US2367846A

US2367846A - Sound recording and reproducing apparatus

Info

Publication number: US2367846A
Application number: US419360A
Authority: US
Inventors: Sr Albert W De Sart
Original assignee: UNITED ACOUSTIGRAPH CORP
Current assignee: UNITED ACOUSTIGRAPH Corp
Priority date: 1941-11-17
Filing date: 1941-11-17
Publication date: 1945-01-23
Anticipated expiration: 1962-01-23

Description

' P) 2Q M45 A. W. @E s/mgsR SOUND RECORDING AND REPRODUCNG APPARATUS 5- Sheets-Sheet f Filed NOV. 17, 1941 NVENTOIZ BVM @s/ma W WN @im WJTI. A W

jm 23 w45 A. w. DE sART, sR

SOUND RECORDING -AND REPRODUCIG APPARATUS 5 Sheets-Sheet 2 Filed NOV. 17, 1941 n EE.

ATTORNEY jam 239 'i945 A, W DE S'AR-.r` SRv 2,367,846

SQUND RECORDING AND REPRODUCING APPARATUS Filed Nov. 17, 1941 5 Sheets-Sheet 5 IV l BWM

TTOR N-EY Jm- 23 1945. A. w. DE sART, sR

SOUND RECORDING AND'REPRODUCING APPARATUS 5 'Sheets-Sheet' 4 Filed NOV. 1'7, 1941 y TON EY Jan. 23, 1945. A. w. DE sART, SR

SOUND RECORDING AND REPRODUCING APPARATUS 5 Sheets- Sheet Filed Nov. 17. 1941 \NVENTOR /J/ff nf wmf 5r. BY jf ATToR N EY Patented Jan. t23, 1945 soUND RECORDING AND aEraonUoxN'G APPARATUS Albert W. De Sart, Sr., Los Angeles, Calif., as-

signor to United Acoustigraph Corporation, Los Angeles, Calif., a corporation oi' Nevada Application November 17, 1941, Serial No. 419,360

11 Claims. (Cl. 179-100.41)

This invention relates to sound recording and reproducing apparatus. More particularly it relates to stylus heads that are adapted to cooperate with a member capable of carrying a record, such as a loop, a cylinder or a disc. Y

Stylus heads of this general characteristic, capable of being optionally used either for recording or reproduction purposes are now well known. They usually comprise a mounting for a stylus that permits the stylus to vibrate. For recording purposes, for example, the stylus is caused to be vibrated yby the aid oi electricalimpulses corresponding to the sounds to be recorded, there being a translator for translating the electric current impulses into a vibratory force, actuating the stylus. Such a translator may take several forms, such as an electromagnetic device or an electro-dynamic device; of the stylus cause the cutting or embossing of a record groove upon a record blank.

For reproduction purposes, the grooves oi the record with which the stylus is'in contact impart mechanical vibration to the stylus. chanical vibrations are translated into electrical impulses by the translator, and these impulses (if necessary through an' amplifier system) operate an air actuator, such as a telephone receiver or loud speaker; or the impulses may be used if desired for re-recording.

The groove record with which the stylus cooperates may be either of the lateral groove type walls of the grooves are smooth, but the. bottom of the groove carries the undulations, and the stylus is in contact with these undulations.

When, for example, a stylus is cooperatingv The movements4 with a lateral .groove type of record, any teml porary or permanent irregularity in the bottom of the groove is translated as an impulse. Such an irregularity may be in the form oi' a speck of foreign matter. The resultant operation oi the apparatus is correspondingly irregular. It is one of the objects of this invention to obviate the response of the stylus to such irregularities, as by so mounting the stylus that irregular motions thereof have no effect upon the translator.

It is another object of this linvention to provide a stylus head the design of which is adaptable readily to its utilization with a hill-and-dale type or with a lateral groove type record, although each specific embodiment is capable of cooperating with only one type.

y It is still another object of this invention to provide an improved form of dynamic type stylus head, said dynamic type being characterized by the provision of a very light coil mounted for movement in accordance with the stylus movedegree of delity is obtained.

This invention possesses many other advantages, andhas other objects which may be made more easily apparent from a consideration ofv several embodiments of the invention. For this -purpose there are shown a few forms in the drawings accompanying and forming-part of the present specification. AThese forms will now be described in detail, illustrating the general principles of the invention; but it is to beunderstood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is bestgdeflned by the appended claims.

In the drawings:

Figure 1 is a sectional view oi a stylus head illustrating one form. of the invention, drawn to a greatly enlarged scale, and illustrating a portion of the record blank that cooperates with the head;

Fig. 2 is a front elevation thereof, partly broken away;

Fig.A 3 is a sectional view taken along plane 3-3 of Fig. l;

Fig. 4 is a view similar to Fig. 1-i1lustrating the adaptation of .the mechanism to a hill-and-dale type of record;

Fig. 5 is a wiring diagram illustrating the manner in which the stylus head may be connected..`

in an appropriate circuit;

Fig. 6 is a side elevation partly in section of another form of this invention, the scale being greatly enlarged, and illustrating a portion of` the record blank that cooperates with the record; Fig. 'l is a sectional .view taken along plane 1-1 of Fig. 6;

Figs. 8, 9 and 10 are detail sectional views taken respectively along correspondingly numbered planes in Fig.6;

Fig. l1 is a sectional view taken along plane Fig. 12 is a pictorial View of the stylus arm illustrated in Fig, 6, and its associated elements: Fig. 13 is a view similar to Fig. 6 of a further modified form of the invention, the figure-[being greatly enlarged;

Fig. 14 is a detail section taken along plane Fig. l5 is a view similar to Fig. 13 of a further 4modified form of the invention, the figure being greatly enlarged; i

Fig. 16 is a pictorial view of one of the supporting elements utilized in connectionwith the form shown in' Fig. i6; y

Fig. 17 is a pictorial view illustrating the mag.-

netic circuit utilized in connection with the apparatus illustrated in Figs. 6 and 7 Fig. 18 is a view similar to Fig. 13 of a further modied form of the invention. the ligure being greatly enlarged;

Fig. 19 is a sectional view taken along plan I9-I9 of Fig. 18;

Fig. 20 is a wiring4 diagram illustrating the Aadaptation of the form of the invention illustrated in Figs. 18 and 19 in a complete recording and reproducing circuit; and Fig. 21 is a fragmentary sectional view on an enlarged scale, taken on a plane 2I2I of Fis. 1. In the form of the invention illustrated in Figs. 1, 2 and 3, a flexible member I capable of carrying a record is illustrated. This record carrying member may be in the form oi a ilexible loop or a disk or the like; it is shown in this instance as looped over a driving roller 2. The record carrying member I may be made from any appropriate plastic material, such as an acetate 0r the like.

The stylus 3 which may represent either a recording or a reproducing stylus is shown as mechanically cooperating with the record blank I. The description of the mechanism will proceed for a recording operation, but it is to be understood that the apparatus may be used for reproduction purposes by appropriate-change in connections; and if necessary by appropriate change of the character of the stylus 3.

The stylus 3 is shown as fastened in the lower end of a stylus arm 4. For this purpose the stylus arm 4 is provided with a deep aperture into which the stylus 3 is inserted. The stylus 8 is fastened in position as by the thumb screw 5.

The stylus arm 4 is arranged to vibrate about an axis provided by the aid of appropriate bearing structures. For example, the stylus arm may carry a central hub 8 (Fig. 2) provided at its opposite ends with shallow conical recesses lfor the reception 'of the cooperating conical ends of the pivot screws 1 and 8. These pivot screws are threaded within the ears 9 and I0 formed integrally with a cover member II, which will be described in greater detail hereinafter. The

screws

1 and 8 may be locked in place by appropriate lock nuts 1' and 8'.

By the aid of this pivotal mounting. vibrations of the stylus 3 are permitted about the axis of the pivot screws 1 and 8. An inspection of Fig. 1

` shows that this vibration is in a direction lateral to the grooves formed on the member I, producing a lateral groove record.

The vibrations of the stylus ann 4 are made to correspond to electrical impulses. In this way the configuration of the lateral walls of the I6 is used for the accommodation of a field coll I1 adapted to be supplied with direct current from any appropriate source. This coil tele-V scopes over the central core I4.

An annular air gap Il is formed between the extending end I8 of the core Il and the cover member II, which is appropriately apertured for this purpose. This cover member II is made from magnetic. material; l it is shown as supported by the annular wall I8 vas by the aid of the internal threaded iiange 2l, cooperatingwith external threads on the wall. Within the narrow air gap I8 thus formed is located the axially movable dynamic coil or voice coil, comprising the axially spaced sections 2 I-22. When electrical impulses are fed to the coil 2I-22 a dynamic force, as is well understood, is produced in an axial direction with respect to the coil.

The coil sections 2I and 22 are supported upon a very thin cylindrical support 23 having an end flange 24. These

parts

23 and 24 are made from appropriate insulation or non-magnetic material. The end flange 24 is shown as mechanically connected to the upper end of the stylus arm 4. Accordingly the vibratory force created by the electro-dynamic action is impressed upon the stylus arm 4 to vibrate it in accordance with the impulses imparted to the coil 2I272.`

In order to provide a-yielding damper against the vibration of thevarm 4,` use may be made of a pair of rubber-like damper members 25 disposed upon opposite 4sides of the arm 4. These members may be made for example of Viscaloid. They are -fastened in place at their opposite ends by the aid of the bracket members 24 shown most clearly in `Fig. 2, as well as by the aid of the screws 21 which pass through the bracket members as well;l as through the damper members 25. These screws may be threaded into 40 the cover II.

groove are formed in accordance with these electrical impulses, such as may be produced in a circuit by a microphone or the like. The translatins device whereby the electrical vimpulses are transformed into mechanical vibrations ,ofv the arm 4 includes in this instance an electrodynamic structure.. Thus there is a magnetic .frame I2 of general cylindrical configuration.

This frame I2 may be appropriately supported .upon a cylindrical bar I3 passing through the I5 which projects beyond the 'left hand end of the cylindrical' wall Ilot the frame I2. The annular space between the core I8 and the wall In order to ensure accurate axial guiding for the movement of the voice coil 2I, 22, use is made of a flexible spider structure 28 shown to best advantage in Fig. 3. The spider structure 28, which may be of paper, or of other suitable light, resilient material, is fastened adjacent its outer edge as by the aid of the screws 2S to a shoulder 3o formed around the inner edge of the cover member II. A plurality of spring arms 3| formed integrally with the outer edge of the spider serve resiliently to support the inner hub portion 32. Into this hub portion is fastened the right hand end of the cylindrical support 23.

The coil 2I22 is shown as made in two section, wound however in an additive sense. The annular air gap Il is made in two parts to conform to the sections. as by the aid of the annular groove 88l formed on the cover member I I and a corresponding annular groove 34 formed on the core extension I8. Accordingly there are formed two separated paths for the magnetism between the annular exterior surface of the extension I8 and the interior annular surface of the cover II.

Inthe event that the apparatus is used for reproduction, the coil sections 2l and 22 are moved by the mechanical vibration of thestylus arm 4 produced bythe record. Movement of the coil 2I-22 in either direction sets up additive current impulses in the two coil sections. These current impulses may then be passed to appropriate ampliiler circuits and to sound translating devices.

A push-pull amplifier circuit system is diagrammatically illustrated in Fig..5, wherein the coil sections 2I-22 correspond to the dynamic coil. These coil sections are connected in the conventional manner to one winding 36 of a push- 'transducer 39. If the transducer is a microphone the push-pull amplifier circuits amplify the microphone currents and finally pass the amplified impulses to the coil sections 2| and 22. In the event that the system is used for reproducing purposes thevtransducer 39 is a telephone receiver or loud speaker or the like, fed with amplified impulses through the amplifier circuit 38, the input side of which is now connected to the transformer coil 31.

In the form illustrated in Fig. 1,'the stylus 3 is adapted to form, or reproduce from, amlateral groove record. It is possible by simple arrangement of the parts to provide hill-and-dale recording or reproducing. Such a form is illustrated in Fig. 4.

The stylus larm 4o 1s shown in this instance as pivotally supported by the aid of the ears 4| formedon the cover member 42. The stylus arm 40 supports the stylus 43 in a direction transverseto the length of the arm 40; and the 'axis of the core I5 is made substantially parallel with the axis of the stylus 43. Accordingly the me,

chanical vibrations imposed upon the arm 40 either in recording or reproducing effects the axial position of the dynamic coils in the saine manner as before; but these mechanical vibrations are produced by motion of the stylus 43 in a direction substantially along the axis of the stylus.

In the form of the invention illustrated in Figs. 6 to 12 and 17, the member 44 corresponds to the record carrying member l of Fig. l. This record carrying member 44 is shown in this instance as carried over a roller 45.

Cooperating with the member 44 is a stylus arm 46. The stylus arm' '46 in the present instance is intended to produce or reproduce a lateral groove record. The stylus 41 (Figs.v6, 11 and 12) is shown as appropriately fastened into an enlarged boss 48 carried at the right hand extremity of the arm 46. By the aid of a movable supporting mechanism the entire stylus head is moved toward the right as viewed in Fig. 11 over the roller 45. For this purpose there is diagrammatically indicated a movable supporting arm 49 l(Figs. 6 and 7) To the right hand extremity of the arm 49 is fastened-the stylus headas by the aid of a 'pair oft-screws 50. These screws engage a base member 5|- forming the main support for the stylus head. A cover or casing 53 .as of sheet metal may have its lower edge telescoped over the edge of the base 5| and may be fastened as by the aid of screws 52 to the base 5I.

The stylus arm 46 is arranged for vibratory movement about an axis 54 (Figs. 6 and 11) The arrangement is such thatvibratory movement of the stylus arm 46 about the axis 5 4 forms the useful movement of the arm; and any movement about an axis transverse to the axis 54 has no effect upon the translating device that converts mechanical vibrations into electrical impulses (for reproduction). orr vice versa (for recording). Any minor irregularities in the bottom of the record groove either in permanent form or assmall particles of foreign matter have no effect upon the useful movement of .the moving element of the translating device.

Inorder to ensure these results a long an accurate bearing guide is provided for thestylus arm 45. The bearing structure incorporating this guide nevertheless is so arranged as to pro- V.

vide a minimum of friction, while yet ensuring complete restraint of vthe stylus arm vibration 5 about the axis 54. The structure by the aid of which this is accomplished will now be described.

The stylus arm 46 for the sake of lightnessv and rigidity is shown as formed of a tubular element. Its left hand end as viewed in Fig. -6 and as indicated in Fig. 12 is accommodated in a shallow concave saddle formed on the bottom end of a. generally cylindrical member 55. This member 55 extends through an aperture 261i in base 5I. Member 55 forms the moving portion of the bearing structure. The arm 46 may be appropriately attached to. this element 55 as -by the aid of a screw 56 (Fig. 6), which passes diametrically through the stylus arm 46.

TheA cylindrical member 55 forms a series of knife edges axially spaced along the axis 54, at least some of them being angularly offset from others. Thus for example, adjacent the lower part of the member 55 a cut-out portion is formed to provide the knife edge '55 (Figs. 10 and l2). Immediately above the knife edge 56 the cylindrical member 55 is cut away to form a similar knife-edge 51 (Fig. 9) but angularly.

spaced by 180 from the knife edge 55. Immediately above the knife edge 51 there is formed a knife edge 58 (Figs. 8 and l2) angularly alined with knife edge 56'. Lastly, the upper end of the cylindrical member 55 is formedk with a knife edge 59 (Fig. '7) angularly alined with knife edge d J1. By providing appropriate bearing points for 3'5 all four of the'se knife edges, the cylindrical memberx55 is completely restrained from deviating from the axis 54. The various cooperating knife edge rests will now be described.

' In order -to support these rests, use is vmade of a generally rectangular 4block 60- (Figs. 6, 8 and 9) attached to the base member 5I. edge rest 6I (Fig. 9) cooperating with the knife edge 51 is formed as a-right angle extension of a flat strip 62. This extension 6| is resilient, and exerts-a restraint on the edge 51. Strip 62 is mounted as by the aid of the screws 63 upon one side ofthe block 60. To permit accurate adjustment of the knife edge rest 6l with relation to the knife'edge 51, the strip 62 is provided with the large clearance apertures 64 through which the screws 63 pass.

A similar fiat strip 65 is fastened to the block 80 for forming the resilient knife edge rest 66 to cooperate 'with the knife edge 58 (Fig. 8).

Arranged on top of the block 60 is a fiat strip 86 (Figs. 6 and '1) forming a knife edge seat and adapted to cooperate with the uppermost knife edge 59. A limiting stop against upward moven operating with the knife edge seat 68 (Figs. 6, 7

and 10). This knife edge seat may be appro- 05 priately fastened as by screws 66 tobase mem'- ber 5|.

The knife edge rests provided lby the uppermost member 68 and the lowermost member 68 form rigid seats for their respective knife edges. while the intermediate seats are to some extent yielding. The extreme knife edges being oppositely faced, serve as the maior guides; the 'in'- `termediate seats ensure, by their` resilience, that these end knife edges will be urged accurately into the rigid seats. r 1

The knife -The lowermost knife edge 55 is shown as co- Oscillatory movement of the cylindrical member 55, produced during the process of reproduction by oscillation of stylus 41, serves to vibrate a dynamic voice coil (Figs. 7 and l1). This dynamic voice coil as will be-explained hereinafter vibrates axially within a narrow'annular air gap. Its axis is transverse'to the stylus arm 'axis 54. It is carried by a thin insulation cylinder 1|. One end of this cylinder is formed as a spider 12 formed integrally with a tubular exten-l sion 13` (Figs. 6 and 7).

The mechanical connection between the coil support 1| and the cylindrical member 65 may be best explained in connection with Figs. 6, '7, 1l and 12. Joined to the spider 12 is a thin resilient strip-like' member 14. Firmly attached as by soldering or the like to the .end of this member 14 is a thin flexible strip 15 fastened into a slot in the free end of a cylindrical arm 16. This cylindrical arm in turn is iirmly attached to the upper portion of the cylindrical member 55 and in general radial direction thereto.

Upon oscillation of the stylus arm 46, 4the arm 16 is caused to oscillate in accordance therewith. These oscillations are translated into axial oscillations of the voice or dynamic coil 10.

In order to guide the coil substantially accurately in an axial path and to provide a resilient force opposing the oscillations, use is made of a pair of supporting standards 11 and v16 shown most clearly in Figs. 6, 7 and 11. These standards are formed of thin resilient metal. They are attached as by the aid of screws 19 to a supporting block 80 fastened to the top of the base 6|. The upper ends of both of these

standards

11 and 18 are formed with concave saddles in which the tubular extension 16 rests. The tubular extension 16 is permanently attached to these saddles. As the coil 10 oscillates, these standards are correpondingly flexed.

The magnetic circuit f or forming the annular air gap in which the dynamic coil 10 is movable is illustrated to best advantage in Fig. 1'?.

- Thus there is a pole piece 8| having an annular conguration surrounding the coil 10. This pole piece 8| may be supported as by the aid of a rectangular extension 82 (Figs. 11 and`17) abutting and fastened to the upright .supporting strip 83. The lower edge of this supporting strip 83 passes through the slot 84 of the base 5| (Fig. 7) and is attached to the edge of the base 6| (Fig. 11).

Cooperating with the pole piece 9| is a cylin- -drical core member 8l formed as part of another pole piece `86. This pole piece 86 is also attached to the upright support 83.. The cylindrical extension 85 of the pole piece 86, in conjunction with the annular member 8|, detlnes the small annular air-gap.

In order to provide the magnetic force for producing the magnetic iluxacross the gap, use is made in this instance of a permanent horseshoe magnet 81 (Figs. 6, '1 and 11). This permanent horseshoe magnet is so arranged that its poles respectively cooperate with the pole pieces 82 and 86.v It needs nospecial fastening means, as the magnetic attraction between ,seaafie ineii'ective to alter the direction of relative move'- ment between the coil 10 and the pole pieces.

'I'he resilient extensions 6| and 66 act to maintain knife edges 56' and 59 of member 55 against their respective bearing surfaces4 and thus prevent rel-ative movement in a vertical direction between stylus arm 46 and the structure of the stylus head. In this way as stylus 41 rises and falls due to irregularities in the loop 44 or roller 45 or both, the entire stylus head structure together with the attached end of a supporting arm 49 is moved up and down.

However, minute irregularities on the bottom of the record groove, such as roughness or other imperfections in the record material, whichis always present to some extent, or foreign matter, may cause undesired vibratory movement of arm 46 in a vertical direction, quite analogous to movement imparted to a stylus arm by a hill and dale or vertically cut record. Such movement has a deleterious effect in the reproduction of a lateral cut record. The flexible connection 14 serves to effectively prevent any such vertical vibration of stylus arm 46 from reaching coil 10, which is effectively restricted to truly axial movement by means of

supports

11, 18. No hill and dale effect of the record can therefore inuence the movement of this coil.

For recording purposes, the coil 10 is fed with current impulses, and the resultant axial oscillations of the coil result in lateral vibrations of stylus 41.

In the form just described, the

resilient standards

11 and 18 serve to support the dynamic 'coil 10, and also serve to provide a resilient resistance to vibration. In the form of the invention illustrated in Figs. 13 and 14, these effects'are obtained in a somewhat different fashion. In this form of the invention, the moving coil 68 is mounted coaxially on a exible spider 89 of light, resilient material, for example paper having the radial arms 90. The outer edge of this spring spider` is attached as by screws 9| to a ange 92 provided on the annular pole piece 9 3. 'I'his pole piece 93 is otherwise ofthe same structure as the annular pole piece 8| illustrated in Figs. 6 and 7.

In this form of the invention the knife edge bearing is dispensed with. Instead, use is made of a spring hinge 94. This spring hinge 94 is firmly fastened along one longitudinal edge in a slot formed in the upright support 95, and its lower end projects through the base 98. Upright support 95 is provided with a lateral extension 96. 'I'hs lateral extension is fastened as by screws 91 to the top of the base member 98. This base member 98 corresponds in general to the base member 5| o! the form shown in Figs. 6 and '1.

'Ihe hinge spring 94 is provided with three laterally extending projections 99, |00 and 0L clamped in a slot formed in aV movable upright member |02. This movable upright member at its lower end is provided with a saddle for the accommodation of the stylus arm |03. A strap |04 serves to attach the stylus arm |03 to the bottom of the upright member |02.

In this instance the stylus arm |03 is so ar- 2,se7,e4e

These two spiders are in turn'rigidly attached' ranged that it lmay yield in response to radial movement of the stylus 41 without transmitting any material force to the stylus head. For this purpose the stylus arm |03 is cut away as indicated at I to form a thin resilient portion in the arm |03 adjacent its supported end. Accordingly in the event there be any irregularity in the bottom of the record groove, the stylus arm |03 is merely exed upwardly without transmitting such fiexure to any of the moving parts of the translating device.

In the form illustrated in Fig. 6, the stylus arm to each other as by the intervening tubular support |34 corresponding t0 the tubular support 13 of Figs. 6 and 7. 'I'his tubular support |34 is mounted on the

resilient standards

11 and 18.

Provisions are also made in this form for making the appropriate electrical connections. Thus -the center -lead |33 between the coils |25 and |23 is connected to a ground connection |36, soldered or otherwise connected to an appropriate grounded part of the mechanism. The end leads |31 and |33 are joined to binding posts |33 43 as well as the arm 13 which connects the dynamic or voice coil with the bearing structure are shown as extending in the same general radial direction. In some instances, due to the inherent mechanical resonance of the vibratory parts it may be advisable to provide angular separation between the upper connecting arm 13 and the stylus arm. This maybe readily accomplished in a manner shown'most clearly in Figs. 1-5 and 16. In this form ofthe invention, the

, stylus arm similar in structure to the stylus arm 43 of Fig. 6, is disposed along a radius spaced 180 from a radius of theconnecting arm 13.

Furthermore in this form the alternate arrange-l ment of the knife edge is somewhat different. The cylindrical member I2 corresponding to the cylindrical member 33 of the form shown in Fig.

6 is provided with four knife edges ||3, ||4, ||3 and ||3.\ The lowermost knife edge ||3 is now directed toward the supporting block ||1, and

cooperates with a knife edge seat formed at the` end of a strip ||8 placed underneath the block ||1. Thus'the knife edge 3 is pointed toward the stylus 41, just as in the first form of Fig. 6.

The next knife edge ||4 is directed away from the block ||-1 and is provided with a knife edge rest formed on the end of the strip H3, similar to strip 33 of Fig. 8. The third knife edge ||3 is seated in the notch |20 (Fig. 16) formed on a knife edge rest 12|. 'I'his knife edge rest |2| vis shown as a casting integral with -a block |22 to which the

standards

11 and 13 are attached.

The uppermost knife edge ||3 is provided with a knife edge rest formed at the extremity of the strip |23, similar to strip/32 of Fig. 9. As before the block ||1 may be provided with a projection |24 extending over the axis of the cylindrical member ||2 in order to limit vertical movement thereof.

In order to make it possible to utilize a rnechanical push-pull principle in connection with the translating device, the stylus arm 43 may be associated with a pair of voice coils |23 and |23, as shown in the modification of Figs. 18 and 19.

This form of the device is substantially the same as that illustrated in Figs. 6 and 7, except that.

now there are a pair of permanent magnets 01 and |21. most clearly in Fig. 19, are disposed respectively on opposite sides of the bearing member 33. Both of them are provided with pole piece. structures corresponding to pole piece `structures 32 and 30 ci Figs. 6 and '7. 'I'he pole piece structures for the magnet |21 are designated by the reference4 characters |23 and |23. Upright support |30, corresponding to the upright support 33. is provided for these pole piece structures |23 and |23 The casing |3| is of course wider to take care of the extra width of the head. The rod 13- as The magnets 31 and |21, as shown i switch mechanism ,|43 is before is joined to the resilient strip 14. The r tubular supports for the coils |23 and |23 are l joined respectively to the spiders |32 and |33.

respect to a push pull amplifier system that may be connected Nto the coils.

Such a connection. optionally capable of recording and reproducing, is illustrated in Fig. 20. Here thedynamic stylus head |42' corresponds to the form illustrated in Figs. 18 .and 19. 'I'he two leads |31 and |33 and ithe intermediate ground connectionv |33 is also shown in Fig. 20.

In order to provide a balanced and sensitive4 circuit, free from extraneous harmonics, the mi crophone |43 as well as the reproducer |44 are also shown as incorporating push-pull dynamic elements, shown djagrammatically in the figure.

In the event' that recording position as shown in Fig. 2 'Ihe circuits for the recording operation can en be traced as follows: from the microphone 43 to the input side of push-pull amplifier system |43. This pushpull amplifier system has its output circuit conneoted as by leads |41 and |43 to the stationary contactsl |43 and |30 respectively, of switch 43. Switch blades `|3| and |32 then connect lby way of leads |33 and |34 to the input side of another push-pull amplifier system |33. The output of this amplifier system is connected by leads |30 and |31 to the switch arms |33 and |39 respectively. The contact points |30 and |3| contacted by these switch arms are joined to the leads |31 and |33 for operating the head |42. Thus as the circuits are now established, operation of microphone |43 causes operation of the stylus head |42 to cut a lateral record.

For reproducing purposes, Athe switch blades are moved as by a common actuating rod |32 so as to assume the dotted line position. When this is effected. the microphonel |43 is disconnected and the speaker |44 is connected in a manner now to be outlined.

It has been determined experimentally in connection with push pull voice coils as 2| and 22, that if these coils are each partly within and partly without the air gap, greatly improved resuits are obtained. Figs. 1, 4 and 19 all disclose the coils so arranged. Referring to Fig. 21, which is a large scale detail of the coils of Fig. 1, showing the coils 2|, 22 at rest or in their neutral position, it will be seen that thecoils are sym- I metrically arranged on supporting tube 23 with respect to air gap I9 and recesses 33, 3l, but in opposite senses, that is coil 2| projects out of the air gap toward the left and coil 22 projects out of the air gap toward the right. Thus each coil 2| and 22 is unsymmetrically arranged in its respective gap, although the two coils are symmetrically disposed on opposite sides of a plane of symmetry normal to the gaps. Each coil 2|, 22 has its mid-point adjacent the respective end of the gap I9, preferably so located that somewhat over half the length of the coil is outside the air gap. Similarly, in Fig. 19, coils |25 and |26 have a substantial portion of their windings outside their respective air gaps. When number 23 is urged to the right from the neutral position (Fig. 21) by the stylus, coil 2| takes dominance since it is moving into the magnetic field; when it moves to the left coil 22 similarly takes dominance. Since the vibrations of the stylus in reproduction cause such alternate movement of the coils, a push pull effect is impressed on the amplifier. In recording, the output from a push pull ampliiier influences coil 2| and 22 with alternately greater intensitvin a generally similar manner.

What is claimed is: Y

1. In a device of the character described, a stvlus arm, means mounting said arm to permit vibratile movementl oi' said arm about an axis, a translating device cooperating with the stylus arm and having an element mechanically connected to said arm, so as to vibrate in accordance with the vibrations of the armabout said axis, and means ensuring that vibrations of the arm about any axis transverse to said axis produces substantially zero motion ofthe said element with respect to other parts of the translati118 device.

2. In a device of the character described, a vibratory stylus arm, a knife-edge bearing structure for the arm, said bearing structure having axially and angularly spaced knife edges, to restrain vibration of the arm about an axis, and a translating device cooperating with the arm.

3. In a device of the character described, a vibratory stylus arm, an elongated bearing structure associated with the arm to restrain vibrations of the arm about an axis, said structure including a series of axially spaced knife edges, said knife edges being angularly spaced around the axis, said arm being supported adjacent one end ef the bearing structure, a translating device having a movable element, and a connection between the element and the other end of the bearins ltrlwture. i

4. In a device of the character delribd. a

vibratory stylus arm, an elongated bearing structure associated with the arm to restrain vibrations of the arm about an axis, said structure including a series of -axially spaced knife edges, f

said knife edges being `angular-ly spaced around the axis, said arm being supported adjacent one end of the bearing structure, a translating device having a movable element, a connection between the element and the other end of the bearing structure, and an extended resilient support for the element.

5. In a device of the character described, a vibratory stylus arm, a knife-edge bearing structure for the arm, said bearing structure having a pair of axially spaced knife edges and knife edge seats to restrain vibration of the arm about an axis, said knife edges being angularly spaced from each other and means acting intermediate the knife edges forresiliently urging the knife edges against their seats.

6. In a device of the character described, a vibratory stylus arm, means cooperating with the arm for restraining the vibrations about an axis, said arm being adapted to yield in a direction transverse to the vibrations, and a translating device having a movable element mechanically connected to the arm.

7. In a device of the character described, a vibratory stylus arm, a spring hinge cooperating with the arm and restraining vibrations of the arm about an axis, means forming a magnetic air gap, a coil axially movable in the gap, means resiliently supporting said coil in the gap, and a connection between the coil and the arm.

8` In a device of the character described, a vibratory stylus arm, a spring hinge cooperating with the arm and restraining vibrations of the arm about an axis, said arm yielding resiliently in a direction transverse to the vibrations, means o forming a-magnetic air gap, a coil axially movable in the gap, means resiliently supporting saidcoil inthe gap, and a connection between the coiland the arm.

9. In a device of the character described, a vibratory stylus arm, an elongated bearing structure for restraining the vibrations of the arm about the axis of the structure,said arm being disposed adjacent one end of the structure, a pair of means forming'a pair of annular magnetic air gaps, said gaps being coaxial but spaced along their common axis, said common axis being transverse to the axis of vibration, a pair of coils respectively disposed in said gaps, and a connection between the other end of the moving part of ,utshe bearing structure and connected to both co 10. In a device of the character described, a stylus arm, a stylus carried by the arm, and disposed transversely of the arm, a knife-edge bearing structure for the arm, and having an axis transverse to ,the arm, said bearing structure having axially and angularly spaced knife-edges, and a translating device' cooperating with said arm.

11. In a device of the. character described, a stylus arm, a stylus carried by the arm, and disposed transversely of the arm, a knife-edge bearing structure for the arm, and having an axis transverse to the arm, said bearing structure having axially and angularly spaced knife-edges, as well as at least one resilient knife-edge seat, cooperating with one of said knife edges, and a translating device cooperating with said arm.

' ALBERT W. DE BART, Sa.