Reasons for using seamed speaker cones?

[Rhodesplyr]

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.

The hang of your voice coil is no laughing matter! :-) It's one reason to employ a speaker reconer whom you trust to do the job correctly. Most musical instrument speakers, historically, have used overhung coils, as far as I've been told, and some speaker places, even some well-known ones, employ people who will sometimes grab any voice coil that will work and turn your speaker into one with an underhung voice coil. The speaker will work, but it won't sound the same, especially when pushed hard.

I'm fortunate to have a brother who can purpose-build a speaker. Given a selection of cones, voice-coils, spiders, etc..., he can choose--via a mysterious black art process--the parts that will suit the application and, to an extent, the voicing of the speaker. I just had him do this with a Utah basket that a client wanted to re-use, and he gave us just what we wanted by using a different cone and spider.

[J M Fahey]

Old (alnico era) guitar speakers had a very narrow gap, to better use the weak alnico magnets available.
How did they manage that?: by making a very stiff cone and suspension.
The original "spider", which gave speaker suspensions their traditional name, were not even made out of corrugated pressed phenolic impregnated cloth as today, but a disk of phenolic paper (same material as cheap PCBs, although thinner), punched so it had some "arms" which made it look like a ... yes, you guessed well, .... like a "spider".
Anybody who repairs real old speakers will know this for sure.
I have an old 12" Alnico magnet Jensen, pulled from a 16mm projector labelled "1943", "Property of US Navy". I haven't yet been able to make a new voice coil for it. I mean, one that fits !!!
Wider gaps came in vogue when cheap large ceramics allowed for sloppyness, not to forget acoustic suspension speakers and their thick wire, long throw coils coupled to soft large suspensions and soft foam or impregnated cloth surrounds.

[jrfrond]

The voice coil gap is super-critical, because it ultimately determines how well the heat from the coil can be dissipated into the magnetic structure, which basically acts as a big heat sink. A narrower gap allows better heat transfer. In some high-power applications, ferrofluid (which is VERY pricey stuff BTW) is introduced into the gap to improve heat conduction. One of the issues with neodymium speakers is that the much-reduced magnetic mass makes for a poor heat sink, which is why you see vent holes, cooling fins, etc. in the basket and magnet structure, but they still do not have the heatsinking abilities of higher-mass magnets. JBL gets around this in their neodymium drives by splitting the voice coil into two sections for the "Dual Differential Drive" system, which commenced with the original Eon series. Each voice coil half has it's own gap and venting to assist heat dissipation. It's a very good system, and I must say that their neodymium drivers seem to last the longest. Be that as it may, no amount of heatsinking will help out-and-out speaker abuse. You can "read" the burn marks on a voice coil to determine exactly how it failed. Sometimes the coil gets so hot, the wire just falls off the form into the gap. I've pulled out many a voice coil as a single, long strand.

When building a recone from scratch (i.e. not using a preassembled OEM kit), I always pay close attention to the original manufacturers specs, and carefully hang the voice coil so that it is centered within the magnetic structure. The reconing process is critical, and not for hacks.

[Rhodesplyr]

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.

I've got a JBL D120F in my own guitar amp at the moment, and I have to admit that my personal preference is for speakers with cones that don't introduce a lot of harmonic distortion, whatever other colorations the speaker may add. It's probably why I also like 1950s field-coil speakers for guitars; they have their own sound, but it's not from cone distortion.

The horrible-sounding stock Eminence speaker from this Dean Markley guitar amp went into a client's Leslie Model 16, where it sounds great--firing into a rotating foam drum.

[jrfrond]

The horrible-sounding stock Eminence speaker from this Dean Markley guitar amp went into a client's Leslie Model 16, where it sounds great--firing into a rotating foam drum.

I'm not surprised. Most Eminence speakers are really bright when listened to on-axis. Firing down into foam was probably the perfect application for that speaker.

[Ronsonic]

I read something interesting on this, and I wish I could remember where, perhaps google would help me.

The primary appeal of the formed "seamless" cone is that it can be curved. This makes the outer section more flexible and breaks up resonances. Seamed cones tend to be more rigid for and would be more prone to "bell" resonance but that is dampened by the seam itself. Just as welding a seam in an actual bell would tend to kill it.

So what you get it a lighter, rigid cone with a slightly different dispersion and more self damping behavior.

I'm sure this is non-trivial.

Seamed cones show up in some very heavily engineered speaker systems, not just guitar mojo stuff. The Yamaha NS10 comes to mind. I'm pretty damn sure Yamaha chose that for real engineering reasons, not just because they were handy.

[Rhodesplyr]

The primary appeal of the formed "seamless" cone is that it can be curved. This makes the outer section more flexible and breaks up resonances.

Still, the vast majority of formed cones are not curved. The curved cones I'm most familiar with are JBLs.

Seamed cones tend to be more rigid for and would be more prone to "bell" resonance but that is dampened by the seam itself. Just as welding a seam in an actual bell would tend to kill it.

The claim that seamed cones are more rigid flies in the face of every real world example I've ever dealt with.

So what you get it a lighter, rigid cone with a slightly different dispersion and more self damping behavior.

More self-damping behavior? That's definitely not what I find when I sweep them with a sine wave across their frequency range in free air.

Seamed cones show up in some very heavily engineered speaker systems, not just guitar mojo stuff. The Yamaha NS10 comes to mind. I'm pretty damn sure Yamaha chose that for real engineering reasons, not just because they were handy.

I'm betting that this is what you read:

The Yamaha NS10 Story

With all due respect, I think you're generalizing too much based on some very case-specific claims made in this article. There tend to be important differences in construction between a speaker designed to be used as a bass driver in a sealed box and a full-range musical instrument speaker built primarily to be used in an open-backed guitar cabinet. But even given the same speaker, it won't behave at all the same in a sealed box as it does in an open-backed cabinet. Try it if you don't believe me.

I also happen to be in the camp of those who don't get what people like about the NS10 :-) Based on the article you're quoting, their success was something of an accident. I wouldn't trade my KEF 104/2s or Dynaco A25s for them.

[Mark Hammer]

Though certainly not resolved yet, and likely to carry on after this post, I just wanted to thank you folks for your gentle and informative replies to my earlier post. Very much appreciated.

Seamed cones were a property of older Jensen and Rola speakers, and so were slender coil-gaps from your description. But the original post dealt with seamed cones in general, which can also include those brands/models with optimal coil-gaps, spiders, "coil hanging", etc., and those without. Judging from your comments, a seamed paper cone can be a marker of a well-made speaker, but it should not be treated as reliably so, 100% of the time with any and all brands/models/vintages. Caveat emptor!

[Rhodesplyr]

Seamed cones were a property of older Jensen and Rola speakers, and so were slender coil-gaps from your description. But the original post dealt with seamed cones in general, which can also include those brands/models with optimal coil-gaps, spiders, "coil hanging", etc., and those without. Judging from your comments, a seamed paper cone can be a marker of a well-made speaker, but it should not be treated as reliably so, 100% of the time with any and all brands/models/vintages. Caveat emptor!

Mark--Just a couple of things.

I did a bit of Google image searching, and, based on that, one might be able to generalize that Jensen tended to use seamed cones for their lower power-handling speakers. In other words, I think you're more likely to find a seamed cone in a Jensen P10R than on a P12N. Of course, then, as now, you can choose the cone you want.

I've personally seen a lot of Jensen, Rola, and Heppner speakers in of Hammond Organs, Hammond tone cabinets, and Leslie speakers, and you don't find that many seamed cones in those applications. (I would suspect that organ tones can cause some intermodulation effects on flexible cones.) I'm sure an exception can be found, but I'd bet that the majority of higher-power handling Jensen speakers had formed cones, not seamed.

Narrow voice coil gaps ARE optimal for higher sensitivity and better voice coil cooling. Are you suspicious of this statement? The downside of narrow voice coil gaps was and is that they require tighter tolerances on pole piece and top plate machining, voice coil dimensions, and more careful assembly. Wider voice coil gaps allow you to get away with being a bit more sloppy about how you make a speaker, but they do NOT, in and of themselves, make a better speaker.

[J M Fahey]

Not disagreeing with anybody, just trying to add some little extra bits:
all "old" Alnico speakers I've ever repaired had incredibly narrow (for today's standards) VC gaps.
Those guys found their magnets expensive and sure wanted to pull the best out of them.
Clearly a little extra lathe and mounting time was not a waste.
As a side note, since I started this "hobby" in the late 60's and was a very nosy and curious kid (still the same, just remove the "kid" label, he he) , I got to know and have long chats (they would have called them "police interrogatories") with wonderful old guys with tons of experience.
One bit I remember is that speakers (which were glued with nitro cellulose "speaker cement") were built and left on shelves *at least* for 15 days.
The centering shims had to be left on up to the last day, when you could apply the dustcap and magnetize them.
When I asked why, they told me that otherwise they would soon be back, scratching, and would have to be reconed ... this time waiting the required 2 weeks.
Way back then I got it as another "don't know why, just do it" piece of knowledge, now I understand the narrow gaps forced them to do that, to let the glue dry *fully* (it contracts by doing so, since it's solvent based, and de-centers the VC , even if a tiny amount), plus the cone and suspension setting in their definitive position, while suffering natural humid and dry days.
As I mentioned elsewhere, stiff suspensions also contributed to keep centering, although the side effect was reduced bass.

[Mark Hammer]

I'm on exactly the same page as you, and I think I alluded to it earlier, but maybe not articulately enough. That is, narrow voice coil gaps ARE a property of a more efficient, and sometimes "better", speaker but they need to be paired up with exquisite alignment. The narrow gap, by itself does not achieve the desired ends. If the manufacturer is not prepared to hang that cone/coil assembly juuuuuusssst right, in a narrow gap, then there is the risk of the coil rubbing against the magnet assembly and generating more friction and heat than the entire assembly can likely dissipate. Besides, any friction impairs the coil from behaving in true piston-like fashion.

It's ironic that once upon a time, subwoofers were the domain of audiophiles. Nowadays, subwoofers represent some of the cheapest crap out there, because the cone doesn't require all that much in the way of design to move efficiently, magnets are cheap, and power ratings like 300W (because the coil gap is immense to reduce the burden on the maker to achieve a slender coil-gap and it actually takes 10W to start the damn speaker moving, because its so heavy and inefficient) impresses the hell out of naive consumers.