The Re-coned 416-8C's

[bfish]

Ron,

Doping is done only on the cone compliance (surround), specifically, from the inner edge of the frame where the surround is glued, to the outer edge of the cone (just the pleats). The purpose is to damp cone movement to the desired degree, and is achieved when the cone will move a specified distance when a given amount of force is applied (mm per gram deflection). Think of it as mechanical attenuation. You're effectively 'stiffening the spring'. The obvious question that arises here is 'how much is correct?'. These parameters are usually known only by the manufacturer, which is why we test, do a little, then retest, until performance is as near spec as possible. Even if the deflection parameters were known, few would have the means to measure it with any degree of accuracy. Once you've determined how much doping is required for a particular application with a particular dope, repeating the procedure on successive units becomes much easier. I'm not trying to be vague, that's just the way it is.

NOW, keep in mind that some surrounds may be pre-doped, and require no further treatment. Paper or foam compliances seldom need doped. Cloth compliances, which have an open-weave appearance similar to gauze, often do.

The specific type of dope also varies per application. There are both solvent-based, and water-based dopes, each with particular applications. I don't believe the old, black, sticky dope Altec used on many models is even still available, I think it was called Flex-Air. Like most reconing products, none of them are readily available to the general public.

[bfish]

Orange County speaker retails small bottles of the 3 most common glues, I think $15 will get a bottle of each. They probably have shim too.

I bought a roll of shim stock long ago that I use. It's white plastic, 1-1/8" wide x 0.005". It would be a little thin for GP apps with lots of air, but for the snug Altecs, its just right. I cut a couple of pieces just long enough to wrap around the pole piece without overlapping. Sometimes you can get 2 full wraps in, sometimes just one. Then I cut several short shims, about 2", and slip them in vertically until tight, in as many equally spaced spots as possible. I'd say the average Altec 3" coil will shim tight at .010" to .015". Plastics best, no memory, and even thru the 2-3 layers, you can still see the inner former surface, and any marks you may have placed there.

The reason to insert the final shims endwise, is to reach the 'far end' of the former, to make sure its not cocked. By inserting the first 2 wraps till they're flush with the former end, you've got more than half the former length shimmed, and nothing's in the way of the rest of the process. Shimming till tight not only keeps the coil in the sweet spot, but keeps the shims from vanishing....ooops!

Do a dry fit to check it all out, should be snug, but not so tight as to move the shimmed coil when installed. If you got the coil leads facing the terminals, break out the glue. The white can be used everywhere, including doping, thins with water, and gives you about 20 minutes to smooth, check, whatever. The honey's really best for the coil joints and the spider/frame, but it's quicker, 5 min or less, and the black is for the cap and leads, 30-45 minutes. Keep some acetone handy for boo-boos. I've done several using only white.....we do have some really good glues today.

On doping...those pros know from experience how many coats of what dope give the correct damping. Lacking that experience, I suggest a sensitivity test before applying any. Then, IF NEEDED, one thin coat, then retest, repeating until you find the spot you're looking for. Once you put on a little too much, there ain't no lookin' back.

[RonSSS]

Doh! After posting, I figured out that you meant the surround.
Bill at gPA sent me a bottle of what he uses. It's solvent based, and is clear. Of course it looks black when applied.
When I get to that point, I'll experiment!
Thanks,
Ron

[gearjammer]

Correct it is CLEAR and only looks black when applied!!! and if you put a light on the backside of the surround it does not even look black at all!!!

[Brek]

I resently refoamed my 411s. I got generic surrounds from Simply Speakers. The instructions stated it didn't matter if you glued the surrounds on the top or bottom of the cones. It wouldn't change the sound.

BTW, the speakers sound wonderful. Good mid and low bass. Lots of punch.

[amh]

Hey RonSS,

Found some more info if you ever consider doing your own re-cone. This is from a newer Altec service sheet and follows bfish's outline almost exactly. The difference is this sheet is titled "Replacement diaphragm assembly kit B method" and appears to cover kits that have the cone and VC separate as opposed to pre-assembled. It also lists some actual adhesive and dope brands (no idea if they are still available).

The additional steps to secure the cone to the VC are as follows. Taken from the point in the instructions where the spider is glued in.

10) Fasten spider by pressing down against cemented surface of speaker frame, completely around perimeter of spider.

11) Apply proper cement to surface of speaker frame where edge of cone rests. See chart for proper cement.

12) Place new cone loosely in position, checking that VC leads are inside cone apex and aligned with eyelets in cone.

13) Fasten outer edge of cone by pressing down against cemented surface of speaker frame, completely around speaker.

14) BE CERTAIN THAT CONE APEX IS FREE AND EVENLY SPACED AROUND VOICE COIL SUPPORT JUNCTION. ALLOW APEX TO SEEK IT'S OWN LEVEL ON VOICE COIL FORM.

(your 1/8" Ron. If this step is missed it's a sunken cone)

14) Apply proper cement to area of cone apex/voice coil support junction. See cement chart.

15) While cement is still wet, lay voice coil leads along inside surface of cone.

16) Allow 10-15 min of drying time for cone-voice coil junction cement, before passing voice coil leads through eyelets in cone.

From here onward the procedure matches bfish's outline.

And the mystery glues are......

Atlas 9A1007 (dust dome to cone and VC leads to cone)

Moyen 222 (cone and gaskets to frame on some models)

Moyen 3055 (cone and gaskets to frame on some models)

Loctite 422 (VC to cone on some models)

Leebond 3025 and Leebond catalyst (VC to cone some models)

Air-Flex 510 (cloth surround dope)

This procedure would explain sunken cones if not done properly. Hope this helps.

[RonSSS]

Thanks Alex!
More good info.
I think we are getting this nailed down.
I will be doing my own re-cones. I found nice clear plastic shim stock here in varying thicknesses.
For the glues, I think I'll go to my local reconer. They have the stuff for sale even.
Thanks again!
Ron