US2672525A - Sound translating device with resonating and damping chamber - Google Patents

Description

March 16, 1954 c, PYE 2,672,525

SOUND TRANSLATING DEVICE WITH RESONATING AND DAMPING CHAMBER Filed June 16, 1950 2 Sheets-Sheet l INVENTOR. HAROLD C. PYE

ATTORNEY H. c. F'YE NG DEVICE WITH RESONATING March 16, 1954 SOUND TRANSLATI AND DAMPING CHAMBER 2 Sheets-Sheet 2 Filed June 16, 1950 FIG. 5

26o 460 c lo'oo zo'o o 40'00 INVIISQ'TOR U "A e req ency yc es per 5 con BY Z O u n w 0 o m m w 8 82:22 0 303 22:80 E 2:32,... .ucaom ATTORNEY Patented Mar. 16, 1954 SOUND TRANSLATING DEVICE WITH RESO- NATING AND DAMPING CHAMBER.

Harold C. Pye, Oak Park, 111., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application June 16, 1950, Serial No. 168,630

Claims.

The present invention relates in general to sound translating devices and methods of making the same and moreparticularly to improvements in telephone receivers of the permanent magnet type and methods of making the same.

It is an object of the present invention to provide an improved sound translating device which is of extremely simple, economical, light weight, and rugged construction, is compact in arrangement, and is eflicient in operation.

It is another object of the invention to provide an improved sound translating device which has a uniform frequency response over a greater range than heretofore.

In general, the objects as set forth above are in part attained in accordance with the present invention by providing a sound translating device which includes a plastic cup shaped housing; two pole pieces, the ends of which are molded into the housing; a permanent Alnico bar magnet separating the pole pieces and completely molded or rather imbedded in the housing; a diaphragm; a front resonating chamber so constructed and dimensioned that its natural acoustic resonating frequency is approximately 4000 cycles per sec- 0nd; and a damping means in that front chamber for decreasing the peak amplitude at that natural frequency. Briefly explained, the frequency response range is first extended by effecting a natural resonant peak at 4000 cyclesand then by flattening the natural peak ordinarily produced by such resonance, the response curve is made practically uniform from 200 to 4000 cycles per second.

A feature of the improved sound translating device is the arrangement of the permanent magnet within the plastic housing such that magnetization may be accomplished after the complete assembly of the receiver unit; thus eliminating foreign magnetic particles within the field structure that may be attracted during the assembly of a magnetized bar magnet.

Other objects and features will be evident and a com lete understanding of the construction and operation may be had from a perusal of the description in conjunction with the accompanying drawings, in which:

Fig. 1 shows a side sectional view of the sound translating device taken along the line AA of Fig. 2.

Fig. 2 shows a bottom elevational view of the device with a diaphragm assembly removed therefrom.

Fig. 3 shows a top view of the plastic housing.

Fig. ,4 shows a side view of the plastic housing.

Fig. 5 shows a sectional side view of the plastic housing taken along the line BB of Fig. 3.

Fig. 6 shows an exploded View illustrating the method of assembling the device shown in Fig. 1.

Fig. 7 is a typical graph showing the extended frequency response range of the improved sound translating device.

Referring now more particularly to the drawings, there is illustrated a sound translating device in the form of a telephone receiver which includes a shield I formed from a magnetic sheet metal, such as steel, which acts as a magnetic shield for the device. Any extraneous foreign unwanted signals present will be prevented from interfering with the sound translation by means of this shield; and conversely, the flux produced by the magnetic field structure itself will be pre vented from influencing any other magnetic devices in proximity with the sound translating device. The cup shaped plastic housing 2, which, of course, could be constructed of any non-magnetic conductive material, is molded with the permanent magnet 3, preferably made of an aluminum nickel cobalt alloy having a coercive force greater than 500 oersteds and a remanence greater than 10,000 gausses, imbedded therein. T-shaped pole pieces 4 and 5, preferably made of Allegheny electric metal, are also partially (the tops of the Ts) imbedded in the molding operation and are located one on each side of the permanent magnet 3 in a parallel relationship. The lower portion of housing 2 flanges out and forms a smooth annular ring 6 for providing a bearing surface for receiving diaphragm 5. Housing 2 also has scooped out recess portions 8 and 9 for enabling th magnetization of permanent magnet 3 after the device has been. assembled, but before the shield is attached. Fig. 1 illustrates this feature quite well as it can be seen that magnet 3 is accessible for a magnetizing operation any time until the shield I is affixed. Terminal assemblies [0 and II, preferably constructed of brass and also molded within housing 2, provide connecting points for th two leads coming off the coils I2 and l3 as illustrated in Fig. 2. Holes l4 and l 5 in housing 2 are provided in order that the cord tips of the two leads (not shown) extending to the receiver can be inserted to effect the connection in a simple operation. This feature is best illustrated in Fig. 5 where it can be seen that a cord tip inserted into hole It will make connection with terminal l0 and, of course. one side of the coil. Holes l0 and I! are provided in order that set screws may be inserted to anchor the cordsin place. Rectangular opening H3 in the housing 2 is provided in order that an anchoring means for the cords may be attached for transferring the burden of the cord strain from the terminals. The magnetic field of the structure thus comprises the two pole pieces 4 and upon which the coils l2 and [3 of the receiver arepiwound andh a permanent magnet 3 which, inconjunction with the diaphragm] and the pole pieces 4 and5, forms a substantially closed magnetic circuit interrupted only by the narrow air gaps extending between the pole iacesa of the pieces 4 and 5 and the diaphragm]. The

coil winding i2 is wound upon the pole piece 5 between winding heads 31 and SS; constructedof insulating material, and is insulated--from- -the'= pole piece 5 by a layer of insulating material 41 which may, for example, comprise \varnishedm tion to the diaphragm 1, "aninner" plate ifly a clamp plate 28min annularasupporting andspace ring 2|, an assembly ring 22'; and a front cover 25, constructed of Bakelite in thewpresent em bodiment-,- witha i-fibrous damping member il i afilxedtheretos- The clamp .plate zllqis provided with a projecting.annulariportionzmt having a smooth upper surface=which is adapted to cooperate with the oppositely disposed lower surface ot the annular ring portion 6 of the housing-2 to clamp the peripheral n edge. of the diaphragm 'r'l therebetween. The'clamping surfaces ofthgtwo annular portions 6 and M-areso formed that :the-

peripheral edge of:the"diaphragm] is clamped-v therebetween with uniformpressure at all points aroundthe outer circumference ofthediaphragm.

Front cover 251*has a clamping"ring tlcmadeof aluminum in the presentembodiment, molded into the Bakelite with theaid o'fsix 'loondinev holes l 34, :and provides :a projecting ring for crimping in order to hold said cover in place-as illustrated in Fig: 1. Inaccordance with one-feature of the invention, the inner plate 19, in conjunctionzwith" the diaphragm l and the annular-ringfi, defines:

a damping chamber adjacent the: inner surface of the diaphragm -I, while theclamp plate 20,2 in" conjunction with the diaphragm"! 'andu'front cover 25with damping member 26;: a souncbabe sorbent 'felt washer i-n thezpresent embodiment defines-a resonating chamber adjacent the outer surface of the diaphragm l. The dimensions of thedampingchamberuand of therestricting passages communicating therewith are so proper-i tioned that the peak ain the' response charactei isticof the device causedrby the' natural periodof vibration of the diaphragm T is substantially;

r so characteristic of the .device.- 'More particularly;

reduced to flattenit-he overall frequency'response the inner plate l9; whichis constructedof nonmagnetic material, such, for example, as aluminum, is providedewithithree openings is and-has: mounted thereon in spacedapart relation a. hat;

annularwring Zhwhich defines a relatively long,

narrow, restricted and annuIar passage-2! "com-- municating between the interior of the housing 2 and the chamber-formed by the inner plate l9 and the-diaphragm I; By suitablyiproportioning the size of the holes23yaand the length'andwid-th i of the restricted passage 21; thereis achieveclthe desireddampingrr: efiect over. the 'rband gOf .:.frc'- quencies within which the natural period oi "vie braliionrof i-thewdiaphragm :1 is most i effective to Inches Diameter ofachamber 1.688 Depth of chamber .020

Diameterof -holesrfl .076 Depth of passagezl .003 Widthof ring 24".; .319 Outer-diameter{ofaring 24 1.444

Theiinner plate l9 has formed therein a pair of slots 30 and 3| through which the pole face ends of-t-he polepieces '4 and 5 extends A cross slot 32 connecting, thetwo' slots 3ll and :3 l \is also provided A for preventing: the circulation ,of eddy currents in the inner-plate l9. The dimensions of the slotswv 3E) and 3| aresubstantially greater thanlthe cross sectional dimensions of-ithec-polet-face ends .oi the *pole: piecesl and 5 so thatrelatively larger, airxgaps are provided between the a-djacentisur-t. faces of the: polepieces andzthei innemplate 19. A By virtue of this-arrangement.theacouplingibem tween themagnetic circuit ofsthe magnetic field structure and the-inner plate 19 is extremely loose and the production of. eddy currents in ithetplate is substantially prevented.

The front "cover 2 5, which, :in conjunction with the diaphragm- 1, damping. memberiZBHand clamps, plate 20, deflnesia resonating chambenfadjacenta the outer surfaces of .the .diaphragm is provided with six passages or,.ho1es 28 sthroughwwhich," sound waves are transmitted from. .tha resonating chamber. to the exterior of ..the ...device..... In.(ac1.., cordance with another .feature, of the. invention, the dimensions of this frontpresonating chamber and of the passages 28 .are .so .proportionedithatn the naturaliperiodof ivibrationiotthe chambers occurs at approximately..4,000 cycles pe seconds;

whereby theresponse of themovinglsystemis mar.. terially, enhancedat frequencies in that regional, However, in order to reduce the actualipeak, or-M dinarilyi produced. at the natural ,frequencyiof .a w resonating chamber vandlthus. in effect flatten .the i n response ,curve in thatcregion, damping member .i

26 utilized; To achieve this greater. and more uniform response in the frequency region indicate ed,, it has ,beenifoundi. thatthe. following. dimensionswfor (theiresonating chamber and theipasm sages 72B are satisfactory:

Inches.

Outer. diameter, of chamber. adjacent tdiae phragm 1.688; Maximum depth of chamber .093 Diameter of each passage 28, ,.102 Depthiofeachflpassage 28 ,.050"

Insjidecdiametcr, of dampingrmember 26 Ire .625 0utside.,dia rneter. of clamping member 2.6 ,1.188f Depth of damping member 265.1. .050-

In constructing the device described aboveythe plastichousing 2 is, of course, flrs't'formed with magnet 3 andpole'wpieces 4 and 5' moldedthereimc The coils l2 and I3, connected in series at point: 36 :(Fig. 2) with their associated swindingf heads 31, 38,? 39 "and 40,: are "then *-*inserted: over epolex; pieces '5 and 4 and cemented to the housingnt. 2 The" two'i remainingrdeads :irom isaid pole lpiedes arcrsoldered to terminals iln andxl l."- 1' Artu -this field structure assembly is completed the diaphragm assembly is mounted upon the rim of the cup shaped housing 2. To this end, the inner plate [9 is forced within the snugly engaging side walls of the annular ring 6 to abut against surface 35 of housing 2 and cemented to winding heads 31 and 30. This operation is [performed with the flat annular ring 24 mounted upon the inner plate ill, by means of rivets and washers, and during the performance thereof the pole face ends of the pole pieces 4 and 5 pass through the slots 30 and 3! provided in the plate 19. The next step in the construction of the device is to clamp the diaphragm 7 between the clamping surfaces of the two ring portions 6 and 29 pro- .jecting respectively from the housing 2 and the clamp plate 20. While the diaphragm is clamped in position, the assembly ring 22 with the annular ring 25 inserted or telescoped therein is telescoped over the clamp plate 20 until the flange portion 44 thereof engages the tapered surface of the clamp plate 20, following which the rim of the assembly ring is bent or crimped over as indicated at 45 to engage the diaphragm assembly rigidly secured to housing 2. The next step in the construction of the device is that of magnetizing the magnet member 3 by positioning this 'member in a strong direct magnetic field. After the device is fully constructed shield l is placed over housing 2 and front cover 25, with damp- 3 arranged in the manner set forth above, an attractive force is normally exerted upon the diaphragm 1 by virtue of the flux produced in the magnetic field structure by the permanent magnet 3. When incoming signal current traverses the coils l2 and I3, the steady state flux is increased and decreased in the usual manner in accordance with the undulations of the signal current. The variations in the flux traversing the diaphragm 1 cause this diaphragm to vibrate in the usual manner so that sound waves are transmitted by way of the passages 28 to the exterior. The provision of the inner damping chamber defined by the plate l9 prevents an excessive response of the diaphragm l at frequencies approaching the natural frequency of vibration of the diaphragm-approximately 1,000 cycles per second. Also, the provision of the front resonating chamber, with the damping means, defined by the cover 25 enhances the response of the moving system at frequencies in the upper .7

portion of the operatin range-approximately 4-,000 cycles. Thus, a substantially flat response characteristic, as illustrated in Fig. 7, typifying good fidelity of reproduction, is obtained.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made herein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

Having described my invention in detail, what I claim and desire to have protected by issuance of Letters Patent of the United States is:

1. In a sound translating device, a housing, a

diaphragm mounted within said housing, said diaphragm having a predetermined response characteristic over an operating frequency range when mounted within said housing for substantially free vibration, said diaphragm also having a natural frequency of vibration such that said response characteristic peaks at frequencies in the low frequency end of said range, an inner plate mounted within said housing and displaced from said diaphragm to define a first chamber adjacent the inner side of said diaphragm, means comprising a second plate mounted upon said inner plate in spaced apart relation for defining a passage communicating with said first chamber, the spacing between said plates being so proportioned that said first chamber acts substantially entirely as a damping chamber effective to remove said peak from the response characteristic of said diaphragm at frequencies in the low frequency region of the range, means defining a second chamber adjacent the outer side of said diaphragm having a, passage communicating therewith, the dimensions of said last-mentioned passage being so proportioned that said second chamber acts substantially as a resonating chamber effective to peak the response characteristic in the high frequency region thereby increasing the range, and damping means comprising a sound absorbing member within said second chamber rigidly mounted at a distance from said diaphragm for removing said peak in the high frequency region thus effecting uniform response over a greater range of frequencies.

2. In a sound translating device, a housing, a diaphragm mounted within said housing, said diaphragm having a predetermined response characteristic over an operating frequency range when mounted within said housing for substantially free vibration, said diaphragm having a natural frequency of vibration such that said response characteristic peaks at frequencies in the low frequency end of said range, an inner plate mounted within said housing and displaced from said diaphragm to define a first chamber adjacent the inner side of said diaphragm, means comprising a second plate mounted upon said inner plate in spaced apart relation for defining a passage communicating with said first chamber, the spacing between said plates being so proportioned that said first chamber acts substantially entirely as a damping chamber to remove the low frequency peak from the response characteristic of said diaphragm and substantially to decrease the response of said diaphragm at frequencies within a band of frequencies extending from a frequency of the order of 1500 cycles per second toward the low frequency end of said range, a front cover for said device in spaced apart relation with said diaphragm to substantially define a second chamber adjacent the outer side of said diaphragm, an opening in the central portion of said cover communicating with said second chamber, said opening being so dimensioned and proportioned that said second cham- K ber resonates and increases the response of said diaphragm at frequencies within a band of frequencies extending from a frequency of the order of 3200 cycles per second and such that the response characteristic peaks at a frequency of 4000 cycles per second, and a sound absorbing annular damping member mounted on the inner side of said cover and completely removed from the diaphragm for removing the high frequency peak thereby effecting a uniform response up to 4000 cycles per second.

v3. In arsound; translating, device, a molded housing having a-magnetic field structure includi ngla. bar magnetand apair of pole pieces molded intb; the rear, section thereof, said pole pieces projecting into the interior of said housins coils housing, adjacent the pole faces of said bar magnet to facilitate magnetization of said bar magnet after the formation of-said sealed chamber.

4,; In a sound translating device. a molded bersalso molded intothe rear section of said l m siitg,- coilsr; mounted on said pole pieces and electrically connected to said terminal members,

a diaphragm structure and a front cover secured .tothe open end of said housing in spaced apart relation to form a sealed chamber to the rea of diaphragm structure and a resonating chamberforward of said diaphragm structure, exter nal recesses insaid housing on oppositesides of saidbar magnet to facilitate magnetization thereof after the formation of said sealed chamber in order to prevent adherence of magnetic particles to said field structure during the as- ,8 .sembling, and externaltrecesses in said. housing on two sides of said terminal members toperm it access thereto for: connections to, said coils.

5. In asound tr'ansiatingdevice as claimed in claim 4, a magnetic shield enclosingsaid housing for preventing externalelectrical interferences from influencing said field structure and to preventthe flux produced by said magnetic :field structure from: influencingother external, devices in, proximity thereof.

Referencesfiited in the file ofthis patent UNITED STATES PATENTS Number Name Date;

1,415,361 Jones May 9, 1922 1,718,351 Gruber June 25, 1929 1,847,702 Thuras Mar. 1,1932 2,110,908 Hartman Mar. I5, 1938 2,187,236 Hansdorf Jan. 16,, 1940 2,205,669 Pye June 25,1940 2,205,670 Pye June 25,1940 2,298,765 Horlacher Oct. 13, 1942 2,423,014 Gilman June 24, 1947 2,431,022 Brodie N 0V. 18,1947 2,458,158 Gilman Jan. 4, 1949 2,496,483 Massa Feb. 7', 1950 F0REIGN- PATENTS Number Country Date 491,509 Great Britain Sept'j5', 193B

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