Cracked cones... repair or replace?

S

Saxguy1962

New Member
Hi all... I have just cracked my Mission 732 cones after inadvertently hitting them with some "Manson" and forgetting to dial down. I notice that the cones are so brittle, and cracks run around just by merely touching them!

I love these speakers, and apart from the now rapidly deteriorating cones, they suit my setup, and I would hate to have to bin them.

So, first question, can I re-cone them? Are the parts available? Or... any alternative cones out there that would deliver the same sound and drop right in?

I did notice on an old blog that someone re-coned some speakers, but where he got the cones from he didn't say!

Thanks.
 
Are the cracks in the cone or in the roll suspension? 'Run around' sounds like the foam has disintegrated, in which case the repair is cheap and easy.
 
Hi Nat.
The cracks are in the cones themselves. They look like some sort of translucent plastic, which has turned brittle with age I guess. If you touch a "crack" with your fingernail, the crack just spreads out like pane of broken glass.
 
Oh dear. I think you need to find replacements. If Falcon is still around, they might be able to suggest something - that's assuming you are in England, which may not be a justified assumption. On the other hand, they might be able to suggest something anyway.
 
Given your location and the availability of replacements and doubtful availability of rebuilding services or parts, I would suggest a hail Mary attempt at repair.

"paint" the cones with epoxy.

it may not be a perfect solution, but I doubt you can get a perfect fix.
 
Oh right - your avatar makes it clear you aren't anywhere near England. So I agree with blhagstrom that you don't have anything to lose by trying to repair them. I think I would try the kind of stiff tissue paper used to wrap fancy presents, and try to cut it to conform to the cracked parts of the cone, fit it into the cone, then paint it with epoxy, using as little as possible to get it to stick to the cone. The tissue will strengthen the cone more than just epoxy will. Try not to use any more than necessary in order to change the resonant frequency as little as possible.
 
... so, if i was still in the UK, could I get replacement cones to make the repairs?
I'm thinking surely there is a better option than painting them up with epoxy, as this must change the sound, and they will look shabby too.
Oh well, it might just push me into my first speaker build project!
 
No idea if they are available, and certainly it's worth looking, if you are willing to pay the freight. Or you might be lucky and find a pair the next town over - if they were sold in NZ, as opposed to brought by someone from the UK, then probably there is more than one pair in the antipodes. The nothing to lose theory is that, while you are looking, an ugly compromised speaker is better than nothing. And it might give some insight into whether it is worth pursuing a possibly expensive pair of woofers - if you hate the high end of the speakers, that would suggest that you won't be too happy even with the exact replacement woofers.
It is true that you might enjoy redesigning the speakers to use more available woofers. Just be aware that this could be even more expensive than the original replacements would be, and might be much less successful, though, typically, in the first blush of enthusiasm, every DIY job sounds great. It's only later you realize that speaker design is harder than it appears.
 
I know what you mean when you say "first flush of enthusiasm"... I have read one or two speaker design books previously, and I admit to being more than a little blown away. In fact I have one book right in front of me, The Loud Speaker Design Book, By Vance Dickason. That is quite a technical book alone.

As for the not happy with the high end, not sure where you got that, as I am okay with it. I do however, admit to an error (doh!) in that I did forget to adjust the volume level... bah! I must have had these for nearly thirty years, so I guess they dont owe me anything.
 
If you have enough power to crack the cones, an epoxy paint job isn’t going to change much as far as sound.

FWIW, there are speakers with factory coated woofers that were intended to give strength and mass to the cone. Infinity Monitor Jr have that. It takes either more power or sloppy damping factor to get the bass out of them. Or just lean on the bass control a bit more.

Speaker drivers are basically an electric fan.
A motor (the voice coil and magnet) and a fan blade (the cone). All it does it cause air disturbance. Sound is just vibrations in the air, higher and lower pressure waves.

Given the age of the gear and the parts (electrolytic capacitors age, surrounds and spiders age) they already don’t perform like the used to. And that may not be a bad thing. I have some gear that I know has issues but it sounds wonderful.

A thin layer of something to strengthen them is a fine idea, but something strong and light that absorbs the epoxy is the trick.

Oh and FWIW, a trick I’ve seen and used to fix up paper cones is to just paint them with Aleen’s glue.

I’ve seen epoxy repairs done to valuable graphite cones and they turned out great and were still valuable. I think the artist used tissue paper to help keep the epoxy in place. Sort of like fiberglass repair work where the mat is saturated with resin.


Good luck with your mission to repair your Missions.
 
For some reason, I gave myself the impression that you picked up the speakers and the fell to pieces before you really had a chance to listen to them. Clearly I didn't read your original post carefully.
Having looked at it again, it seems to me that you must have one of the series of Missions that had polypropylene woofers - Argonauts, or some thing like that. They were a successful line, so there may be more chance of getting a replacement woofer than I assumed, and maybe even in New Zealand. Many plastics crosslink over time and get brittle, but I don't think that it is endemic to polypropylene drivers, so there may be some out there.
Incidentaly, gluing to polypropylene isn't the easiest thing in the world, so the epoxy idea may not work, even if it's worth a try.
 
Gluing low-energy plastics like polypropylene isn't easy, as Nat noted. It would be an understatement to say that polypropylene is largely inert for the purpose of traditional adhesives.

One of the few adhesives I know of that will do it without spells, incantations, and magic, is 3M's Scotch-Weld DP-8005, a two-part adhesive able to bond polyethylene, polypropylene, and TPO without special surface preparation. See:
And a description and review of it:

I just pulled those off the Interwebs to save you the trouble of finding them. No connection to either.

Some of the reformulated cyanoacrylates claim to be able to bond when a surface activator is used, but these adhesives tend to be brittle, have poor hydrolytic stability (degrade with moisture), and offer poor strength. Loctite makes a two-part system, which I never had even the slightest success with on the plastics upon which it was claimed to work. See:
 
I've had very good luck with Plastix, though now that it's Plastics maybe the formulation is different. My problem with it is simply that it is almost never available in local stores. It seems that they make some, ship it, and then wait til it runs out to make more. That can't be actually their business plan, but it seems that way.
 
Plastix is the former name of the Loctite "Plastic Bonder" product I above described. This accounts for your difficulty in locating a supplier.

The activator is heptane.

This product is equivalent and, as described, is similarly unsuitable for the same reasons.
 
I've been using it when I can find it for over a decade now, possibly two. So it's not the name change.
I've never tried it on polypropylene cones, so I don't doubt that you are right about its ineffectiveness for that purpose.
I've wondered what the activator was, and I've wondered if the superglue itself is the same as regular, and it's just the heptane that makes the difference. Do you know? Sometimes the superglue itself gets hard while there is still heptane left, and it would be nice to be able to use it with regular superglue.
 
The Plastix product is made by Henkel, just like the Loctite "Plastic Bonder" brand. I looked it up when you described it.

The physical appearance of the packages identical. That's no guarantee the product is identical, of course, but many times products are differently branded for different distribution channels to avoid pollution of the brand name. If you look at the Fantastik sold in fancier stores it is branded as Fantastik, whereas in Target and Walmart is is branded as "Scrubbing Bubbles". So I would conclude the same sort of issue is in play here. Different distribution channel.

The heptane is the surface activator in the magic-marker like pen, and is not added to the cyanoacrylate. It cleans the surface, partly dissolves plastics susceptible to this (heptane attacks the surface of many plastics, including styrene and ABS), and probably contains some amines (NH3 molecules, name is similar to "ammonia" for this reason) to accelerate the curing process.

Cyanoacrylate hardens because it polymerizes into an acrylic. What happens is the polymer is made and then cracked into monomer which is pH adjusted, i.e. made acidic, to prevent it from curing. Atmospheric CO2 slowly neutralizes the acid. If you want to do an experiment, add baking soda to the CA and you'll see it rapidly cure, but in a rough form which is bubbled and irregular. This is why CA must be applied in a very thin layer and when used in thicker layers must be built up in separate cures.

A similar reaction with CO2 sets lime and plaster.

The basic difference between the types of CA is modification of the end to make it more or less rubbery. This is why surgical glue is flexible.

Anyway, that Plastix product appears to be identical to the Plastic Bonder one.
 
Very interesting - I'm curious how you are so knowledgeable. Are you a chemist or work with different glue types? Thanks for the information.
 
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