Reasons for using seamed speaker cones?

[Rhodesplyr]

Starting from the principle that matching an amp to a speaker is one of the more important considerations in the final sound of a combo amp, I'm wondering: what's the point of the seamed speaker cone vs. a one-piece?

Googling "seamed cone" and guitar, I see lots of places touting seamed speaker for "that vintage tone," but nowhere do I see any discussion of what the advantages or disadvantages of a seamed cone are.

It seems to me that the additional stiffness of the seam, especially where it's in a straight line from voice coil to surround, might produce some unevenness in the way the cone flexes. Or maybe that's the point...

[hrbay]

Good question you conjure... I would think cost is/was the big part, they were cheaper to produce. If it was a big positive difference today you would see the freakier folks doping up lines radially on their seamless cones instead of at the surrounds. Don't know. Some one will.

[Enzo]

Frankly, I wouldn't read too much into it.

The line of thinking: I like the old vintage tone, I see older speakers often had seams, therefore the seam must be why I like the sound. That is invlid reasoning, but whatever, folks think that way. Post hoc, ergo propter hoc.

When Leo Fender bought speakers from various suppliers back when, he wasn't thinking seamed vs un-seamed. He was thinking 10" speaker for guitar, who can supply it at a good price? A flat sheet of paper stock can be easily cut to fold into a cone. many speakers were made that way. One can take a piece of cone stock and form it into a cone, but that is a more complex deal. Of course once the machinery is set up, they can crank them out all day long.

[Mark Hammer]

It's a bit like the scene in "Spinal Tap" where Nigel Tufnel tries to make a big deal of the fact that the knobs go to 11. Rob Reiner, in the role of filmmaker Marti DiBergi, just sees knobs and wonders why 10 couldn't be the most, which mystifies Tufnel who places near mystical belief in the fact that the knobs go to 11.

A lot of older speakers used paper cones for a variety of reasons. One is certainly that is was cheap. But you will also note that it is rare, if near impossible, to find guitar or "hi-fi" speakers from the 50's and very early 60's that had foam surrounds or big magnets. So if you wanted to move lots of air and get big bass from a smallish magnet, using less precise coil gaps (and efficiency decreases as the coil gap gets bigger), then you really needed to have a light stiff cone that could be moved easily with less wattage. Light and stiff meant paper, and paper cones were invariably seamed. The seam doesn't add anything other than mojo...just like chickenhead knobs that go to 12...or 11.

[Rhodesplyr]

I was just told by a speaker expert I talked to that seamed cones were used primarily because they were cheaper to make. When a number of smart people I ask agree on a reason for something, I tend to think that they probably have the right answer :-)

To Mark: This may be an issue of semantics, but I have any number of paper-cone musical instrument speakers from the 1950s that don't have seamed cones, like the ones that Rola and Jensen supplied to Hammond and Leslie. Also, while most of the seamed cones I've run across are light, they are also often softer/more mushy than cones formed from pulp. Are you using a term other than 'paper' to refer to cones formed from pulp? You definitely lose some energy to cone flex with a mushy cone.

In fact, unwanted harmonics from cone flex was one of the issues with a Blues Deville amp I worked on recently, which has seamed-cone 10"s made by Eminence. I swept them individually with a sine wave generator, and they all had some quirky resonances at different pitches. I did the same to a 1950s Rola 12" yesterday (formed cone), and it was clean at all frequencies.

[jrfrond]

Regardless of why they were ORIGINALLY spec'ed, along the way it was found that they SOUNDED different, just like tubes.
Seamed paper cones tend to be thinner and don't break up as evenly as a stiffer molded cone, plus they also have a paper surround. What they offer is more complex overtones. It all really depends on what you like.

[J M Fahey]

Modern cones are made by the "felted" process, where the cellulose paste is vacuum sucked through a cone shaped sieve made out of wire screen material or a turned aluminum mold/die with a zillion little holes (look closely at a cone surface), then pressed by a male cone die to dry and compact it.
The male part can be heated by steam or electricity to yield a ready-to-use cone out of the die, and is the preferred modern method.
This yields cones which can only go up to a certain density and down to a certain thickness.
The old seamed process starts with a very different material: although the basic cardboard is still made by felting (in huge, long, continuous screen belts) which can provide miles of raw paper or cardboard, that sheet is further compressed between two huge rollers, which give it a density (and thinness if necessary) impossible to achieve by the other method.
Both cone materials are very different and, more important, *sound* different.
Just hit them with a fingernail.
Don't think that the old method was better, far from it, but there is a physical difference explaining a sound difference.
For once not only Mojo here.

[jrfrond]

I do a lot of reconing and see a lot of old speakers, and I can tell you that most of the seamed paper cones were even thinner than what we see today as replacements. These much thinner cones yield a lot more harmonic distortion than their thicker counterparts.

Another property of a more flexible cone is that it is less efficient at moving air, whereas a molded, ribbed cone as used in many subwoofer driver is design to generate a nice, stiff column of air with little harmonic distortion.

[Mark Hammer]

You confirmed what I had assumed; that seamed paper cones were made from materials produced in a different manner, and would be denser material as a consequence.

And yes, the simple presence or absence of a seam is but one tiny element in a fairly complex recipe. There is the ribbing, the nature and design of the paper surround, the overall size of the cone, the coil diameter relative to the cone diameter, and so on. Selecting speakers by whether they are seamed or not, is a bit like shopping for a wife by hair colour.

[jrfrond]

Selecting speakers by whether they are seamed or not, is a bit like shopping for a wife by hair colour.

The sad fact is that both of these have already been done. :O

[Rhodesplyr]

John, Good point.

My point of view may be influenced at the moment by the fact that the "complex overtones" of the stock speakers in his Blues Deville were a big part of what a recent client of mine was complaining about. (One speaker actually ended up having a damaged voice coil and had to be replaced.) I had to spend a while explaining to him that these artifacts were inherent to the speakers and that there was nothing I could do about them unless he wanted to replace all his speakers.

But, just to be clear, are you talking about the speakers' ability to *reproduce* signals produced by the amplifier, or are you talking about harmonics *introduced* by the speaker itself as a result of a thin, flexible cone?

[jrfrond]

John, Good point.

My point of view may be influenced at the moment by the fact that the "complex overtones" of the stock speakers in his Blues Deville were a big part of what a recent client of mine was complaining about. (One speaker actually ended up having a damaged voice coil and had to be replaced.) I had to spend a while explaining to him that these artifacts were inherent to the speakers and that there was nothing I could do about them unless he wanted to replace all his speakers.

But, just to be clear, are you talking about the speakers' ability to *reproduce* signals produced by the amplifier, or are you talking about harmonics *introduced* by the speaker itself as a result of a thin, flexible cone?

Both actually. Lighter, thinner cones can better reproduce higher harmonics. Look at what we are talking about here: most of the prized vintage speakers used very thin paper cones with small voice coils wound on featherweight paper forms, as opposed to the more common Nomex, Kapton, or even aluminum used currently. These speakers has much lower power handling capabilities, because overheating the voice coils would cause them and the cones to go up in flames. However, the combination of the lightweight cone assembly and the cone flexion that occurs due to their inherent flimsiness made for a very harmonically rich signal emanating from the speaker. Cone flex causes harmonic distortion. at the OTHER end of the vintage speaker spectrum was the JBL D120F, which stayed clean as a whistle in those old Twin Reverb's, where they were offered as an option.

[Mark Hammer]

Please feel free to smack my hand on this one, but I think there is much to be said for the effect of use on a paper surround, compared to the effect os use on a foam or rubber surround. Stated more directly, I think paper cone flexion changes over time and use.

There probably also needs to be a distinction made between the cone construction/materials of those older speakers, and the precision of the speaker assembly. So, reducing the gap between the magnet and coil will increase efficiency, holding the magnet strength constant. But unless that sucker is lined up just right, smaller gap increases the risk of heat buildup through mere friction. And, of course, having a light cone/coil assembly that moves quickly becomes tantamount to rubbing two sticks together even faster - you make smoke.

So, I think it is fair to suggest that part of the "harmonic complexity" of such older speakers is due to the cone materials and fabrication method, but another part may well come from the somewhat poorer alignment of the coil in the gap that was more typical of speaker manufacturing all those decades ago.

[jrfrond]

No smack Mark!

Like ANY musical instrument (and I do consider speakers to be part of the electric/electronic instrument chain), ALL factors are interactive. Surround type and material, doped/undoped, spider flexibility, voice coil weight, wind depth and material, dust cap material/type, cone type, even basket type and of course magnet type, gauss. There is also the "hung" spec (OK, I DO hear a coupla guys laughing here!). There's "underhung", "overhung" and "well-hung" (of course! ). Go read up on it on the web. Speaker design is fairly-complex, but like pickup design, also a bit of a black art, particularly when it comes to guitar speakers. Too many details and info to elaborate on here, but there are certain principles that apply, and like anything else, there are mods that can be applied as well.

There wasn't really any gap alignment problem years ago. It's still done the same way, in fact: with shims. The difference today is that we have better adhesives that won't shear under stress, and there's a LOT of stress loads on speaker components.

[Rhodesplyr]

Mark,

I haven't measured them myself, but I've read that Jensen preferred a narrow voice coil gap, but this necessitated more precisely-made voice coils and construction. This is all pretty well-known, of course. Narrow gaps have many advantages, but it means tighter tolerances on everything, which is more expensive. I certainly don't think that poor voice coil alignment was typical of speakers made in the 1950s. I have several Jensen and Rola speakers from the 1950s that still work perfectly. The paper voice coils formers are vulnerable to moisture damage; if they get damp and swell, they'll rub or lock up. And there were other precision speaker-makers in the old days like Stephens Tru-Sonic. I know someone who has cast aluminum frames and Alnico magnets from Stephens that are still waiting to be built into speakers. If anyone wants a really nice 15" built to order, I can refer you :-)

In contrast I've seen speakers from the 1970s that weren't really quite as well made as ones from 20 years earlier. I've heard rumors that the Jensen Chicago factory was closed down around 1971 in part because the machines they'd been using for years were worn out and needed to be retooled or replaced.

You are incorrect about one thing--the heat buildup issue. Metal is a much better conductor of heat than air, and, believe it or not, voice coils actually dissipate much of the wasted heat energy (of which there is a lot) via direct radiation to the sides of the voice coil gap. In fact, one factor in the failure of voice coils via overheating is the amount of the coil that's *out* of the gap during large excursions.