US1557386A - Electromagnetic device - Google Patents

Description

Oct 13, A. L. THURAS ELECTROMAGNETIQ DEVICE Filed 0619.8, 1923 i Patented Oct. 13, 1925.7

- UNITED STA.

TES

ALBERT L. THURAS, OF EAST ORANGE, NEW JERSEY, ASSIGNOR T WESTERN IXLIEIC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y,A CORPORATION OF NEW' YORK. v

Ermcnomaennrrc DEVICE.

Applicationled October 8, 1923. Serial No. 667,154.

T o all whom it may concern.:

Be it lrnownvthat I, ALBERT L. THURAS, a citizen of the United States, residing at East Orange, in the county of Essex, State of New` Jersey, have invented certain new and useful ,Improvements yin Electromagnetic Devices, of which the following is a full. clear, concise, and exact description.

This invention relates to electromagnetic devices and more particularly to magnetic structures for telephone receivers and the like.

The object of the invention in general is to provide a vibratory system particularly adapted for telephoneapparatus which, as a whole. will have such variable mechanical properties with frequency and displacement that the vibrations of the system will only be limited by its internal mechanical resistances and the radiation resistance of the air, within the range of the frequencies ofim- -portance in sound reproduction.

In accordance with the general features of the invention the vibratory system of a magnetic device is provided with elastic means7 which at zero frequency, provides a Y force opposing the magnetic pull on the armature in a manner such as will give a resultant restoring iforce proportional to the displacement of the armature, and which,

under operating conditions makes the vibratory system resonant at substantially`\ all frequencies ofA importance in sound reproduction.

In its preferred embodiment, the invent-ion provides in an electromagnetic device responsive to sound wave energy vibrations,

an armature operable in response to said vibrations, a vlbratorv member associated with the armature an a plurality of thin sheets of material such as paper or aluminum foil supported in the form of a loose pack against each side of the vibratory member, the sheets in each vpack being sufficiently loose to provide air films between adjacent sheets.

When the armature of a telephone ro ceiver of the balanced armature type is in its neutral position in the magnetic field,- there is` no tendency for it to move toward the pole pieces. However, any displacement from its neutral position will create a pull which increases very rapidly with the displacement and tends to draw the armature to the pole pieces.v Heretofore, in response to vibrations at the various ceivers employing balanced armatures,' in order to prevent the armature from striking the pole pieces it has been necessary to rely upon eitherthe stiffness of the diaphragm` alone or the stiffness of the diap hragm and Some auxiliary means such as a spring att-ached to' the armature. These means were necessarily designed to provide an elasticity which was sufficient to overcome the pull on the armature for the o5 maxlmum displacement, no 'particular attensystem in which the amplitudes of -vibration were not proportional to the forces applied thereby causing distortion and the large elasticity with its larger mass resulted in an inefficient system for radiating sound) energy. In-an ideal magneticv system, the

pull on the armature would be inversely proportional to the square of the separation between the armature'and the pole pieces. The pull vs. displacementcharacteristic in this-case would be represented by a parabola.

This is, however, only roughly true in the commercial types of receivers but the displacement characteristic, due to the magnetic field, is of this general form. It is,

therefore, necessary in order that no distortions will result due to the unbalance of the elasticity in the magneticeld to provide a restoring elasticity having the negative characteristic of the elasticity of the magnetic field. If these opposing elasticities were exactly balancedthe armature would not return to its' neutral position when displaced. It is, therefo e, desirable, in order to insure a large and accurate response and prevent freezing of the armature that the mechanical elasticity be slightly greater by a constant amount for all positions of the armature than the magnetic elasticity. This will provide a restoring force proportional to the di lacement of the armature.

e above discussion refers only to the static, or non-operating conditions of the vibrating system but it is also necessary to consider the system when operatin in refrequen- Y cies`- within the sound range. In order to provide a system which'is reasonably responsive to all of the frequencies of the impressed.,`

mechanical constants of thin air films, the

- .spaced relation.

,coils and secured to the pole pieces by means elasticity of which as is well known varies,

within a certain frequency range, substan-A tially as the square of the frequency. Reference is had to E. C. Ventes paper published in the Physical Review, vol. 10, page 39, and I. B. Crandalls paper published in the Physical Review, vol. XI, page 449.

Referring to the drawings, Fig. l-shows a magnetic system suitable for telephone receivers 'employing the invention in one form;

Fig. 2 is an end view of the magnetic system shown in Fig. l;

Fig. 3 shows a modification of the invention;

Fig. 4 is a cross sectional -view of the modification shown in Fig. 3;

Fig. 5 is a modified form of the invention as shown in Figs. 3 and 4; and

6 shows displacement vs. elasticity characteristic curves forvstructurcs providacting upon each otherwithout considering ed with and without the invention.

Y In the construction shown in Figs. 1 and 2, the magnetic structure comprises an electromagnet 7 to the opposite ends of which magnetic pole pieces 8 and 9 fare respectively secured. Each of the pole pieces is provid- :ed with a pairof pole extensions 10, 10 1 which are separated to receive a pair of translating coils 11, 11 therebetween and in Extending betweenthe yof screws 12, 12are torsion members 13, 13 carrying armature 14firmly secured to the members by brazing or other suitable means. The pole piece 8 is secured to the upper side of one end of the magnet 7 and the pole piecei9 tothe lower side lof the other end so as to bring the pole extensions 10, 10

of one pole piece in overlapping relation to those of the other pole piece. The coils 11, 11 are located on the opposite side of the members 13, 13 with the ends 15 and 16 of the armature extending through the openings in the coils, the openings being made of such a size as to permit free movement of `the armature during operation of the receiver. The ends and 16 of the varmature 14 extend between the opposing pairs of the pole extensions 10, 10 of the pole pieces 8 and 9 and the end 15 carries a rod 17 secured to the vibratory diaphragm 18. Also secured to the end 15 of the armature 14 is a vibratory member 19 parallel to the diaphragm 18. l'he ends of the vibratory member 19 may be supported between the elastic cushions 20 at each end by means of members 21 and 22 at one end and members 23 and 24 at the other. The cushions 20 are built up of a number of sheet-'fs of thin,niatei11alsuchas, aluminum foil or a er an el ual number*V of sheets beinfT disposed on each side of the vibratory member 19. The ends of the vibratory member 19 and also' the ends ofl the vsheets are"pejrfo rated to lreceive the screws 25, 25.' `The members 21, 22, 23 and 24 are beveled on the surfaces between which the cushions 2O are clamped so `as to provide a larger space for ness with frequency may be of'a more coniplex function due to a grcaterLor lesser number of layers being in motion at different frequencies. In order to compensate for the magnetic pull on the armature due to the steady field, it is only necessary to take into y account the elasticity providedby the sheets the elasticity due to the air'- cushion.1 However, in order to cause the vibratory system to respond withthe greatest amplitude for-r all of the impressed frequencies, advantage is taken of the elasticity Aof thev air between adjacent leaves of the cushions, It is well known that if a plate is placed inrclose face to face relation withv a vibrating diaphragmthe elasticity of the air will increase substantially as the square of the frequency. For this effect the air film should have a ythickness approximately of the orderl of A .0005 of an inch. Inasmuchy as the displace-` ment of thevibratory member of loud speaking receivers, electromagneticrecorders and reproducers is considerably larger than this, it is necessary, in order to obtain the same variation in elasticity with respect` to the frequency toprovide alpliirality of spaces each of which may besomewhat smaller but which will total anlamount sufficientto permit the vibratory member in such devices Eto rgspond properlyl to thev largest lamounts of energy which may be used. I

In the modification shown in Figs. 3 and-1 there is provided adplu'nger 31 attached to the ends of the armature by means of. a rod 30 and operating in a cylindrical chamber 32 attached to a plate 33 which in turn is secured to the magnet 7. Disposed on one sdeof the plunger 3l are al plurality of` thin discs 34 of aluminum foil or paper and on the opposite side of the vplunger are a. plurality of similar discs 35: perforated at their centers to receive the iod 30. The operation of this modification is substantially the same as that disclosed in Figs. l and 2. Fig. 5

. This arrangement discloses a further modification of the structure shown in Figs. 3 and 4. Inthis modiication, heavier discs 36 and 37 of different thicknesses -are used between the aluminum discs 34 and 35 respectively which results in a variation of the effective mass as well as the elasticity with frequency.

Referring to the curves shown inFig. 6, curve A represents the variation in elasticity with displacement due to` the magnetic pull on the armature. Curve B represents the variation in the mechanical elasticity with' the displacementas obtained by the cushioning means in accordance with the inventiolr., Curve C represents the variation in elasticity with displacement of the armature in the same receiver without the cushioning device of the invention but with an ordinary spring to overcome the force of the magnetic field. Curve D represents the resultant elasticity due to the combined effec-ts of the elasticity of the magnetic field shown by curve A and the mechanical elasticity of the cushioning means shown by curve B. Curve D is obtained by subtracting curve A- from curve B. It will be noted from this curve -that the elasticity decreases as the displacement of the armature increases. Thls re- ,sults in distorting the electrical sound energy which is impressed on the receiver.

A satisfactory cushioning device may be designed by using one hundred circular layers of .6 millpaper with an area of approximately 1/2 square inch, where the separation is such that the fraction of the totalspace occupied by the pa er is approximately .2.

as been lfound to be effective for a receiver of the type disclosed in Patent 1,365,898 of January 18, 19211 to H. C. Egerton. The number of leaves, the dimensions and the space factor will' obviously vary 'for magnetic systems of different construction. n

Although the invention has been shown 'as applied to electromagnetic systems for telep one receivers it may be readily adapted to any electromagnetic device having a vibratin armature.

e invention claimed is.:

1. In a magnetic structure, a magnet producing a steady magnetic field, an armature disposed in said ield, and cushioning means exerting a force on said armature which varies at zero frequency with displacementof the armature in the same lmanner as the force due to the magnetic pull on the armature.

2. In a magnetic structure, an armature,

I a magnet producing a force on said armature varying 1n a predetermined manner with the displacement of said armature, and cushioning means producing an opposing force on' said armature varying with the displacement in the same manner as the magnetic force. 3. In a magnetlc structure, a magnet, a

pair ofpole pieces carried by said magnet, avibratory armature in operative relation with said pole pieces, a member secured to said armature and adapted to vibrate therewith, and cushioning means for applying restoring forces through said member to said armature said forces varying with the displacement in accordance with the magnetic force due to said magnet.

4. In a magnetic structure, the combination with a magnet producing a steady magnetic field and pole pieces carried by said magnet, of a vibratory system comprising an armature is operative relation to said wpole pieces, a vibratory member attached to said armature, and air cushioning means applied to said member for `maintaining the elasticity of said system substantially constant for all positions of the armature in the magnetic field.

5; A magnetic structure comprising a magnet producing a steady magnetic eld, pole pieces attached to said magnet, an armature in operative relation to said pole pieces, and means for compensating forthe magnetic pull on said armature, said means comprising a plurality of air cushions dise posed on each side of said member whereby a constant resultantelasticity is provided for all displacements of the armature.

6. A magnetic structure comprising a magnet producing a `steady magnetic field, pole pieces attached tosaid magnet,'an armature in operative relation to said pole pieces, and means for compensating for the magnetic pull on said armature, said means comprising a vibratory member, a plurality of thin sheets of material, and means for supporting said sheets loosely on each side of said vibratory member whereby cushions are formed to provide an elasticity greater by a constant amount for all displacements of the armature than the elasticity due to the magnetic field.

7. In an electromagnetic device having a steady Jmagnetic field, a vibratory system comprising an armature disposed in said field, a plate attached to said armature, a plurality of thin sheets of material, means for supporting said sheets on each side of said ',plate, and means for supporting said sheets loosely in contact with each other and with said plate whereby cushions are formed providing a restoring force proportional to the displacement of the armature.

8. In apparatus for' the t-ransmissionof sound wave ener a cushioned vibratory system resonant orall frequencies within the easily audible range and having a constant elasticity for all displacements thereof at zero frequency. l

9. In apparatus for the transmission'of soundwave energy a vibratory system oomrising a plurality of air cushions provid-y mg a rconstant elasticity for all displacements at zero frequency and; anne-elasticityVv variable as the square ofthe vfrequencies ofthe vibrations Within the range 1of importance.

10. Ajvibratory systemfor the transmission of soundwave energy, said systemhaving mass and Eelasticity one of Which varies so thatitstotal elastic reactance 4is substantially equal to its totaleective mass reactance at all frequencies Within the range of.

tially asthe'square of the frequency, said elasticity being so related to the mass that the system as a Whole is resonant 4throughout the sound frequency range.

12. In a vibratory system for the transmission'of sound energy having a plurality of connected masses in `,which the aggregate dynamiclel'asticity and the aggregate efy.fective mass change Withfrequency so as to produce resonance throughout the sound frequency range.4 v'

13. A vibratory system for the transmission of sound -Wave `energy comprising a pluralityl of connected masses, the aggre ate effective/mass of which remainsconltant With frequency; anda structureconsisting of a 'pluralityof separate sheets of thin material and intervening thin 'air films arranged to come into action successlvely yto produce an elasticity which increasesy substantially as theA square of the frequency tance is just'equal to the aggregate effective Ymass reactance.y

15. A device iny which thev total effectivev vibrating mass decreases as the frequency ,quency to be transmitted the elastic reacincreases and the elasticity increases 'as the being substantially equal: to the mass `reacvfrequency increases, the elastic reactance 1 tance throughout the voice frequency range'. 16. In a vibratory system for* the transmission of sound Wave energy, a vibrating ysystem having a totali-resultantconstant elasticity Withl frequency and lhaving a plu-- rality of elements Whose aggregate eectivef vibrating mass decreases as'the square ofl the frequency, to causeV saidsystem to be resonant throughout` the range.

1923. f f i ALBERT L. THURAS.

Isound frequency 'l l In witness whereof, lI hereunto subscribe my name-this 27th day of September A. D.

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