US1614327A

US1614327A - Loud-speaking telephone receiver

Info

Publication number: US1614327A
Application number: US680597A
Authority: US
Inventors: Adolph A Thomas
Original assignee: Individual
Current assignee: Individual
Priority date: 1923-12-14
Filing date: 1923-12-14
Publication date: 1927-01-11
Anticipated expiration: 1944-01-11
Also published as: USRE17186E

Description

Jan. 11, 1927. A. THQMAS LOUD SPEAKING TELEPHONE RECEIVER Filed 1923 2 Sheets-Sheet 1 5 ./s I I INVENTOR Jan. '11, 1927. I A THOMAS 1,614,327

' LOUD SPEAKING TELEPHONE RECEIVER Filed Dec. 14,1925 2 Sheets -Sheet 2 Patented Jam-.11, 1927.

UNlTED STATES; PATENT Q'OFFIICE'.

0mm. 'rn'o ut'as, a NEwYoRx, n. Y..

i LO UD SBEAKING rarnrnonn necmvriar Application filed December 14,1e'2sj. Serial no, 680,597.

My invention relates to telephone instruments. and its main object is to provide a loudspeaking receiver-particularly adapted for use. in radio reception, although not limited to this field.

One of the main sources of trouble encountered in theoperation' of radio loudspeakers heretofore on the market, is due to the armature or diaphragnrof the magnet striking the pole pieces when the air gap is adjusted too close. To obtain .a strong re- .production through these p'riordevices. it is necessary to adjust the armature or diaphragm as closely as possible to the magnetic pole pieces, but, when that is done, the armatureior diaphragm is liable to strike the pole pieces when a strong current passes through the speaking coil. -.'1he result is a distortedreproduction. On the other hand, .when the air gap between the magnet and its armature (or diaphragm) is increased so as to avoid-the danger of the armature striking the pole pieces. the effect of the current in the coil isiweakened, and the resultant reproduction is correspondingly feeble.

One of the main purposes of my invention is to overcome the foregoing defects and difliculties in prior loudspeakers'and to this end I haveprovided a l'oudspeaking telephone receiver in which themagnetic efi'ect of the coil on the armature may bevaried independently of theair gap between the armature and the pole pieces. This regulation of the magnetic efiiechof the speaking coil, as I may call it. is accomplished by varying the reluctance of the magnetic path.

of the flux set up by the current in the coil. One of the simplest ways of varying this magnetic reluctance is to provide an adjust- T able iron core for the coil. In the practical embodiment, which I preferat the present time, thecore Oftll coil is made in two sections. one of which is adjustable with respect to the other, so that the sections may either be brought closely together, to form a continuous core, or may be separated by an air gap. By simply ad ust1 ng-th1sa1r gap,

I the magnetic effect of the coil on the armature is varied accordingly, 'without varying or disturbing the air. gap between ture and the pole pieces. f

In accordance with a further feature of be used like a the arma my invention." I provide magnet in which one orboth of the polepieces are bifurcated and the bifurcations of each polepiece are feature previously.

correspondingly increased or diminished efiect.- A Myinvention -further comprises improved means for mounting the operative parts in a readily accessible position within an outer;

casing, WhlClI is adapted to carry a horn and be supported on a stand, or which may for connection with a fixed horn,

cabinet;

phonograph horn enclosed in a The foregoing and other objects and ad I vantages of my invention will become clear from a detailed description of the accompa-nyingv drawings. which show my invention in two illustrative embodiments. In thesedrawings- Fig'l isatransverse cross section on line 1-1 of Fig. 2, showing a loudspeaking telewith my invention; p

Fig. 2 is a top plan view in section; proximately on the broken line 2-2 i Fig. 3 is an enlargedfragmentary View in cross-section. approximately on line 33 .phone receiver constructed in accordance of Fig. 2, showing means for adjusting the. 7

air. gap .in the core of the coil:

Fig, 4 is a cross-sectionv on line 4-4 of Fig. a

Fig. 5 is a detached perspective view of operative parts in the .construction shown in Figs. 1 and 2; v

Fig.6 is a; fragmentary view'jin crosssection o'n line 66 of Fig. 2E Fig. 7"is a fragmentaryview in crosssection on line. 7-7 ofFig. 2;.

Fig. 8 isan enlarged fragmentary view the casting which directly supports the:.

loo

of an adjustable connection between the armature and the diaphragm for varying the veffective leverage between the two;

or supportindicated as a whole by B, as

' pole pieces best shown in Fig. 5. This support, which may conveniently be cast or molded out of suitable non magnetic material, such' as aluminum orbakelite, consists of a circular base 1, airing 2, and connecting posts 3. If desired, these parts may be made separate and rigidly secured together, but'it is preferable to mold or cast them in a single rigid piece. So it will be understood that when I refer to the part It as a. casting, I use the term merely for convenience.

-On base 1 are mounted two permanent steel magnetsM and M, which are oppositely arranged and suitably spaced from each other at their polar ends. The magnets. are firmly held on base 1 in any practical way, as by screws :12 passing through the base into the magnets. magnets are so arranged that their like poles lie opposite each other. Tothepoles- N and S of magnet M are secured 4

Y ole pieces

4 and 5, and to the poles Nand g of magnet M are secured pole pieces 4 and 5'.

These pole pieces are refe'rably of soft iron,

or other material of iigh' magnetic permeability. Any suitable means may be used for holding the pole pieces infirm contact with the magnets. In the drawings I have shown the polepieces attached directly to the polar ends of theniagnets by screws 6.

As seen in Fig. 2, the pole pieces extend toward each other at their tips and are separated by an airgap a of a width depending upon the width of the ends of the armature,-

to be presently referred to. The tips of the. are cut away to form curved concave ends 7. The curvature of these ends is preferably in a circle struck up from the axis of rotation of the armature, for a pur-' pose that will presently become clear.

evident that the magnets M and M constitute in effect a single magnet having a bifurcated north pole 4-4 and a bifurcated south pole 5 5. Although I have referred to the magnets M and M as permanent magnets, they may obviously be in the form of electromagnets.

Between the

pole pieces

4 and 4 is mounted acoil C, and between the

opposite pole pieces

5 and 5 is arranged a similar coil C. The coils C and C are connected in series and in eifect constitute a single coil. It will As shown in Fig. 2,the 7 It is :ceiaaar be understood, of course, that the coils C and G are properly connected in a suitable telephone eircuit in which the current varies in accordance with sound waves intended to be reproduced by the receiver. For convenience I will, therefore, refer to the coils C--U as the telephone coil.

The posts 3 of casting B are preferably so spaced that the magnets with their pole pieces and coilsmay be inserted and re .moved as a unit through the space between best shown in Fig. 3. The fixed section 8 terminates in a conical recess 10, into which fits closely the tapered end of movable section 9. When these correspondingly shaped ends. of the two core sections are brought together, they form a continuous iron core. When the section 9 is moved away from the section 8, an air gap is formed, which decreases the magnetic effect of the coil to an extent dependingupon the width of the air gap, other factors being considered equal.

This will be understood by those skilled in p the art, without further explanation.

The airgap formed in or at the end of core It, when once adjusted may be said to be fixed or permanent in that it is notaffected by the vibratory movements of the armature. In other words, while the airgap between the pole pieces and the vibra tory armature is variable, the controlling airg'ap provided for the core of each coil is stationary and Wholly independent of the armature airga As faras,I know, this feature is broadly new, and it may be employedin various combinations in electric instruments of the telephone type other than Nil) the specific embodiment shown in the drawadapted to engage similar screw-th reads in the pole piece through which the section passes. Section 9 isprovided with an cxtension'in the form of a stub-shaft or arbor 12, preferably of non-magnetic bearing material. On the arbor 12 is mounted a small fine-toothed gear wheel 13, which is so connectedwith the shaft that it rotates the same and yet allows axial movement of the shaft 12 with respect to the gear wheel. This connection may be formed by providing the gear wheel '13 with a lug or key 14, arranged to engage in an axial'slot or groove 15 in shaft 12. In this way, the gear locked to' the shaft so as to rotate the same when the gear wheel is rotated, and at the same time the'gear wheel allows axial movementofthe shaft due tothe screwethreaded mounting of the-core section 9 in the associated polepiece. The gear wheel 13 is retated in one directlon or the other bya-wo'rm 16 formed on or secured to a pin 17, which cally locked in adjusted position against turning and can be operated only through the manually controlled'worm 16.

hen it is desired'to adjust the core see.

tion 9 relatively to the fixed section 8, it N is only necessary to turn the finger piece 18 one way or the other, until the required adjustment has been secured, as the operator will determine from the acousticefi'ect of j the -coil., When the

core sections

8 and 9 are in contact with each. other, the magnetic effect of the coil is a maximum and the acoustic eiiect of the instrumentjls correspondingly loud. \Vhen the core section 9 is separated from the section 8 by an airgap, the ultimate acoustic ellect of the coil decreased in a degree'depending upon the width of the air gap. To inform the operator which way to turn-the finger piece 18, suitable notations may lee-provided on. the. finger piece'and the base 1 to indicatethe loud and'isoft movements of the finger piece. The operative connections be tween finger piece-18 and the movable'.core' section 9 are such as to secure'a very delicate adjustment of the core section, so that the air gap-in the core may be adjusted to a very small fraction of an inch. Theadjoining ends of the core sections 8 and 9' may he cut of? straight, but I prefer to shape theni con1cal. so as to secure a better and liner adjustment.owingto the increased area i of the cone-shaped air gap Between the tips orfrce ends of pole pieces.4--4"and 5 -5 is mounted an armature A. which may simply be a. short flatlmr of iron ot ihe right size and dimensions,

depending upon the relative arrangement,

and size of the pole pieces- The armature is operatively supported lietweeuthe pole piecos int.an v practical way. In the drawings I have shown a U-shaped bracket 21 wheel 13 is always v,atthe. center.

two may be used.

' having a pairof projecting arms 22 and 23'.

between which is pivoted a'stud 24 constructed to hold the armature'A. .In Fig.

1, the stud 24; is shown slotted to receive the armature and support the'same rigidly mounted on'the base 1 of casting B, as by means of screws or bolts 25 passingthrough the lower arm 23 into the base 1 (see-Fig. 6). Any other practical mounting for the arma- The armature A is of such size dimensio'ns' that in its normal position the ends thereof practically span the air gap 0 between each pair of pole pieces, as shown in Fig. 2. If the pole pieces are widerthan (hex-armature, the polar tips 7 may be reduced to the same width as the armature','as indicated in Fig. 7 This tends to reduce magnetic leakage. Furthermore, the ends of the armatureare so shaped as to move The bracket 21 115 firmly in close proximity past the curved tipsrfof the pole pieces 44' and 5-5'.without' acair gap between the pole tips-7 and the armature is always maintained at a minitually touching the same. In this way'the I wide its arc ofvibration under the influence of coil C I Also',it should be noted that the adjustment of either core section has no effect on the normal magnetic flux, so that an air gap produced in the core does not increase thereluctance of the path traversed by the flux otmagnetM-MT. As will be clear from F 2, the construction of field magnet and armature is such that there is practically no magnetic leakage. This arrangement produces an instrument of high sensitivity and efficiency. The clearance be-. tween thecorrespondingly .curved polar tips 7 and the ends of the armature maybe made. assmall asmechanical' conditions permit. This minimum air gap, which yet makes it impossible for the armature to rattle against the pole pieces, causes a weak current in coil CC' to produce a maxinun'u' response of the armature. 'lVhen both coils on the armature' There is no shuntinp or diverting of any part bf the normal field flux from the operative air gap between the pole pieces and the armature. This constanmaintenance of the normal magnetic field at full strength in its relation to the-armature causes minute current variations in the C and G are used the are sowo-und that speaking coil or coils to produce a maximum etiect on the armature, thereby impartlng to the instrument a high degree t sensitivity. The practical value of anormally' the speaking coil, react strongly on the ar-' mature. When I 'say that the armature is always subject to the full strength of the normal magnetic field, and that the magnetic regulating device for the flux of the coil does not divert or shunt any portion of the normal magnetic held from the armature, -I do not mean that the normal field.

flux passes through the length of the armature as shown in the illustration of Fig. 2. l simplymean that practically the full strength of the magnetic field is always exerted on the vibratory armature across the operative air gap or air gaps, irrespective oi any particular arrangement of magnet and armature. 0f course, it will beunder stood that due. allowance is made for such magnetic leakage or losses as cannot possibly be avoided in the mechanical construction of the invention, no matter how carefully carried out.

On the ring f casting B is mounted an acoustic diaphragm D of proper design and material. There are many-kinds and styles of diaphragms on the market suitable for this purpose. The most common material of which these diaphragms are made is mica, which is moisture-proof and gives a strong reproduction. Some peopleprefer a diaphragm of wood, especially maple, which gives a more pleasing reproduction than mica, though perhaps notso strong.

Diaphragm D is held in place on the ring 2 in any practical way. In the embodiment shown inthe drawings, the supporting ring 2 has an inwardlyprojecting shoulder or flange 26- and a screw-threaded wall 27.

--The diaphragm is clamped firmly in osition by a. screw-threaded ring 28. t is preferable to clamp the diaphragm between a pair of washers 29 of -felt, leather, rubber,

' or other sound-absorbing material.

crank com rising along arm 33 and a short. 'arm 34. he free end of the long arm 33 is To the ring 2.is fixed a bracket 30 having a pair of spaced lugs 31", between which is pivoted at32 a lever indicated as a whole by'L. This lever is in the form of a bel-l D, as indicated at 35 in Fig. 1. The short arm 34 of lever "L is provided with a lateral extension 36, "which may be an integral part of the lever. The free end of the extension 36 is connected to the armature A by a rod or stiff wire 37,-or any other practical means. The point at which the rod 37 is Connected to thearmature depends upon the amplifying ratio which it is desired to the lengths of the arms 33 and 3d of lever L,

any desired leveragebetween the armature and the diaphragm can be secured. These calculations are well. within the skill of the man conversant with this art.

In Figs. 8 and 9, I have shown a modified form of connection between the armature.

and the diaphragm. In this construction, the connecting lever, indicated as a whole by L, comprises a long arm 38, a lateral extension 39 and an adjustable short arm indicated as a whole by J. This arm comprises a pair of short rods or pins 40 and 4E1, which are. adjustably connected together through an oppositely screw-threaded nut 42. The ends of the pins 40 and 4:1 are in screw-threaded engagementwith this nut, and by turning the nut one way or the other, the pins are drawn closer together or forced apart. In this way the effective leverage between the pivot point 82' and the lower end of the arm J can be adjusted as required. The arm J is at its lower end connected to the armature through a suitable link 4:3, which may be a -stitl wire or any other practical connection. The adjustable lever L is applicable in the construction shown in Figs. 1 and 2, and to avoid re etition of drawings, it will be understoo that the lever L may be substitutedfor the lever Ii.

Although I have shown a specific form of adjustable arm J, it is clear that in the broad aspect of my invention there are various ways of carrying out this idea, and

' Figs. 8 and 9 are, therefore, to be considered as merely illustrative.

The support or casting, B, which carries the operative parts of my new loudspeaking telephonereceiver, is preferably constructed to be inserted as a umt into-an outer casing. In Fig. 1, there is anouter'casing or housing indicated as' a whole by K. This casing may be cast or molded as a single piece of any suitable material, such as bakelite, aluminum and the like. Casing or housing K is of proper size and design to receive the casting B and all parts carried thereby. The lower inner end of casing K is screwthreaded to receive the screw-threaded section 44 of casting B, which thus forms a cap or housing for the lower end of the cas-' ing. To permit easy manipulation of casting B in screwing it into or out of the casing K, the base 1- of the casting may be formed with a sli htly projecting flan e or rib 45, which is easily grasped by the firi gers. 4130 When the casting B is properly screwed into the outer casing K, the top of ring 2'and annular clamping ring 28 rests against-a shoulder 46 formed inside of the casing, as shown in Fig. 1. i

The top. of outer casing K-is provided with a. centralopening which is surrounded by a flange or extension 47 adapted -,to receive the inner'end of a born 48 For this purpose the extension 47 may be made slightly cone-shaped, so as to provide a tight fit for the born. When the outer casing K is used to support a horn 48, the-casing is mounted on a suitable base or stand T,

which is provided with anopening 49 of proper size'to rec'eive casing K. As seen in Fig. 1, the casing has,an annular shoulder 50 which rests ontop of the stand T. Casing K fits snugly and firmly into the stand '1 without the necessity of; any fastening devices. The frictional securing means thus formed by the snugly engaging surfaces of base T and easing K is sufficient to hold the casing rigidly .on its supporting base. To

remove the casing K and all parts carried thereby, it is only necessary to. separate it fromthe stand T, which is easilydonewithout the use of tools. The instrument may be used without the stand T, as when it is desired to connect it to a phonograph horn embodied in a cabinet; In that case the extension 47 on the cover of casingK is so shaped as to fit over the small end of a mounted horn.

In Fig. 10 I have shown a slightly modified form of outer casing and support for the operative parts. The outer casing K is preferably cast ormolded in a single piece and also constitutes the stand or base for the instrument. vI'n other words, the outer casing K and a stand '53. The cylindrical portion 52, of the cover has screw-threads 54 arranged -to' engage corresponding screwthreads 55 of a support indicated as a whole by B". The support B is generally similar to the support B. previously described in detail, and is adapted to'carry the operative parts in the same way as described in "connection with. support B. I

Although I have shown and described the magnet M.N 'as provided with two coils C and C, in the broader aspect of my invention it is sufficient if only one coil is used.

In that case, the other pole piece would be solid and not bifurcated. Personally, I prefer t0 use a coil for each end of the' armature, so as to secure the greatest effect with a'weak current.

The operation of my new receiver will be clear to anyone skilled in the art and I need not, therefore, go into any details on this point, I need only say that normally the armature A is held in a neutral or balanced position between the tips of the pole pieces,

consists of a cover "51, a cylindrical wall 52,

effect of the coils and the armature vibrates ,in a manner well understood. These vibrations are in accordance with thecurrent vari- .ations in the coil and are transmitted in increased ratio through the connections previously described. In this way, the smallest vibrations ofthe armature are repeated by the diaphragm in magnified movements, so

that the sound produced ma be heard at a distance.

While I have herein shown and described a specific form of magnetic structure and armature arrangement, I want to make it clear that I have done so merely by way of example'and that the feature of adjusting .the magnetic effect of the coil 0n the armature can be used with any other practical construction of magnet and the vibratory member operated thereby. v

In the broaderaspect of my invention, the particular means for varying the effect of the telephone coil independently of the air' gap between the armature and the pole pieces, may be carried out in other practical Ways than the one herein shown and de scribed for the sake of illustration. For instance, t his feature of my invention can be used in a construction where the armature is in the form of a diaphragm of magnetic material "ence of the coil.

phragm D is not necessary. Therefore, in the claims, when I mentlon an armature Without reference to a diaphragm, I'mean broadl any movable magnetic member arranged to be. influenced by the magnet. When I magnetic effect of. the coil, I .do not, of course, mean the variations produced by the variable current in the coil, since those varia tions are automatic and beyond the control of the user of the instrument.

In radio reception, broadcast programs vary all the way from the reporting of sport-v ing events to the rendition of music by bands and orchestras. The same loudspeaker will [usually not reproduce all of these diflerent numbers satisfactorily without adjustment or regulation of the magnetic effect of the coil in the loudspeaker. \Vhen a person de sires a loud number on a program reproduced softly, he adjusts the loudspeaker to decrease the magnetic efiect of the coil on the armature. 'In the particular instance illustrated in the drawings, this is done by turning the finger piece 18 in a direction to produce an air gap between the core sections by the diaphragm adapted to vibrate under the influ- In such a case theJdiaspeak of varying or adjusting the 8 and 9. On the other hand, when, for instance, a violin solo is broadcast, the instrument would probably be adjusted to give out a maximum volume of sound. This would be effected by closing the air gap between the

core sections

8 and 9, in the particular construction shown in the drawings.

Either core or both cores B may be adjustable. For simplicity, I have shown each core adjustable independently of the other,

while the pole pieces are made of a material of high permeability." -Expressing this difrents.

ferently, the retentivity of the pole pieces and coreis lower than that of the steel body of the magnet. It is well known that the steel or steel alloy used for permanent magnets is hard steel, so. as to retain the magnetization. The high retentivity of hard steel causes it to be less susceptible to'variations in the magnetizing or demagnetizing force. Hence, in those prior telephone receivers where flux variations due to variable impulses in the talking coil must pass through the body of the permanent body, the efficiency of the instrument is lowered, because the steel mass of the magnet offers considerable resistance to flux variations, and this resistance increases with increased frequency of the variable magnetizing cur- This objection and disadvantage is obviated in aconstruction embodying my invention, where the flux variations produced by coil C or C take place only in the associated pole pieces and core outside the steel mass of the magnet. In other words, variations in magnetic fiux'are confined to a path of high permeability, so that variable impulses in the telephone coil produce 'flux changes with minimum loss and maximum efiiciency. Y

Although I have herein shown and described, certain specific constructions, I- would have it understood that I have done so for the sake of explaining my invention to those skilled in the art, and not by way of restriction or limitation' It will be apparent that the various features of my invention may be mechanically embodied-in other forms than herein set forth. As far as I know, I am the first to provide a telephone instrument in which the magnetic effeet of the telephone coil is controlled without changing the normalair gap between the magnet and the armature, and without diverting or shunting any portion of the normal magnetic field from the armature.

As previously explained, the per- Hence, way. I may add that in the drawings I have not attempted to show the operative parts in mathematically calculated proportions, since therelative sizes and dimensions of those partswill vary in different embodiments of the invention, and also since the (orrect design of the instrument in each case isreadily determined by the man skilled in this art.

It will be understood that, although the illustrative embodiment shown in the drawings has been described as a telephone receiver, the various features of my invention are equally'applicable in various other electrical instruments of that type.

I claim as my invention: 1. In a telephone receiver, 'a magnet, a vibratory armature operatively associated with thepoles of said magnet, a coil for causing vibration of said armature, and manually controlled means for regulating the magnetic effect of saidcoil on the normal field of said magnet independently magnetpoles, .said regulating means being arranged to operate without diverting any portion of the normal magnetic field from the armature. 2. In a telephone receiver, a magnet, a vibratory armature operatively associated with the poles of said magnet, a coil for causing vibration of said armature, and manually controlled means for varying the reluctance of the magnetic circuit produced by said coilwithout varying the air gap between the, armature and the magnet poles, said regulating means being arranged to operate without diverting any portion of the normal magnetic field from the armature.

3. In a telephone receiver, a magnet, a

I claim this idea in a fundamental fil of the air gap between thearmature and the vibratory armature operatively associated with the poles of said magnet, a coil for causing vibration of said armature, a magnetic core for said coil, said core being arranged outside the normal flux path of said magnet so as not to divert any portion of the normal magnetic field from the armature, and means for varying the magnetic permeability of said core, whereby the magnetic effect of said coil on the field of said magnet and therefore on the armature is varied accordingly.

4. In a telephone receiver, a magnet, 21 vibratory armature operatively associated with the poles of said magnet, a coil for causing vibration of said armature, a magnetic core for said coil, said core Cons sting of separable sections arranged outside the normal ilux path of said magnet so as not to divert any portion of the normal magnetic field ;'from the armature and means for adjusting one section relatively to the other for varying the magnetic effect of sad coil on said armature.

5. In a telephone receiver, a magnet having oppositely arranged pole pieces, one of said pole pieces consisting of a par of spaced-limbsor bifurcations, a magnetic (ore connecting the limbs of said bifurcated pole piece, a vibratory armature operatively assoc ated with said p'olepieces, a coil on said core to cause vlbratlon of said arma ture, means for-regulating the -magnetic -effeet of said coll on the normal field of said magnet, independently of the air gap be a coil on said core to cause vibration of said fl'armature, means for varying the magnetic permeab'lity of said corewithout-diverting any portion of the normal magnetic field from the armature and thereby controlling the magnetic efi'ect of said coil on the nor- 9 mal field of said magnet, and an acoustic member controlled by said armature.

7. In a telephone receiver, a magnet having oppositely arrangedpole pieces, one of spaced limbs or bifurcations, a magnetic core connecting the limbs of said bifurcated pole piece, said core consisting of separable sections arranged outs'de the normal flux path of said magnet so as not to divert any 0 portion of the'normal magnetic field from the armature, a v'bratory armature operatively associated with said pole pieces, a coilon said core tocause vibration of sad armature, means for adjusting one core section relatively to the other for varying the a magnetic efiect of said coil onsaid armature, and an acoustic member controlled by s'aid armature. v

' 8. In a telephone receiver, a magnet having pole pieces, a vibratory armature-mounted in operative relation to said 'pole' pieces,

the ends of said armature being separated from the respective pore-pieces by a practically minimum air. gap and arranged to 5 move past the polar faces of the pole pieces W'thout striking said pole pieces during the maximum vibrations of the armature, a coil forcausing vibration of said armature, means for varying the magnetic effect of said coil on the normalfield of said magnet Withoutvary'ng said minimum air gap and Without divertingany portion of the normal magnetic field from the armature, and arr acoustic member controlled by said. ar- 5 mature. I I

'said pole pieces cons'sting of a pair of 9. In a telephone receiver, a" magnet having pole pieces, a vibratoryarmature mounted in operative relat on to sald pole pieces,

the ends of said armature being separated from the respective pole pieces by a practically minimum air gap and arranged to move past the polar faces of the pole pieces Without striking sa'd pole pieces duringthe 'maximum vibrations of the armature, a coil for causing vibration of said armature, manually controlled means for varying the reluctance of the magnetic circu t produced by said coil without varying said minimum air gap and Without diverting any portion of the normal magnet c field from the armature, and an acoustic member controlled by said armature.

10.: In a telephone receiver, a magnet having pole pieces, a vibratory armature mounted in operative relation. to said pole pieces, the ends of said armature being separated from the respective pole pieces by a practi cally minimum air gap and arranged to move past the polar faces of the pole pieces without striking said pole pieces during the maximum vibrations of the armature, a col for causing vibration of said armature, a magnetic core for said coil, said core being arranged outside the normal flux path of said magnet so as -not to dlvert any portion of the normal magnetic field from the armature', meansffor varying the magnetic. permeability ofs'aid core to regulate the 'mag netic effect of said coil on the armature independently of said air gap, and an acoustic member controlled by sa d armature.

11. In a telephone receiver, a magnet, a

.vibratory armature extending between the poles of said magnet, a coil for causing vi- 'bration ofsaid armature, and means for regulating the magnetic effect of said coil on said armature without varying the normal path of the flux of said magnet across the air gap between the magnet poles and the armature.

12. In a telephone receiver, a vibratory armature operatively supported in a magnetic field, an acoustic member, means for so connecting said acousticmember.with said armature that the vibrations of the armature are transmitted in increased ratio to said acoustic member, said connections including a device supported on a fixed pivot,

and manually operable means for adjusting said connecting device to vary" the trans-' mission ratio between said armature and said member."

13. Ina telephone receiver, a vibratory armature operatively supported in a magnetic field, an acoustic member, connections between said armature and said member for transmitting the vibrations of the armature in increased ratio to said member, said connections including an arm supported on a fixed pivot and means for varying the efl'ective leverage otsaid arm to vary the transmission ratio between said armature and said member.

141. In: a telephone receiver, 'an acoustic diaphragm, a pivoted bell-crank lever having a long arm and a short arm, means for connecting the free end of said long arm with the center of said diaphragm, a vibrating armature operatively mounted in a magnetic field, means for pivotally supporting said armature independently of said lever,

and means for connectlng the free end of said'short arm to said armature, whereby the Vibrations of said armature are transmitted to said diaphragm in increased ratio.

15. In a telephone rcce'ver, an acoustic diaphragm, a vibrating armature operatively mounted in a magnetic field, a pivoted bell crank lever having a long arm and a short arm, means for supporting said armature independently of said lever, means for connecting the tree endof said long arm with the center of said diaphragm, means for connecting the free end of said short arm to said armature, whereby the vbrations of ,said armature'are transmitted to said diaphragm in increased ratio, and means for adjusting the effective lengthof said short arm.

16. In a loud-speaking telephone receiver, 'anouter casing having a cylindrical section provided with a screw-threaded port-on, a

support removably fitting into said cylindrical section and held in place by said screw-threaded portion, said support comprising a base and a rin an acoustic diaphragm mounted on'sai r1ng,electrom agnetic' mechanism including a vibratory arcarried thereby constitutin mature mountedon said base, and an operative connection between said diaphragm and said armature, said support and all parts a unit insertable into and removable from said outer casing. v .1

17. In a telephone receiver, a pair of magnets having their like poles arranged oppositely and spaced from each other, a polar projection extending from each pole, the polar projectionsoi each pair of like "poles constituting a. bifurcated pole piece having an air gap between the free ends of the pro-,

jections, a vibratory armature normally held substantially in alignment withthe air gaps of said polar projections, a magnetic core arranged between each pair of polar projections, a coil on each core for causing vibrajections, a'vibratory armature normally held substantially in alignment with the air gaps of said polar projections, a magnetic core arranged between each pair of polar projections, a coil on each core for causing vibration of said armature, manually adjustable means for controlling the magnetic eifcct of one or both coils on said-armature, and a diaphragm operatively connected to said armature.

19. In a telephone receiver, a pair of mag:

nets having their like poles arranged oppositely and spaced from each other, a polar projection extending. from each pole, the polar projections of each pair of like poles constituting a bifurcated pole piece having an air gap between the free ends of the projections, a vibratory armature normally held substantially in alignment with the air gaps of said polar projections, a magnetic core arranged between each pair of polar projections, a coil on each core for causing vibration of said armature, manually operable means for varying the reluctance of the magnetic circuits produced by said coils without adjusting the air gaps of said polar projections, and a diaphragm operatively connected to said armature.

20. In a telephone receiver, a pair of magnets having their like poles arranged oppositely and spaced from each other, a polar projection extending from each pole, the

polar pro ections of each pair of like poles constituting a bifurcatedpole piece having "an air gap between the free ends of the projections, a vibratory armature extending lengthwise between the air gaps of said polar projections, an adjustable magnetic core arranged between each pair of polar pro ections, a 0011 on each core for causing vibration of said armature, means for ad 'justing said cores to vary the magnetic effect of said coils on'the' armature, andv a diaphragm operatively connected to said arma- .coil for causing vibration of said armature,

and an adjustable core extending through said coil for regulating the magnetic ell'eci of said coil on said armature independently of. said pole pieces. I

22. lln an electric instrument. a magnet having pole pieces, a vibratory armature operatively associated WltllSLllLl pole pieces, there being an operative air gap between the armatureand the magnet, a coil operatively associated with said armature, a magnetic core for said coil,and means for varying the magnetic permeability of said core independently of said air gap, whereby the movements of said armature do not a'll'ect the adjusted permeability of the core.

23. in an electric instrument, a magnet zvided with a magnetic ly associated with said. armature, a magnetic core for said coil, and means for producing an adjustable air. gap in the core independently of said operative air gap, wherebythe movements of said armature do the adjusted air gap in the core.

24. In an electric instrument, amagnet having pole pieces, an'armature operatively associated with said pole-pieces and separated therefrom by an air gap, and a coil procore consisting of sections Which are relatively adjustable inpieces and said air gap, whereby the movements of said armature have no effect c of said sections.

25. In an electric instrument having a magnet and a movable armature, a coil having a magnetic core, and controllable means for producing an adjustable air gap in said core and malntaining said air gap as ad-;

justed independently of the movements of said armature.

26. In an electric instrument having a movable magnetic armature, a coil provided with a magnetic core consisting of relatively adjustable sections for producing a variable air gap therebetween, andmeans for mounting said sections independently of said armature.

27. In a telephone receiver, a magnet having a bifurcated pole piece, an armature operatively associated with said ma net, a magnetic core between the bifurcations of said pole piece, a coil on said core, and

, means for varying the magnetic permeability of said core to control the magnetic effect of said coil on the flux passing through said bifurcations and the armature.

28. In a telephone receiver a magnet, a movable armature operatively associated with said magnet, a coil for controlling said armature, and adjustable magnetic means arranged outside the normal flux path of said magnet for controlling the "magnetic elfect of said coil on saidarmature independently of the normal air gap between the magnet and the armature.

29. In a telephone receiver, a magnet for maintaining a normal magnetic field, said magnet having pole pieces,'a movable magnetic member operatively associated l w1th said pole pieces, a coil for controlling the operation -of said member, and ad ustable magneticfmeans independent of sa d pole piecesumd said member for controlling the reluctance of the magnetic circuit of said coil.

30. In a loudspeaker, a magnet structure having four pole pieces, like poles being arnot disturb v having pole pieces,

on the adjusted position lever at the junction diaphragm, and an a magnetic bar pair of spaced like poles, separate from the main a coil mounted on each bar I between like poles, whereby the normal field flux does not pass through said coils, and acoustic means operated by the combined action of said magnet and coils.

31. In a' telephone instrument, a magnet one of said pole pieces being bifurcated, an armature operatively associated with said pole pieces, a magnetic core connecting the limbs of said bifurcated polepiece and arranged outside the normal flux path of'said magnet, and a coil SU1'- 32. A telephone instrument comprising a rounding said core.

pair of magnets having their poles arranged oppositely and spaced from each other, a

polar projection extending from each pole,

the polar projections of each pair of like oles constituting. a bifurcated pole piece aving an air gap between thefree ends of the'projections, a vibratory armature operatively associated with said polar projectrons, a magnetic core arranged between each pair of polar pro ections, a coil on each core, and-a diaphragm operatively connected with said armature.

33. In a telephone instrument, a base, a magnet mounted on said base, an armature operatively associated with said magnet, an acoustic diaphragm mounted substantially parallel with said base, a bell-crank lever consisting of a long arm'and a short arm, both of said arms being separate from said armature, means for freely pivoting said securing the free end of said long arm to said diaphragm, and means for connectinr said armature to said short arm, whereby the movements of said armature are transmitted to said diaphragm in increased ratio.

34. In a telephone instrument, a pivoted bell-crank lever consisting of means for conneeting the 'free end of said long arm with said diaphragm, a vibratory armature mounted in a magnetic field and arranged to vibrate in a plane substantially perpendicularto the plane or axis of vibration of said operative connection be tween said armature and the short arm of said lever.

35. In an electric instrument, a magnetic system including an adjustable bar to regulate certain flux values of said system, means for supporting said bar for combined rotary and axial movement to adjust its position relatively to a fixed part of said system, a gear mounted on said bar to rotate the same and thereby cause axial adjustment of said bar, the connection between said gear and said bar permitting axial movement of the of'said arms, means for latter, a worm for operating said gear, and a manually operable member for actuating said worm.

' '36. In an electric instrument, a magnetic system including an adjustable bar to regulate certain flux values of said system, means v forjsupporting said bar for combined rotary and axial-movement to adjust its position relatively to a fixed part of said system, a

member for rotating said bar and therebyv adjusting the same axially,a second member engaging said first member for operating the latter, the engagement between said members automatically locking said bar in adjusted position and positively preventing movement of said bar except through said second member, and means for controlling said second member.

37. In an electric instrument, a base, a magnet mounted on said base, an adjustable magnetic bar associated with said magnet, means for mounting said bar for combined rotary and axial movement relatively to said magnet, a hand-operable rotary member extending throughsaid base and accessible from outside the instrument, and a micrometer. driving connection between said bar and said member for imparting simultaneous rotary and axial movement to said bar in, either direction. y

38. In an electric instrument, a magnet, an armature operatively associated with said magnet, a coil for causing vibration of said armature, a magnetic core for said coil, said core consisting of a fixed section and an axially adjustable section, the. adjacent ends of said sections being respectively in the shape of a conical recess and a conical extension to provide a cone-shaped air gap between said sections, and means for adjusting the second section relatively to the fixed section for varying the Width of said air gap.

39. In an electric instrument having a movable magnetic armature, a coil provided with a magnetic coreconsisting of relatively adjustable sections for producing a variable air gap therebetween, the adjacent ends of said sections being respectively in the shape of a conical recess and a conical extension to provide a cone-shaped air gap between said' sections, and means whereby said air gap is maintained as adjusted independently of the movements of said armature.

etO. In a telephone receiver, a magnet structure comprising a pair of bifurcated pole pieces oppositely arranged, a vibratory armature mounted in operative relation to said polepieces, a magnetic core arranged between each pair of bifurcations so as to be outside the normal flux path of said magnet, a coil on each core for controlling the vibration of said armature, and a diaphragm operated by said armature. f

41. In a telephone receiver, a magnet structure comprising a pair of bifurcated pole pieces oppositely arranged, a vibratory armature mounted in operative relation to said pol'e'picces, a magnetic core arranged between each. pair of bifurcations, a coil on each core for controlling the vibration of said armature, manually adjustable means for controlling the magnetic effect of ,one or both coils on said armature, and a (liaphragm operated by said armature.

421111 a telephone receiver, a magnet structure comprising a pair of bifurcated pole pieces oppositely arranged, a vibratory armaturemounted in operative relation to said pole pieces, a 1nagnctic.core arranged between each pair of bifiu'cations, a coil on each core for controlling the vibration of said armature, manually operable means for varying the reluctance of the magnetic circuits produced by said coils without adjusting the normal air gap between said pole pieces and said armature, and a diaphragm operated by said armature.

43.,In a telephone receiver, a magnet structure comprising a pair'of bifurcated pole pieces oppositely arranged, a vibratory armature mounted in operative relation to said pole pieces, a magnetic core arranged between each pair of bifurcations, a coil on each core for controlling the vibration of said armature, means for adjusting said cores to vary the magnetic effect of said coils on the armature, and a diaphragm operated by said armature. I

44.. In a telephone instrument, a magnet having a vibratory armature, a diaphragm,

a lever mounted between its ends on a-tixed' pivot, one end of said lever being connected to said diaphragm and the other end to said armature, and means for adjusting the effective length of said lever between its pivot and one end thereof to vary the transmission ratio between said armature and said diaphragm.

45. In a telephone instrument, a magnet, a vibratory magnetic member operatively associated with said magnet,- there being an operative air gap between said magnet and said member, a pair-of coils operatively associated with said vibratory member, and a magnetic core for'each coil, the magnetic circuit of each coil having a predetermined fixed air gap separate from said operative air gap.

46. In a loudspeaker, a pair of permanent magnets arranged with their like poles in spaced relation, an iron bar connecting each pair of like poles, a coil mounted on each bar between like poles, so that the normal field flux does not pass through said coils, and acoustic means operated by the combined action of said magnets and coils.

47. In an electric instrument of the telephone type, a magnet structure having rigid pole pieces connected by a pair of magnetic cores, there being a predetermined fixed airlll) ' magnet having a predetermined airgap,

gap 1501' each core to provide a magnetic path of predetermined reluctance through each core,.a coil on each core, and a vibratory magnetic member in operative relation to said pole pieces, the airgaps in said magnetic paths through the cores being independent of the variable airgap between' said pole pieces and said vibratory member.

magnet, pole pieces attached to said magnet in magnetic contact therewith and having means to provide a magnetic path with being of greater permeability than said permanent magnet and including said pole pieces in series, a coil in said magnetic path H between the pole pieces,

i member in operative relation to said magnet and coil.

and a vibratory 49.1n a telephone receiver, a permanent pole piecesof greater permeability than the magnet itself, said pole said magnetic path pieces being in-- magneticcontact with said magnet, a coil associated with said pole piecesior producing a varying flux, means whereby the flux variations occur in a path including said pole pieces and a predeter-Y saidpath'beingout-v mined airgap in series, side the mass of said permanent magnet, and

p a vibratory member controlled by said flux 48. In a telephone receiver, a permanent variations, said independent of said member.' v

50. 'In atelephone-receiver, having a permanent magnet, va polar attachment for said predetermined airgap being the vibratory movements of magnet comprising a, pair of pole pieces con nected by a transverse-magnetic'core carrying a coil, said core within said coil, and a vibratory magnetic memberin operative relation to said magnet and coil, said pole pieces and core forming a variable magnetic circuit of greater permeability than said permanent ma net.

providing an airgap ,ADOLPH AaTHMAS.