US1795948A - Reproducing device - Google Patents

Description

J. 5. :HIGH

REPRODUCING DEVICE March .10, 1931.

Filed July 50, 1927 gsheets-sneet l INVENTOR Jurgen S. /7/' /7 BY I ATTORNEY March 10, 1931.

' J. 5. HIGH 1,795,948

REPRODUCING DEVICE Filed July 30, 1927 2. Sheets$heet 2 INVENTOR Jurgen 5., High ATTORNEY t vice versa.

' I Patented Mar. 10, 1931 um'rso s'rA'ras- PATENT *OFFlCB.

JURJENs. men, or wr'nxmsnune, rmms'xnvnnm, nssmnon. 'ro wnsrmenousn ELECTRIC-8: MANUFACTURING compan A conronn rrou or PENNSYLVANI v REPRODUCIN G DEVICE Application filed July 30, 1927. Serial No. 209,447.

of usefulness in connection with reproducing p devices of the type known as loud speak- 5 ers, it is also applicable to manyother electrodynamic devices designed and intended to translate electrical current, or electrical po- 7 tential variations into mechanical movements or into air-pressure fluctuations and Substantially all'telephone receivers and loudspeakers in common use up to the present time may be divided into three general classes, according to the manner 'in which the p electrical variations are-translated into mechanical movements, i. e., those in which a magnetic diaphragm is directly actuated by an electromagnet, those in which an armature connected to a diaphragm is caused to vibrate by magnetic means and those in which a coil finovin in a magnetic field is connected to a diap ragm to transmit mo- 7 tion thereto.

- Sound reproducers of the last above-men-.

--' tioned type are greatly handicapped by the necessity of providing flexible leads between the moving coil and the source of electrical variations, which eventually break and thus cause trouble.

In his Patent No. 1,167,366, Fessenden 5 previously utilized, thus eliminating the necessity for moving-leads. Although theoretically operable,-the Fessenden device extremely inefficient and fails entirely to meet the exacting demands imposed u n aloud speaker for the reproduction of high-quality music, such as is at present bein recorded on phonograph records and being roadcasted by various radio transmitting stations. a. One object of my invention. acdordingly, is to provide a reproducing device analogous, in some respects, to the device shown in the aforementioned Fessenden patent, in which theefliciency,i. e., the relation of sound-energy output to electrical energy input, is greatly improved.

Another object of my invention is to provide a sound reproducing device of the type points out that a single short-circuited turn may. be substituted for the multi-turn coils referred to wherein neither high nor low frequencies are accentuated in the sound out- The above objects and other incidental and relative thereto, l attain by the utilization of an improved magnetic clrcuit, and by c p providing a moving, short-circuited actuatingelement of a eculiar type to cooperate therewith. Speci cally, my improved magnetic circuit includes a plurality of air-gaps, as 50 distinguished from the single air-gap of priorconstructions. In addition, I have greatly reduced the losses caused by eddy-currents in the magnetic field elements by so laminating the said elements that an extremely high impedance is introduced into the path normally followed bysuch currents.

Among the novel features of my invention are those particularly set forth in the'appended claims. The invention itself, how-7o ever, both as to its organization and its method of operation, together with further objects and advantages thereof, will best be understood from a consideration of. the following description of certain specific embo'd- 15 iments, taken in connection with the accom panyingdrawings,in which: 1

Figure 1 "s a sectional view of one embodiment of my invention in which a permanent magnet is utilized.

Fig. 2 is a sectional view taken alon a line corres onding to the line 11-11 of ig. 1, as seen 'ombelow. 1 .Fig. 3 is a view, partly in section and partly in elevation ,-of afurther modification of my invention. v Fig. 4-is a sectional view taken alon a. line corresponding to the line IV-IV of ig. 3,

1 as seen from below.

individual laminations employed in building up the central pole piece shown in Fig. 5. y

7 is a 1 view of one of the lamination! utilized in the construction of the annular pole piece illustrated in Fig. 5, and

Fig. 8 is a sectional view, taken along a line It corresponding to the line VIH-VIII of Fig. 5, as seen from below, illustrating the manner in which the pole pieces are laminated.

magnetic material is mounted on the extension 4 and is provided with a channel 6 in which is positioned a coil of wire 7 adapted to carry fluctuating currents which are to be translated into air-pressure variations.

The outer ring-shaped extension 3 of the base plate carries a second circular element 8 of magnetic material upon which is mounted,

by means of a plurality of screws 10 or analogous devices, a base plate 11 of non-magnetic material, provided with an extension 12 into which the small end of a horn may be inserted. A light cup 13 of any suitable non-magnetic material is supported with itsedge or skirt 14,

lying in the magnetic field existing bet-ween the circular element 8 and the interioncircu lar element 5 which carries the coil 7. The cup is preferably spun from a sheet of alumim'um, not over 4 mils thick, and is suspended from an annular mounting ring 15 made of soft rubber or analogous material. The-outer edges ofthe suspension ring are clamped between the circular element 8 and the base plate 11. g

The circular element 5 carrylng the coil 7, is magnetized to have one polarity, while the ring .8, carried by the magnetic base plate 1, is given the opposite polarity. If these elements are made of a material such as cobalt steel, a strong magnetic field will exist across the gap between the extension 8 and the flanges of the central circular pole piece 5. The gap may be made extremely small, and, in one actual embodiment of my invention, it was approximately 24 mils.

en analternating current is caused to flow in the coil 7, this coil acts as the primary of a step-down transformer, the secondary of which is the skirt of. the cup 13. The potentials set up, therefore, in the skirt are in such direction as to cause eddy-currents to flow aroundit. 'These eddy-currents, reacting with the fixed magnetic field in which the cup lies, cause the cup to move in the air gap with an amplitude and frequency corresponding to the amplitude and frequency of the exciting current in the coil.

The bottom of the cup is essentially a piston-diaphragm and its motion causes a compressional wave to emanate from the opening in the magnetic base plate 1 in phase with a rarefaction wave emanating from the .vided with a plurality memes phenomenon, which is more apparent at high frequency, the eddy-currents induced in the cup 13 will tend to crowd toward the free edge and toward that portion thereof which merges into the diaphragm portion. The crowding of the current, at high frequencies, away from the mid-section of the skirt into those regions thereof subjected to the densest magnetic field markedly increases the elficiency of the device over similar devices known to the prior art. Inasmuch, however,

as the uneven distribution of the eddy currents is the more pronounced the higher the frequencies involved, the device tends to some extent to accentuate the higher frequencies at the expense of the lower, notwithstanding the fact that the Foucault, or eddy-current losses in the pole pieces increase as the frequency is raised. 3

A fair balance between the response to high and low frequencies may be obtained by properly'laminating the pole pieces in the manner clearly shown in Fig. 2, but, in spite of this precaution, the device, as shown in Fig. 1, is very apt to be preferentially responsive to high frequencies. r a 4 In order, therefore, to provide a device which is inherently capable of giving an even response over a wide range of excitation frequencies, I have added an additional air gap tothe magnetic circuit illustrated in Fig. 1, and have so positioned this additional air gap that the permanent flux thereacross cooperates with eddy-currents induced in the cup at low frequencies. A further modificat1on of my invention is illustrated in Fig. 3.

Referring specificially to Fig. 3, a central pole piece of cold-rolled steel has afiixed to one end thereofa core 21 of nickel-iron alloy by means of a bolt 22 which passes through the bottom of an opening 23 in the coreand is threaded into an opening 24 in the pole piece. The core is preferably proof radial saw-cuts, as shown in Fig. 4. v A circular collar 25 of non-magnetic material, such as brass or bronze, encircles the core 21 and is retained thereon by a set screw 26.. The collar 25 carries an annular polepiece assembly which comprises a plurality of discs 27, 28 and 30, preferably made of a 'nicket-iron alloy, and having aligned central openings through which the core" 21 extends. Those portions of the discs immediately adjacent to the central core are provided with radial saw-cuts, as shown in Fig. 4..

The disc 27 has a portion 31 thereof offset from the disc 28, and thedisc 30 also has a central offset portion 32. The annular space between the ofiset portion of the disc 27 and the central disc 28 accommodates a coil 33, while a similar annular coil 34 is positioned in the space between the offset portion of the disc 30 and the central disc. Thesecoils are are tensioned toward each otherby a plural-' ity of bolts 44. The long ends 45 and 46 of electrically connected in series-aidingrelation and are designed to carry. the currents representing sound frequencies. The assembly of discs may be. held together bya plurality of bolts 35,as shown,'and the entire assembly is held in position on the collar 25 by a plurality of similar bolts 36. The air gap between the core 21 and the inner edges'of the discs 27, 28 and 30 is made extremely small and may be of the order of 5 mils. The magnetic circuit is completed through two L-shaped permanent magnets 37 and 38,

made preferably of cobalt steel, and rectangular in cross section. The short ends 40 and 41 ofthe magnets are held in contact with one end of the central pole piece 20 by means of. a plurality of collars 42 and 43, which the permanent magnets abut the inner disc 27 of the ole-piece assembly and are main,- tained in rm contact therewith by the action of a plurality of set screws 47 carried by a non-magnetic bridge-member 48 which is af-. fixed to the end of the pole piece by means ofa plurality of screws 50. The collars and the tie rods are of non-magnetic material.

The discs comprising the annular polepiece assembly are preferably made of a nickel-iron alloy and are laminatedv as illustrated in Fig. 4, and a diaphragm housing device 51 of non-magnetic material, provided with an extension 52"uponf which a horn may be mounted, is afiixed, by a plurality of bolts 53, to the pole=piece assembly. The diaphragm housing comprises a circular element 54 which is held directly in contact with the pole-piece assembly and a second circular element 55 clamped thereto by a plural-- .ity of screws 56. A diaphragm is held between the two elements, pressure thereon 'being exerted by the screws 56.

The diaphragm 57 carries a cylindrical element 58, preferably spun from aluminum having a thickness not appreciably greater than 4' mils. The element'58 encircles the central core and lies in the air gaps deter mined by the inner edges of the pole-pieceassembly discs. -The cylindrical element is attached to the diaphragm by a plurality of integral extensions 60, which are so proportioned as to inter-pose a definite amount of compliance between'the diaphragm and the said cylindricalmember.

Inorder that the cylindrical member may be accurately centered in the air gap, the holes in the diaphragm housing element 54, through which the bolts 53 extend, are purposely made somewhat larger in diameter than the said bolts, thus permitting the diaphragm housing to be shifted laterally with respect to the pole-piece assembly, before the bolts 53 are tightened. The centering operation may be easily accomplished while the device is being first assembled, or while itis in operation later,-by merely loosening the screws 53 and moving the diaphragm housing until any audible rattles or scraping sounds disappear. it is preferable to energize the device by a relatively low-frequency current of high amplitude, in order that any defects in the centering may be detected.

The magnetic circuit for the flux set up by the current variations in the coil 33-34 may 'be traced from the inner edge of the disc 27, through the adjacent portion of the central core 21 and back through the inner edge of the disc 30. The inner edge of the central disc is not subjected to flux variations caused by the current in the coil, and con rents, at lowfrequencies, which are not so.

crowded toward the ends of the cylindrical element, react with the flux across the gap In the initial assembly,

between the central disc 28 and the core and are, consequently, equally as effective as the high-frequency currents in causing motion of the cylindrlcal elements. Y

The complete embeddingof the actuating coil in the pole-piece, as distin ished from the manner in which this. coil is mounted according to the aforementioned patent to Fessenden, results in a decided increase in the efliciencypf the device. Such construction also permits a very decided reduction in the widthlof the air gap, which not only tends to reduce the leakage flux, but also permits the permanent flux to moreefiiciently "react with the eddy-currents induced in the cylindrical element.

By providing a plurality of spaces in which the primary or actuating coil may be wound, the reluctance of the magnetic circuit which carries the flux induced by the varying current in this coil is greatly reduced, and, at the sametime, the reluctance in the fixed magnetic circuit is also diminished. In addition, the provlsion of one set of air gaps to cooperate with those portions of the cylindrical element which carry. the major portion of the eddy-currents at high frequency and another air gap to cooperate with that portion of the cylindrical element which carries the currents at low frequencies results in a device which neither accentuates the high nor the low frequencies.

I have also found itfeasible to further increase the sub-division of the air gap and the actuating coil, but the improved results obtained do not seem to be commensurate with the additional expense involved.

Instead of providing the solid central core and the circular disc-shaped pole pieces with radial saw-cuts to minimize losses caused by eddy-currents, it is possible to construct the said pole pieces from a plurality of laminations in much the same manner as the armature of an electric motor is constructed. As an example of this type of construction,

, reference should be made to Figs. 5 and 8,

which illustrate only the magnetic element thereof, the diaphragm housing, the diaphragm and the cylindrical diaphragm-actuating element being omitted therefrom.

Referring specifically to Fig. 5 a central pole-piece 65 of magnetizable material carrying a magnetizing winding 66, is mounted in the interior of a cup-shaped element 67, also made of magnetizable material, and is held in position by means of a bolt 68. The end of the pole-piece opposite the end that is in contact with the cup-shapedqelement is provided with an axialopening in which are radially positioned a plurality of laminations 70 shaped as shown in Fig. 6, which laminations are separated one from another, by insulating material and are held in position by a metallic wedge 71.

' A non-magnetic spacer disc 72 is mounted on the pole-piece immediately adjacent to the portion thereof which carries the laminations 7 0, and interposed between this disc and the cup 67 is a ring 73 of magnetic material provided witha channel 74 concentric with the opening in the central pole-piece. A plurality of laminations 75, shaped as shown in Fig. 7 and made of magnetizable material, are arranged radially of the central pole piece, the inner ends thereof being spaced a slight distance therefrom, and a portion of the'outer ends lying in the aforementioned channel 74. The laminations 75 are clamped firmly between the ring 73 and a similar ring 76, a plurality of tie-bolts 77 serving to hold the assembly of rings and lamination's together.

Each of the laminations 75 has a'plurality of extensions 78 which, when the said lami nations are arranged radially, as shown in Fig. 8, constitute the boundaries of circular grooves adapted to receive and hold the portions of a winding 80 through which the currents representing sound-frequencies may be passed.

The. exact contours of the laminations and 78 are not material, it being entirely feasible to so modify them that they may be stamped or punched from fiat sheets with less waste than the forms shown byway of illustration.

My invention is mainly advantageous in that it enables the provision of a loudspeakerof the eddy-currenttype that has an even response to a Wide range of actuating frequencies. Further, by laminating the pole pieces and by imbedding the speechwinding therein I have greatly reduced the attendant losses, and have produced a loudspeaker that has a high degree of efficiency.

Although I have illustrated and described only a few specific embodiments of my invention, numerous obvious modifications thereof will be suggested to those skilled in the art. -My invention, therefore, is not to be limited except in so'far as is necessitated by the prior art, and by the spirit of the appended claims. 1

I claim as my invention:

1. In reproducing apparatus, a magnetic ,circuit comprising a pole in the form of an inner core, a second pole having more than two annular portions surrounding the inner pole and forming therewith more than two air-gaps, and a cylindrical movable element fitting over said inner pole and lying partially in said air-gaps.

2. In reproducing apparatus, a magnetic circuit comprising a pole in the form ,of an inner core, a second pole having more than two annular ortionssurrounding'the inner pole and orming therewith a plurality of annular air-gaps, a cylindrical movable element fitting over said inner pole and lying partially in said air-gaps, and a continuous coil of wire comprising sections completely imbedded in the annular spaces between said annular portions.

3. In reproducing apparatus, a magnetic circuit comprising apole in the form of an inner core,'a second pole having more than two annular portions surrounding the inner pole and orming therewith a plurality of annular air-gaps, a cylindrical diaphragmactuatin element fitting over said central pole an lying partially in said air-gaps, re-

silient supporting means for said element, and

inner cylindrical core, and a second pole having annular portions surrounding and projecting toward the inner pole and forming therewith a plurality of air-gaps, the said annular portions being radially laminated.

6. In reproducing apparatus, a magnetic circuit comprising a pole in the form of an inner cylindrical core, and a second pole having annular portions surrounding and projecting toward the inner pole and forming therewith a plurality of air-gaps, both said inner pole and said annular portions being radiall laminated, whereby the circulation of ed y-currents therein is impeded.

7. In reproducing apparatus, a magnetic circuit comprising a pole in the form of an inner core, a second pole having annular portions surrounding and projecting toward the inner pole and formin therewith a plurality of air-gaps, both 0? said poles being radially laminated, andv a plurality of annular coils of wire imbedded in the annular spaces between said annular portions.

8. In apparatus for sound reproduction, a cylindrical metallic diaphragm-actuating element, a diaphragm, and a plurality of independent connecting devices between said diahragm and said element, said devices each having an axially rigid portion and a portion flexible in the direction of movement of said diaphragm.

9. In apparatus for sound reproduction, a cylindrical metallic diaphragm-actuating element, a diaphragm, and a plurality of devices connecting said element and said diaphragm, said devices extending substantially axially of said element and each having an axially rigid portion and a flexible portion.

10. In apparatus for sound reproduction, a cylindrical metallic diaphragm-actuating element, a diaphragm, and a plurality of devices connecting said element and said diaphragm, said devices-being integral with said element and extending axially thereof, each of said devices having an axially rigid portion and a flexible portlon.

11. In apparatus for sound reproduction, a cylindrical metallic diaphragm-actuating element, a diaphragm, and a plurality of independent devices connecting said element and said diaphragm, said devices each comprising a portion extending axially of said element and a portion extending perpendicw' larly to the axis of said element, whereby the connection between said element and said dlaphragm may be given a predetermined amount of resiliency.

In testimony whereof, I have hereunto subscribed my name this 23rd day of July 1927.

.JURJEN s. HI

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