US2476685A - Dual purpose transducer with recording damping means - Google Patents

Description

July 19, w K. RlEBER DUAL PURPOSE TRANSDUCER WITH RECORDING DAMPING MEANS Filed Jan. 26, 1946 2 Sheets-Sheet 1 INVEN TOR.

4 MZZJMA/Z/J-M/ July 19, 1949. w. K. RIEBER DUAL PURPOSE TRANSDUCER WITH RECORDING DAMPING MEANS 2 Sheets-Sheet 2 Filed Jan. 26, 1946 INVENTOR.

MM MX QW Patented July 19, 1949 DUAL PURPOSE TRANSDUCER WITH RECORDING DAMPING MEANS William K. Richer, Los Angeles, Calif.

Application January 26, 1946, Serial No. 643,777

10 Claims. 1

My invention relates generally to phonographic apparatus of the type wherein the sound record is produced in or transcribed from an undulating record groove in a moving disc or cylinder.

More particularly, my invention relates to reversible, electro-mechanical transducer means employed in apparatus of the class stated to produce, or reproduce from the sound groove.

It is well known that various electro-magnetic phenomena are reversible; i. e., motion of an electric conductor in a magnetic field produces current in said conductor or conversely current in the conductor causes motion of same in a ma netic field. This principle is frequently used in the designing of transducers for phonographic apparatus.

The term transducer as used herein denotes energy translating means for converting electrical pulsations into mechanical vibrations or means for performing the reverse functionconverting mechanical vibrations into electrical pulsations. Specifically, a transducer for converting electrical to mechanical energy is referred to as a recording head, and when used to convert mechanical to electrical energy is referred to as a playback head.

It is the usual practice in the art to provide in the recording head an embossing or engraving stylus which is adapted to be vibrated by the transducer in accordance with electrical pulsations delivered thereto, and this vibrating stylus is employed to produce the undulating sound groove in a moving record. To reproduce sound from this record, a stylus carried in a playback head is made totrack the moving sound groove, the undulations in which cause mechanical vibrations of said playback stylus, which vibrations generate in the transducer a pulsating electric current which may be delivered to suitable amplifying means. It is obviously desirable in phonographic apparatus of the class stated to make use of the same transducer for both the function of recording and the function of playing back, using the same stylus to produce the groove and to track it for transcription thereof.

In order to secure optimum eificiency of energy transfer in a transducer which is used for both the above purposes, however, it is necessary to provide apparatus which may be suitably adapted between functions. Several factors complicate the design of such apparatus.

A major consideration, for example, in the design of transducers of the class stated is the means provided to mount the device for suitable motion across a moving record medium during rill-100.41)

Y the function of recording or playing back. During the recording function, this mounting must be relatively rigid in order that translatory motion thereof across the moving record produces the requisite spiral or helical groove. It is desirable, on the other hand, that the playback head mounting provide a small amount of lateral leniency in order that the playback stylus may faithfully track the record groove regardless of minor lateral deviations thereof.

Another factor of prime consideration in the design of dual purpose transducers is that of damping. During the recording process it is necessary to provide considerably more damping than is necessary during playback.

Still another factor for consideration is that of record engaging pressure of the stylus. Since during recording it is necessary to deform the record medium, considerably greater pressure on the stylus is required than in playback.

Still another factor is that of mechanical stifiness or spring factor of the vibrating stylus. Recording heads of optimum efficiency are relatively stiff compared to eilicient playback heads.

A major object of the present invention is to provide a dual purpose transducer which may be selectively used for recording or playing back a phonographic sound record and in which the adaptation to either of the above purposes is made by a single simple manual adjustment.

Another object of my invention is to provide a transducer as described which is aresonant within a relatively wide range of audio frequencies.

A. further object of my invention is to provide a transducer of the class stated which is capable of relatively high efficiency during recording and hence requires a relatively low gain amplifier.

Summing up the foregoing discussion, it will be seen that for optimum results in recording, the mechanical system of a transducer should be relatively stiff, have relatively high damping, and exert relatively great record-engaging pressure. In addition, the mounting of the recording head must be rigid to lateral motion thereof.

For playing back, on the other hand, the system should be relatively lenient, relatively undamped, and have relatively light record-engaging pressure. In addition, the mounting of the playback head must be provided with lateral leniency.

These and other objects of my invention will become apparent from a more complete description taken in connection with the drawings, in which:

Fig. 1 is a plan view of a transducer embodying my invention and shown in operative engagement with a disc-shaped record;

Fig. 2 is a side elevational view of the apparatus shown in Fig. 1;

Fig. 3 is an enlarged plan View of the framework of the transducer shown in Figs. 1 and 2;

Fig. 4 is an enlarged isometric view of a stylus adapted for use in the transducer shown;

Fig. 5 is an enlarged transverse section of a portion of the transducer taken on the line E5 in Fig. 2;

Fig. 6 is an isometric view of a coil support clip employed in the transducer;

Fig. 7 is a vertical section of a portion of the device taken on the line 7-l in Fig. 5; and

Fig. 8 is a coil form employed in the device.

Briefly, my invention employs a structure resembling that in electric meters of the DArsonval type. A movable frame carries the coil and stylus and is mounted in a magnetic field so that current flowing through the coil causes swinging motion of the coil within the field and hence of the stylus which is thus adapted to record alternating or pulsating electric current as undulation in a sound groove. Conversely, when said stylus is allowed to track or follow a moving sound groove having undulations therein, consequent vibratory motion of the stylus and hence the coil in the magnetic field causes alternating current to flow in the coil.

A hinged weight is mounted with the transducer in such manner that it may be selectively rested on, or lifted from the stylus, thus to add or remove pressure, damping, and stiiiness to the mechanical system whereby to adapt the device for either recording or playing baclc as hereinbefore stated.

Referring now to the drawings for a more detailed description, it will be seen that the numeral H indicates a transducer constructed according to my invention and pivotally mounted by a shaft i2 to a tone arm 13 for vertical swinging motion above a rotating disc record I l. While the device herein described and illustrated is adapted for use with various types of phonographic apparatus, it is illustrated herein as embodied in a disc-type recorder-transcriber wherein a record-carrying turntable l5 rotates and moves in translation simultaneously to produce a spiral record track in the surface of the record. Such phonographic devices are well known in the art and hence need no further description herein.

A stylus 15 for selectively producing or playing back from a spiral groove in the record 54 is carried in a substantially vertical position by a U-shaped clip H of light metal, preferably aluminum, the stylus passing through two holes near the bases of the horizontally projecting arms of the clip H and being retained therein by an inwardly projecting boss is pressed in the vertical portion of the clip H, and engaging a dent 19 in the stylus H5. The clip l7 also carries a coil 29 wound of relatively fine wire on a barrelshaped coil form 2!. The coil form 2! is slipped onto the clip I'i against out-turned ends of the arms 22 and 23 and is retained in this position by the stylus [6 as best seen in Fig. 7. The clip, coil, and stylus form an integral unit which is pivotally mounted to a fixed barrel-shaped core piece 24 by two pointed pivots 25 and 2G pressed into the latter and engaging cone-shaped pivot bearings formed in the arms 22 and 23 of the clip ll.

The clip, coil, and stylus assembly mounted as described is now adapted to swing about pivots 25 and 26; and as will be seen from an examination of Fig. 5, such swinging motion produces lateral motion of the stylus point relative to the direction of record motion thereunder.

In order now that the aforesaid swinging motion shall produce alternating current in the coil 23 or conversely in order that alternating current in the coil shall produce said swinging motion, it is necessary to impose a magnetic field on the coil having its flux line running transversely as seen in Fig. 5. The permanent magnetic field is produced in a permanent magnet 21 and is carried forward and through the walls of the coil 23 by two soft iron pole pieces 23 and 29. It is desirable to have a relatively strong magnetic field passing through the walls of the coil 28, and to this end the core piece 24 is constructed of soft iron and the inner ends of the pole pieces 23 and 29 are concave following the general contour of core piece 2Q. ifhe flux path so produced is indicated by dotted lines in Fig. wherein it will be seen that a large proportion of the flux lines pass through coil-receiving gaps 38 and 3!.

The core piece. 24 is supported between the ends of the pole'pieces 28 and 29. and spaced therefrom by a T-shaped support member 32 which is clamped into suitableslots in the inner faces of the pole pieces. In order that the sup port member 32 does not shunt the magnetic circuit, it is constructed of diamagnetic material such as brass. A clamping screw 33 of diamagnetic material passes through a clearance pole in one of the pole pieces 25? and is threaded into the other 28 in order to pull the two pole pieces 23 and 29 together thus to clampv the support member 02 and the magnet 21 inplace as shown in Fig. 3.

A pair of very light tension coil springs 3 1 and 35 serve the dual purpose of centering the stylus it within limits of its lateral motion, and carrying current from the coil-26. to suitable connecting leads 36 and 37 for connection to an amplifier or other electrical device as may be desired. The springs 33 and-35 are anchored at their forward ends to suitable tie points 38 and 35 in the rim of the coilv form 2;! and at their rearward ends to upstandirngv lugs id and ll mounted by an insulating bridge &2 to the support member 32.

A hinged weight it is pivot-ally mounted between two upstanding ears 4d and formed in the rearward portion of pole pieces 23 and 29. As will be seen from an examination of Fig. 2, the weight i3 is adapted to be swung to a forward position where it rests on, the top end of the stylus it or to a rearward. position shown in phantom lines where it rests on a bridge member ii: mounted across the rearward ends of pole pieces '28 and 29. A -Small block iler rub her or similar resilient material is cemented to the surface of the weight iel'at its forward end and positioned to engage the upper endci the stylus it when the weight is in its for-ward position. The stylus to. ispointed-on, its upper end and hence adapted to penetrate slightly into the rubber block .47. Thus, when the weight rests on the stylus iilas shown bythe, solid line in- Fig. 2, the rubber bloclgdl provides. added stillness and damping and the weight provides. additional p e o press e. s ylus. it into. the record it for the purpose of producing agroove therein. Thus, it will be seen that when the Weight is in its forward position, the transducer is adapted as a recording head.

When the weight is in its rearward position, it acts as a counterpoise, thus substantially reducing the record-engaging pressure of the stylus l6 and adapting the transducer H for the purpose of playing back. With the weight 43 in its rearward or playback position, the clip, coil, and stylus assembly is relatively free to move laterally and thus accommodates the device to follow a sound groove in the record M regardless of minor lateral deviation therein. While deviations in the groove will result in some swinging motion of the coil in the magnetic field, current in the coil produced by this relatively slow swinging motion will be extremely small and of subaudible frequency, the only detectable current flow being that caused by the undulations in the groove of audible frequency.

As shown in Fig. 3, the pole pieces 28 and 29, the support member 32, the core piece 24, and the magnet 2'! form a unitary frame structure for the transducer which is pivotally mounted to a fixed tone arm l3 for vertical swinging motion above the moving record l4. Additional control means (not shown) may be provided t swing the transducer upward and clear of the record for the purposeof changing records.

In order to produce a sound record, the turntable I5 is moved to one of its limits of translatory motion (shown in Fig. l), and a record blank placed thereon. The stylus is now engaged with the record and the weight 43 swung forward to its recording position. The record is rotated and translated simultaneously, thu to produce a spiral groove therein by the action of stylus l6. Undulations will be produced in the groove corresponding to the audio frequency electric current delivered to the coil 26 through leads 36 and 31.

Now to play back this record, the stylus It is disengaged from the record 14, the turntable i5 is returned to its original position, the stylus again engaged with the record, and the weight 43 moved to its rearward or playback position. The stylus will now track the spiral groove in the rotating record l4 and audio frequency alternating current will be delivered by the coil 20 corresponding to the undulations in the groove.

Thus, it will be seen that my device fulfills all of the objects hereinbefore stated requiring only the single operation of swinging the weight into one of its two positions to adapt the transducer for the purpose of either recording or playing back.

While the particular apparatus herein shown and described in detail is fully capable of attaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative of the presently preferred embodiment of my invention, and that I do not mean to limit myself to the details of construction or design herein shown, other than as defined in the appended claims.

I claim:

1. In a dual purpose phonographic transducer, the combination of: a laterally movable armature; a stylus held in said armature for lateral motion therewith and adapted to engage a moving record-receiving blank; pressure exerting means adapted to selectively produce or release pressure of engagement of said stylus and record blank; and resilient means adapted to be interposed between said pressure means and stylus whereby to resiliently constrain lateral motion of said stylus when said pressure means is engaged therewith.

2. In a dual purpose phonographio transducer, the combination of: a laterally movable armature; a stylus held in said armature for lateral motion therewith and adapted to engage a moving record-receiving blank; a pivotally mounted weight adapted selectively to rest on or be lifted from said stylus while the latter is engaged with said record blank; and resilient contact means mounted on said weight and adapted to be interposed between said weight and stylus whereby to resiliently constrain lateral motion of said stylus when said weight rests thereon.

3. A dual purpose phonographic transducer which includes, in combination: stylus means adapted to engage a moving sound record receiving blank; electro-magnetic means adapted to selectively produce or detect vibration in said stylus; a weight adapted to selectively rest on said stylus means whereby to increase pressure of said engagement of said stylus and record blank, or to be lifted from said stylus whereby to decrease said engagement pressure; and resilient contact means mounted on said weight and adapted to be interposed between said weight and stylus whereby to resiliently constrain said vibration of said stylus when said weight rests thereon.

4. In a dual purpose phonographic transducer, the combination of: a laterally movable armature; a stylus held in said armature for lateral motion therewith and adapted to engage a moving record-receiving blank; a pivotally mounted weight adapted selectively to rest on or be lifted from said stylus while the latter is engaged with said record blank; resilient means mounted on said weight and adapted to be interposed between said weight and stylus whereby to resiliently constrain lateral motion of said stylus when said weight rests thereon; and electro-magnetic means selectively adapted to produce vibratory motion of said armature or to detect such motion thereof.

5. A dual purpose phonographic transducer which includes, in combination: a pivotally mounted armature frame; an electric coil mounted on said frame for swinging motion therewith; a fixed ferro magnetic core piece disposed within said frame; magnetic field producing means adapted and positioned to produce a strong magnetic field permeating said coil; stylus means fixedly mounted in said frame for motion therewith and adapted to engage a record blank; relatively lenient spring means operatively associated with said frame whereby to resiliently constrain same to a substantially central position within limits of said swinging motion of the same; a hinged weight adapted to selectively rest on said stylus means whereby to increase pressure of engagement of said record by said stylus means, or to be lifted therefrom to reduce said pressure of engagement; a relatively stiff resilient contact member in said weight adapted to further constrain said swinging motion when said weight rests on said stylus; and conductor means connected to said coil whereby selectively to induce vibratory motion thereof, or detect vibratory motion thereof.

6. A dual purpose phonographic transducer which includes in combination; stylus means adapted to engage a moving sound record receiving blank; electro-magnetic means adapted to selectively produce or detect vibration in said stylus; pressure exerting means adapted to selectively engage said stylus means whereby to increase pressure of said engagement of said stylus and record blank, or to be disengaged from said stylus whereby to decrease said engagement pressure; and means operatively associated with said pressure means adapted to resiliently constrain said stylus concurrently with said increase of pressure.

7. A dual purpose phonographic transducer which includes in combination: stylus means adapted to engage a moving sound record receiving blank; electro-magnetic means adapted to selectively produce or detect lateral vibration in said stylus; pressure exerting means adapted to selectively engage said stylus means whereby to increase pressure of said engagement of' said stylus and record blank, or to be disengaged from said stylus means whereby to decrease said engagement pressure; and a block of resilient rubber on said pressure means adapted and positioned to engage said stylus means concurrently with said increase in pressure whereby to resist said vibrations.

8. A dual purpose phcnographic transducer which includes in combination: laterally movable stylus means adapted to engage moving sound record blank; electromagnetic means adapted to selectively produce or detect lateral vibration in said stylus means; pressure exerting means adapted'to selectively engage said stylus means whereby to-increase pressure of said engagement of said stylus and record blank, or be disengaged from said stylus means whereby to decrease said engagement pressure; and a member movably mounted adjacent said stylus means, adapted to selectively engage, or be disengaged from said stylus means, andoperatively connected to said pressure means whereby to be moved thereby to apply lateral constraint to said stylus means concurrently with said increase of pressure and remove said constraint concurrently with said decrease in pressure.

9. In a dual purpose phonographic transducer, the combination of a laterally movable armature; a stylus held in said armature for lateral motion therewith and adapted to engage a moving record receiving blank; pressure exerting means adapted to selectively apply or release pressure engagement of said stylus and record blank; and a movable resilient member adjacent said armature operatively connected to said pressure means whereby to be moved thereby to apply lateral constraint to said armature upon said increase of pressure.

1G. In a dual purpose transducer, the combina tion of: a laterally movable armature; a stylus held in said armature for lateral motion therewith and adapted to engage a moving record receiving blank; a weight movably mounted adjacent said armature and adapted when moved to selectively apply or release pressure of engagement of said stylus and record blank; and a 1nov-- able resilient member adjacent said armature operatively connected to said weight whereby to be moved thereby to apply lateral constraint to said armature upon said increase of pressure.

WILLIAM K. RIEBER.

Name Date Thomas Feb, 26, 1935 Number

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