It’s everywhere. We take it for granted, blow our noses on it, wipe…. and yet, paper has been a vital part of sound reproduction from the earliest days. Despite the appearance of high-tech, exotic materials, it’s still an important material for loudspeaker cones. In some cases, the old ways are the best.
In the early years of audio, pretty much every method of reproducing sound that can be imagined, had been tried. If you think electrostatic, planar, or plasma loudspeaker drivers are recent innovations—guess again. By the 1920s, all those and many more had been tried, and nearly all were rejected on the basis of nonlinearity, low output, high cost, or even lethality.
The winner by default was the moving coil driver with a paper cone.
As was the case of Mark Twain, the rumors of the paper cone’s demise have been greatly exaggerated. Way back in 1962, audio entrepreneur Irving M. “Bud” Fried wrote “Farewell to the Paper Cone” in an early issue of Stereophile—but there is still a place in the world for the “old-fashioned” variety of speaker cone.
Like it or not, all engineering is a matter of choosing compromises. Fried’s reference to the “turgid, mushy sound” of paper cones was of course a generalization, and of course those words were carefully chosen to highlight by comparison the merits of the bextrene-coned speakers that he happened to sell. Fried was a master wordsmith and marketer, as well as a trained attorney, and he very much had a horse in that race.
Listening to those bextrene-coned speakers now, their characteristic hollow, tubby resonances are readily apparent. They may have been better than the mass-market paper coned small speakers Fried indicts, but they largely swapped one set of problems for another…which is a very human thing to do. Critics refer to the sound as “Tupperware”, which is overstating the case—but it is a vivid, easily-understood characterization.
But what about paper? How can a material that generally has very little strength and no internal rigidity possibly be used to make sound?
First, let’s understand that the paper used in making loudspeaker cones isn’t the same stuff as paper towels, or the ream you cram into your ink-jet printer. From the earliest days of add-on speakers that perched atop a battery radio set, manufacturers tweaked the cone material, experimenting by adding felt, cloth, hemp, all manner of fibrous materials to the pulp mix. You’ll see some cones that look like the construction paper you cut with blunt-nosed scissors in grade school; some look and feel more like common cardboard; still others have a mottled appearance more like handmade fine art material than an industrial product. The light weight of a paper cone was especially important back in the day of flea-powered amps and radio receivers, and continues to make them favorites of aficionados of low-powered SET amps today.
The Stromberg-Carlson speaker was a fairly common unit from the early ’20s. It was designed to set on a table top alongside a radio, or on top of the tabletop radio itself. Several things are immediately apparent: we see a seam where the paper cone was cemented together—later speaker cones were generally press-formed on an internal or external screen, to provide a seamless cone. From the perspective of most cone drivers, this is back-to-front, with the center point of the cone being the closest point to the listener, rather than the farthest. You’ll also notice that there is no dust cap in the center of the cone—and that’s because this particular speaker was driven by a lever arrangement attached to the brass cap or ferrule seen in the center. Most speakers of the era were of the field coil/electromagnet variety, but this one has a horseshoe permanent magnet.
By the way, this particular speaker is not small—it’s about 16″ in diameter, and I would assume that it’s fairly hefty, given the large cast metal base and frame.
I can’t even look at that large, exposed cone without getting the willies. In high school I owned a 1936 Philco floorstanding cathedral radio (bought for $12, thank you), and while tightening a connection with a screwdriver on the back of the set, slipped and punched a neat hole in the 15″ paper cone. While not a fatal error—mending with Scotch tape didn’t noticeably alter the sound—it gave me an appreciation of how easily paper cone drivers could be damaged.
The cone shape itself has multiple functions. Shaping the paper into a cone provides structural strength and rigidity, compared to that of a flat sheet of paper. It also moves a greater volume of air compared to a flat surface, and provides mechanical leverage, increasing the velocity of the air it moves. The cone form also provides some of the acoustical transformer effect which horns provide, more effectively coupling the driver to the air.
Further strength and acoustical adjustments can be provided by reinforcing the cone with concentric or radial ribs. In the most extreme example of this, the coaxial full-range (and you know that that term really means “we tried to cover everything with one driver, and mostly did it”) RCA LC-1 designed by the legendary Harry F. Olson (who has been mentioned more than once in these columns) was originally manufactured with a pretty conventional, lightly-ribbed cone. Subsequent versions (LC-1A, -B, and -C) featured added-on conical domes and a two-piece center deflector or “butterfly” which acted to diffuse the sound and prevent beaming. Presumably, the conical add-ons strengthened the cone, and given Olson’s expertise, the additional mass must have been useful, for some reason.
I am admittedly a materials nerd, and can happily spend hours searching websites of companies like Kurt Müller, which provides cones, domes, and diaphragms for many prominent speaker manufacturers. Given the time and resources, I'd also happily research and document the types of paper and other materials used in loudspeakers. This piece has barely scratched the surface of the topic of paper cones---but I hope it has punched a hole in the myth that paper cones are obsolete. ;->
