US3003191A - Method of making a transducer diaphragm - Google Patents

Description

U dStat wnee METHOD or MAKING A 'mANsn cnR an I Luth,?9% 1 st S Holland, Midi.

Filed pi s, 1958, S01. No. 758,597 7 invention relates to a transducer diaphragm and a sothat the diaphragms have poor transient response." In

order to have good transientresponse, the di method ofmakingthe same in which the diaphragm has started abruptly byqenergization of the voicecoil and must above desired characteristics.

a One of the features ofthis invention is to providea transduccrdiaphragm comprising a lightweight uncompressed fibrous sheet and a self-sustaining cured resin coating on the sheet, the sheet being expanded and subfimfially ssm s er b e. c i eet and resin 'has an apparent density less thane itsfabsolute ther feature of the invention is toprovide an i1nproved method ofmaking a transducerv diaphragm. com

prising'providing a mold having a surface of the desired diaphragm shape and contour, applying to the a thin fibrous sheet material, applying a liquid thermosetting resin and curing the resin while the material and resinare relatively free andunconfined;

The transducer diaphgrams of this inventionhave the rac mes 0st. 19., tes

with most fibrous materials will alsocanse an andlooseningof'the fib'ers and a setting of they The dried sheet material .with the is then with a liquid thermcsetting and is partially cured to adherent yet flexible The sheet material isthen removed from the mold, trimmed at the edges and center to the'shape [and dimensions of the diaphragm, r'eplacedon the mold surface and theatre is completed to produce a strong, self-sustaining low'density p fl -f f a v The following examples are illustrative only of methods and diaphraginseirilzyodyiug'"the invention: 7

t Exar;nple1 l'fln this'exainple, I diaphragmwas provided fora, 10 inch cone. A disc 01 cotton muslinhaving athreadcount of about) it 40 and such as a loudspeaker cone must be capable of being about} inilsY thick wa @t' incircular shapewith a diameter about'two' inches'la'r'gerthan' the diameter of the cone. A 5 solution; of polyacrylamide was prepared, with the polyacrylamide being of such grade to produce a viscosity of about 5 in the*5 water solution.

The mold was he'atedin an oven to about 115" c. and a mold release wax applied to the mold with the wax being made up of equal parts of paralfin wax and carnauba wax to-which enough Stoddard Solventhad been to produce a soft paste. After the mold had been coated" with this release wax, the cotton muslin was dipped in water, most of thewater squeezed out until the muslin Other; features and advantages of the "invention be apparent from the following description of. certain em-- bodimentsthereof. In producing the diaphragms ofv this invention, a moldof the desired shape and contour is used., The uncured diaphragmiis arranged on thesurface of this mold and cured in afrelatively and unconfined state under substantially no pressure so that the resuln'ng will have a, low apparent gravitywhen compmd to its absolute gravity. As is well known, a material in.

an ,expanded'open statewill have a specific gravity, called the ,apparentspecific gravity,.that ismuch less than its absolute or true or. density. Thus, for example, pure cellulose has an absolute or trueldensity of.l.583. Yet, certain forms of cellulose'such ascertain, ty es, of wood may have a density as lowas 0.32.

In'fthis invention, any type of mold may be usedas desired. 7 This mold must have a suriace, preferably a1 convex surface when a cone is being molded, has,

generally the shape and contours of the diaphragm. In the generalprocess, a sheet of. fibrous material somewhatlarger than-the finishedjdiaphragm is placed on the mold surface and is coated withva binder:

with the solution,-it is heated waive-on the water time, the mold and me were from was just damp and the muslin then stretched smoothly over themold surface. lmmediatelythe above polyacryl' amide solutionswas brushed on the cloth, with suflicient pressure being applied to press the cloth down in contact with.the vmold and to coat the cloth thoroughly. The heated mold "caused. theJvater to. steam; thereby.

oi the .waterand-causingthecotton fihcrsftoiswell.

mold wasthen placedinthe oven to.,drivefofl 1M1 traces of the water. :1, I H i when the mold andrnuslinfwas dry, the mold; was

rcmovedgtrom the ovenand.a liquid resin mixture of 1'2- grams ofiepoxy resin (epoxideeguivalent 17S2l'0)"fand 3 grams of tri ethylene tetrarninc wasi'bruslied 'q fthe muslin in the mold; 'The mold and the thusly coated muslin were then returned tojthejoven and permitted to remain there until the resin had, reached an stagejinji s cuiin'gibut before theresin-had hardened I to the oven for completion of the cure which took about four, or five minut M the ind pfvtvhq quip and thecone removed from the mold.

g this rocedure, the muslin sheet and appliedcoating materials'were f y lw' si m l ns 99 was. extremely strong, yetfihad sound In example, substantially the same procedure was f l ws s tha *P YF: fis t e. 9 m sl t sa a 1 5 sm a l sf a s -mg -i' c n o sewar s w mid "a maxim mii depthfstjthlefcenter of 2% inches, an outside diameierbrswi' a conventional mold i loudspeaker I tailmfi finished cone' had a center voice coil opening of .1 inch diameter. The resin used had the following ingredients:

Epoxy resin--epoxide equivalent 175-210- 140.

Epoxy resinepoxide equivalent 225490- 60 parts/wt. Titanium dioxide 3. Precipitate calcium carbonate 3-4 microns 27. f--the above a 12. Triethylene tetramine 3.

In this example, the cloth was wet as set outabove and uniformly formed in the hot mold with polyacrylamide as described above in Example 1.: The mold and shaped cloth was held in the oven at 135 C. for /2 minutes, and removed from the oven and the resin applied to the c'oth, returned to the oven and the resin precured for five minutes. At the end of this time, the partially cured cone is removed from the mold, punched and trimmed as described above and again cured for three minutes in the oven as set out above before the finished cone was removedfrom the oven. The entire procedure took about 17 minutes. The resulting cone weighed 13% grams, had anaverage thickness of mils .and a specific gravity of 1.15 to 1.18.

This compares with conventional materials cured under heat and pressure which have specific gravities of from 1.45 to 1.5. The new cone had excellent strength and when installed in a loudspeaker was found to have excellent transient responses. The frequency response on sweep frequency was free of peaks and valleys.

Y Example '3 V In this example, the cone was prepared by the method set out in Example 2, but here a polyester resin was used instead of the epoxy resin. The polyester resin was a copolymer of an alkyd resin and styrene. The polyester resin was a liquid with a styrene content of about 35% by weight. The resin mixture used had a viscosity of about 1 poise and the following constituents:

a .Grams Polyester resi Qailcillm carbonate 3 Titanium dioxide l 0.3 Peroxide catalyst 0.3

p The same procedure in making the diaphragm was followed here as was followed in Example 2. The initial curing time. was 8 minutes in the oven at 115 C. and the final curing was for 81 minutes. The cone weighed 14% grarnsand had a mean thickness of 14 to 15 mils.

Example 4 In this examplea series of cones were made by the method of Example 2, using the following b nder solutions:

Methylcellulose 5% sol. in water of 15 cps.

methylcellulos'e.

Methylcellulose 30% sol. in water of 15 ,cps.

' methylcellulose.

Hydroxyethylcellulose- 5%-.-300 .cps. I-LE. cellulose. Sodium carboxy methyl- In this example a series of cones were prepared. bythe method of Example 2, using in place of the triethylone tetramine, ethylene diamine, diethylene-triamine,and tetraethylene pentamine.

Example 6 In this example, the cone was prepared by the method set out in Example 2, using the same materials and curing temperatures. The mold was such that the resulting cone had a maximum depth at the apex of 2 /8 inches: and a diameter of 10% inches. The cone had a central opening for a 1 /2 inch voice coil and weighed 19 grams and had a thickness of 13-15 mils. When the cone was fitted as a partof a loudspeaker, the frequency. response was found to be very smooth, extending down to approximately cycles per second' and had a barely. audible harmonic response. The high frequency response extended to 15,000 cycles and transient response was very good.

In. general, the diaphragm of this invention is made of fibrous sheet material preferably produced n'om fabrics such as cotton, wool, glass cloth or the various synthetic fabrics suchas nylon, Orion and Dacron and various combinations of these. The resins that may be used are any thermosetting resin that can be applied in a liquid state and that can be cured to a strong solid. These include epoxy resins, phenol or urea aldehyde resins and the various copolymer resins of alkyds and monomers copolymerizable therewith particularly styrene.

The water soluble binder or stiflener which is preferably initially applied to the fibrous material sheet includes polyacrylamide', the various alkyl celluloses, hydroxyalkylcelluloses, and alkali metal salts of carboxy akyl celluloses and polyacrylamide.

Having described my invention as related to the embodiments set out herein, it is my intention that the invention be not limited by any of the details of descrip-' tion, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

I claim:

1.1Tl'1e method of making a transducer diaphragm,

' comprising: providing a mold having a surface of the desired diaphragm shape and contour; applying to said surface a thin fibrous sheet material; wetting said sheet material with water to aid in obtaining intimate contact of said material with the mold; heating said sheet material to above the boiling point of water to drive ofi the water and loosen thefibers in the material; applying to said material a liquid thermosetting resin; andcuring said resin while said material and resin are free and unconfined.

2. The method of making a transducer diaphragm, comprising: providing a mold having a surface of the desiredldiaphragm shape and contour; applying to said surface a'thin fibrous sheet material; wetting said sheet material with water to aid in obtaining intimate contact of said material wth the mold; coating said material with a water solution of a binder; heating said sheet material to above the boiling point of water to drive oif the water and loosen the fibers in the material; applying to said material a liquid thermosetting resin; partially curing the resin-to as'elf-sustaining condition to form a blank; removing the' blank from the mold and cutting it to the desired dimensions; replacing the blank in the mold; and curing said resin while said material and resin are free and unconfined. V

3. The methodof claim 2 wherein said binder is a solution of a-member of the class consisting of polyacrylamide, the alkyl c'elluloses, the .hydroxy alkylcelluloses,

5 alkali metal salts of carboxy alkyl cellulose, and alkali metal salts of polyacrylamide, and said resin is a member of the class conssting of epoxy resins, phenol aldehyde resins, urea aldehyde resins, and alkyd-styrene copolymers. 5

References Cited in the file of this patent UNITED STATES PATENTS 1,759,387 Bateholts May 20, 1930 10 Charters Apr. 19, 1938 Nagelvoort Feb. 14, 1939 Fletcher Aug. 4, 1942 Gerathy Aug. 27, 1946 Nebesar Nov. 11, 1952 Brennan June 2, 1953 Nottebohm Oct. 4, 1955 Pessel Feb. 7, 1956 Lampman Mar. 27, 1956