US2412718A - Recorder - Google Patents

Description

Dec. 17,I 1946. R. DALL? ET AL RECORDER Filed Aug. 7, 1943 2 Sheets-Sheet l Dec. 17 1946. R. DALLY ET A1. 2,412,718

RECORDER Filed Aug. '7, 1943 2 sheets-sheet 2 20 3' /z/ j Y 1 sy y 4 @CQJ y Patented Dec. 17,7 1946 RECORDER Roy Dally, Francis H. Goldsmith, and David J. Munroe, Racine, Wis., assignors to Webster Electric Company, Racine, Wis., a corporation of Delaware Application August 7, 1943, Serial No. 497,778

The present invention relates to recorders for recording sound or other vibratory effects upon records such as phonograph records. The invention is equally applicable to recorders of the engraving type which utilize a cutting tool or recorders of the embossing type the stylus oi which does not remove material from the record but merely displaces it.

One of the objects of the invention is the provision of an improved recording unit which is adapted to be used at extreme temperatures, such as for example 56 C. to -1-120" C.

Another object of the invention is the provision of an improved recorder unit which has stable characteristics at all of a relatively wide range of temperatures, such as those which might be encountered in winter in arctic regions and those which might be encountered in the hottest seasons in the tropical zone.

` The recorders of the prior art which utilize rubber or other similar resilient material as a support for the armature or for damping material, are not suitable for use at extremely cold temperatures because under such conditions the rubber freezes or becomes more rigid so that it is practically solid and ordinary damping materials would also freeze or become substantiallyv solid.

'Under such conditions, knife edges will frost and change their characteristics, due to the collection of moisture, and the recorders of the prior art do not have stable characteristics at the extremes of temperature for which the present invention is adapted.

VAnother object ofthe invention is the provision of an improved recorder which records sound with high fidelity and with a minimum amount of distortion or divergence from delity, so that the sound may be faithfully reproduced by suitable high iidelity reproduction mechanism.

Another object of the invention is the provision of an improved recorder of the class described in which there is a better mechanical response for a minimum amount of electrical in-put than with the devices of the prior art, and in which the performance of the recorder will not vary over a long period of use under the most adverse conditions. g

Another object of the invention is the provision of an improved recorder construction which is simple, compact, sturdy, and which has a minimum number of parts so that it may be manufactured at a low cost and so that it may be placedwithinthe range'of a vast number of users, .l

14 Claims. (Cl. 179-100.111)

Another object of the invention is the provision of an improved armature construction which takes the form of a resiliently mounted metal body having a predetermined mass with respect to the resilient characteristics o its mounting so that it is tuned to vibrate at a predetermined frequency.

Other objects and advantages of the invention will be apparent from the following description and accompanying drawings in which similar characters of reference indicate similar parts throughout the several views.

Referring to the drawings, of which there are two sheets:

Figure 1 is a side elevational view showing a tone arm, turntable and recorderunit embodying the present invention;

Fig. 2 is a bottom plan view of the recorder unit;

Fig. 3 is a top plan View of the recorder unit with the housing removed;

Fig. 4 is aside elevational view of the recorder unit with the housing shown in section;

Fig. 5 is a plan view of the armature of the recorder unit;

Fig. 6 is an end View of the recorder unit with the housing in section to expose the mechanism of the unit;

Fig. '7 is a vertical sectional View taken on the plane of the line 'l-'l ofFg. 6 looking in the direction of the arrows;

Fig. 8 is a sectional view on an enlarged scale, taken on the plane of the line 8-8 oi Fig. 7 looking in the direction of the arrows;

Fig. 9 is an end elevational view in partial section, taken on the plane of the line 9-9 oi Fig. 7 looking in the direction of the arrows;

Fig. 10 is a rear elevational view of the top portion of the recorder unit with the lower portion in section on the plane of the line lll-l0 of Fig. 'l looking in the direction of the arrows;

Fig. 11 is a vertical sectional view taken on the plane of the line Il-Il of Fig. 7 looking in the direction of the arrows, showing the mode oi support of the pole pieces on the magnet;

Fig. 12 is a fragmentary sectional view taken on the plane of the line |2-I2 of Fig. 3 looking in the direction of the arrows; and

Fig. 13 is a fragmentary sectional view similar to Fig. '7 showing the construction when the recorder is of the engraving type rather than the embossing type of Fig. 7.

Referring to Fig. 1, 2B indicates a'cabinet or othersupport for a tone arm column 21| which supports a tone arm 22 for pivotal movement on.v

3 a vertical axis. The support carries a turntable 23 on a turntable shaft 2d for supporting the record and the tone arm 22 has the recorder' unit t pivotally mounted upon the tone arm by means of the pins or shafts 2l.

In other forms of tone arm which are mounted on the column 2l `for vertical and horizontal movement, the recorder unit may be xedly secured to the end of the tone'arm.

The recorder unit 2E (Fig. 4) preferably comprises an cuter housing i8 which is formed by the lower supporting plate 2S and the rectangular housing member 39. The mechanism of the unit preferably comprises a permanent magnet 3l (Fig. 3) in the form of a rectangular block of magnetic material of high coercive force such as for example Alnico provided with pole pieces 32, 33, spool 34, electrical coils 35, and armature 35.

The magnet 3i is preferably provided with ground plane surfaces 31, 3S for engaging the pole pieces 32, 53 so that the air gap may be accurately predetermined and the magnet is preferably fo'rmed with grooves 39, iii (Fig. 7) located in each of its opposite s ides for receiving the screw bolts di, 42. i

y Grooves 3S and it may have flat side walls and half cylindrical end portions and are preferably slightly largerthan the screw bolts to permit of' come lateral and longitudinal adjustment. The Alnico of which the magnets are `made is preferably cast in bars having oppositely disposed grooves Se and li@ and the bars are cut off to length and provided with the accurately ground plane surfaces 31 and 38.

The pole pieces t2, S3 are similar in construction, but are oppositely located right hand and left hand members. They may be constructed of any suitable metal, such as cold rolled steel or soft iron, and may either be cast or made of sheet metal. -Each pole piece has a rectangular body portion (i3, which maybe of the saine width as the thickness of the magnet block 3 i.

The body portion e?, of each pole piece has a pair of spaced through bores it, e5, one of which is countersunk at 136 for receiving the screw bolts 4l, @E and the heads thereof. o

The apertures il in the pole. piece 32, for example, may be threaded to receive the threaded end 5:8 of the ends of the screw bolts (il, 42., and by means of the screw bolts the two pole pieces are frictionally clamped on the magnet block 3l.

The apertures 4t, 15, andi?, l arel suitably spaced from each other so that the screw bolts are located in the grooves 33 and il@ in the magnet block 3l, with a slight amount of clearance between the bolts and the walls of the grooves for adjustment.

Each pole piece is preferablyrprovided at its rear end with a groove it of rectangular cro-sssection slightly spaced from the end and adapted slidably to receive the rear wall 5l), comprising a sheet of insulating fiber for supporting the connectors 5l, 52. The fiber sheet is slightly deeper than the width of the pole piece bodies 43, and is provided with laterally projecting ears 53, 5d, which effect a complete closure of that end of the housing in the assembly, as shown in Fig. 10.

The connectors 5i, 52 may be similar in construction, andV each may consist of a short strip of sheet metal, having a T-shap-ed end portion 55, for engagement with a conductor, the strip being secured to theV ber endl wall 555 by a tubular rivetl 56.

At its opposite end, each pole pieceN 3 2 or' y33 is preferably formed with a pair of inwardly ex.-

4 tending parallel anges 5l, 58, 59, SQ, which serve as the lpole pieces proper and which when as sembled with the armature 36 and the magnet 3l provide anequal air gap clearance at 6|, S2 at the xed end of the armature 36 and also 63, te which indicates the air gaps at the movable end of the armature lit.V

The pole piece flanges 5l, 5B., 59, 5d are substantially rectangular in shape, the two upper ,f the groove '13.

ilanges 5l and 59 being longer than the lower flanges 58 and 5S in order to provide the same air gap at t3, Sil o-n each side of the thin portion of the armature ,S as is provided on each side of thY relatively thick portion of the armature 3@ adjacent the pole piece anges Sil, 5i.

When the pole pieces are formed of sheet metal, the outer lcorners at 65 between the body flange and the pole piece anges will be rounded but the inner corners 66 will be ground or otherwise cut out to substantially rectangular form so as not ito interfere with the seating of the spool 315 which is to be placed between them.

' The spool iiii'consists of an insulating spool which is preferably made of initially plastic moldable material and it has a pair of parallel Vend flanges (il, 58 (Fig. 8) carried by a central tubular portion E59. The tubular portion Eil has a through aperture 'it of substantially rectangular.

shape for passing the armature 36 with a suitable clearance so that the armature is nctengaged in any way by the spool.

l'Spool 34 carries the insulated coils of conducting wire 35 preferably of enameled Wire since a greater eiiiciency may be attained in some cases by such wire. The coils 3 5. may'consist of a great number of turns of ne wire or a few turns of relatively heavy wire, since the impedance and the conductivity of the coil may be made any ceiving the pole piece flanges 51, 59.

The cross section of this shallow groove 13 is y substantially rectangular and complementary to the shape of the pole piece flanges 51, 59k Vso that the pole pieces must be slid laterally on the spool 34 and the spool ts inside the pole piece flanges 'l-El when the pole piece anges 51, 59 are in Thus the spool 34 and the coil which it carries are positively anchored with respect to the pole pieces, which is of particular importance in a recorder where there is a tendency toward motion of the coil'due to the varying voltage impressed on the coil.

The width of the spool flanges B8 between the pole piece bodies 43 is such that these flanges 68 pivotal Adjacent its other end,`the bottom plate 29 is provided with a rectangular aperture (Fig. 2) of sufficient size to pass the larger end of the armature with a clearance and the aperture 16' is in substantial registry with the rectangular bore 10 in the spool 39. Bottom plate 29 may be secured to the magnet and pole piece assembly by means of the screw bolts 11, 18 passing through the apertures 19 in the bottom plate 29 and threaded into the threaded apertures 80 in the lower pole piece flanges 58, 60.

In order to assure the accurate air gap spacing of the accurately ground ends of the pole pieces, the bottom plate 29 is formed with a pair of rectangular spacer ribs 8|, 92 which extend longitudinally of the bottom plate on the upper side thereof and which are accurately spaced from each other. These ribs may be formed by a pressing operation which leaves a corresponding groove 83 in the bottom plate above each rib.

Ribs 8| and 62 are accurately located with respect to grooves 89, 85 formed in the lower face of the pole piece flanges 50 and 69. When the screws 11, 19 have been partially driven into their bores, ribs 3|, 82 may be 'pressed into grooves 89, 55 to effect an accurate and predetermined spacing of the pole piece'faces at the air gaps 6|, 62.

If desired, a similar spacing member, that is, another plate 29, may be used on the other side of the assembly with corresponding ribs andV grooves, but in most cases the accurate spacing of the pole pieces for a predetermined air gap may be accomplished by merely utilizing spacing ribs and grooves on one side oi the assembly.

The bottom plate 29 also supports the armature 36 and for this purpose bottom plate 29 (Fig. 7) is provided with a pair of spaced through bores 86, 81 located longitudinally of each other in the bottom plate and on opposite sides of the aperture 16.

The armature 96 is preferably of the mass or inertia tuned type, being formed with a lower thick body portion 89, which is substantially rectangular in plan and large enough only to provide suificient body for permitting the formation of a stylus socket 89 and a-screw threaded bore 90 side by side, the latter bore being at an angle to the stylus socket.

In the embossing type of recorder, with th stylus at an angle, as shown in Fig. 7, the stylus 9| is located in the socket 39, the socket extending, for example, at an angle of from twentyeight to thirty degrees to the vertical, while the screw threaded socket or bore 99 may be vertical, and the threaded bore 99 intersects the stylus socket 99.

The set screw 92 has a pointed end 93, which may be of substantially conical shape, but which has an angularity less than that of the stylus socket; that is, less than twenty-eight degrees, so that the point 93, rather than the body of the screw 92, strikes the shank of the stylus 9|.

As the shank of the stylus 9| may be of soft material, such as aluminum, the point 93 may cut a depression in the stylus shank, after which it will drive the stylus rmly into the end of the socket 99 and secure it very iirmly against any movement with respect to the armature.

The stylus socket 89 is preferably a relatively close t with the shank of the stylus 9| to facilitate this firm securement; but, in any event, the

stylus is driven toward the end of the socket and toward that side of the socket which isV opposite to the screw `92, by driving the screw 92 home in its threaded bore 90.

In other embodiments of the invention, where the recorder is of the engraving type, the stylus socket 94 may be vertical, while the threaded bore 95 may be at the same angle to the stylus socket previously described.

The body portion 88 of the armature 3B is provided withthe plane sides 96, 91, which extend upwardly past the pole piece anges 50 and 60 into the spool bore 10. At the points 98 on each side of the armature 36, the armature in its preferred form has a wedge-shaped portion, its plane sides 99|00 tapering inward from both sides to the point |0|.

From the points |0| to the end |02 of the armature, `the armature takes the form of a very thin at plate, having the plane sides 103, |04. The relative proportions of the armature Darts with respect to the spacing of the pole piece flanges 51-60 is such that the air gaps at 6|, 62, 63, 64 are al1 equal.

The construction, shape, and proportions of the parts of the armature may be made such that it will be tuned to vibrate at any desired resonant frequency, such as, for example, 5,000 cycles per second.

Armature body 88 is provided at its front and back with supporting flanges |05, |06, comprising the small rectangular portions integrally secured to the armature and provided with threaded bores |01 for receiving the screw bolts |08, |09. These supporting flanges |05, |06 for the armature are joined to the thick body portion 88 of the armature by intermediate torsion flanges l l0, (Figs. 5 and '1). These torsion flanges ||0, are also integral parts of the armature, and the supporting flanges |05, |06 and the torsion anges may be rectangular in cross-section, and are relatively thin, being the size of the thin reed portion ||2 of the armature (Fig. 8). The torsion flanges ||0, permit the armature to vibrate between its pole pieces due to the twisting of these torsion flanges under the forces which are applied t0 the armature by the magnet and coil assembly.

In order to assure the accurate location of the armature between the pole pieces with equal air gaps 63, 64 and 6|, 62 on both sides of the armature, the bottom plate 29 is preferably provided wtih a longitudinally extending groove ||3 of substantially rectangular cross section, which is located at such point, substantially midway between the side edges of the bottom plate on its upper face so that when the supporting flanges |05, |06 of the armature are secured in the groove H3, the armature is located midway between its pole pieces.

In order to prevent dust from entering the aperture 16, it may be surrounded by another deprestion H4 (Fig. 3), which may be rectangular in plan so` that it surrounds the opening 16; and this depression may be slightly deeper than the groove H3 for the purpose of spacing the plate 29 from the torsion or hinge portions H9, l

so that they are free of all restraint. This de- 7 the mechanism of the unit. This housing member 30 may be box-like; that is, provided with substantially rectangular sides H5, H6, and end wall l Il, formingan integral part of the top wall HS. l

The side walls it, l may be as long as thek top wall l I8 and they may be bent downwardly at right angles at |59 so that they are parallel to eachl other. The Width or". the side walls l l5, l it is preferably such that they may each carry a guide ii'ange ld, 2l which is bent inward at right angles at the lower edge of each side wall and is located below the bottom plate 29 when the housing member 3i] is slidably mounted on the unit.

The end wall lil may be narrower so that` it may extend, only from the top wall H8. to the upper surfaces oi bottom plate 29. The inner end' of the housing' dit may be open. and it will be closed by the ber plate 59 when the housing is mounted on the unit.

Housing Se may be mounted on the unit by sliding the assembly, which comprises the bottom plate and all of the other parts, endwise into the inner open end with the flanges lill, l2! underneath the bottom plate 29 until Ythe bottom plate 29 is received in the slot 22 which is open between the end wall lil and guide flanges |20, I 2|. Housing member 30 may be held in such position by irictional' engagement.

The operation of our improved recorder is as follows: It may be constructed in a recorder of the engraving type with the needle vertical, as shown in Fig. 13, if desired, in which case the stylus or needle is intended' to cut away the record in the pre-formed groove to record sound or other vibratory motion.

In other embodiments of the invention it may be constructed in the form of an embossing recorder with the stylus disposed at an angle as shown in Fig. 7 where it is only intended that the stylus shall displace a part of the material of the record at the groove where the recording is made.

The recording unit may be Xedly secured inside a tone arm which has a suitable weight and which is mounted for universal movement; that is, for movement across the record and for movement toward and away from the record. In other cases the recording unit may be pivotally sup'- ported on a tone arm which is merely provided' with pivotal movement on a vertical axis, as the recording unit itself is mounted pivotally on the tone arm for pivotal movement about a horizontal axis, as indicated at El in Fig. 1.

Electrical impulses which are impressed upon the coil of the recorder by suitable sourceduring the recording are, oi course, modulated in accordance with the sound or other record to be made, and these electrical impulses cause variations in the flux in the armature, which react with the flux emanating from the poles f the permanent. magnet to cause the armature to vibrate, dueto the resilient characteristics of the torsion hinge portions and the mass of its parts, which areY dis posed at a predetermined distance from the axisl of the vibratcry motion.

During this vibration there is Aa torsion or twisting movement at the torsion portions or torsion hinges HQ, l ll of the armature. The natural period of the armature depends uponthe re'- sults desired, as it may be rvaried lby varying the torsional characteristics of these torsion portions and the weight and thickness of the` thin portion and.' other parts or proportions of the armature.

8 Asthe` armature vibrates,y the stylus: which it carries is caused'. to vibrate, the movement of the stylus being a maximum at its cutting or embossing end, and this movement is in proportion to thevariations in the sound or other record which is bei-ng made.

.The present device has noknife hinges or other relatively movable parts which may have theirl and4 ridges and. mounting anges on the' pole pieces', bottom plate and' the armature attaching flanges, which also ensures a uniformity ofthe characteristics 0f the units when manufactured inmass production.

The entire armature' and the stylus may be removed, if desired', to change the characteristics or repair the device, and the stylus itself is. also readily removable, if necessary, for any purpose. The stylus is more firmly secured in its socket in this` device than. in the devices of the. prior art of which we are. aware, and the mass of. the armature is greatly reduced by the use of our impro-vedl mode oi securing the stylus to the armature.

The` entireassembly is easy to manufacture and assemble, is sturdy, andcapable of use for a long period of time withouty any necessity for repair. It is unlikely to be affected either by any jolts or Jars- Whilewe have illustrated a preferred embodiment of our invention, many modifications may be. made without` departing from the spirit of the invention,- and wedo not wish to be limited tov the precise details of` construction set forth, but

. desireto avail ourselves of all changes within.'v the scope: ofthe-appended claims.

Having` thus described' our invention, what we claim: as new and. desire to' secure by Letters Patent of the United States, is:

l. In a recording unit for' recording sound and thelike; the combination of a non-magnetic supporting plate: with al permanent' magnet of' high coercive'A force and aY pair of pole pieces, said pole pieces being formed withopposing pole faces i carried by substantially U-shaped end portions and saidmagnet being clamped between body portions of said pole pieces, the assembly being supported by saidsupporting plate andsecured thereto by threaded members, andthe saidv pole pieces and plate being provided with complementary aligning and spacing ribs and' grooves whereby the air space between pole piece faces is accurately predetermined and maintained, and a spool for supporting a coil, said spool having upper and 1 lower end flanges tting between the U-shaped pole piece end portionsto anchor the spool'againstA lateral movement.

2; In a recording unit for recording sound and Y thev like, the combination of a non-magnetic supporting plate with a permanent magnet of high n i9. by said supporting plate andsecured thereto by threaded members, and the saidpole pieces and plate being provided with complementary aligning and spacing ribs and grooves whereby the air space between pole piece faces is accurately pre determined and maintained, and a spoo-l for supporting a coil, said spool having upper and lower end anges fitting between the U-shaped pole piece end portions to anchor the spool against lat-J eral movement, and said spool having grooves for parts of said pole piece end portions for anchoring the spool against longitudinal movement.l

3. In a recording unit for recording sound and the like, the combination of a non-magnetic supporting plate with a permanent magnet of high coercive force and a. pair of pole pieces, said pole pieces being formed with opposing pole faces carried by substantially U-shaped end portions and said magnet being clamped between body portions of said pole pieces, the assembly being supported by said supporting plate and secured thereto by threaded members, and an armature located between the pole piece faces and integral torsional means carried by said armature and fixedly secured to said supporting plate whereby movement of the armature is accompanied by distortion of an integral supporting part of said armature.

4. In a recording unit for recording sound and the like, the combination cf a non-magnetic supporting plate with a permanent magnet of high coercive force and a, pair of pole pieces, said pole pieces being formed with opposing pole faces carried by substantially U-shaped end portions and said magnet being clamped between body portions of said pole pieces, the assembly being supported by said supporting plate and secured thereto by threaded members, and an armature located between the pole piece faces and integral tor-` sional means carried by said armature and fix edly secured to said supporting plate whereby movement of the armature is accompanied by distortion of an integral supporting part of said armature, said armature having a predetermined mass with respect to said integral torsional means for determining the vibrational characteristics of the armature.

5. In a recording unit for recording sound and the like, the combination of a non-magnetic supporting plate with apermanent magnet of high Y,

coercive force and a pair of pole pieces, said pole pieces being formed withopposing pole faces carried by substantially U-shaped end portions and said magnet being clamped between body portions of said pole pieces, the assembly being supported by said supporting plate and secured thereto by threaded members, and an armature located between the pole piece faces and integral torsional means carried by said armature and xedly secured to said supporting plate whereby movement of the armature is accompanied by distortionV of an integral supporting part of said armature, said armature having a predetermined mass with respect to said integral torsional means for determining the vibrational characteristics of the armature, and'threaded means for securing said armature to said supporting member.

6. In a magnetic instrument having an armature movable in accordance with sound variations, a supporting and securing structure for a stylus carried by said armature, comprising a lower armature portion of suicient size to provide a body for a pair of intersecting bores, one of said bores being relatively deep and serving as the socket for a stylus shank and the other of said bores being-threaded to receive a Vset screw, said bores intersecting and the set screw engaging the said shank of the stylus, both of said bores extending upwardly into the bottom of the armature, said bores being located on an angle which is less than theangle of the point of the set screw whereby the extreme point of the set screw is adapted to engage the stylus shank to drive it into the socket and to secure it therein. l

7. An armature assembly for a sound recorder 4comprising a supporting plate of non-magnetic material, said supporting plate being provided with an aperture for passing an armature part, a magnet and pole piece assembly carried by said plate and having upper and lower opposed pole piece faces spaced from each other a predetermined amount, an armature carried by said supporting plate between said pole piece faces, said supporting plate having a groove for receiving complementary parts of said armature whereby the armature is located in a predetermined central position between said pole piecefaces.

8. An armature assembly for a sound recorder comprising a supporting plate of non-magnetic material, saidv supporting plate being provided with an aperture for passing an armature part, a magnet and pole piece assembly carried'by said plate and having upper and lower opposed pole piece faces spaced "from each othera predetermined amount, an armature carried by said supporting plate between said pole piece faces, said supporting plate having a groove for receiving complementary parts of said armature whereby the armature 'is located in'a predetermined central position between said pole piece faces, and threaded members carried by said armature and supporting plate holdingthesaid parts of said armature in said groove.

9. An armature assembly for a sound recorder comprising a supporting plate of non-magnetic material, said supporting plate being provided with an aperture for passing an armature part, a magnet and pole-piece assembly carried by said plate and having upper and lower opposed pole piece faces spaced from each other apredetermined amount, an armature carried by said supporting plate between said pole piece faces, said supporting plate having a groove for receiving complementary parts of said armature whereby the armature is located in a predetermined central position between said pole piece faces, said pole pieces and said supporting plate being provided with complementary projecting parts and recesses for determining the spacing of said pole piece faces.

l0. An armature assembly for a sound recorder comprising a supporting plate of non-magnetic material, said supporting plate being provided withan aperture for passing an armature part, a magnet and pole piece assembly carried by said plate and having upper and lower opposed pole piece faces spaced from each other a predetermined amount, an armature carried by said supporting plate between said pole piece faces, said supporting plate having a groove for receiving complementary parts of said armature whereby the armature is located in a predetermined central position between said pole piece faces, said pole pieces and said supporting plate being provided with complementary projecting parts and recesses for determining the spacing of said pole piece faces, and threaded means for securing the pole pieces to the supporting plate and also for securing the armature to said supporting plate.

11. In a magnetic recorder assembly, a support,

comprising a vibrating portion, Va torsional portion, and a supporting flange, said armature being secured to said support by means oi said supporting iiange with said armature located between the faces of said opposed pole pieces, an insulating plate carried vby said support, and a housing comprising a box-like member having top, side, and end flanges and guide ilangesadapted to be slidably engaged under said support, said end wall being spaced from said guide flanges, and said support having a projecting end portion to be received between said end Wall and guide flanges.

12. In a magnetic sound equipment, the combination of a permanent magnet structure comprising a source of magnetomotive force and having a pair of parallel legs of magnetic material, said legs being provided with substantially U- shaped pole pieces opposing each other, an electric winding carried by a spool located in said U- shaped pole pieces, an armature comprising an integral metal member formed with a vibrating portion adapted to be located between the pole pieces, reduced torsional portions on each side of y said armature, and attaching flanges carried by said torsional portions, a supporting plate of nonmagnetic material provided with a groove for receiving said attaching flanges of said armature and with threaded members armature to said supporting plate, threaded members for securing said supporting plate to one of the flanges of each of said pole pieces, said supporting plate and the adjacent flanges of each of said pole pieces having complementary align ing grooves and ridges for deiinitely determining the air gap space when said grooves and ridges are secured in engagement with each other by said threaded means.

13. In a chuck structure for sound equipment, the combination of a vibrating member provided with a body having a pair of bores, one of which extends substantially axially into said vibrating for securing said member and the other of which extends at an acute angle to the rst-mentioned of said bores, both said bores emerging at the free end of said vibrating member, the second of said bores being threaded, and a threaded member having a tapered sharp point, in the latter of said bores, the

nrst of said bores containing a stylus having a relatively soft shank, said point being at such an angle that the extreme end of the point engages in said shank, driving said stylus against the opposite side of its bore, andcausing said stylus to bottom rmly in its bore. i

14. In an armature structure for sound equipment, the combination of a magnetic structure having pole pieces of substantially U shape with upper legs adjacent each other and lower legs adjacent each other, with a nonmagnetic member secured to two adjacent legs of said magnetic structure, and holding them in predetermined spaced relation, an armature of the inertia type adapted to vibrate at a predetermined tuned frequency, said armature having a relatively thin upper body portion spaced from the adjacent legs of the magnetic structure by a predetermined air gap on each side, and having a relatively thick lower body portion provided with a chuck also spaced from the adjacent legs ar predetermined amount, which legs have a proportionately larger spacing from each other, the thin end of said armature being integrally secured to a pair of laterally extending torsional flanges which are thinner in the dimension transverse to the armature than in the dimension longitudinally of said armature, Vand are provided with a predetermined resilient characteristic, depending upon the mass of the'armature and the frequency at which it is to vibrate, said torsional iianges being integrally joined to enlarged attaching flanges having bores for receiving threaded members that are secured to said supporting plate.

' ROY DALLY.

FRANCIS H. GOLDSMITH. D. J. MUNROE.

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