US2224854A - Magnetic sound recording and reproducing - Google Patents

Description

Dec- -17 1940- s. J. BEGUN 224,854

MAGNET I C SOUND RECORD ING AND REPRODUC ING Filed March 24, 1938 8 SheeLS-Sheet l IN V EN TOR.

Sem/se/oh Begun BY A TTORNE Y Dec. 17, 1940. s. J. BEGUN 2,224,854

D MAGNETIC SOUND RECORDING AND REPRODUCING Filed March 24, 1938 8 Sheets-Sheet 2 lNvFN-row SEMI JOSEPH BEGUN BY D SMMMXM ATTORN EY 17, 1940- s. J. BEGUN MAGNETIC SOUND RECORDING AND REPRODUCING Filed March 24, 1938 8 Sheets-Sheet 3 M1 :rolo/rane INVENTOR. I Semi seph Byun BY* S Mohmk?m A TTORNEY Dec. 17, 1940. s. J. BEGUN 2,224,854

MAGNETIC SOUND RECORDING AND REPRODUCING Filed March 24, 1938 8 Sheets-Sheet 4 ',l m9 /l/a /oy 24 INVENToR. Sem: Josep/1 Begun BY S f/1m ATTORNEY Dec. 17, 1940. s. J. BEGUN 2,224,854

MAGNETIC SOUND RECORDING AND REPRODUCING Filed March 24, 1958 8 Sheets-Sheet 5 Sem/ @sep/7.583017 BY S M .l

v ATTORNEY Dec. 17, 1940. s. J. BEGUN 2,224,854

MAGNETIC SOUND RECORDING AND REPRODUCING Filed March 24, 1938 8 Sheets-Sheet 6 [98 A TTORNEY DOC. 17, 1940. s J, BEGUN 2,224,854

MAGNETIC SOUND RECORDINGAND REPRODUCING Filed March 24, 1938 8 Sheets-Sheet 7 Nlcrophone Volume i Amplifier Mofor INVENTOR. Sem: Jbse/v Belyun ATTORNEY Dec. 17, 1940. s. J. BEGUN 2,224,854

MAGNETIC SOUND RECORDING AND REPRODUCING Filed March 24, 19:58 a sheets-sheet s 6C 24e 503 307 303 6B ,0B

soo/

24A INVENTOR.

Sem/Jsaln/z Begun A T'TO RNE Y Patented Dec. 17, 1940 PATENT OFFICE MAGNETIC SOUND RECORDING AND REPRODUCING Semi Joseph Begun, Bronx, N. Y., assignor to Magnetone Inc., Cleveland, Ohio, a corporation of Ohio Application March 24, 1938, Serial No. 197,851

25 Claims.

ThisI invention relates to magnetic sound recording and reproducing and more particularly to devices for magnetically recording sound on a magnetic sound carrier, such as tape, suitable for speech correction, objective speech andr language study, and many other applications, although various features of the invention are not limited to magnetic tape sound carriers or such particular applications.

Although many efforts have been made in the past to provide a magnetic sound recording and reproducing device utilizing an endless magnetic sound carrier, prior devices of such type did not prove practical because their design and construction had inherent defects resulting in breakage, fluttering and other operating troubles.

Among the objects of the invention are:

A magnetic sound recording apparatus comprising an endless coiled magnetic tape sound carrier for retaining and reproducing sound records, magnetic transducing means cooperating with said carrier for recording and reproducing sound while said carrier moves past said transducing means, and guide means including at least two revolvably mounted spaced guide rollers having a substantially uniform cylindrical guide surface for guiding said tape as a helix coiled around the outer surfaces of said spaced guide rollers, one of said guide rollers, having frictional driving engagement with portions of said tape helix, being driven by external forces for impelling said tape helix past Said transducing means while at least one other of said guide rollers is frictionally driven by the moving tape helix and has sufficient mass for exerting on the tape helix inertia reaction forces which suppress fluttering of the tape helix and maintain it at the required uniform speed; such arrangement in which the spacing between the guide rollers is sufficiently large and the effective guide roller surfaces engaged by the tape helix is sufficiently small to permit lateral slippage of the tape portions of the helix over the roller surfaces while traveling along the path of the helix; such arrangement in which the effective length of the helix portions frictionally engaged with the guide roller surfaces is so proportioned in relation to the effective length of the free helix portions extending between the spaced guide rollers and the inertia of the guide roller masses frictionally driven by the tape helix is sufficiently large to permit limited slippage of the helix tape portions over the guide roller surfaces while maintaining sufficiently effective frictional engagement between the helix and the guide rollers for maintaining the required unl- (Cl. 17g-100.2)

form speed of the tape along the helical path I around the spaced rollers; such arrangement having a frame revolvably supporting the opposite ends of said guide rollers and constituting With said guide rollers a spool-like structure on the outer periphery of which the tape helix is guided; such arrangement in which a tape driving motor mechanism having operative connections to said guide means and amplifier means having operative connections to said magnetic transducing means are conned in the interior of said spool-like structure; such arrangement in which the surface of said guide rollers is of a hard material, the substance of which prevents generation of audible sound by its engagement with the successive portions of the tape helix.

Such endless tape magnetic vrecording arrangement in which a plurality of tape layers are Wound one over the other for operation as independent signal carriers, in conjunction with distinct magnetic transducing heads; such arrangement in which the individual tape layers form parts of distinct endless carriers; such arrangement in which the different tape layers are interconnected to form parts of one endless carr1er.

An endless tape magnetic recording arrangement comprising an endless magnetic tape having an inner convolution frictionally engaged by a driving roller which drives the inner convolution at a uniform speed past the magnetic transducing means toward the outer tape coil convolution so as to keep all outer tape convolutions surrounding the inner convolution suiciently loose and permit the adjacent tape convolutions to slip past each other without excessive friction.

The foregoing and other objects of the invention will be best understood from the following description of exemplications thereof, reference being had to the accompanying drawings, wherein Fig. 1 is a front elevational view, partially in section, of the interior structure of a magnetic sound recording and reproducing apparatus for language study and similar applications;

Fig. 2 is a side elevational view, partially in section, of the device of Fig. 1;

Fig. 3 is a top View of the device of Fig. 1;

Fig. 4 is a cross sectional view of a control mechanism for use in such device;

Fig. 5 is a fragmentary view similar to Fig. 1 illustrating a modified tape guiding arrangement for such device;

Fig. 6 is a diagram of the circuit connection and the cooperative relations of the elements of the device of Fig. 1;

Figs. 7 and 8 are Views similar to Figs. 3 and 1, respectively, illustrating a modified form of endless tape guiding arrangement;

Fig. 9 is a top view of another exemplication of an endless magnetic tape sound recording and reproducing device;

Fig. 10 is a front elevational view of theidevice of Fig. 9;

Fig. 11 is an enlarged elevational detailed view, with parts shown in section, of the motor mounting of the device of Fig. 10;

Fig. 12 is a side view of the amplifier chassis with the control mechanism of the device of Fig. 10;

Fig. 13 is a front elevational View of the plier chassis of Fig. 12;

Fig. 14 is a diagram of` the-electrical 'circu'it connections and the cooperative relationship of the various elements vof the device of Fig. 10;

Fig. 15 is a cro'ss sectional detailed view of the control arrangement mounted o n the amplifier chassis panel shown in Figs'. 12 and 13;

Fig. 16 is a perspective View of the housed complete device shownin Figs. 9 to 15;

Fig. 17 is a front elevational View similar to Fig. 1 of another form of such apparatus;

Fig. 18 is a top view similar to Fig. 3 exemplifying schematically another type of magnetic recording device of the invention;

Fig. 19 is a front view of the device of Fig. 18.

No person can hear his own voice as he hears the voices of others. This is due to the fact that all external sounds are transmitted to the inner ear of the listener through the air in the ear canal while the speaker receives much of the sound emitted by himself by conduction through the bones, the flesh, and other channels within his head.

Although the fact that a person cannot hear his own voice as he hears the voices of others has been known for a long time and there has long existed an urgent need for a simple device that would enable speakers, actors, singers, students of elocution and foreign languages, persons having speech defects, such as stuttering and lisping, and all those desiring to hear their speech or voice, no simple, practical apparatus meeting these requirements have been available heretofore.

If the student could hear his own voice as he hears the voices of others, he could readily perceive his mistakes. Only by hearing a good reproduction of his voice is the student able to study his voice objectively and improve and train it by self-correction.

In the past, only mechanical recording was available for voice training by self-correction. However, to make a disc record and play it back requires manual work and dexterity. In addition, each disc can be used for recording only once. Since voice *training by self-correction requires recording and listening frequently to the recorded voice, a simple foolproof recording system requiring no special handling and enabling unlimited use of a single sound carrier would be ideal.

Furthermore, experience in voice training with mechanical sound recording has shown that the very fact that the student is aware, consciously or subconsciously, that his recording remains permanent on the record and that each recording involves an expense subjects him to mental strain which prevents him from being his own self during the recording. In most cases he must be assisted by another person in handling the recording apparatus, and the presence of any person prevents the student from recording in a relaxed mental state as he would ordinarily do if left by himself.

The present invention provides magnetic recording and reproducing apparatus eliminating these difficulties and making available an ideal medium for effective voice study and training as well as speech correction.

A single endless recording medium is used over and over again for new voice records. A small magnetic transducer head records and reproduces the speech without any observable change in the recording medium; the process of making a new record obliterates the'preceding recod. 'Ihe speaker can hear his voice as soon-as it i`s recorded, and can repeat the reproduction as many times as he desires. A single grip controls all the recording and reproducing operations. By a simple operation, the student may compare his own recording with a model record until by succession of his own recordings, he learns all his deficiencies and reaches an approach to the model record. The student is able to do it all by himself, without the presence of others, in a perfectly relaxed state, and is thus enabled to make progress in a short period of time.

All the operating and control elements of the recording and reproducing system are arranged and correlated to permit easy and economical construction and assembly of the apparatus of the invention and to assure its foolproof operation when in use.

One exemplification of an apparatus of the invention is illustrated in Figs. 1 to 6. Inside of a suitable enclosing casing, not shown for the sake of clarity, is mounted a unitary mechanical structure combining all the operating elements of the apparatus. It comprises a rectangular frame structure consisting of a front frame I and a similar rear frame 2 formed of metallic angle bars reinforced by corner braces 3 and held together by cross bars 4 and diagonal struts 5.

In the corners of the rectangular frame are mounted four cylindrical guide rollers 6 having bearings 'I journalled on stationary shaft 8 extending through holes in the opposite corner braces 3 and suitably locked in place, as by cotter pins inserted through the shaft ends.

On the top of the frame I, 2 are mounted two cross-over guide rollers 9, I0 journalled on stub shafts I I that are held by brackets I2 which are adjustably fastened to the top sides of the frame. A long endless magnetic carrier in the form of a tape I3 is Wound in the form of a helix, seen in Figs. 2 and 3, over the four guide rollers 6, a cross loop portion I4 of the tape passing over the cross-over rollers 9, l0 from the front end of one bottom roller 6 to the rear end of the other bottom roller 6, as seen in Figs. 1 and 3, so that when the endless tape is driven along the guide rollers 6, consecutive portions of the tape pass crosswise between the cross-over rollers 9, I0 mounted on the top of the frame. The cross loop portion I4 of the tape traverses between the two hinged halves of a magnetic head I 5 which are held locked by a latch spring I6, the hinge joint I1 of the magnetic head being adjustably supported by an upright of a bracket I8 fastened to the rear frame 2. The magnetic head I5 may be of the construction described in the German Patent No. 352,810 of March 11, 1919.

A driving motor I9 carried on a resilient vibration absorbing bracket 20 is mounted on two cross bars 2| secured to the bottom of the frame I, 2, and drives through a pulley 22 and a belt 23 the end of one lower guide roller 6 at a reduced speed. Since the periphery of the motor driven lguide roller 6 engages a substantial length of each tape loop, the periphery of the roller exercises a frictional driving force on the tape and imparts to the entire tape a speed equal to the peripheral speed of the motor driven roller 6. The endless driving belt 23 has uniform cross section and is free from protrusions so as to reduce the noise and speed fluctuations or fiuttering of the endless carrier loops.

To guide the successive loops 'of the endless tape I3 in its travel along the helix, comb-like guide bars 24 having guide slots 25 are mounted'.

in front of the guide rollers 6 towards which the tape loops travel for maintaining the endless tape along the helix.

Each loop of the endless tape helix I3 is thus driven by the frictional engagement of a loop portion with an arcuate portion of the motor driven guide roller 6, and each of the other guide rollers 6 are, in turn, driven by the individual tape loops at the peripheral speed of the motor vdriven guide roller by reason of their similar frictional engagement with each loop.

In the endless carrier operating arrangement described above, the guide rollers 6 and the loops of the endless sound carrier I3 form thus a moving system in which the mass of the sound carrier is only a small, practically negligible fraction of the total moving mass, consisting mainly of the revolving guide rollers 6 which participate in the motion of the endless carrier I3. Each of the carrier driven guide rollers 6 has a substantial frictional engagement with the moving endless carrier I3 and thus the inertia of these guide rollers has the effect of equalizing any speed fluctuations of the motor driven guide roller 6 caused by the inherent small speed fluctuations of the driving motor.

In the course of its travel, each portion of the endless tape I3 cornes successively into frictional engagement with successive longitudinal portions of each guide roller 6 until it traverses the entire length of each guide roller 6 from one end to the other. As a result, each tape portion traveling over an arcuate surface portion of a revolving guide roller does not move in a purely circular path, but along a slightly helical path,

sliding laterally along the surface of the guide roller while it travels in its helical path.

Ihis lateral sliding motion imposes strains on the elements of the endless carrier I3 which affect the uniformity of its motion and, if excessive, may cause rupture of the endless carrier. The difficulties that would be caused by such lateral sliding motion are eliminated by making the surface of the guide rollers 6 uniform and proportioning the lengths of the frictional engagement of the traveling carrier loops with the revolving guide roller surfaces in relation to the length of the intermediate free loop portions, so that the greater part of the lateral motion of the endless carrier takes place over the free non-engaged portions of the carrier loops and only a negligibly small lateral motion takes place While a traveling loop element is in engagement with a revolving roller. In the arrangement of the invention, trouble-free operation of the long endless carrier is secured by providing a plurality of spaced carrier guide rollers, each of a uniform diameter, arranged so as to secure the required relationship between the engaged and non-engaged lengths of the individual carrier loops as described above, and utilizing the space within the helix formed by the endless carrier for locating the accessories required for the operation of the system as described herein.

Furthermore, by arranging the cross rollers 9, III so that their periphery projects slightly beyon the alignment plane of the two guide rollers 6 from which, and towards which, the cross loop I4 is guided, the effective length of the carrier-' loop which is slightly twisted in bringing the` tape` I3 from one end of the helix to the other includes not only the length of the cross loop I4 itself extending between the two cross rollers 9, IU', but also the two additional tape lengths exn tending from the opposite ends of the cross loop substantially uniform speed of the long endless carrier under the absence of fluttering and mechanical noise is secured with a simple mechanism.

With this arrangment, the motor driving the roller 6 at a substantially constant speed will notwithstanding small speed fluctuations of the driving motor impart to the cross portions I4 of the tape a constant velocity through the magnetic head essential for satisfactory recording and reproducing of sound.

In the upper part of the frame structure above the motor is mounted an amplifier 30 having its chassis attached to two cross bars 3I which are riveted to the sides o-f the rear frame 2. A loudspeaker 32 of conventional design is supported by a baffle plate 33 which has its edges fastened to the uprights of the front frame I and holds the speaker 32 in the space between the amplifier 3l) and motor I9.

To control and indicate the progressive travel of the tape I3, one of the guide rollers 6 may, as shown in Fig. 4, be provided with a reduction gear mechanism comprising a gear 34 which is locked to the shaft, as by a pin, and drives in a planetary motion two directly-engaging pinions 35 revolving on a spindle 36 carried by the roller 6 and driving, in turn, a gear which rotates loosely on the roller shaft 8 and drives through a pinion a coupling gear disc 49.

The coupling gear disc 40 is loosely mounted on a dial shaft 4I journalled in, a bearing hole of a corner plate 42 attached to the front frame I, and has secured to its rear end a spring friction coupling member 43 which establishes a friction coupling between the coupling disc 40 and the dial shaft 4I for driving the control disc 44 which is attached to the front end of the dial shaft 4I and is driven by it. The control disc 44 has a pointer grip 45 and is normally locked in a stationary position shown in Fig. 4 ready for starting a recording operation by a control lever 46 which is pressed into engagement with a stop slot 4'I on the periphery of the control disc 44 by the projecting spring blades of a multiple blade ISISy recording switch 48 engaging a cam 49 on the rear of the control lever 46.

In the normal locked position of the control disc 44 shown in Fig. 4, the coupling gear 40 slips along the coupling surface of the spring coupling 43, and the released contact blades of switch 48 establish the reproducing connections. When the control lever 46 is lifted from the disc slot 41, the control disc 44 is released and driven through the coupling between the disc 48 and the spring coupling 43 while the periphery of the control disc 44 holds the control lever 46 .in the outward position in which it holds the spring blades of switch 48 in the recording position until the control disc 44 completes a full rotation and is again stopped by the engagement of control lever 46 with the stop slot 41 under the pressure of the spring blades of the switch 48 on the lever cam 49.

The gear ratios of the gear drives 34-35- 38-39-40 are so proportioned that the coupling disc 40, and when the control disc 44 is coupled with it, also the control disc 44, makes one complete revolution when the guide roller which drives the reduction gears has made the number of revolutions required for passing one complete length of the endless tape through the magnetic head.

This control mechanism enables the user to start the motion of the recording control disc 44 at any time, at any point on the tape, by lifting the control lever 46 from the disc slot 41. The unlocked control disc 44 starts rotating and holds the control lever 46 in the recroding position during one revolution of the control disc required to complete a new record on the entire length of the endless tape, while the pointer 45 indicates on a surrounding stationary scale the progress of the moving tape I3 through the magnetic head during the entire length of the recording operation, and the control disc 44 as well as the control lever 46 are automatically locked in the reproducing position after the record is completed.

By lifting the control lever 46 at a selected point of the travel of the tape and turning the control disc pointer 45 to a selected portion of the scale, for instance, to a point 180 advanced against the reproducing position, only the next half of the tape length will be re-recorded while leaving on the preceding half of the tape length a previously recorded sound sequence that is to be repeated. Flexible control of the recording and reproducing operations is thus obtained.

Fig. 6 illustrates the electrical circuit connections and the cooperative relationship of the various elements of the apparatus. The motor I9 which drives one of the four guide rollers 6 which impels the endless tape I3, for instance, in clockwise d'rection, is energized from a standard domestic light circuit indicated by a plug socket 50 through a motor switch 5I, While the amplifier 38 with its circuit elements is independently energized by a switch 52.

The magnetic head I5 has a pair of obliterating magnets 55 actuated by windings 56 for obliterating a previous recording and a pair of transducing magnets 51 actuated by windings 58 for recording or reproducing sound under the control of the multiblade switch 48. The recording switch 48 has four contact blades 68, 6I, 62, 63 cooperating with two sets of contact springs under the control of the lever cam 49 to establish reproducing connections in the normal position shown in Fig. 6 and recording connections when the contact blades 60-6I--62-63 are exed by the inwardly pressed lever cam 49.

In the reproducing position of the recording switch 48 shown in Fig. 6, when the control disc 44 is locked by the control lever 46, the contact blade 6I connects the input lead 61 of the amplier 38 to the transducer coil lead 68 for supplying the sound currents induced by the magnetic records in the moving tape elements in the two serially connected transducer coils 58 of the transducer magnets 51 to the amplifier 30, which in turn supplies amplified sound frequency currents through output lead 69, by way of the switch contact blade 63 and the reproducer lead 10, to the loudspeaker 32 which reproduces the recorded sound, the various circuits being completed through grounded leads indicated in a conventional way.

In the recording position of the recording switch 48 with the control lever 46 lifted from engagement with the control disc slot 41 and held in outward position by the periphery of the disc 44, the flexed contact blades 60-6I-62-63 establish the various recording connections. The outwardly flexed contact 6I connects the input lead 61 of the amplifier 30 to the potentiometers 1I, 83 and therethrough to a microphone jack 12 and a phonograph jack 13 for recording sound with a microphone 14 or a phonograph head 15 which may be detachably connected to the jacks by plugs 16, 11, respectively.

It" a record is made with a carbon microphone 14, as shown in Fig. 6, its small exciting current may be conveniently supplied from a dry cell 18 which is normally disconnected from the operating circuits by normally open relay contacts 19 that close only when relay coil 8D is energized by the closure of the two main supply switches 5I, 52. With such arrangement, the amplifier input circuit from the tap of potentiometer 1I is completed through the upper spring contact of jack 12 to the potentiometer ground 8| to permit adjustment of the input voltage by the tap on the potentiometer 1I, and from the tap of the potentiometer 1I through jack 12 to the microphone 14 and therefrom through return lead 82, contact blade 68, contacts 19, to the ungrounded terminal of dry cell 18.

If the record is to be made with the phonograph head 15, its plug is inserted into the phonograph input jack 11, flexing the upper spring contact and connecting the phonograph potentiometer 83 to the amplifier input circuit in lieu of the microphone potentiometer 1I.

The amplifier 30 amplies the sound current input received through lead 61 from the microphone 14 or from the phonograph head 15 and delivers the amplied sound currents through output lead 69, flexed contact blade 63, output potentiometer 84 to potentiometer ground 85, and from the tap of the potentiometer 84 through condenser 86, flexed contact blade 62, transducer lead 68 to the transducer coils 58, back to ground, the potentiometer 84 permitting adjustment of the input to the transducer coils 58 for optimum recording conditions. The flexed contact blade 68 completes also an additional supply circuit for supplying through resistor 81 a magnetizing D. C. current to the obliterating coils 56 and through resistor 88 demagnetizing D. C. current to the transducer coils 58, the auxiliary dry cell 18 which supplies the exciting current for the microphone being suflicient for supplying the required currents for the magnets 55, 51 of the magnetic head. The current supply socket 50 with the switches 5|, 52 and the jacks 12, 13

for the microphone and phonograph are mounted on the frame opposite suitable openings in the casing walls so as to be readily operated from the exterior of the casing.

The unitary mechanical structure of the apparatus of the invention described above in connection with Figs. 1, 2, 3, and 4 combines in cooperative relation all the operating elements required for magnetically recording and reproducing speech and may be placed as an assembled structure Within a suitable casing which encloses all the interior operating parts and has only an opening for the speaker and openings through which the various control elements of the apparatus may be easily actuated.

Such magnetic recording and reproducing apparatus enables high quality recording and reproduction of sound. The fundamental operating principles of such magnetic recording and reproducing system will now be explained by reference to Figs. 7, 8 and 9 of the drawings.

In the apparatus described in connection with Figs. 1, 2, 3 and 6, the same transducer magnets 51 are used for recording and reproducing.

To start the apparatus, the user has merely to close the supply switches 5I and 52. 'I'his starts the motor and energizes all the operating circuits. The user may now start recording by actuating the control lever 46 to release the control disc 44 and establish the recording connections. As he speaks, the pointer 45 indicates the progress of the recording and the user knows exactly when the recording is completed. As soon as the recording is completed, the recorded sound is reproduced and the user can hear his recording as many times as desired. He can start a new recording at any instant on any point of the tape by actuating the control lever 46, and does 40 not have to wait until a recording has been repeated in order to start a new recording. I-Ie may repeat a recording on only a portion of the endless tape by operating the lever and advancing the pointer 45 to a point of the scale which in- 45 dicates how much of the recording period and the recording medium he selects for lmaking the new recording, whereupon he may make a new recording on the selected portion of the previous record without obliterating another selected part 50 of the previous record.

By the new apparatus of the invention, a person desiring to learn a language isfree from the burden of handling the recording medium, such as a disc or film. A student of speech, or of a 55 foreign language, can hear his own speech as soon as it is recorded and, without Waiting, he may repeat the recording and reproducing operations as many times as desired. By plugging in a phonograph or radio receiver lead to jack 13,

60 he may record a model sound sequence from another record or a broadcast that he desires to imitate on a portion of the carrier and compare such model recording with his own recordings made on a different part of the carrier, which v65 he is able to obliterate at any time by a new recording of his own voice without obliterating the model recording.

The apparatus of the invention serves thus not only as a simple foolproof mirror of the voice,

70 but it also enables a student of speech and languages to compare his own speech with a sample speech recorded from a phonograph or a radio on one portion of the tape, while he uses another portion of the tape for making his own record.

The novel features embodied in the magnetic recording and reproducing apparatus described above in connection with Figs. 1 to 5, which proved satisfactory in actual operation, eliminate the diflculties encountered in the prior elforts to devise an apparatus of such type. 5

One source of such difliculties is the fact that even slight differences in the diameter or irregularities in the surface of the guide rollers tend to impart to different frictionally engaged elements of the continuous magnetic sound carrier 10 different driving forces which subject such moving magnetic sound track to excessive strains. These difliculties are greatly aggravated if more than one of the track guide rollers is forcibly driven by external forces, or if the guide rollers 15 do not have a uniform cross section. Similar serious difficulties are also caused when diiferent loop portions of a continuous magnetic sound carrier are guided over uneven surfaces which subject different loop portions to abnormally large 20 forces and resist slippage of the tape loops subj ected to such forces. Such disturbing forces tend to build up cumulatively until they bring about the breakage of a weak spot of the moving endless sound carrier and causes entanglement of 25 the released carrier loops in the moving mechanism. Such disturbing forces also subject the guide rollers, their bearings and the associated apparatus structure to excessive stresses, increased wear, and bring about noisy operation. 30 Larger driving motors able to supply the excess of power absorbed in wearing out the operating parts are required for such troublesome carrier drives.

Such diliiculties are also caused by the fact that 35 in travelling along its helical path from one end of the guide rollers to the other, each tape element must undergo a lateral motion. Such lateral motion of the longitudinally driven tape subjects the tape elements which are in engagement with the guide rollers to lateral strains. As a result, such prior devices were a continuous source of trouble and, in addition, they were noisy. To be satisfactory, all the elements of a magnetic sound recording device must operate without noise, and the magnetic sound carrier must be driven at uniform speed without being subjected to substantial strains.

The various elements of the simple magnetic recording apparatus described in connection with Figs. 1 to 3 cooperate in a way which eliminates the difliculties encountered in prior devices of this typer and secure trouble-free, foolproof and noiseless operation while maintaining the speed of the tape highly uniform and free from fluttermg.

The surfaces of the guide rollers 6 are made of a material which prevents generation of audible sound when it comes into driving engagement with the loops of the magnetic tape. Commercially available synthetic resin tubes, either of the laminated or the non-laminated type, such as micarta, proved satisfactory for such use. 'I'he guide comb bars 24 which guide the individual tape loops are likewise made of such material. 65 Since the apparatus is designed tooperate without gear drives, all sources of possible noise arel thus eliminated and its operation is noiseless.

The t-ape loops are driven at the required speed by applying the motor driving forces only to y70 one of the guide rollers on which the tape loops are guided. 'Ihe other guide rollers are designed and arranged to have sufficiently large masses and suflicient frictional engagement with the motor driven tape loops so that they are re- 75 volved at a peripheral speed equal to the effective speed of the tape loops, and that the inertia reaction of the tape-driven guide rollers exert on the tape loops equalizing forces which prevent fluttering of the'tape speed caused by the inherent speed iluctuations of the relatively small driving motor.

This fluttering eliminating action of the tape driven guide rollers is rendered highly effective by limiting the frictional driving engagement of the motor driven guide roller to a fraction of the total frictional driving engagement of the tape helix with the tape driven guide rollers. As a result, even small motors, which operate with relatively great speed uctuations, are sufficient for driving a magnetic tape helix, which itself has only a negligibly small mass, at a highly uniform speed. Actual performance in recording piano music, which presents extremely high requirements in respect to flutter-free motion of the recor-d carrier, has proved that the simple magnetic recording apparatus of the invention described in connection with Figs. 1 to 5 is an ideal medium for recording such music. In the device of Figs. 1 to 6, such flutter-free operation is secured by making the total equalizing effect of the masses of the three tape driven guide rollers three times greater than the effectiveness of lthe motor driven guide roller. However, satisfactory flutter-free motion may, in most cases, be obtained if the equalizing effect of the tape driven guide roller is made at least equal or larger than the effectiveness of the motor driven roller in driving the endless tape.

Each cylindrical guide roller has a uniform cross section so as to enable the helically moving tape elements Which are in engagement with the guide surface to slide laterally over the guide surface without imposing excessive strains on the tape elements. The diameter of the guide rollers is made large enough to prevent excessive periodical bending of the tape elements when they come periodically into engagement with the cylindrical guide rollers, and to maintain the required frictional driving engagement between the guide rollers and the tape loops. The guide rollers are spaced suiiiciently far apart so that the greater part of the lateral motion of the helically moving tape loops takes place over the relatively long tape loop portions extending between the spaced guide rollers and only a small lateral motion takes place while a moving tape element is in engagement with the surface of a guide roller.

This arrangement makes it possible to subject the tape loops to sufficient tension for securing the frictional driving engagement between the several guiding rollers and the tape loops required to maintain uniform, flutter-free tape speed, and to utilize the relative long free tape portions extending between the spaced guide rollers as elastic shock absorbers for elastically yielding to a momentary abnormally large force impressed on a tape loop, for instance, by an inaccuracy or unevenness in the surface of a guide roller, before the slippage of the tape loop over the relatively short length of its frictional engagement with the guide rollersis able to remove such abnormal force and secure the normal substantially uniform operating tension of the tape loops. The spaced guide rollers and the tape loops are designed to cooperate in maintaining the tape under sufficiently large tension for securing flutter-free frictional driving engagement between the tape loops and the guide rollers, while keeping the tension of the tape loops and their frictional driving engagement sufciently small to permit equalization of abnormal forces impressed on a tape loop by limited slippage over the engaged roller surfaces. As a result, the necessity for special, more or less complicated tape tensioning equalizing means is eliminated.

The multiple roller system of the invention reduces materially the effective arcuate length of the tape engaged by the driving roller, keeping down the total forces that can be frictionally imparted to the carri-er by the driving roller and thus further contributing to the reduction of the fluttering of the tape caused by speed fluctuations of the driving motor.

By making the guide rollers of substantially uniform cylindrical diameter, the simple structure of such rollers assures smooth travel of each loop of the long endless carrier along the helical path, reducing lateral strains and substantial friction losses at the engaging surfaces of the revolving rollers and the helically travelling carrier elements.

BY spacing the guide rollers so that the greater part of the lateral motion of the endless tape in moving from one end of the helix to the other takes place over the free non-engaged portions of the carrier loop and only a very small lateral motion takes place while a carrier element is in engagement with a guide roller, the lateral strains are still further reduced and rendered completely harmless.

The space which is thus allotted to the mechanical operating structure of the endless carrier system in order to secure these advantages and overcome the prior operating difficulties is utilized for housing the motor, amplifier, driving and control mechanism, and other accessories required for magnetically recording and reproducing sound and thus obtain a mechanically compact, foolproof, self-contained operating structure in which the long endless carrier helix extends out of the way along the protected boundary of the occupied space without substantially occupying -any of the allotted space.

The self-contained frame structure of the endless carrier magnetic recording and reproducing machine so arranged, which thus combines all its effective operating elements and accessories, forms at the same time a spool-like unit in which the frame sides at the opposite ends of the guide rollers serve as protective spool heads projecting slightly beyond the outer boundary of the guide roller space along which the endless carrier travels. This spool-like apparatus structure makes it possible to wind all the loops of the carrier helix on the guide rollers directly from the supply spool, just as any ordinary spool is wound, without danger of entangling, and makes possible simple and quick manufacture of long endless magnetic carrier devices in which all loops of the endless carrie-r helix are placed in their operating positions with the tension required for satisfactory operation.

By combining the endless magnetic carrier with a control mechanism having a movable control member arranged to be selectively driven in a predetermined synchronized relation to the moving carrier for controlling the duration of the recording operation, a simple single grip control makes possible starting a new record on any selected portion of the endless carrier; and a simple single grip control makes it possible to confine the new recording to a selected portion of the endless carrier without obliterating 'a selected portion of a previous recording.

The features of the invention described in connection with Figs. 1 to 4 and 6 may be applied to other magnetic recording and reproducing arrangements.

In Fig. 5 is shown a modified construction of the guide roller arrangement for an endless carrier magnetic recording and reproducing apparatus of the type described in connection with Figs. 1 to 3, in which instead of providing one guide roller in each corner of the frame structure I-2, several smaller rollers 9| are revolvably mounted -in each corner between the opposite side frames I and 2 of the self-supporting frame structure for guiding an endless magnetic carrier helix I3 of such apparatus. Such roller arrangement makes more space available Within the interior of the frame structure for housing the accessories of the apparatus and enables a reduction of the over-all size of the complete magnetic recording apparatus. By using a larger number of smaller guide rollers, the ratio of the length of the tape elements frictionally engaged by the guide rollers to the ratio of the frictionally non-engaged tape elements may be materially increased, thereby further reducing the lateral strain imposed on the carrier element in t'he course of their travel along the helix.

Several endless-carrier-helix guide roller arrangements of the type described above may be nested one within the other. Thus, as shown in Fig. 5, a carrier-helix guide roller arrangement with several guide rollers in each corner may be combined with an internally mounted set of revolvably mounted guide rollers 92 for guiding another endless carrier helix 93 Within the outer frame structure. Several such carrier helices may be combined to form a single endless carrier, for instance, by a cross loop portion 94 traversing from an end of the helix traveling on the outer set of guide rollers to the corresponding end of the helix guided on the inner set of guide rollers.

In Figs. 2 and 8 is shown another construction of the mechanical arrangement for guiding an'endless magnetic carrier in which the cross loop, for connecting the end of the endless helix I3 guided by the guide rollers 5 revolvably mounted in the corners of the frame structure |-2 of Figs. 1 to 3, is located within the boundary of the frame structure. To this end, two crossover rollers are mounted on two brackets 96 which are fastened to the opposite frame sides I, 2 so as to align the cross loop with the magnetic head I5 which is likewise located within the frame structure and mounted on a suitably fastened bracket 91 in a way similar to the arrangement described in connection with Figs. 1 to 3.

This cross loop arrangement subjects the relatively short loop portion extending between the cross-over roller and the adjacent guide roller to a substantial twist and thus imposes on the carrier element larger strains than in the arrangement described in connection with Figs. 1 to 3 in which a very great lengthof the loop approaching each cross-over roller takes up the strain imposed by the cross-over twist. However, the arrangement described in connection with Figs. 7 and 8 has the advantage that the entire loop structure including the cross-over loop is within the boundary vof the rigid frame structure which carries the operating mechanism of the apparatus so that the frame structure may be supported'on any ofits sides without special care.

endless carrier magnetic recording and repro-y ducing apparatus exempliiying the invention. As in the arrangement of Figs. l to 3, a iront frame |0| and a rear frame |02 are joined into a rigid spool-like self-supporting frame structure in the corners of which are revolvably mounted four cylindrical guide rollers 6 having shafts 8 for guiding in conjunction with the guide bars 24 a long endless magnetic carrier in the form of a tape I3 along a helix which is completed by a cross loop I4 extending between cross-over rollers I0 mounted on the top of the frame. The sides of the frame structure are braced by flanged side plates |05 instead of the diagonal struts of the frame in Figs. 1 to 3.

The magnetic head I5 is mounted on an inwardly projecting frame bracket |08 and one of the loops of the helix is arranged to travel between the hinged halves of the magnetic head by two aligning rollers |09 which are held on extensions IIO of the bracket |08 on which thev magnetic head I5 is mounted. By combining the bracket |08 of the magnetic head I5 with the supports |I0 of the alignment rollers |09 into a unitary mechanical structure, simple and positive automatic alignment of the magnetic head I5 with the cooperating tape loop portion passing through the head I5 is assured, and at the same time the tendency of the tape portion traversing the head to vibrate and become a source of possible tape noise is reduced.

The driving motor I9 with its pulley 22, which drives through a belt 23 one end of a bottom guide roller 6, has its resilient vibration absorbing bracket 20 mounted on the cross bars 2| of the frame in the way shown in Fig. 14 so as to permit adjustment of the tension of the belt 23 and nterpose additional vibration absorbing means between the bracket and the frame while increasing the vibration absorbing capacity of the support. To this end, the legs ||I of the motor bracket 20 on the side facing the motor driven roller 6 are held clamped to the supporting bracket 2| between two cushioning washer blocks I|2 of vibration absorbing material, such as rubber, and the legs III on the other side of the motor bracket 20 is arranged to be adjustably clamped by clamping screws I I4 and a compression spring I|5 to the other cross bar 2| of the frame. This arrangement permits easy adjustment of the tension of the driving belt 23 while'interposing an additional mass of vibration absorbing material between the motor and the frame structure which must be isolated against motor vibrations to prevent mechanical noise.

The loudspeaker 32 indicated in Fig. l0 by dotted lines is housed in the interior of the frame and held in place by a baffle board (not shown) which is attached to the frame as in the arrangement of Figs. l to 3.

As shown in Fig. 10, the ampliiier IIS has its chassis located inside the frame structure |0I- |02, being secured to the side wall |05 and the transverse bars I|'| suitably bent to accommodate the loudspeaker structure 32.

The mechanical and electrical elements of the amplifier and their correlation with the other elements of the apparatus is shown in Figs. 12 to 14. The box-like amplifier chassis ||6 is provided with an upwardly projecting front panel ||8 reinforced by a brace ||9 so that the panel forms a part of the front wall of the casing |20, shown in Fig. 16, in which the assembled frame structure |0||02 with its elements is housed in the way shown in Fig. 19.

Associated with the exposed panel wall H8 of the amplifier I6 is a control mechanism for controlling the operation of the mechanical and electrical elements of the apparatus.

To control and indicate the progressive travel of the endless carrier |3, one of the revolving guide rollers 6 drives through a suitable speed reduction mechanism, such as a flexible shaft |26 and two worm drives |21, |28, the control shaft |30 of the control mechanism being revolvably mounted in an opening |34 in the panel wall I6 and a hole in a bracket |35 mounted on the rear of the panel ||6 in the way shown in Fig. 15. The worm gear |36 of the iiexible-shaft worm drive |28 is suitably fixed, as by a pin, on the control shaft |30 on which is slidingly keyed a friction coupling disc |31 which is pressed by a coupling spring |38 so as to engage with its coupling surface, which is covered with a layer |39 of friction material, such as cork or felt, the surface of a control disc |40 which is revolvably mounted on the control shaft |30.

In the arrangement of Fig. l5, the coupling disc 40 is provided with a hollow shaft extension |4| which is revolvably mounted in the journalling opening |34 of the panel ||8 and serves as the bearing for the front end of the control shaft |30. To assure foolproof operation, oil impregnated washers |42, of felt or similar material, are placed adjacent the bearing surfaces of the revolving elements of the control mechanism so as to maintain the bearing surfaces 1ubricated and assure quiet operation of the mechanism.

To the projecting stub shaft end |4| of the control disc |40 is secured a pointer 43 which serves also as a grip for rotating the control disc relatively to the coupling disc |31. A dial |44 with a suitable scale is mounted on the panel behind the pointer |43 and the reduction gear drive connection between the control shaft |31 and its driving guide roller 6 is so proportioned and arranged that when the control disc is coupled to the coupling disc |43, the control disc |40 will make one complete revolution when the guide roller has made the number of revolutions required to pass one complete length of the endless carrier I3 through the magnetic head 5, while the movement of the pointer |43 along the scale of the dial |44 indicates the progress of the travel of the complete length of the endless carrier.

At a point along the periphery of the control disc |40 is provided a stop notch |45 shaped to engage a control rod 46 slidably mounted in a bushing |41 extending through the panel wall I8 so that when the control rod 46 is in the position shown in Fig. 15, the control disc 40 will remain locked in place and the rotating friction coupling disc |31 will not be able to impart the revolving motion to the control disc |40. By momentarily pushing the actuating rod |46 through pressure on its actuating button grip |48 so as to bring the control rod |46 inwardly till its annular groove |49 is brought into alignment with the control disc |40, the control disc is released, and it will be rotated by its frictional coupling connection with the worm-driven coupling disc |31. The slowly revolving periphery of the control disc |40 engages the groove |49 of the control rod |46 and holds it in the inward `dotted line position |48 until after one complete revolution of the control disc |40, the stop notch |45 releases the control rod 46 from its inward position |48 whereupon it is returned to its normal outward position by the pressure of the spring blades of the recording switch |50 pressing on the switch cam 5| provided on the inward end of the control rod |46.

As shown in Fig. 15, the control rod |46 of the control mechanism may be actuated by a flexible push-rod extension |53 that is enclosed in a flexible` tube |54 provided with a coupling collar |55 which is detachably coupled to the rod bushing |41, so that by actuating the push-rod extension |54, the push-rod plunger |56 will push the actuating button |48 of the control rod |46 of the control mechanism to release the control disc.

Fig. 14 illustrates diagrammatically the electrical circuit connections and the cooperative relationship of the various elements of the appaenergizing switch |58 enables independent ener- I gization of the amplifier supply transformer |60 through a series resistance |59 so as to maintain the amplifier in a prepared standby condition and assure that, during the periods when the apparatus is to be used, the amplifier is ready to operate as soon as the main motor energizing switch |51 is closed. With this arrangement, the auxiliary supply switch |58 may remain closed, for instance, during the whole day, so as to maintain the operating circuits associated with the amplifier energized at a reduced voltage at which all the amplifier tubes will be sufficiently preheated so that upon closure of the motor switch |51, there will be substantially no delay in getting the apparatus to operate for reproducing or recording sound.

A typical amplifier I6 suitable for the recording and reproducing apparatus of the invention is shown in Fig. 14. It comprises electron discharge amplifier valves I6I, |62, each provided with a cathode |63, an anode |64 and a control electrode |65 which are connected as consecutive stages of an amplifier between an input transformer |66 having a primary input winding |61 and an output transformer |68 having a secondary output winding |69. The amplifier circuits are arranged to be supplied from a direct current source, shown in the form of a rectifier |10 having' anodes connected to the secondary windings of the supply transformer |60, and a cathode connected through a filter network including a filter choke coil |12 and the exciting coil |13 of the loudspeaker 32 to positive supply terminals |14, |15 for the anode circuits of the electron discharge valves ISI, |62, the midpoint of the anode supply winding of the rectifier |10 being connected to ground.

As shown conventionally in Fig. 14, the heater filaments of the electron amplifier valves |6|, |62 are energized by the supply transformer |60 and,

as explained above, when the auxiliary amplifier switch |58 is closed, they are energized at a reduced supply voltage so as to heat the cathodes to a temperature at which they will be quickly brought to the normal operating temperature upon closure of the motor switch |51 when the apparatus is to be set into operation for recording or reproducing.

The recording switch |50 has live contact spring blades ISI, |82, |83, |84, |85, which are normally biased to the position shown in Fig. 14, in which they establish, with the associated sets of contact springs in their normal position shown in Fig. 14, the reproducing connections, and also press the switch cam and its operating rod |46 into the locking notch |45 of the control disc |40, and are arranged to break the reproducing connections and establish recording connections when the contact blades ISI-|85 are flexed by the inwardly pressed switch cam |5| of the control rod |46, while the control disc |40 rotates and holds the control cam in its inward position.

In the reproducing position of the recording switch |50 shown in the drawings, its blades |8| to |85 establish the following circuits: The unfiexed contact blade |83 connects the lead from the ungrounded end of the amplifier input windying |51 including the corrective network |61A to the transducer coilsl 58 of the magnetic head for impressing upon the input transformer |66 of the amplifier the sound currents induced in the transducer coils 58 by the traveling magnetic waves of the carrier; the unflexed blade |82 connects a tap of reproducer volume control potentiometer |16 which is connected across the secondary winding of the input transformer |66 to the input head of the input stage amplifier valve so as to deliver suitably amplified currents to the output transformer Winding |69 through lead |11, by Way of contact blade |85, to the actuating winding of loudspeaker 32 which reproduces the recorded sound, the various circuits being completed through grounded connections indicated in a conventional way.

In the recording position of the recording switch |50, its flexed blades |8| to |85 break the normal reproducing connections and establish the following recording connections: 'I'he flexed blade |8| connects the ungrounded contact of the input jack |18 of a microphone |19, which is indicated as being of a self-generating type, such as a dynamic or velocity microphone, through a lead including a corrective network |61B to the input transformer winding |61 of the amplifier; the iiexed blade |82 connects a tap of a recording volume control potentiometer |86, which is connected across the secondary winding of the input transformer |66 to the control grid of the input stage amplifier valve |6| so as to deliver ampliiied recording currents to the output transformer winding |69 of the amplifier which is connected by way of a blocking condenser |81 and the iiexed switch blade |83 to the transducer coils 58 of the magnetic head for recording the sound waves on the magnetic carrier; the flexed contact blade |84 connects a lead from a suitable D. C. voltage tap of the D. C. amplifier supply to the obliterating coils 56 of the magnetic head for producing a magnetic flux obliterating the previous recording, while a branch circuit by Way of the iiexed blade |83 supplies the required demagnetzing current to the transducer coils 58 of the magnetic head to secure the desired magnetic recording conditions; and the flexed contact blade |85 breaks the connection of the reproducer lead |11 from the output transformer winding |69 to the reproducer 32 and connects it to a dummy resistor load |86, the various circuits being completed through oommon grounded connections indicated in a conventional way.

In the arrangement described above in connection with Figs. 14 and 15, a separate volume control is provided for the recording process and a separate volume control for the reproducing process. The recording volume control is made inaccessible and adjusted so as to record the high frequency range with maximum recording iiux density possible without detrimental distortion. The volume control for the reproducing process is accessible to the user so that he may adjust it according to his requirements.

The arrangements described above will give satisfactory performance without the use of corrective networks for securing a linear and iiat overall performance characteristics over the entire frequency range. However, as explained hereinabove, and as exemplified diagrammatically in Fig. 17, such corrective networks may be included in the operating circuits for improving the quality of the overall performance of such magnetic recording and reproducing system.

In its general arrangement and operation, the magnetic recording and reproducing apparatus of Figs. 9 to 16 is similar to that described in connection with Figs. 1 to 6. All the operating elements required for magnetically recording and reproducing speech are located within the frame structure along the periphery of which is guided the endless carrier on which the sound is recorded and from which the sound is reproduced, and all the control elements for operating and controlling the apparatus are mounted so as to be readily accessible to the user. By providing a standby amplifier switch |58 for energizing the amplifier tubes at a reduced voltage, the apparatus may be maintained in standby position all day long, with the electron discharge valve sufficiently heated so that at any time when the apparatus is to be operated for recording and reproducing and the main motor switch |58 is closed, its operation will be instantaneously started while preserving the life of the ampliiier tubes.

Although the magnetic recording and reproducing apparatus described above has a fixed length of the endless carrier, it lends itself for operation with different recording and reproducing times by varying the speed at which the endless carrier is driven. Thus, for instance, in some applications, it may be desirable for one type of speech training to have the student or user record a long sequence of sentences and hear it repeated immediately after recording, and in other cases the user may want to have repeated only a short sentence or a few words which he desires to master.

Various types of controls may be used in such variable speed drives for the endless carrier of magnetic recording apparatus. Thus, either a variable speed motor may be used for controlling the speed of the traveling tape, or any variable speed mechanism, such as a Reeves drive, may be interposed between the motor and the carrier driving roller for controlling the speed of the traveling carrier. The lowest possible carrier speed is determined by the minimum quality required from such apparatus. If the carrier travels at double speed and the recording time is reduced by one-half, sound recording and reproducing of much better quality is obtained.

Such apparatus may also be combined with automatic means for indicating the volume level at which the recording is carried on. To this end, a glow tube, such as a neon tube, may be suitably connected to operate in accordance with the operating conditions of the output transformer |63, for instance, by providing the output transformer with a special winding which is So arranged as to indicate by the glow condition of the indicating tube the level of the recording. The operation of this recording level indicating device may be controlled by associating suitable control contacts with the recording switch so as to connect the indicating device only while a recording is being made.

In Fig. 17 is shown another type of magnetic recording and reproducing apparatus in which a plurality of magnetic sound carriers are arranged to be driven and guided by a common mechanical drive arrangement for selectively recording and reproducing sound by means of the individual magnetic sound carriers. The specific apparatus shown in connection with Figs. 26 and 27 is intended for use as a language machine, but the principles underlying the arrangement of this apparatus are applicable to many other uses.

As in the arrangement described in connection with Fig. 10, a front frame IUI with a similar rear frame |82 are joined into a rigid self-supporting frame structure in the corners of which are revolvably mounted four cylindrical guide rollers 6 for guiding in conjunction with guide comb bars 24 a plurality of superimposed endless magnetic tape sound carriers along a helix in a way similar to the single tape helix of Fig. 10. Although any number of superimposed tapes may be conjointly driven and guided by such arrangement, the apparatus illustrated in the drawings is shown as having three superimposed endless tape carrier helices, namely, I3A, I3B and IEC, which are completed by three superimposed cross loops I4A, IIIB, IIIC extending between the cross-over rollers I0 mounted on diagonally opposite corners of the frame structure in a way similar to the arrangement of Fig. 10.

Each of the endless carriers I 3A, I3B, I 3C is provided with its own magnetic head I5A, I5B, |5C, respectively, each having a set of obliterating magnets with obliterating windings 56 and transducer magnets 5'1 with transducer windings 58. 'Ihe three magnetic heads are mounted on inwardly projecting frame brackets in a way similar to the arrangement of Fig. 10 so as to guide each of the endless magnetic tapes through their respective magnetic heads by means of the associated sets of alignment rollers ID9A, IIISB, |IJ9C. The several independent endless sound carrier tapes are driven in common through the driving motion imparted Vby the motor I9 to one of the guide rollers 6 in the Way described hereinabove. An amplifier IIS, loudspeaker 32 and the other accessories used in recording and reproducing sound on the several sound carriers are mounted within the frame structure IUI- |02 as in the prior devices.

The control mechanism for controlling the recording and reproducing arrangement is of the type described in connection with Figs. 17 and 21.

Obviously, the recording and reproducing apparatus of the type described in connection with Fig. 17 is not limited to the use of three traveling carriers, and depending on the various applications of such apparatus, any number of distinct magnetic sound carriers may be arranged and combined for many other applications depending on their particular requirements.

In Figs. .18 and 19 is shown schematically an endless magnetic carrier sound recording and reproducing apparatus in which a plurality of superimposed magnetic tape helices are joined into a long endless magnetic tape sound carrier for recording and reproducing long sound records. The endless tape I3 is guided by guide bar combs 24A, 24B, 24C, 24D on cylindrical guide rollers 6A, 6B, 6C, 6D which are mounted in the corners of a rigid self-supporting frame structure as in the arrangement described in connection with Figs. 9 to 11, one of the guide rollers 6A being driven in anti-clockwise direction by a motor I9 through a belt 23.

The endless tape I3 is wound in the form of a plurality of helix layers over the outer surfaces of the four guide rollers 6A, 6B, 6C, 6D. The successive helix layers are interconnected into a long endless magnetic tape loop by superimposed cross-over tape portions guided over the crossover rollers I Il, IBA, IUB mounted in the diagonal corners of one frame side in a way similar to the arrangement of Figs. 9 and 10, each cross-over tape portion connecting the end of one tape helix layer with the beginning of the next tape helix layer. A cylindrical pressure roller 298 which is mounted alongside of the motor driven guide roller 6A and is pressed towards its surface by a spring biased lever arrangement 299 maintains an inwardly deflected portion of each tape loop of the inner tape helix layer in frictional engagement with the surface of the motor driven guide roller 6A, so as to impart to the portion of the endless tape I3 passing through the magnetic head I5 a uniform speed required for recording and reproducing sound.

This roller arrangement makes it possible to wind a long endless magnetic tape I3 in the form of a plurality of interconnected superimposed tape helix layers guided in their travel along the helical path dened by the guide rollers 6A, 6B, 6C, BD and the guide bar combs 24A, 24D associated therewith in a way similar to the arrangement described in connection with Figs. 9 to 1l. The magnetic head I5 with its alignment roller |09 are suitably supported within the frame structure so as to be traversed by one of the loop portions of the inner helix for recording and reproducing sound on the successive elements of the endless tape in a way similar to the arrangement described in connection with Figs. 9 to 15.

To simplify the explanation, only two superimposed helix layers of such endless tape arrangement are shown in Figs. 18 and 19, the dotted-line tape loops wound around the rollers 298, 6A, 6B, 6C, 6D representing the frictionally driven tape loops of the innermost tape helix and the full line tape loops wound around the rollers 6A, 6B, 6C, 6D representing the tape loops of the additional helix layers of the endless tape I3 loosely wound over the tape loops of the innermost dotted-line tape helix.

Starting with the cross-over portion of the front loop 30|, of the inner dotted-line tape helix layer, as it moves from the cross-over roller IDA mounted in the rear corner of the frame toward the cross-over roller IIJ mounted on the diagonally opposite corner of the frame, the tape passes over the outer surfaces of the guide rollers 6C, 6D, 6A with which'it is held in frictional engagement by the pressure roller 298, and continues over the outer surface of the guide roller 6B to the starting point of the second tape loop of the inner dotted-line tape helix layer. Thereafter, the tape continues its travel along the successive tape loops of the second dotted-line inner helix layer, the pressure roller 298 maintaining an inwardly deflected portion of each tape loop of the inner dotted-line helix in frictional engagement with the motor driven guide roller 6A.

After reaching the position of the rearmost loop 303 of the inner dotted-line tape helix layer, the tape is guided over the rollers 6B, 6C, 6D, 6A and pressure roller 298 to the cross-over roller IOB which is offset against the cross-over roller IOA by the width of one tape spacing. Thereafter, it moves along the cross-over loop 305 from the cross-over roller IBB to the cross-over roller I on the opposite diagonal corner of the frame and continues as the front loop 306 of the outermost full-line helix around the four guide rollers 6C; 6D, 6A, 6B without engagement with the pressure roller 298. It continues thereafter its travel along the successive loops of the outermost full-line helix over the four rollers 6B, 6C, 6D, 6A till its rear loop 301, after passing the guide roller IOA, arrives as the cross-over tape portion 308 at the starting point of the dottedline cross loop portion 30| leading to the front loop 302 of the innermost helix. If the endless tape I3 contains more than two helix layers, the tape element would move below the successive tape loops of the outermost helix from the front loop 306 of the second helix to the rear loop 301 of the second helix until it emerges again above the cross-over roller IOA as a cross-over tape layer underlying the uppermost cross-over tape layer 308`which leads to the beginning of the front loop of the next underlying helix. Its motion would thus continue along successive underlying helix layers from the front loop of each helix to the rear loop of each helix, traversing a cross tape layer extending from cross-over roller IDA to cross-over roller I0 as it passes from the rear loop of one helix layer to the front loop of the next underlying helix layer, until the rear loop 301 of the helix layer directly overlying the innermost dotted-line helix layer merges into the innermost dotted-line cross tape layer 30I which starts the front loop 302 of the innermost dotted-line helix.

Sound is recorded and reproduced on the moving endless tape I3 by the magnetic head I5 under the control of a control arrangement of the type described in connection with Figs. 9 to 11.

In the multi-layer helix guide arrangement shown in connection with Figs. 18 and 19, each element of the moving endless tape, after traveling in frictional engagement with the guide cylinders from one end to the other end of the innermost helix layer, starts again its travel in the outermost loosely Wound helix layer, and after completing its motion in the outermost helix layer, it continues its motion successively along each intermediate helix layer until it reaches the beginning of the innermost helix layer, where it again comes into frictional driving engagement with the motor driven guide roller 64.

In other words, assuming an endless tape guiding arrangement of the type shown in Figs. 18 and 19 having three tape helix layers, only the loops of the rst innermost helix layer are in direct frictional engagement with the guide rollers 6A, 6B, 6C, 6D and are subjected to the driving action of the motor driven guide roller 6A. After traversing the entire length ofthe inner rst helix layer from one end to the other end of the guide rollers, each tape element passes over the oset cross-over roller IOB and the oiset cross loop 305 to the beginning of the rela.

tively loosely Wound outer helix layer; thereafter, each tape element traverses the entire length of the outer helix layer and passes from the end of the outer helix layer over cross-over rollers IOA and I0 to the beginning of the second intermediate helix layer; and after traversing the entire length of the intermediate second helix layer, it again passes over the cross-over rollers IOA into the path oi the cross loop which merges over the cross-over roller I0 into the front loop of the innermost rst frictionally 15 driven helix layer.

The cross tape layers extending above the cross tape 30| from the cross-over roller IOA to the cross-over roller I0 serve as interconnections from the end of each overlying helix to the beginning of the next underlying helix. The exposed clearance end loop 303 of the innermost helix layer is oITset against end loops of the overlying helix layers and leads through the offset cross tape Iportion 305 from the offset crossover roller IUB to the cross-over roller I0 so as to serve as the interconnection from the end of the inner frictionally driven helix layer to the beginning of the top tape helix layer which is wound sufficiently loose so as to provide enough inner helix over the outer peripheral portion of the guide roller as in the arrangement of Figs. 9 to 15.

With this arrangement, only tape portions of the inner tape helix layer are subjected to the frictional driving forces of the motor driven roller 6A. The other superimposed tape helix layers are free to slide over the underlying tape helix loops without being subjected to any substantial tension. As a result, a plurality of tape helix layers interconnected into a long length of endless magnetic steel tape may be guided along a plurality of guide rollers for recording and reproducing sound without imposing substantial stresses on any portion of the long endless tape.

The outer helix loop layers superimposed on the innermost frictionally driven helix layers are not subjected to any substantial friction forces and may be made loose enough so as to be free to slip over the underlying layers.

By providing a plurality of spaced guide roll- 50 ers for guiding the superimposed helices in the way described in connection with Figs. 18 and 19, only relatively short portions of the total length of the endless tape are in direct contact with each other and the outer helix layers may be 55v Wound sufliciently loose so that even along the portions at which they are in engagement, the frictional forces are negligible and do not aiTect the operation of the tape. Such frictional forces may be further reduced by suitable lubrication of the moving tape, for instance, by placing lubrieating pads along the paths of the tape loops.

The control arrangements described above in connection with the various exemplications of the invention form part of the subject matter of my copending application Serial No. 340,030, iiled June 12, 1940, and are claimed therein.

The features of the invention described above in connection with the various exemplications thereof will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims be given a broad construction commensurate with the scope of the invention within the art.

I claim:

l. In a magnetic sound recording apparatus, an endless coiled magnetic tape sound carrier for retaining and reproducing sound records, magnetic transducing means cooperating with said carrier for recording and reproducing sound while said carrier moves past said transducing means, and guide means including at least two revolvably mounted spaced guide rollers having a substantially uniform cylindrical guide surface for guiding said tape as a helix coiled around the outer surfaces of said spaced guide rollers, one of said guide rollers having frictional driving engagement with portions of said tape helix being driven by external forces for impelling said tape helix past said transducing means, at least one other of said guide rollers being frictionally driven by the moving tapehelix and having sufficient mass so as to exert on the tape helix inertia reaction forces which suppress fluttering of the tape helix and maintain it at substantially uniform speed. i,

2. In a magnetic sound recording apparatus, at least one endless coiled magnetic tape carrier for retaining and reproducing records, magnetic ltransducing means cooperating with said carrier for recording and reproducing a record while said carrier moves past said transducing means, and guide means including at least two revolvably mounted spaced guide rollers having a substantially uniform cylindrical guide surface for guiding said tape as a helix coiled around the outer surfaces of said spaced guide rollers, one of said guide rollers having frictional driving engagement with portions of said tape helix and being driven by external forces for impelling said tape helix past said transducing means, at least one other of said guide rollers being frictionally driven by the moving tape helix and having sufficient mass for exerting on the tape helix inertia reaction forces which substantially suppress fluttering and maintain at substantially uniform speed the tape elements moving past said transducing means, the spacing between said guide rollers being sufficiently large and the effective guide roller surfaces engaged by the tape helix being sulficiently small to permit lateral slippage of the tape portions of the helix over fthe roller surfaces while traveling along the path of the helix.

3. In a magnetic sound recording apparatus, at least one endless coiled magnetic tape carrier for retaining and reproducing records, magnetic transducing means cooperating with said carrier for recording and reproducing a record while said carrier moves past said transducing means, and guide means including ait least two revolvably mounted spaced guide rollers having a substantially uniform cylindrical guide surface for guiding said tape as a helix coiled around the outer surfaces of said spaced guide rollers, one of said guide rollers having frictional driving engagement with portions of said tape helix and being driven by external forces for impelling said tape helix past said transducing means, at least one other of said guide rollers being frictionally driven by the moving ftape helix and having suiiicient mass for exerting on the tape helix inertia reaction forces which substantially suppress uttering and maintain at substantially uniform speed the tape elements moving past said transducing means, the effective length of helix portions frictionally engaged with the guide roller surfaces being suiiiciently small and the eifective length of the free helix portions extending between the spaced guide rolle1` surfaces being sufficiently large for permitting limited slippage of tape helix portions over the guide roller surfaces while maintaining suiciently effective frictional driving engagement with the revolving roller surfaces to assure substantially uniform speed of the rtape past said transducing means.

4. In a magnetic sound recording apparatus, at least one endless coiled magnetic tape carrier for retaining and reproducing records, magnetic transducing means cooperating with said carrier for recording and reproducing a record while said carrier moves past said transducing means, and guide means including at least tWo revolvably mounted spaced guide rollers having a substantially uniform cylindrical guide surface for guiding said tape as a helix coiled around the outer surfaces of said spaced guide rollers, one of said guide rollers having frictional driving engagement with portions of said tape helix and being driven by external forces for impelling said tape helix past said transducing means, at least one other of said guide rollers being frictionally driven by (the moving tape helix and having sufficient mass for exerting on the tape helix inertia reaction forces which substantially suppress fluttering and maintain at substantially uniform speed the tape elements moving past said transducing means, the spacing between said guide rollers being sufciently large and the effective guide roller surfaces engaged by the tape helix: being sufficiently small to permit lateral slippage of the tape portions of the helix over the roller surfaces while traveling along the path of the helix, the effective length of helix portions frictionally engaged with the guide roller surfaces being suiiiciently small and the effective length of the free helix portions extending between the spaced guide roller surfaces being sufficiently large for permitting' limited slippage of tape helix portions over the guide roller surfaces while maintaining sufficiently effective frictional driving engagement with the revolving roller surfaces to assure substantially uniform speed of the tape past said transducing means.

5. In a magnetic sound recording apparatus, at least one endless coiled magnetic tape carrier for retaining and reproducing records, magnetic transducing means cooperating with said carrier for recording and reproducing a record While said carrier moves past said transducing means, and guide means including at least two revolvably mounted spaced guide rollers having a substantially uniform cylindrical guide surface for guiding said tape as a helix coiled around the outer surfaces of said spaced guide rollers, one of said guide rollers having frictional driving engagement with portions of said tape helix and being driven by external forces for impelling said tape helix past said transducing means, at least one other of said guide rollers being frictionally driven by the moving tape helix and having sufficient mass for exerting on the tape helix inertia reaction forces which substantially sup-

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