US2524297A

US2524297A - Method of manufacturing loud speakers

Info

Publication number: US2524297A
Application number: US727566A
Authority: US
Inventors: James P Quam
Original assignee: QUAM NICHOLS Co
Current assignee: QUAM NICHOLS Co; QUAM-NICHOLS Co
Priority date: 1947-02-10
Filing date: 1947-02-10
Publication date: 1950-10-03
Anticipated expiration: 1967-10-03

Description

Oct. 3, 1950 J. P. QUAM 2,524,297

METHOD OF MANUFACTURING LOUD SPEAKERS Filed Feb. 10, 1947 4 Sheets-Sheet .l

J mes Fflua r11.

fl Z arr-14? 5/.

06L 3, 1950 J, QUAM 2,524,297

METHOD OF MANUFACTURING LOUD SPEAKERS Filed Feb. 10, 1947 4 Sheets-Sheet 2 Jmaj I? flan/777.

jzlfor'rvgy.

Oct. 3, 1950 J. P. QUAM 2,524,297

METHOD OF MANUFACTURING LOUD SPEAKERS Filed Feb. 10, 1947 4 Sheets-Sheet s .74 mes Euam flfforng.

Oct. 3, 1950 J. P. QUAM 2,524,297

METHOD OF MANUFACTURING LOUD SPEAKERS Filed Feb. 10, 1947 4 Sheets-Sheet 4 JZmas Pflqam.

JI liar/1g Patented Oct. 3, 195% METHOD OF MANUFACTURING LOUD SPEAKERS James P. Quam, Chica go, 111., assignor to Quain- Nichols Company, Chicago, llll., a corporation of Illinois Application February 10, 1947, Serial No. 727,566

11 Claims. I

The present invention relates to sound reproducers and more particularly to a method of manufacturing sound reproducers of the electrodynamic or moving cell type in which the coil is disposed so as to be freely movable in an annular field associated with a permanent magnet.

Substantially every modern radio receiver includes a sound. reproducer generally referred to as a loud speaker or speaker. There are on the market today many radio receivers which are quite inexpensive and which are sold in a highly competitive market. To make possible the sale of such receivers at such relatively low prices, it is essential that the cost of the loud speakers employed therewith is maintained at a minimum. However, such low cost speakers are still required to give very satisfactory operation. One of the problems in manufacturing loud speakers or sound reproducers of the type mentioned above employing a permanent magnet is that of providing suitable facilities for rigidly assembling the permanent magnet of the field structure of the speaker with the other parts thereof in a manner so as to produce efllcient operation and also to assure a satisfactory annular gap for the movable voice coil. Functionally, such facilities must providefor uniform metal-to-metal contact between the magnet pole faces and the abutting surfaces of the field members without any intervening non-magnetic material in order to assure operation at maximum efficiency. In addition, no displacement of the parts relative to each other even when subjected to heavy jars must occur. The elimination of relative displacement'between the field structure parts is of particular importance in structures where the permanent magnet supports a pole piece defining one pole face of the gap, which structures are commonly employed in speakers of the type used in inexpensive receivers, for in such speakers displacement between the field structure parts results in an intolerable distortion of the air gap dimensions;

In view oi the above discussion, it will be apparent that assembly facilities for manufacturing such loud speakers or sound reproducersmust low cost per se and. must be such as. to the use of low cost methods of assembly minimum number of machine opera one of the structure parts- This is p2 ticulariy true of the permanent magnet which gen lly 'ses. a. cylindrical barmagnet :formed of a very. brittle. alloy which. is very difficult to inachina. Generally the. two. end surfaces of the bar. magnet are precisionground.

Ll J

The field structure of such loud speakers generally comprises a pot or magnet housing and a pole piece. In manufacturing the speaker it is desirable to unite in a rigid manner one ground face of the magnet with a fiat precision ground surface of the magnet housing and also to' unite in a similar manner the other ground face on the magnet with a flat precision ground face on the pole piece.

At the present time, there are several different methods employed in rigidly uniting such permanent magnets to the rest of the fieldl structure of sound reproducers of the type referred to above. It has been suggested to pass a bolt through the magnet housing and magnet into threaded engagement with a tapped hole in the pole piece. This is quite uneconomical because permanent magnets employed in speakers are manufactured by many sources today as stock items without an opening for a bolt, and the procuring of magnets with a cored hole therethrough would considerably increase the cost of the magnet and consequently, would increase the cost of the loudspeaker so asto produce a. noncompetitive device.

It has also been suggested to employ are welding to weld the permanent magnet to the. field structure. This is particularly expensive from the manufacturing standpoint and is unsatisfactory from a salvage standpoint since if the welding operation is done incorrectly so that the pole piece is not centered, it is substantially impossible to salvage the field structure ofthe speaker which will be brought'out' in greater detail hereinafter.

It has also been suggested to employ a. solder foil positioned between the ends. of. the magnet and the pole piece and magnet housing respectively, which solder foil is subsequently melted by induction heating. or the like. Since solder is non-magnetic, however, and the efficiencyof the magnetic stnucture dependsupon the magnet being in almost perfect contact with the magnet housing and pole piece-without intervening solder, this method: although of relatively low' cost, is generally found to be unsatisfactory froman efiicienoy standpoint.

A fourth method has sometimes beenlemployed in which the permanentmagnet is cemented: to the magnet housing and pole piece; The cost of this cementing operation is relatively low' but by virtue of the fact that most cements have the property ofcontinuing to shrink over a period of time, there is a tendencyforthe cement to pull away from those parts which it is intended permanently tocsecures In add-itibn,-ce-

ments are not stable and are affected by humidity, weather conditions and the like, so that this method is generally not satisfactory.

Accordingly, it is an object of the present invention to provide a new and improved method of manufacturing sound reproducers of the abovementioned type overcoming the various disadvantages encountered in the prior art methods enumerated above.

It is another object of the present invention to provide a new and improved method of manufacturing loud speakers employing exceedingly simple facilities whereby manufacture of a loud speaker at a very low cost is made possible.

Still another object of the present invention is to provide an improved method for rigidly securing a substantially non-machinable loud speaker field magnet to other parts of the speaker field structure.

It is a further object of the present invention to provide a new and improved process of manufacturing a sound reproducer whereby an improved field structure is obtained of compact and rugged construction which is exceedingly simple 'to manufacture and which is very eiiicient in operation.

Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the present invention, reference may be had to the accompanying drawings in which:

Fig. l is a side View of a sound reproducer or loud speaker manufactured in accordance with the method of the present invention;

, Fig. 2 is a sectional view of the loud speaker of Fig. 1 showing the detailed constructional features thereof;

Fig. 3 is a sectional View similar to Fig. 2 of a sub-assembly of the sound reproducer of Fig. 1 essentially comprising the field structure thereof; Fig. 4 is an exploded perspective view of the parts of the sub-assembly of Fig. 3, together with various elements employed in maintaining this sub-assembly in assembled condition during several steps of the manufacturing process of the sound reproducer.

: Fig. 5 is a sectonal view somewhat similar to Fig. 3 of the sub-assembly embodying the magnetic field structure during one step in the manufacturing process thereof following assembly of the various parts thereof shown in Fig. 4; Fig. 6 is a somewhat schematic view illustrating a series of steps in the manufacturing process of the sub-assembly of Fig. 3;

Fig. '7 is an enlarged sectional view substantially taken on line l--? of Fig. 6 of a portion of the appaartus shown in Fig. 6 employed in the manufacture of a sound reproducer in accordance with the present invention; and

Fig. 8 is an enlarged view of another piece of apparatus illustrated schematically in Fig. 6 and employed in one of the steps of the process of the present invention for manufacturing sound reproducers.

In order better to understand the manufacturing process or method of manufacture comprising the present invention, reference may first be had to Figs. 1 and 2 of the drawings which show the structural details of a sound reproducer or loud speaker manufactured in accordance with the present invention. As illustrated in Figs. 1 and 2, this sound reproducer or loud speaker generally designated as [0 is of the well known dynamic type extensively used in radio receivers of modern. construction. The loud speaker It] comprises a diaphragm supporting frame or basket i i which is suitably fastened as by welding or the like to one member of the field structure generally designated at 12 and commonly referred to as the magnet housing or pot. This magnet housing or pot i2 is illustrated as of U-shaped configuration having legs [2a and l2b. An opening 13 is defined in the longer leg I2a of the U-shaped magnet housing IZ. The basket II is illustrated. as being fastened to longer leg lZa of the U-shaped magnet housing l2 which leg has the opening i3 defined therein. The field structure of the loud speaker If! in addition to the magnet housing i2 comprises the permanent magnet M which is preferably a cylindrical bar magnet formed of a magnet alloy having a composition of 8 percent aluminum, 14 percent nickel, 24. percent cobalt, 3 percent copper, and 51 percent iron, commonly referred to as Alnico. To complete the field. structure, there is provided the pole piece 55 which comprises a portion l5a of cylindrical configuration of smaller cross-secton than the magnet [4 so that one end thereof extends into the opening H3 in the leg I2a of the pot l2 as is clearly shown in Fig. 2 of the drawings so as to define an annular air gap l6 between the boundaries of the opening I3 and the pole piece 55. The other end of the pole piece If: includes enlarged button portion 15b having a diameter substantially equal to that of the bar magnet 14 which as was mentioned above is of general cylindrical configuration by virtue of the fact that manufacturers of such magnet material have chosen this shape for speaker magnets.

In addition to the field structure described. above, the loud speaker Ill also comprises a conical diaphragm l1 clamped at its outer edge Ha to a stepped portion Ila, of the basket H by means of a suitable clamping ring l8 formed of any suitable material such as cardboard or the like. Also, the sound reproducer ill includes a driving coil assembly which includes a tubular coil support l9, preferably formed of suitable paper or the like, which coil support is cemented or otherwise rigidly secured to the apertured apex of the diaphragm l1 and positioned so as to extend into the annular air gap 16 defined by the field structure. A diaphragm driving coil or voice coil 26 is wound upon the coil support IQ for movement within the air gap l6 defined by the field structure comprising the magnet housing i2 and the pole piece IS. The terminal conductors, not shown, of the driving coil 20 are brought out between the coil support l9 and the adjacent edge of the diaphragm IT to extend through openings in the diaphragm I! to terminals carried by one of the legs of the frame or basket H. These terminals are insu ated from the frame or basket H in any conventional manner.

Adjacent the junction point between the coil support l9 and the diaphragm I! there is provided a flexible air porous and preferably corrugated spider Zl which extends radially from the coil support 19 and is used to center the diaphragm driving coil 20 in the annular air gap l6 of the field structure. The outer periphery of the spider 2! is clamped against the stepped portion 22a of a clamping member '22, suitably fastened as by welding or the like to the leg lza. of the magnet housing l2, by means of a clamping ring 23. A suitable dust button 24 formed of felt or the like is applied over the end of the tubular voice coil support 19 adjacent the diaphragm l1 thereby dustproofing the moving parts of: the: loud speaker I 0.

In accordance with the. new: and improved method of the present invention: for manufacturing the loud speaker Ill described above, the field structure comprising the: members. I2, I4 and I5; the basket ll, andthe clampingzmember 22 are united in a sub-assembly asshown in Fig. 3 of the drawings which sub-assembly is generally designated by. the.- reference numeral 25. The firststep in the process of making the sub-assembly comprises the fasteningsof, the basket H and the clampingmember 22 to the U-shaped magnet housing. or pot I2 by anysuitable means, preferably by spot welding or: the like These members I I and 22. are positioned so that when fastened to the-pot l2 the: axes thereof coincidewith the. axis of the" opening I3 in the leg l2a of the U-shaped magnet housing- I2.

For the purpose of' ensuring low. reluctance flux paths through the field structure the inside face of the short leg [25 of the U-shaped magnet housing or pot I2 is ground so as to provide a flat surface for engaging one precision ground'endi of the bar magnet Ml This ispreferably done following the assembly of the magnet housing or'potl2 with the basket It and clamping member 22. Then theassembly of the magnethousing I2, basket H and clamping member 22 are positioned asshown in Fig. 5 of the drawings with theleg [2a of the pot l2 resting on a suitable support; notshown. The enlarged end or button l5b on th-epoie piece l5 is also ground flat so as to ensure good magnetic engagementwith the other end of'the bar magnet I4 when assembled in the-manner shown in: Figs. 3 and 5 of the drawings. Following this; the pole piece I5 has the portion I511, thereof inserted through an opening 26a in a splash shield 26 preferably formed of a piece of kraft paper or the like, The opening 26a is of'such a diameter as to substantially fit over the cylindrical end I51; of the pole piece I5. The pole piece [5 and bar magnet M are then assembled so as to assume the positions shown in Fig. 50f the drawings with the splash shield 26 disposed as shown, the purpose of which will become apparent as the following description proceeds.

Thenext step in the assembly oper-ation of the present invention comprises the insertion" of a ring portion' 21a ofa ring gauge 21 into the air gap lti defined between the boundary-o-fthe opening I3 in the pot I2 andtlie pole piece I5. The gauge 21 ensuresthe centering of'the polepiece I5 or the portion I5a thereof in the opening I3 thereby providingan accurately formed annular air gap I6.

In order to hold the field structure in the assembled relationship shown in" Fig; 5 of the drawings, a suitable clamping member generallyindicated at 28 in Figs. 4 and 50f the drawings is provided. Any'suitable' clamping member may be employed butit should be capable of being readily and quickly inserted and removed from its clamping position; As illustrated, the clamping member 28 is admirably suited to carrying out the process of the present invention and comprises a U-shaped member 29 suitably fastened as by welding orthe like to a base member 30. A reciprocably'movable plunger 3| is disposed-for reciprocating movement'in aligned openings defined in the base member" 30 and the bight of the U-shaped member 29. Asuitable manuallyengageable extension 31w fastened to the". reciprocating plunger 3 i between the. bight of. the I U-shaped member 29: and the base member 30 is. provided. A compression spring 32 is disposedbetween the extension 3 Ia and the bight of theU-shapedmember so as to bias the plunger 3| intolthe position shown in Figs. 4 and 5 of the drawings. Upon moving the extension 3 la, which is normally biased into engagement with the basew30, in a direction toward the bight of the U.-shaped member 29, the plunger 3| may be retracted to a position whereby the end thereof extending through, the base 30 is substantially flush: with the base. By virtue of the construction of the basket or frame member I II, which is provided with a plurality of openings llb therein, the clamp 28 is readily adapted to be disposed for clamping the field structure in assembled relationship as shown in Fig; 5 of the drawings. With; the plunger 3| extending through the central opening in the ring gauge 2.!- which opening has a diameter of the same order-of magnitudeas that of the plunger 3| and with the base 301bearing against-the basket frame Hr as shown in Fig; 5 of the drawings, the compression spring 32. acting through the plunger 3| forces the pole piece I5 so as to clampingly engage the bar'magnet' l4 between the leg [2b of the pot I 2 and the pole piece l5 as is clearly shown in Fig. 5 of the drawings. The clamp 28 may. readily be removed and inserted by manually compressing spring 32 through finger manipulation of extension 3la. It will be noted that theassembly of Fig. 5 of the drawings generally designated as 25 to distinguish it from the subassembly 25 comprises three elements not forminga: partofthe final speaker-sub-assembly 25, namely, the splash shield '26; the gauge 21 and the clamping member 28.

To permanently hold the field'structure in rigid assembledrelationship, it is desired in accordance with another step in the process-of the present invention to solder the adjoiningground surfaces of the magnet housing I2, the bar magnet M: and the pole piece I5. The next step in the process comprises centering of the magnet l4 relative to the button I5b of thepole piece I 5 followed' by theapplication of a suitable flux to the joints tobe soldered. With the assembly positioned as shown in Fig. 5, a suitable flux is applied as bymeans of a brush or other suitable applied to the joint beand the bar magnet M as well: as to the joint between the pot I2 and the bar magnet I4. This flux should not be applied to, any other surfaces than those mentioned above; thereby eliminating any danger of the solder adhering to any other parts. The flux used: and applied preferably comprises a liquid compound consisting of zinc ammonium chloride, potassium bromide and sodium fluoride in solution with a suitable wetting agent. This flux serves two purposes namely, that of cleaning thersurfaces to be soldered and also in preventing rapid oxidation of the parts to be soldered during r the soldering operation.

With. thefiux appli'ed'as described above, the assembly 25 is heady fOr insertion into a solder bath. The insertion of the assembly 25" into the solder bath is preferably performed by the same operatorwho centers the magnet and applies the fiuxthereto. In order to permit a high speed soldering operation, a solder furnace is preferably employed whi'ch mayinclude any suitable heating means providedwith automatic temperature control mea-ns. As illustrated inFigs. dandlof the drawings, the solder furnace generally indicated at 36 comprises a housing 37 supporting therein a suitable refractory member 38 defining a receptacle 39 for holding molten solder d). Any suitable solder may be employed although preferably comprising substantially ninety-five percent lead and five percent tin.

In accordance with the present invention, the temperature of the molten solder 48 within the receptacle 39 is preferably maintained between 760 and 800 degrees Fahrenheit, with the critical upper and lower limits being 825 and 680 degrees Fahrenheit respectively. For the purpose of supporting the assembled units in the solder bath, there is provided a rotating table if pro vided with a plurality of circumferentially arranged openings 32 therein of such diameter as to receive the lower portion and particularly the field structure of the assembly 25 whereby the field structure may be immersed in the molten solder. The openings 52 are sufliciently small, however, to prevent the frame or basket I I of the assembly 25' from passing th-erethrough whereby the baskets I i are adapted to rest on the rims of the openings 42. The rotary table 4! is suitably supported by means of a shaft 33 for rotation above the solder bath at approximately one revolution per minute. i In accordance with the present invention, the table is slightly tilted so that the distance of the table from the solder bath as indicated at A in Fig. '7 is somewhat greater than as indicated at B, the purpose of which will be brought out in detail hereinafter. Any suitable means for causing rotation of the shaft 43 and the table 4! may be provided. As illustrated, a suitable motor Mi connected through suitable driving means such as belts and pulleys generally designated at for driving the shaft 33 is provided. Preferably, the rotatable table for plate 65 and the shaft '53 are supported for rotation by a suitable mechanism generally indicated at 46 whereby the entire table may be raised from the solder bath to provide access to the receptacle 39 for various purposes. If desired, the means 56, the driving mechanisms M and 45 and the rotatable table 4| with its associated shaft 43 may be supported within the housing 31 which may also be provided with suitable means for carrying away any corrosive fumes or the like.

To afford access to the rotating plate or table II, the housing 3'! of the solder furnace 36 is provided with a loading opening 48 and an unloading opening 49. The assembled units 25 as indicated in Fig. 6 of the drawings are inserted through the loading opening 48 into the openings 42 in the rotatable table 4!. After making almost a complete revolution through the solder bath, these assembled units 25 are removed from the rotatable table 4! through the unloading opening 49. These

openings

48 and 49 are sufficiently large to afford ready access to the rotatable table 4 I.

In accordance with the present invention, the table 4! is tilted as was mentioned above so that the table is farther removed from the solder bath adjacent the loading opening 48 and is closer to the solder bath at a point substantially 180 degrees from the loading opening d8 which is clearly shown in Fig. 7 of the drawings. The reason for this, is to prevent the immediate complete immersion of the portions of the speaker sub-assembly to be soldered thereby reducing the splashing of solder. The gradual immersion of the field structure into the solder also prevents the immediate evaporation of the flux due to the sudden exposure to the intense heat. Furthermore, the grad ual immersion of the field structure during the soldering operation also causes a gradual release of gas by virtue of the chemical reaction on the flux applied to the parts to be soldered thereby eliminating the resultant explosive effects which would cause the molten metal to fly in all directions if the field structure were suddently immersed to its full depth within the hot bath. Upon rotation of the rotary table M the subassembly 25' is gradually immersed to its greatest depth whereby the solder rises not more than 2- of an inch above the button I5a on the pole piece [5 but at least 1- 6- inch above the joint between the bar magnet l4 and the pole piece IS. The splash shield 26 performs a very important function during this operation by preventing solder from splashing above the button i517 of the pole piece 15 and thereby ensuring that solder does not enter the air gap l6 of the annular configuration defined between the pole piece If: and the opening It in the magnet housing or pot l2. Since this air gap I6 is relatively small, it is important that no solder particles are permitted to enter the same and the splash shield 26 performs this function very well.

As was mentioned above, the rotary table M is operated so as to make about one revolution per minute. Suitable means for increasing or decreasing this speed may of course be provided. Each speaker assembly is left on the rotary table EH immersed in the solder for a total of between fifty-two and fifty-five seconds, the heavier as semblies being permitted to remain immersed a slightly longer time than the lighter assemblies. The same thing may be accomplished by permitting the heavier assemblies to be immersed in a solder bath which is at a higher temperature than when lighter assemblies are being processed.

It has been found that for a period of approximately fifteen seconds after removing the subassembly from the solder bath, the solder is in a semi-plastic state and some relative movement between the parts can be accomplished. In accordance with the present invention, the soldered sub-assembly unit 25 is removed from the rotary table 4! through the unloading opening 59 after being immersed the proper length of time and any excess solder associated therewith must be removed from the parts of the sub-assembly unit within the fifteen second interval while the solder is still in a plastic state. The step in the process following removal of the sub-assembly unit 25 from the solder bath through the unloading opening 49 is the removal of the splash shield 26 which has served its purpose. By virtue of the fact that this splash shield is formed of paper, it may readily be removed which removal is aided by the fact that the paper is somewhat charred due to its immersion in the high temperature solder bath.

To further carry out the process of the present invention and within the fifteen second interval following removal of the sub-assembly unit 25' from the solder bath while the solder is still in a semi-plastic condition, the pot or magnet housing i2 of the sub-assembly 25 is momentarily moved into contacting engagement with a vibrator armature 50 of a suitable vibrator unit 5! for applying a vibratory motion thereto. This vibrator unit 5i shown in detail in Fig. 8 of the drawings may comprise any suitable vibrating mechanism. As illustrated, this vibrator comprises a base plate 52 from which is end supported a bar magnet 53 having mounted at the other end thereof the vibrating armature 50 which has its free or vibrating end extending over a suitable solenoid 54. The solenoid 54 is preferably energized from any suitable source of alternating current energy such as the conventional sixty cycle power supply. Suitable adjusting means 55 may be provided to control the air gap between the vibrating armature 50 and the magnetic structure of the solenoid 54. When alternating current energy is supplied to the solenoid 54, the solenoid attracts and repels the vibrating armature 50 once during each cycle. By touching the pot or magnet housing l2 of the subassembly unit 25 to the vibrating armature 53, the pole piece is agitated causing it to center itself within the centering gauge 21.

-By virtue of the pole piece bumping from side to side, the vibration causes more accurate centering thereof within the opening I 3 of the magnet housing 12. Manufacturing experience has proven that when employing the vibrator 51 in the manner described less than one percent of the manufactured units are rejected because of improper centering whereas without the use of the vibrator 5| and performing all other steps in the process in exactly the same manner, the percentage of rejects due to improper centering rises above ten percent. This bumping from side to side of the pole piece occurs because of the small difference between the inside and outside diameters of the ring gauge 21 and the inside and outside diameters of the air gap l6 so that the gauge 21 may be a little tighter in one part of the air gap l6 than in another. The mass of the gauge 2'! is such that vibration thereof causes this gauge to work against the adhesive force of 1 the solder and free itself within the air gap so that it is centered accurately within the manufacturing tolerances permitted.

Several other very desirable results are obtained by virtue of this vibration of the field structure immediately following removal of the sub-assembly 25 from the solder bath. This vibration or vibratory motion permits the plunger 3| of the clamp 28 which applies a constant force to the portions of the field structure desired to be united into a unitary assembly to force the contacting portions between the pole piece I5, the bar magnet I4 and the pot or magnet housing it into more intimate engagement. It furthermore helps to distribute the solder in the joints to be soldered and likewise frees the ring gauge 2'! from the field structure to permit ready removal thereof later in the process of manufacture.

At this point, it should be noted that one of the important advantages of the process of the present invention becomes apparent. That is the salvage of improperly soldered units. If upon removing the unit 25 from the vibrator 5| it is found not to be centered properly, all that is necessary is for the operator to re-insert the subassembly 25' into the solder bath through the loading opening 48 in which case the entire field structure is loosened and recentered by means of the subsequent use of the vibrator. This advantage is particularly important with regard to the welding process mentioned above where following the welding step such salvage operation is substantially impossible.

Following the application of the sub-assembly 25 to the vibrator unit 5| as mentioned above and after the solder is no longer plastic, the sub-assembly is subjected to several cleaning operations whereby it is brushed free of unsightly and harmful deposits of solder and is placed as indicated inFig. 6 of the drawings on a perforated aluminum plate 51 where it is subjected to a blast of cooling air from a suitable coolingfan 58. It has been found that the air cooling step just described was the only practical cooling step since a very large number of rejects were obtained when the sub-assembly was immersed in "a liquid coolant. Rapid cooling resulting upon immersion of the sub-assembly in a cooling bath caused the soldered joints to break up, probably due to the fact that the coefficient of thermal expansion is substantially different for solder than it is for the ferromagnetic members from which the field structure is made.

Following the cooling operation, the spring clamp 28 and the ring gauge 27 are removed so that the sub-assembly 25 is now substantially in the form shown in Fig. 3 of the drawings with the field structure parts bonded together and a substantially accurately defined annular air gap i8 being provided between the pole piece l5 and the pot l2. It will be understood that the ring gauge 2-? and the spring clamp 28 may be reemployed in manufacturing successive units.

The next step in the process of manufacturing the sound reproducer I'll comprises the employment of a hardened check gauge which is inserted into the annular air gap and rotated so as to remove any solder or foreign particles that might inadvertently have-entered the air gap It. The air gap i6 is also gauged for size at this time whereby it is determined whether the manufacturing specifications are complied with.

The sub-assembly 25 as shown in Fig. 3 of the drawings is now moved to a suitable washroom or the like where it is given a caustic bath to remove oil and any charred .paper or solder slag which may have been left thereon. Following this caustic bath, it is taken to the paint shop where a suitable enamelled finish is applied thereto. This sub-assembly 25 provided with a suitable enamelled finish is ready for the assembly room where the diaphragm ll, voice coil support 19, voice coil 20 and spider 21 are suitably applied thereto, together with the application of the dust button 24 whereby the speaker assumes the form shown in Figs. 1 and 2 of the drawings. The bar magnet l 4 is now in condition for magnetization and is placed under the influence of an electro-magnetic field which completes the manufacturing operation of the speaker II] which is now ready for final testing operations.

From the above discussion, it will be understood by those skilled in the art that there has been disclosed a new and improved method for manufacturing sound reproducers which is not only much more economical than most prior art methods but is capable of producing a more efficient unit and in addition, the method. lends itself admirably to salvaging units which have the pole piece thereof improperly centered. The method furthermore is very suitable to mass production of speakers at a minimum manu-- facturing cost, both as to labor and materials whereby the resultant speaker or sound reproducer has a great advantage over speakers produced by competitive processes.

Although there has been described and illustrated herein an embodiment of the present invention relating to the process of manufacturing sound reproducers, it is contemplated thatapplications of the present invention other than the particular embodiment illustrated will suggest themselves to those skilled in the art. It is intended that such other modifications as do not depart from the true spirit and scope of the present invention shall be covered by the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A method of manufacturing a sound reproducer of the type employing a voice coil movable in an annular gap defined in a field structure including a permanent magnet, a magnet housing and a pole piece, which includes the steps of assembling said magnet and magnet housing with a ground surface of said magnet in face engagement with a ground surface of said magnet housing, placing a paper splash shield about said pole piece, positioning a ground surface of said pole piece in face engagement with another ground surface on said magnet with a portion of said pole piece extending into an opening provided in said magnet housing so as to define an annular air gap between the walls of said opening and said pole piece, centering the pole piece in said opening, inserting a ring gauge into said annular air gap, applying a spring clamp to the assembly of magnet housing, magnet, pole piece, splash shield and ring gauge for maintaining said pole piece and magnet under spring tension in assembled position relative to said magnet housing, applying a soldering flux to the edges of the junction between said ground magnet surfaces and the ground surfaces of said magnet housing and pole piece, gradually immersing said assembled field structure in a solder bath to a depth sufficient to cover the flux coated portions thereof to provide a solder connection for the ole piece and magnet and the magnet and magnet housing, said splash shield preventing solder from splashing into said air gap, touching said soldered assembly immediately following removal thereof from said solder bath and while the solder is still hot and plastic to a vibrating device to jar said assembly and accurately center said pole piece in said opening, removing said splash shield and cleaning excess solder from said field structure, applying a blast of cooling air to said soldered assembly to harden said solder, and removing said spring clamp and ring gauge from said assembly.

2. A method of manufacturing a sound reproducer of the type employing a voice coil movable in an annular gap defined in a field structure including a permanent magnet, a magnet housing and a pole piece, which includes the steps of assembling said magnet and magnet housing with a ground surface of said magnet in face engagement with a ground surface of said magnet housing, inserting said pole piece through an opening in a paper splash shield, positioning a ground surface of said pole piece in face engagement with another ground surface on said magnet with a portion of said pole piece extendii ing into an opening provided in said magnet housing so as to define an annular air gap between the walls of said opening and said pole piece, centering the pole piece in said opening, inserting a ring gauge into said annular air gap, applying a spring clamp to the assembly of magnet housing, magnet, pole piece, splash shield and ring gauge for maintaining said pole piece and magnet under spring tension in assembled position relative to said magnet housing, applying a soldering flux to the edges of the junction between said ground magnet surfaces and the ground surfaces of said magnet housing and pole piece, gradually immersing said assembled field structure in a solder bath to a depth sufficient to cover the flux coated portions thereof to provide a solder connection for the pole piece and magnet and the magnet and magnet housing, said splash shield preventing solder from splashing into said air gap, vibrating said assembly to accurately center said pole piece in said opening, removing said splash shield and cleaning excess solder from said field structure, applying a blast of cooling air to said assembly to harden said solder, and removing said spring clamp and ring gauge from said assembly.

3. A method of manufacturing a sound reproducer of the type employing a voice coil movable in an annular gap defined in a field structure including a permanent magnet, a magnet housing and a pole piece, which includes the steps of assembling said magnet and magnet housing with a ground surface of said magnet in face engagement with a ground surface of said magnet housing, positioning a ground surface of said pole piece in face engagement with another ground surface on said magnet with a portion of said pole piece extending into an opening provided in said magnet housing so as to define an annular air gap between the walls of said opening and said pole piece, centering the pole piece in said opening, inserting a ring gauge into said annular air gap, applying a spring clamp to the magnet housing, magnet and pole piece for maintaining said assembly in assembled condition, applying a soldering flux to the edges of the junction between said ground magnet surfaces and the ground surfaces of said magnet housing and pole piece, inserting said assembly in an opening in a rotary table positioned above a solder bath which table is tilted relative to the surface of the solder in said bath so that said field structure is gradually immersed in said solder upon continued rotation of said table to adepth sufficient to cover the flux coated portions thereof to provide a solder connection for the pole piece and magnet and the magnet and magnet housing, vibrating said assembly to accurately center said pole piece in said opening, cleaning excess solder from said field structure, applying a blast of cooling air to said assembly to harden said solder, and removing said spring clamp and ring gauge from said assembly.

4. A method of manufacturing a sound reproducer of the type employing a voice coil movable in an annular gap defined in a field structure including a permanent magnet, a magnet housing and a pole piece, which includes the steps of assembling said pole piece, magnet and magnet housing in abutting relationship with a portion of said pole piece extending into an opening provided in said magnet housing so as to define an annular air gap between the walls of said opening and said pole piece, inserting centering means into said annular air gap, applying a readily removable clamp to the assembly of magnet housing, magnet and pole piece for maintaining said assembly in assembled condition, placing said assembly in a solder furnace for gradual immersion in a solder bath to a depth sufiicient so the portions thereof may be rigidly interconnected thereby to provide a solder connection for the pole piece and magnet and the magnet and magnet housing, applying vibratory motion to said soldered assembly immediately following removal thereof from said solder bath and while the solder is still in a plastic condition accurately to center said pole piece in said opening, cleaning excess solder from said field structure, subjecting said soldered assembly to a blast of cooling fluid to 13 harden said solder, and removing said clamp and centering means from said assembly.

5. The process of manufacturing a loud speaker of the type having a field structure comprising a permanent magnet, a pole piece and a magnet ing said pole piece, magnet housing and magnet in assembled condition, immersing gradually said assembly in a solder bath of a predetermined temperature for a predetermined time to provide soldered connections at the junctions of said magnet with both said housing and said pole piece whereby said field structure becomes a unitary structure with the parts in intimate engagement to provide a very low reluctance path through said field structure, vibrating said assembly upon removal from said solder bath while the solder is still hot and plastic so as to apply a force to said pole piece to center said pole piece relative to said centering means accurately to define said annular air gap, cooling said assembly, and removing said centering means.

6. The process of manufacturing a loud speaker of the type having a field structure including a plurality of members which define an air gap comprising the steps of assembling said members, inserting a ring gauge in said air gap properly to maintain said annular air gap, resiliently maintaining said members in assembled condition, immersing gradually said assembly in a solder bath of a predetermined temperature for a predetermined time to provide soldered connections at the junctions of said members whereby said field structure becomes a unitary structure with the parts in intimate engagement, and applying vibratory motion to said assembly upon removal from said solder bath while the solder is still hot and plastic as to apply a force to said pole piece to center said pole piece relative to said ring gauge and to provide a very low reluctance path through said field structure.

'7. The process of manufacturing a loud speaker of the type having a field structure including a plurality of members defining an air gap comprising the steps of assembling said members, resiliently clamping said members in such assembled condition, immersing said assembly in a solder bath of a predetermined temperature for a predetermined time to provide soldered connections at the junctions of said members whereby said field structure becomes a unitary structure with the parts in intimate engagement to provide a very low reluctance path, and applying vibratory motion to said assembly upon removal from said solder bath while the solder is still hot and plastic so as to apply a force to said members accurately to define said annular air gap.

8. The method of manufacturing a loud speaker of the type having a field structure comprising a permanent magnet, a pole piece and a magnet housing, which includes the steps of assembling said pole piece, magnet housing and magnet so that an annular air gap is defined between said pole piece and another part of said field structure, applying a disposable paper splash shield to said assembly to prevent access of foreign ob- 14 jects to said air gap, inserting a ring gaugedn said air gap, clamping the assembly of said pole piece, magnet housing-and magnet for maintain ing such parts in assembledoondition, immersing said assembly in asolder'bath of -a predetermined temperature fora period of the order or a minute to provide solderedconnections atthe junctions of said magnet with both said housing and said pole piece whereby said field structure becomes a unitary structure with the parts inintimate engagement to provide a very lowreluotance path through said field structure, applying vibratory motion i-tosaid assembly upon removal from said solder bath while the solder is still plastic 30 as to apply a force to said pole piece to center said pole piece relative to said ring gauge accurately to define said annular air gap, removing said splash shield, and cooling said assembly.

9. The process of manufacturing a loud speaker of the type having a field structure comprising a permanent magnet, a pole piece and a magnet housing having an opening therein, which includes the steps of assembling said pole piece, magnet housing and magnet so that an annular air gap is defined between said pole piece and the Walls of said opening, centering said pole piece with respect to said opening, resiliently maintaining said pole piece, magnet housing and magnet in assembled condition, immersing said assembly in a solder bath of a predetermined temperature for a predetermined time to provide s01- dered connections at the junctions of said magnet with both said housing and said pole piece whereby said field structure becomes a unitary structure with the parts in intimate engagement to provide a very low reluctance path through said field structure, and vibrating said assembly upon removal from said solder bath while the solder is still plastic.

10. A method of manufacturing a sound reproducer of the type employing a voice coil movable in an annular gap defined in a field structure including a permanent magnet, a magnet housing and a pole piece, which includes the steps of assembling said magnet, magnet housing and pole piece so that a portion of said pole piece extends into an opening provided in said magnet housing so as to define an annular air gap between the Walls of said opening and said pole piece, inserting a ring gauge into said annular air gap, applying a spring clamp to the assembly of magnet housing, magnet and pole piece for maintaining said assembly in assembled condition, inserting said assembly in an opening in a rotary table positioned above a solder bath which table is tilted relative to the surface of the solder in said bath So that said field structure is gradually immersed in said solder upon continued rotation of said table to a depth sufiicient to provide a solder connection for the pole piece and magnet and the magnet and magnet housing, vibrating said assembly to accurately center said pole piece in said opening and free said ring gauge, cleaning excess solder from said field structure, subjecting said soldered assembly to a blast of cooling air to harden said solder, and removing said spring clamp and ring gauge from said assembly.

11. A method of manufacturing a sound reproducer of the type employing a voice coil movable in an annular gap defined in a field structure including a permanent magnet, a magnet housing and a pole piece, which includes the steps of assembling said pole piece, magnet and magnet housing in abutting relationship with a portion of 15 said pole piece extendin into an opening provided in said magnet housing so as to define an annular air gap between the Walls of said opening and said pole piece, inserting centering means into said annular air gap, resiliently clamping the assembly of magnet housing, magnet and pole piece for maintaining said assembly in assembled condition, placing said assembly in a solder furnace for gradual immersion in a solder bath to a depth sufficient for the portions thereof to be rigidly interconnected thereby to provide a solder connection for the pole piece and magnet and the magnet and magnet housing, applying vibratory motion to said soldered assembly immediately following removal thereof from said solder furnace and while the solder is still in a plastic 16 condition accurately to center said pole piece in said opening, applying a blast of cooling fluid to said assembly to harden said solder, and removing said centering means from said assembly.

JAMES P. QUAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,753,639 Badgley Apr. 8, 1930 1,836,076 Kingsford Dec. 15, 1931 2,306,291 Alons Dec. 22, 1942