are insulated from each other by an insulating strip 56. The inductor element is provided with an intermediately widened portion 38 that is bent into a stift conical shell 36 at the extreme forward or outer closed free end of the loop I3. Ribbon-

like arms

82 and 84, of any desired length, connect the shell 36 to the ends 66 of the loop.

The stylus 3 is rigidly mounted at the bottom apex tip of the cone 36, substantially normal to the substantially horizontal plane of the Inductor loop, and the upper base of the cone is substantially in the plane of the inductor loop. The height of the cone providesthe necessary leverage; the cone shape provides a substantially maximum-stiifness leverfor the mass of material employed for the purpose, inasmuch as a conical shell of a given mass provides a structure of the maximum stiffness to connect the stylus point and a loop of a given size. The conical shell 36 thus connects the stylus 3 and the loop driven thereby to provide a very high ratio of stiffness to inertia, leading to small phase shift between the impressed motion and the electrical output, and correspondingly excellent transient response.

It is not essential that the inductor element be constituted of a single loop I3; it may have as many loops as desired, particularly if greater voltages are needed. A single loop has been found to be ample to provide ordinary useful voltages, but more turns may be desired.

The inductor coil 48 of Fig. 11, for example, made from the blank shown in Fig. 10, is shown provided with two additional loops I5 and I1. In all cases, however, the unit is easy to fabricate, since it may be'made from a thin ribbon blank constituted of some light electrically conducting metal, such as aluminum, Duraluminum or phosprior-bronze, that may be punched from sheet stock. When bent into shape, the ribbon is substantially vertically disposed, in the form of a U-shaped trough or channel, to provide increased stiffness and rigidity. The rear arms 66 of the loop are twisted substantially ninety degrees out of the vertical plane and into the horizontal, as illustrated, for example, in Figs. 9 and 11.

The blank of Fig. 10 is shown provided with ribbon-like arms 4I) and 42 of any desired length between the intermediately widened portion 3l and the ends 66 of the loop. The arm 42 is joined to a further ribbon 44 by a short neck 46.

The body of the blank is bent into the loops I5 and I1, before the rear arms 68 are twisted into the horizontal plane, and the arm 44 is, at the same time, bent downward along the neck 46.

In a modification, the U-shaped channeling of the

side arms

82 and 84 may be extended entirely around the upper or base portion of the conical shell 36, as indicated by the elevation sketch Fig. 13. The function of this channel form is to provide great rigidity of the forward portion of the inductor loop. This rigidity provides that the forward portion, or the inductor loop, which lies in the magnetic iield, shall always move as a single whole, without relative vibration of the electromagnetically active portions of the loop. On account of the disposition of the loop ends 66 in substantially the same horizontal plane as the remainder of the inductor loop, the active portion of the loop is very stiff for lateral forces applied in the plane of the loop. However, because vthe loop ends 66 have the form of ribbons whose width is large in comparison with their thickness, the inductor loop has great flexibility for motion occurring about a longitudinally disposed axis of the loop. When a lateral force or displacement is applied to the stylus 3 positioned at the apex of .the conical shell 36, the only motion which the electromagnetically active portion of the loop can execute is a rotation about the longitudinally disposed axis, and because the inductor loop structure has great flexibility for this torsional motion, the force required on the stylus 3 to produce this motion of the loop is extremely small.

The mass of the inductor-loop element, together with the conical shell and the sapphire stylus, may be made less than approximately 50 milligrams. Most of this mass, owing to the shape and disposition of the inductor loop, is concentrated close to the longitudinally disposed axis of vibration, so that the equivalent mass of the entire vibratory system, as viewed from the stylus apex as a driving point, may be less than about 5 milligrams. The mass reactance of the dynamical moving system, even at the highest frequencies, is thus so small that the forces which are required to be exerted upon the stylus 3 by the record groove are so small that the stylus may be held in positive contact with the record groove when the counterweight is adjusted to produce a net result unbalanced weight on the stylus of less than approximately five grams. In consequence of the small mass reactance of the vibratory system, the wearing of even very soft record materials is minimized and the transient momentary deformation of the record material is so slight that very high frequencies are reproduced without appreciable translation loss.

The mass reactanceof the moving system is so small that very little damping is required to secure resistance control of the motion. The damping is provided partly by a damping membrane I9 connecting the cone 36 at the closed, outer end of thevloop to the pole piece 11 and lying within the loop I3 or 48, and partly by two similar membranes 2| and 23. The membrane I9 is disposed at the extreme forward end of the loop, at the points where the cone 3B is joined thereto, almost on the axis of rotation, where the amplitude of motion is least, and any eiiect of non-uniform elasticity of the material is minimized. The membranes 2| and 23 are disposed at the extreme ends of the loop, and connect the ends 66 of the loop I3 or 48 with the rear portions of the adjacent magnetic structure, bridging the spaces between them. The membranes 2l and 23 absorb and prevent reilection of such undamped vibrations as may reach to these points.

The damping membranes I8, 2l and 23, in addition to providing the required damping of the free vibrations of the inductor loop induced by the stylus motion, provide a means for transmitting a portion of the force pressing the stylus 3 into contact with the record groove, said force being produced by the net unbalanced weight of the reproducer head and tone arm. Thus, it is not necessary to incorporate in the inductor loop rigidity against motion in a. vertical plane so that the loop may be left free to vibrate in any Way except with a lateral translational motion. When it is desired to use as little damping material as possible for reasons of improved high frequency response, the electrical center-tap connection 31 indicated in Fig. 17 may be constituted and disposed in such a manner as to provide substantially for the transmission of theunbalanced weight resting upon the stylus 3 to the tone arm 5, as shown more particularly in Figs. 20 and 21 Together the connection 31 and the damping membranes I9, 2|, 23, provide vertical support for the tone arm and adequate damping for the induced motions of the inductor loop, yet they permit the stylus 3 such great mechanical freedom that the delicate high-frequency modulations in the side walls of the record groove can drive the stylus without themselves exerting enough force to become damaged.

The damping membranes I9, 2l and 23 may be constituted of any suitable damping substance. A suitable rubber-like substance is a nitrocellulose pyroxylin plastic molding material, such as has been sold on the market under the trade marks Viscoloid and Pyralin. It can be dried out from solution in the form of a plastic material having a high coeiiicient of viscosity.

The present invention minimizes the harmonic distortion and poor transient response that usually arises in conventional reproducers from non-uniformity and non-linearity of the magnetic iield, non-linear damping, and mechanical break-up of the moving parts. The non-linear distortion is very low and the transient response is excellent. There is a mechancaLstep-down ratio between the motion of the stylus and the motion of the conductors in the magnetic field, so that it is easy to confine the motion to the portion of the field that is essentially uniform.

A very light, unrestricted vibration translating device is thus provided, adapted to vibrate about an axis which is quite rigid and stiff for lateral displacement in the plane of the loop, but which is very iiexible, so as to move substantially freely, in torsion; a lateral vibrational displacement of the stylus 3 below the plane of the loop is converted into a rotary motion of the stiiened front portion of the loop. No pivots are required to obtain the desired motion of the inductor loop since the longitudinal axis of vibration is established by the inherent differential flexibilities obtained by means of the conformation of the mechanical-supporting and inductor loop itself. As the stylus 3 moves up and down, and to the right and the left, the stylus yields and moves freely in all directions, communicating the appropriate vertical or rotational motion to the inductor loop by virtue of the inherent flexibilities obtained by the conformation of the loop.

The loop I3 or 48 constitutes both the mechanical system .to which the stylus 3 delivers its energy and the electric system for conveying the energy. A voltage is induced in the loop when the stylus needle 3 is caused to vibrate to drive the stylus support. The impedance of the loop is quite low, and may be matched to about 500 ohms by the small transformer l0. By conventional transformation, the electrical energy may be delivered from the low-impedance loop to ordinary communication circuits.

The substantial additional mechanical or acoustical load that is ordinarily produced by the customary diaphragm or magnetic armature or other leverages or loading parts is Wholly lacking from the reproducer of this invention, and because the needle is not loaded, it is required ely to reproduce the motion of the record T/C178. i

One of .the sources of harmonic and phase distortion in present-day constructions arises in the needle itself, because it vlbrates, not as a rigid whole, but as a flexible mechanical system. Because oi this fact, although the point of the needle, that rests in the record groove, may follow the vibrations represented by the groove, the vibration transmitted to the remainder of the mechanical system coupled to the needle is far i'rom a iacsimile of the driving vibrations.

According to the present invention, however, the conical stylus mount and the inductor loop are so light and have such great rigidity on account of their geometrical configuration that the electromagnetically active system vibrates freely as a rigid unit in response to the force exerted on the stylus by the sound track. The needle point impedance is so low that the above-mentioned weight of about iive grams is suflicient to keep the needle point firmly seated ln the record groove with no observable distortion arising from chattering. In the reproduction of hill-and-dale recordings, it may be pointed out that the above- .mentioned unbalanced Weight of about ve grams supported on the stylus point is sufciently great, and the mass of the dynamical system is sumciently small, so that the stylus point is held in iirm contact with the record groove even when the modulation of the record groove requires the stylus point to execute accelerations correspondlng to the maximum recorded level.

Despite the lightness of the moving parts, the device is relatively rugged and simple, and easy to protect from accidental damage. The pressure of the stylus needle 3 upon the record I is so light that the pick-up can be slid radially back and forth across the cut grooves of a lacquer-coated record, without producing either a visible scratch or any blemish that is audible upon subsequent playing. Because of the light pressure and the very flexible nature of the stylus-needle support, the reproducer may even be dropped from a height of an inch or more onto the lacquercoated surface, without damaging either the reproducer or the record. The wear upon even the softest type of present-day record is so slight as to be negligible, so that thelphonograph records last indefinitely.

A diiliculty which has attended the use of such very light unbalanced weight upon the stylus needle as is here described arises from the fact that sudden jars of the turntable or tone-arm mounting may cause the reproducer to bounce out of the record groove, Such an occurrence may be avoided if the mass and position of the counterweighting transformer are so adjusted that the moments of inertia of the portions of the tone arm disposed upon the two sides of each set of pivots are equal, thus causing the centers oi percussion to lic on the lines joining the pivots. When .this condition is satisiled a sudden translational motlon of the pivots will not produce any rotation oi' the tone arm about the pivots, and since the turntable itself must necessarily be .translated by the same amount as the tone arm pivots, there will be no relative motion between the reproducer stylus and the record groove.

The stylus needle may be constituted of a permanent jewel, such as a sapphire or diamond, which may, however, be easily replaced, if sited.

Other details concerning the construction and operation of a reproducer designed in accordance with the preceding principles were expounded in a paper presented by us at the Ann Arbor, Michigan, meeting of the Acoustical Society or America, November 29, 1937, and described briefly in an abstract published in the Journal of the Acoustical Society of America. The model re producer which was exhibited at the mentioned meeting is further described in more detail in a paper published by us in Electronics, March issue, 1938.

As the stylus needle 3 vibrates in the process of tracing the sound track groove of a record which may be modulated up and down as in the hill-and-dale record, or back and forth, as in the lateral record, it necessarily and inherently must follow a path that is not quite the same as the path traced by the recording stylus since the stylus needle 3 has finite size. This phenomenon constitutes a serious source of distortion in the reproduction o1' phonograph records. It is a feature of our inventionthat the characteristics of the specified reproducer are able to reduce this distortion in a considerable measure. We have studied the source and magnitude of this distortion in mathematical detail and have presented our findings at a meeting of the Society of Motion Picture Engineers held in Washington, D. C., April 28, 1938, and at a meeting of the Acoustical Society of America also held in Washington, May 2, 1938. A detailed account of this study has been published in the Journal of the Acoustical Society of America for July, 1938 (vol. 10, p. 14), to which reference is here made. In connection with the features of the present invention which relate to the reduction of this type of harmonic distortion, we make particular reference to Fig. 2 of the published paper referred to, in which it is shown that the included angle of the record groove which is laterally modulated must change as the recording stylus executes a motion perpendicular to the record groove. In order for the motion of the stylus 3 to be entirely controlled by the modulation of the record groove, it will be obvious that at least a portion of the record groove on each side of the midline of the stylus 3 must be in continuous contact with the stylus at all times. Such a condition of positive guidance of the stylus is sometimes called positive tracking and it will be obvious that when this condition is satised the stylus needle 3, in executing the lateral motion corresponding to the recorded groove, must also execute a vertical motion as a result of the change in the included angle of the record groove. In typical commercial reproducers, there is no provision for vertical motion of the stylus relative to the tone arm, with the result that the stylus must ride at some intermediate elevation, at times being driven into the groove because the great mass of the reproducer head cannot be vibrated at signal frequencies, and at other times floating above the groove where it is free to rattle and produce undesirable noise and distortion. This gouging action as a resultvof the pinched' sections of the groove results in eliminating the high-frequency modulations recorded in the groove, tears the record and introduces additional noise, and has other undesirable eilects, such as the introduction of cross-modulation distortion, and the production of excessive wear on the stylus.

According to the present invention, however, the pressure exerted by the stylus needle 3 on the record is so small and the mechanical impedance of the dynamical system for vertical motion is so small that. instead of tearing through `the material oi the record in the pinched sections of the groove, the stylus rises up slightly and'passes over them without causing any damage; and this without failing to follow substantially the center line of the record groove. To speak more exactly, our analysis of the residual distortion in the .reproduction oi.' lateral-cut records shows that the feature of positive tracking incorporated in the present invention results in the total elimination of all even harmonics in the lateral motion of the stylus needle 3. It is, in fact, shown in the reference cited that 'the vertical rise and fall which must be executed by the stylus needle when tracing a laterally modulated groove represent the above-mentioned even harmonics of the otherwise produced tracing distortion. Thus, in a reproducer according to the foregoing specilications, the even harmonics of the tracing distortion introduced by the nite size of the stylus needle 3 are cancelled out of the latera1 motion .of the stylus and appear as induced vertical motion. Such vertical motions would tend to produce a distortion voltage by virtue of the motion of the inductor loop in the magnetic field, but such distortion voltages are prevented from appearing in the output, according to the present invention, because the

side arms

82 and 84 of the loop I3, leading to the cone 36 that carries the needle 3, are both raised and lowered simultaneously. By virtue of the disposition of the magbe as flexible vertically as it is laterally, yet atv the same time capable, for the reproductionl of lateral-cut records, of cancelling out the induced voltages produced by the vertical motion. These ends are facilitated in the present invention by the elimination of the customary pivots.

By reason of the above construction, the dynamical inductor-stylus support system, with the stylus 3 supported thereby, is rendered substantially inertialess, so as to approximate very closely to an idea1 structure the Vibrations of which would ideally not be disturbed by its own mechanical characteristics. It is of small enough dimensions, and sufficiently light and flexible, and it is so supported, that, in effect, it is substantially free to follow faithfully the instantaneous vibrations corresponding to the delicate undulations of the sound recorded in the sound-track grooves of the record, without substantial alteration of these vibrations from what they would have been if ythe dynamical system, with the stylus I supported thereby, were absolutely inertialesa Throughout a uniform-response range as high even as 18 kilocycles, the reproducer reproduces exactly, and with the utmost fidelity, substantially in facsimile, the sound vibrations recorded in the record, without any noticeable eilect of its own on the quality of the reproduced sound.

It is desirable, in order to reduce the tracking angle, which is discussed in the reference cited, that the longitudinal axis of vibration of the reproducer be always tangent to the circular arc of the record. The tangency can not, theoretically, be attained, except at one or two points. According to the modification illustrated in Figs. 12 and 13, the stylus-supporting arm is vmade a little longer than in Fig. 1, so as to enable it to swing somewhat beyond the center of the record, thus reducing the error from this source. The loop I3 is disposed at an angle to the direction of extension of the supporting arm, to correspond. f

According to the preferred embodiment of the invention illustrated in Figs. 12 to 14, the permanent magnet bars 54 of the'embodiment,illus trated in Figs. l to 11, are replaced by a single permanent bar magnet; having a north pole N, shown at 68, and a south pole S shown at 10.

' Two soft-iron pole pieces 12 and 14 are respectively secured to the base by screws 16 passing up through a Bakelite bottom plate 18. The pole piece 11 is correspondingly shown. The forward ends of the tubes 5 are, in this case, held together by a yoke 35 carried by the Bakelite bottom plate 18. The active portion of the loop I3 extends throughout the length of these pole pieces'12 and 14.

'I'his magnetic arrangement permits considerable concentration of the magnetic eld in the air gap being, at the same time, smaller and lighter than the arrangement oi' Figs. 1 to 11, for comparable magnetic efliciencies. If made in rectangular form, the

permanent magnet

68, 10 is of an easily producible shape, as all the parts that require machining are constituted of soft iron.

The arrangement of Fig. 15 is inverted with respect to that shown in Fig. 14, the

permanent magnet

68, 10 being positioned in the space below the loop, so as to have the over-all height of the pick-up, above the record, at a minimum.

In Fig. 16, the magnet 68, 1li is divided into two

parts

25, 21, with the pole pieces 29 and 3I between them, so as to provide a little greater space above the needle and below the lower magnet. With a symmetrical arrangement of this character, it is easier to obtain a uniform magnetic eld than with the devices of Figs. 1 to 15.

Figs. 17 to 19 illustrate ways of utilizing this invention in connection with records of the hilland-dale type. Fig. 18. represents a structure similar to Figs. 12 to 16, with the exception that the permanent magnet is so arranged as to produce a magnetic eld in the Plane of the loop such that voltages introduced by lateral displacement at the needle point will be cancelled, while those voltages that are due to vertical displacement, will aid each other.

The loop I3 only is shown in Fig. 17; the remaining structure may be as in Fig. 1 or Fig. 12. The transformer II! may be conventional, as in Fig. l, but a third connection 31 is illustrated in Fig. 17 from the electrical center 39 of the loop to a divided or split primary winding `II of the coupling transformer. The center 39 may be grounded to the magnetic structure. The current in the two halves of the loop may be made to aid in the split transformer primary winding 4I. A circuit change will thus convert from lateral to vertical. By proper phasing of the three leads at the primary winding 4I, the pickup may be made to respond to either lateral or vertical displacement.

According to the asymmetrical arrangement of the stylus 3 shownv on the asymmetrical cone of Fig, 19, the voltages introduced by vertical motion of the loop I3, which would otherwise cancel each other, do not completely cancel, because they differ in magnitude( This pick-up, therefore, will respond to either lateral or vertical motion of the needle point. The same result may be produced by damping heavily on one side only; or this damping may be combined with the asymmetric cone. 1 It may be pointed out that, in an electromagnetic vibration translating device of the type described above, the interaction coefficient between the electrical and the mechanical system is completely reversible. Thus, if instead of impressing upon the stylus needle 3 a motion, as by the undulating groove of a phonograph record, an electrical input is applied to the terminals of the transformer I0, and thence transformed and conducted as current to the inductor loop I3, forces will be produced by the interaction of these currents and the magnetic field provided. Such forces, depending on whether the connections have been established as described above for hill-and-dale reproduction or for lateral reproduction, will produce either vertical translational motion of the inductor loop or a rotational motion of the loop. Such rotational motion might be utilized, as in a phonograph recorder, to produce late-ral vibrations of a recording stylus.

A modification of the dynamical structure particularly adapted for this service is shown in plan and elevation in Figs. 22 and 23. The inductor element to which current may be led from the transformer I may be wound as a coil upon the cylindrical section 49 surmounting the conical shell 36 which bears a stylus 3 at its apex. The fiat ribbon-like members 66 are disposed substantially parallelly and in the horizontal plane and serve to prevent lateral motion of the inductor element in this plane, remaining free and fiexible in torsion and providing substantially for the establishment of a longitudinal axis of vibration. Similarly, a vertically disposed ribbon-like member 31 is adapted to provide for the communication of the vertical thrust exerted upon the stylus 3 to the tone arm supporting the clamping members 'I8 and 80. The disposition of the three ribbon-like members is shown in greater detail in the sectional views of Fig. 24 and Fig. 25. As in the above-described modifications of the invention, damping may be secured by a Pyralin or other viscous film disposed in the space between the ribbon-like members, as indicated in the plan and sectional views.

Electric currents fiowing in the inductor coil wound upon the cylindrical section 49 thus produce torsional forces acting upon the conical shell 36 when a eld structure, not shown, provides a transverse magnetic field traversing the inductor coil in a direction perpendicular to the longitudinal direction of the

ribbons

66 and 31.

Alternatively, a small mirror might be mounted on the conical shell 36 to yield a new and useful type of galvanometer, as might be used in sound-on-film recording, or as an oscillograph element. A device incorporating the differential fiexibilities which we have described, and connected as we have specified for the reproduction of hill-and-dale records might be employed reversibly to emboss or engrave such hillfand-dale records, or for other service requiring the faithful conversion of an electrical signal into a verticalmotion, as in facsimile reproduction with impression paper. Indeed, the differentially flexible structure which we have described may flnd applications as a purely mechanical vibration translation device whereby, for example, a mirror mounted on the loop I3 may, by deflecting a light beam, record the undulations of a rapidly moving surface.

These, and further modifications and changes, will occur to persons skilled in the art, and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. Phonograph apparatus comprising a stylus adapted to be disposed in contact with the sound track of a record, a support for supporting the stylus in contact with the sound track, the support having a rear portion fixed at one end and a movable` portion carried at the other end, and means for mounting the stylus at the free end of the movable portion only to constitute the movable portion the sole support for the stylus, the movable portion being shaped to prevent substantial mechanical deformation thereof in response to movement of the stylus along the sound track, and the rear portion being flexible in order that it may flex mechanically in response to movement of the stylus along the sound track, thereby to cause the movable portion to move substantially as a whole in response to movement of the stylus along the sound track.

2. Phonograph apparatus comprising a stylus adapted to be disposed in contact with the sound track of a record, means for creating a magnetic field, a support for supporting the stylus in contact with the sound track, the support having a rear portion fixed at one end and a movable inductor portion carried at the other end, and means for supporting the stylus at the free end of the inductor portion only to constitute the inductor portion the sole support for the stylus, the inductor portion being disposed in the magnetic field in order that electric currents may flow therein in response to movement of the stylus along the sound track, the inductor portion being shaped to prevent substantial mechanical deformation thereof in response to movement of the stylus along the sound track, and the rear portion being fiexible in order that it may fiex mechanically in response to movement of the stylus along the sound track, thereby to cause the inductor portion to move substantially as a ,whole in response to movement of the stylus along the sound track.

3. Phonograph apparatus comprising a stylus, means for supporting the stylus, means for creating a magnetic field, and a rigid loop of metal ribbon disposed transversely in the field and constituting the sole support for the stylus.

4. Vibration-translating apparatus comprising a vibratory element, and elastic supporting means for the vibratory element comprising a plurality of ribbon-shaped members disposed in planes intersecting in a common line, thereby to cause the aforesaid common line to become an axis for vibratory rotation.

5. Phcnograph apparatus comprising a stylus adapted to be disposed in contact with the sound track o! a record, a support for supporting the stylus in contact with the sound track, the support having a rear portion xed at one end and a movable portion carried at the other end, and means for mounting the stylus at the free end of the movable portion only to constitute the movable portion the sole support for the stylus, the support being relatively rigid for lateral displacement but relatively very flexible in torsion.

6; Phonograph apparatus comprising a stylus adapted to be disposed in contact with the sound Atrack o1' a record. a unitary support for supporting the stylus in contact with the sound track, the support having a rear portion xed at one end and a movable portion carried at the other end, and means for supporting the stylus at the free end of the movable portion only to constitute the movable portion the sole support for the stylus, the support being disposed substantially in a plane substantially normal to the stylus.

7. A phonograph reproducer comprising a stylus, a support therefor, means carried by the support for creating a magnetic field, a combined electrical and mechanical unitary system carried by the support in the field, and means for constraining the system to move torsionally and preventing it from moving laterally.

8. Phonograph apparatus comprising a stylus adapted to be disposed in contact with the sound track of a record, means for creating a magnetic iield, and a support for supporting the stylus in contact with the sound track, the support having a rear portion ilxed at one end and a movable inductor portion carried at the other end. means for supporting the stylus at the free end of the inductor portion only to constitute the inductor portion the sole support for the stylus, the inductor portion being disposed in the magnetic iield in order that electric currents may ilow therein in response to movement of the stylus along the sound track, the inductor portion being constituted of a rigid loop of metal ribbon disposed transversely of the eld in order that it may vibrate as a whole in torsion without moving laterally in response to movement oi.' the stylus along the sound track.

9. Phonograph apparatus comprising a stylus, and means i'or supporting the stylus, .the supporting means being constituted of a loop of metal ribbon, the loop being provided at its outer end with a stiffened front element having a portion below the plane oi' the loop at the lower end of which the stylus is mounted, whereby lateral displacement of the stylus is converted into a rotary motion oi' the stiiened i'ront element.

l0. Phonograph apparatus comprising a stylus, means ior supporting the stylus, the supporting means comprising a loop of metal ribbon, the front portion of the loop being stiiIened by mechanical shaping and provided at its outer end with a front element having a portion below the plane of the loop at the lower end oi which the stylus is mounted, the front portion of the loop constituting the sole support for the stylus, whereby lateral displacement of the stylus is converted into a rotary motion oi' the stifl'ened segment of the loop, and means tor creating a magnetic field, the stiiiened portion of the loop being disposed in the magnetic field, whereby electromotive forces are generated in the stitfened portion of the loop.

11. Phonograph apparatus comprising a stylus, and means for supporting the stylus, the supporting means comprising a loop of metal ribbon, the loop being provided at its outer end with a relatively light stili! segmento! a conical shell,

vthe stylus being carried by the shell, and the shell constituting a relatively inflexible link between the said outer end of the loop and the stylus, g

12. Phonograph apparatus comprising a stylus, means for supporting the stylus, the supporting means comprising a loop of metal ribbon, the loop being provided at its outer end `-with a stii! iront element having a portion below the plane of the loop at the klower end of which the stylus is mounted, whereby lateral displacement of the stylus is converted into a rotary motion of the front portion of the loop, and means for damping the motion of the loop.

13. Phonograph apparatus comprising a stylus, means for supporting the stylus, the supporting means comprising a loop of metal ribbon, the loop being provided at its outer end with a stiffened` segment having a portion below the plane of the loop at the lower end of which the stylus is mounted, whereby lateral displacement of the stylus is converted into a rotary motion `of the stiffened segment, and means for damping the motion of the stiiened segment comprising a Pyralin element.

14. Phonografph apparatus comprising a stylus,

means for supporting the stylus, the supporting means comprising a loop of metal ribbon, the loop being provided at its outer end with a stiffened front element having a portion below the plane of the loop at the lower end of which the stylus is mounted, whereby a lateral displacement of the stylus is converted into a rotary motion of the stiiiened front element, a pole piece within the loop, and means for damping the front element comprising a Pyralin element disposed between the pole piece andthe front element.

15. Phonograph apparatus-comprising a stylus, means for supporting the stylus, the supporting means comprising a loop of metal ribbon, the loop being provided at its outer end with a front element having a portion below the plane of the loop at the lower end of which the stylus is mounted, means whereby a lateral displacement of the stylus is converted into a rotary motion of the front element, a pole piece within the loop, a spring member connecting the outer apex of the loop with the pole piece, and means for damping the `motion of the front element comprising a Pyralin element disposed between the pole piece and the front element.

16. Phonograph apparatus comprising a stylus, means for supporting the stylus, the supporting means comprising a loop of metal ribbon, the loop being provided at its outer end with a front element having a portion below the plane of the loop at the lower end of which the stylus is mounted, means whereby a lateral displacement of the stylus is converted into a rotary motion of the front element, a pole piece within the loop, a sprinsr mem-ber connecting the outer apex of the loop with the pole piece, means for damping the motion of the rear portions of the loop coinprising Pyralin elements disposed between the said rear portions or between the said portions and the adjacent structure, and means for damping the motion of the front element comprising a of which the stylus is mounted, a pole piece with-L in the loop, and means for damping the front element comprising a Pyralin element disposed between the pole piece and the front element.

18. Phonograph apparatus comprising a stylus, a support for the stylus comprising means for producing a magnetic field and a loop disposed in the iield, the loop being provided at its outer end with a stiffened front element having a portion below the plane of the loop at the lower end of which the stylus is mounted, a pole piece within the loop, an elastic electrical connection between the outer apex of the loop and the pole piece, and means for damping the motion of the front element comprising a Pyralin element disposed between the pole piece and the front element.

19. Phonograph apparatus comprising a stylus, a support for the stylus comprising means for producing a magnetic field and a loop disposed in the eld, the loop being `provided at its outer end with a st'iiened front element having a portion below the plane of the loop at the lower end of which the stylus is mounted, a pole piece within the loop. an elastic electrical connection between the outer apex of the loop and the pole piece, means for damping the motion of the rear portions of the loop comprising Pyralin elements disposed between the said rear portions or between the said portions and the adjacent structure, and means for damping the motion of the front element comprising a Pyralin element disposed between the pole piece and the front element.

20. Vibration translating apparatus comprising a stylus, and means for supporting the stylus, the supporting means comprising a loop of metal ribbon disposed substantially in a plane, with the ribbon partly in the said plane and partly bent out of the said plane into channel form to provide rigidity.

21. Vibration translating apparatus comprising a stylus, and means for supporting the stylus, insulating material carried by the supporting means, the supporting means comprising a loop of metal ribbon disposed substantially in a plane, the ribbon being twisted substantially ninety degrees in the rear portion of the loop, and means for clamping the said rear portion of the loop in the insulating material.

22. Phonograph apparatus comprising a stylus adapted to be disposed in contact Withthe sound track of a record, means for supporting the stylus comprising an intremediately pivoted arm on one end of which the stylus is mounted, an inductor loop mounted on the said end, the other end of the arm carrying a counterweight, the counterweight being adjusted in position so that the center of percussion of the apparatus shall lie on the line joining the pivots, whereby the stylus and the record are maintained in their relative positions Without substantial change thereof during the movement of the stylus over the record.

23. Phonograph apparatus comprising a stylus adapted to be disposed in contact with the sound track of a record, means for supporting the stylus comprising an arm on one end of which the stylus Cil is mounted, the arm being intermediately pivoted to move in two directions at right angles to each other, and an inductor loop mounted von the said end, the other end of the arm carrying a counterweight, the position of the counterweight and the mass distribution of the tone arm being determined so that the centers of percussion for lateral and vertical impulses applied to the arm and the apparatus mounted thereon fall respectively in the lines containing the corresponding pivots in order that the translational movement of the phonograph apparatus as a whole in any direction shall not introduce relative movement between the stylus and the record groove.

24. Vibration translating apparatus comprising a stylus, and sole supporting means for the stylus comprising a loop of ribbon attached to the stylus and formed to vibrate as a whole in torsion or in vertical motion, without moving laterally when the stylus is driven laterally, the loop being adapted to be placed in a magnetic field and used as an electrodynamic generating element without the addition of a separate electric conducting element, thus placing the generating element in the plane containing the axis of rotation so that distortion due to non-linearity of the magnetic field is reduced to a minimum.

25. Phonograph reproducing apparatus comprising a stylus, an inductor loop forming a combined generating element and mechanical support for the stylus, the said loop being disposed in a magnetic field and capable of vibrating vertically without generating corresponding electrical output thereby eliminating the major components of distortion produced by tracing the record groove with a stylus of nite size, the said loop being capable of rotating as a whole to reproduce the recorded material faithfully.

26. phonograph apparatus comprising a stylus, a pivotless inductor loop capable of vibration in a magnetic field when driven by a laterally modulated record groove, the moving parts being light and iiexible and capable of using a stylus tip having an effective radius of less than one thousandth of an inch, thereby substantially eliminating distortion products in reproduction of the recorded sound without damaging the record.

27. Vibration translating apparatus comprising a vibratory element, means mounted on the vibratory element for indicating or recording its motion as a mirror or recording stylus, and elastic supporting means for the vibratory element having different rigidity for deformation in different directions, the supporting means being disposed in substantially a single plane, whereby a longitudinal axis of vibration for the vibratory element is established without the use of pivots.

28. Vibration translating apparatus comprising a vibratory element, a recording or reproducing stylus attached thereto, elastic supporting means for the vibratory element comprising two ribbon-shaped members disposed approximately parallel and substantially in the horizontal plane, whereby lateral motion of the vibratory element is prevented.

29. Vibration translating apparatus comprising a vibratory element. a recording or reproducing stylus attached thereto, elastic supporting means for the vibratory element comprising two ribbon-shaped members disposed approximately parallel and substantially in the horizontal plane. whereby lateral motion of the vibratory element is prevented, and a third ribbon-shaped member disposed substantially in the vertical plane, whereby the mechanical impedance for vertical motion of the vibratory element is controlled, said ribbon-shaped members all being flexible in torsion.

30. Phonograph reproducing apparatus comprising a stylus, vibratory supporting means for the stylus, and electrical means for deriving an electrical voltage from the vibrations of the supporting means, said supporting means being disposed to provide great flexibility for lateral motion of the stylus, whereby the recorded Sounds may be faithfully reproduced in the electrical output, and the said supporting means lbeing disposed so as to provide great ilexibility for vertical motion of the stylus Without producing a corresponding electrical output, thereby removing the principal distortion products otherwise present in the electrical output.

31. Phonograph reproducing apparatus comprising a stylus, vibratory supporting means for the stylus, and electrical means for obtaining an electrical voltage in response to lateral motion only of the stylus, said supporting means being disposed to provide a low mechanical impedance for vertical motion, whereby the stylus may be supported substantially upon both side Walls of the record groove simultaneously and at all times without damage to the record.

32. Phonograph reproducing apparatus comprising a stylus, and vibratory inductor means for supporting the stylus, the said supporting means being proportioned and disposed to provide a low mechanical impedance for lateral or vertical motion, whereby the stylus may be supported substantially upon both side Walls of the record groove simultaneously and at all time without damage to the record.

33. Vibration translating apparatus comprising a vibratory element, a recording or a reproducing stylus attached thereto, and elastic supporting ribbon inductor means for the vibratory element having diierent rigidity for deformation in different directions, the ribbon inductor means being disposed substantially in a plane substantially normal to the stylus and constituting the sole support for the stylus, whereby a longitudinal axis of vibration for the vibratory element is established without the use of pivots.

34. Phonograph apparatus comprising a stylus, inductor means, means whereby the stylus is connected to the inductor means, and supporting means for said inductor means comprising metallic ribbons formed mechanically to provide a longitudinal axis of vibration of the inductor means without the use of pivots.

35. Phonograph apparatus comprising a stylus, inductor means, means whereby the stylus is connected to the inductor means, and supporting means for said inductor means comprising metallic ribbons formed and disposed to provide different rigidity for deformation in dilerent directions, whereby a longitudinal axis of vibration for the inductor means is established without the use of pivots.

36. Vibration translating apparatus comprising a stylus, and a relatively stili unitary supporting and inductor means connected to the stylus, said unitary means being shaped and disposed to provide differential rigidity for deformation in different directions. whereby a longitudinal axis of vibration is established without pivots, the unitary means being disposed symmetrically with respect to the axis of vibration.

Cil

37. Phonograph apparatus comprising a stylus, means for supporting the stylus, the supporting means comprising a loop of metal ribbon. means whereby lateral displacement of the stylus is converted into a rotary motion of the front portion of the loop, and means for damping the motion of the loop.

38. Phonograph apparatus comprising a stylus,

means for supporting the stylus, the supporting means comprising a loop of metal ribbon, means whereby lateral displacement of the stylus is convibratory element, the support having a rear portion fixed at one end and a movable portion carried at the other end, means for mounting the element at the free end of the movable portion only to constitute the movable portion of the sole support for the element, the movable portion being shaped to prevent substantial mechanical deformation thereof in response to vibratory movement of the element, and the rear portion being exible in order that it may Iiex mechanically in response to vibratory movement of the element, thereby to cause the movement portion to move substantially as a whole in response to vibratory movement of the element.

41. Vibration translating apparatus comprising a vibratory element, means mounted on the vibratory element for indicating or recording its motion as a mirror or recording stylus, and elastic supporting means for the vibratory element comprising a plurality of ribbon-shaped members disposed so as to establish substantially a longitudinal axis of vibration for the vibratory element without the use of pivots. 42. Vibration translating apparatus comprising a vibratory element, a support for supporting the vibratory element, the support having a rear portion xed at one end and a movable portion carried at the other end. and means for supporting the vibratory element at the free end of the movable portion only to constitute the movable portion the sole support for the vibratory element, the movable portion being constituted or a rigid loop of-ribbon in order that it may vibrate as a Whole in torsion without moving laterally in response to movement of the vibratory element.

43. Vibration translating apparatus comprising a vibratory element, a support, a loop of thin metal ribbon disposed substantially in a plane, the rear portion of the loop being xed to the support, the front portion of the loop being movable, and means for mounting the vibratory element upon the movable portion of the loop only to constitute the movable portion the sole support for the vibratory element, the loop being relatively rigid for lateral displacement in the plane of the loop but relatively very flexible in torsion.

44. Vibration translating apparatus comprising a vibratory element, and ribbon translating means forming the pole support for the vibratory element, the ribbon means being bent to provide rigidity.

N 45. Vibration translating apparatus comprising a vibratory element, and means for supporting the vibratory element, the supporting means comprising oppositely disposed ribbon means symmetrically bent to provide rigidity.

46. Vibration translating apparatus comprising a vibratory element and sole supporting means for the vibratory element comprising ribbon means attached to the vibrating element and formed to vibrate as a unit in torsion or in vertical motion, without moving laterally when the vibratory element is driven laterally.

47. Vibration translating apparatus comprising a support, ribbon means having a rear portion nxed to the support and a front portion that is movable, the movable portion being provided with a stiff front element having a portion below the rear portion of the ribbon means and a vibratory element carried by the said portion of the stii front element, whereby lateral displacementof the vibratory element is converted into a rotary motion of the stiiened element.

48. Vibration translating apparatus Y.comprising a vibratory element, pivotless ribbon means forming a combined generating element and mechanical support for the vibratory element, the said ribbon means being disposed in a magnetic eld and being capable of vibrating vertically and rotating as a unit.

49. Vibration translating apparatus comprising a vibratory element, vibratory supporting means for the vibratory element, electrical means for deriving an electrical voltage from the vibrations of the supporting means, said supporting means being disposed to provide great iiexibility for lateral motion of the vibratory element, and the said supporting means being disposed so as to provideV great flexibility for vertical motion of the vibratory element without producing a corresponding electrical output.

50. Vibration translating apparatus comprising a vibratory element, a support for supporting the vibratory element, the support having a rear portion fixed at one end and a movable portion carried at the other end, and means for mounting the vibratory element at the free end of the movable portion only to constitute the movable portion the sole support for the vibratory element, the movable portion being shaped to prevent substantialmechanical deformation thereof and the rear portion being flexible in order that it may ex mechanically thereby to cause the movable portion to move substantially as a whole.

51. Vibration translating apparatus comprising a vibratory element, a recording or reproducing stylus attached thereto, elastic supporting means for the vibratory element comprising a plurality of ribbon-shaped members disposed in planes intersecting in a common line, one of the ribbon-shaped members being disposed substantially in the vertical plane, and the other 'ribbonshaped members being disposed substantially symmetrically to the said one ribbon-shaped member, whereby the mechanical impedance for motion of the vibratory element is controlled, said ribbon-shaped members all being flexible to permit torsional vibration about the common line.

52. Phonograph apparatus comprising a stylus, inductor means, means whereby the stylus is connected to the inductor means,. and supporting means for said inductor means comprising metallie ribbons formed and disposed in planes intersecting in a common line to provide diierent rigidity for deformation in different directions and whereby the said common line provides. an axis of vibratory rotation for the inductor means Without the use of pivots.

53. Vibration translating apparatus comprising a vibratory element, a recording or reproducing stylus attached thereto, elastic supporting means for the vibratoryelement comprising two ribbon-shaped members disposed approximately parallel and substantially in the horizontal plane, whereby lateral motion of the vibratory element is prevented, and a third ribbon-shaped member disposed substantially in the vertical plane, whereby the mechanical impedance for'vertical motion of the vibratory element is controlled, said ribbon-shaped members all being flexible to allow torsional vibration about an axis constituting the common intersection of the planes containing the ribbon-shaped members.

FREDERICK V. HUNT. JOHN ALVIN PIERCE.