Centering cone during surround replacement

[Kanga]

Hi All

I have two sets of drivers which need surround replacement.

One is a set of paper coned Boston Acoustics A 60 8" drivers, in which the foam surround is completely gone. The other are my AE1 aluminium cone woofers with aluminium conical dust cap, which have foam that is on the way out but still completely intact.

Reading the Speakerbits site http://www.speakerbits.com.au/pdf/gen_refm.pdf they say that you need to remove the dustcap and insert shims in the voice coil gap to centre the cone before gluing in the new surround. Then you need to replace the dust cap. Is this really necessary, or is there another way of centring the cone while leaving the dustcap alone?

Any experience out there?

Mick

[SY]

Having five cats and a toddler, I have done more than my share of surround replacement. Shimming is the right way to do it. Don't worry, it sounds fiddlier than it actually is.

I've done the shimming two ways: using a conventional set of shims (four of them stuck in the gap at 12, 3 6, and 9 o'clock) and a tubular shim custom made for the VC assembly. The latter, if available, is more convenient, but the former works fine.

[Nappylady]

I've never actually replaced a surround, though I have taken apart a lot of speakers. :-)

I read someplace (don't remember where) that you can do it by feel--moving the cone all the way one way, then all the way the other way, and then finding someplace in the middle to hold the cone whilst gluing it in place.

Shimming is almost certainly a safer bet, but if you can't do that, doing it by feel does seem, IMO, to be doable. Just be very careful. Voice coil rubs really suck.

[Kanga]

Thanks for the replies so far.

I'm not so worried about the actual shimming process, just the process of removing the dustcap and getting a new one back on again, particularly for the AE1s.

For the AE1s, which have existing surrounds that are OK, I was thinking of somehow securing the cone in the current location (not sure how) and then attaching the surround.

For the A60s, the spider seems to be holding the cone concentric, but rotation about an axis running perpendicular to the cone axis is possible. With the speakers sitting with their their magnet on a horizontal surface, the cone seems straight, so again I was wondering about securing the cone in that location and then glueing the surround.

Any further ideas?

Mick

[Nappylady]

Absolutely, when replacing the surrounds, do it with the driver "looking up"!

Actually, there are some 12"ers in my garage (pity I'm not allowed to touch them, I might turn them to gold! ) and the surrounds are almost completely gone, but if you set 'em face up, they still play just fine... power handling is reduced a bit, but they don't rub this way...

[Kanga]

I've now replaced the surrounds on both sets of speakers without removing any dustcaps, so I thought I'd describe how I did it.

For the Boston A 60s, which had no surround left, I made some small triangular shaped blocks from MDF that fitted in the gap between the pressed steel frame strut and the bottom of the cone. These were attached to the frame struts with plasticine so that they could be moved around. When pushing the cone on its top edge the cone tilted over and came to a natural stop. This is presumably where the voice coil hits the edge of the voice coil gap. I assumed that the spider was holding the cone concentric to the magnet assembly.

With the cone facing up, I positioned the four blocks so that the the top of the cone just contacted the block when pushed over to the natural stop, and so that it was parallel to the block when the cone was allowed to find its natural centre position.
This gave an even gap between each block and the cone of around 2 or 3mm. This gap was then filled with cardboard shims so that the cone was snuggly supported at four points.
Then the cone surround was replaced as per normal.

I took a couple of photos of this, but unfortunately they didn't come out well enough to include. The drivers haven't be run in the boxes, but I did run them in using LF sine waves, and there seemed to be no problems.

For the AE1s, which had the surrounds largely intact, it was just a matter of supporting the cones around their circumference in their current positions. I used 4 small bolts to do this, but I won't describe how I supported these bolts, because I don't think it would be applicable to other drivers.

I've been running the AE1s for the last couple of weeks and they are working fine.

For any Aussies looking for surround replacement parts, here's what I found.

Searching the net will turn up Speakerbits quite quickly. They seem expensive for the Chinese surrounds that they were selling.

Another supplier is ME-sound, who sell surrounds really cheaply (maybe the same ones as Speakerbits sell for much more), but the sizes didn't suit my speakers.

I bought mine from Speakerworks in NSW, who claim to be getting high quality surrounds from JBL in the US. They do lots of speaker repair work for manufacturers in Australia, so must be doing something right. Cost was $40 per pair including shipping. Two containers of glue were $5. Don't be put off by the fairly unhelpful woman who answers the phone. If you can talk to Peter, who runs the show, he is very helpful and knowledgable.

Mick

[pinkmouse]

Hi folks, sorry, I missed this thread and now my advice is a little late!

But I will post it for others interest anyway

The glues used especially on dust caps, and most surrounds and spiders are usually amenable to a little softening when heated gently with a hot air gun. The glue doesn't weaken and give way completely, but a little gentle persuasion with a blunted off scalpel blade to prise the bits apart usually works well. This is how I salvaged the surrounds and dust cones in this thread.

If you ever have any old dead drivers that are beyond repair, it is always worth trying to take them apart without damage, the practice will be worthwhile one day!

[Circlotron]

Hey Kanga, what suburb are you in? Hampton Park this end.

[Nappylady]

Careful with the heat-gun idea. My dad and I tried that once and ended up melting the surround. While this wasn't a *huge* loss, it was still rather disappointing... and the smell! YUCK!

[mrfeedback]

Hello Mick,
My tried and proven method is as follows.
Use a small brush or cotton bud, and keep moist the dome glue joint with tolulene, until the glue turns to gel and the dome lifts off easily - up to half an hour depending on the glue.
Cut a strip of suitable thickness paper or card and fit it down into the VC gap as a shim so as to centre and align the VC former.
With card thickness that causes a slight inteference fit, the cone can be raised up and parked higher than the normal rest position by 5-8mm or so - blocks of suitable material can be packed between the underside of the cone and the basket to retain this position.
Carefully glue the new surround to the edge of the cone and ensure that it is perfectly concentric and flat - do a trial fit before adding any glue first.
leave the driver aside for a day or so to allow the new surround to bond to the cone fully.
With the shim in place, apply glue to the basket and slide the cone down to the normal rest position, and carefully press the surround into the glue.
Whilst the glue is still tacky, carefully remove the shim and confirm that the cone can go full travel without scraping.
Keep pressing the surround into the glue periodically until it is firm, and leave the driver aside for a day or so to allow the glues to fully cure.

You should now have a good as new driver.
I have used this method for years, and if done carefully works perfectly well.
Wanna know how to center a Dynaudio single piece cone ?.

Eric.

BTW - Jaycar sell vulcanised surround kits - 8" for AUS$20.00 and they are perfectly fine.