More Adventures in Speaker Re-foaming
I've got a pair of treasured SD Acoustics speakers that have bass drivers in need of a re-foam job. I fancied having a go at this myself, but I didn't want to make a mess of it so I thought I'd get myself a cheap pair of knackered speakers and make a trial run before doing the real thing. The idea being that I could pay next to nothing for them, learn a few valuable lessons and then sell them on as a working pair for, perhaps, a small profit. Great idea - an education in speaker repair and small scale economics all rolled into one and maybe a bit of fun too, for good measure.
So, at the end of last month, I managed to snag a pair of Acoustic Research 44BX's for a very good price indeed. Great, I thought - 3-ways. That'll give me 4 drivers to practice on! In the photo of them, they looked intact, but if I know anything about AR speakers, it's that if the foam hasn't got yet, it's only because no-one's checked them. The minute anyone touches them they'll crumble!
When I arrived at the vendor's place to pick them up, he told me that the mid-range drivers had gone but he hadn't noticed them when he took the photos for the advert. However, the bass drivers had been changed a while ago. So, only two drivers to work on then, but cheaper, so on balance not bad.
I had thought the project might make an interesting subject for a thread on AoS, then, guess what? Just a couple of days later, Alan posted a thread describing in great detail exactly how he had done a similar job - 'Allison Bass driver repair'
In Alan's excellent thread he described how he had chosen to remove the dust caps & use shims to centre the voice coil in the gap - something I had decided that I was going to avoid if possible.
So, somewhat spurred on, but also slightly worried, by Alan's thread, I ordered some foam rings, did some reading and waited. On Sunday, I took the mid-range drivers out of the cabinets:
Totally knackered foam, but the spiders were in good nick, with no sagging at all and plenty of bounce-back.
I noted that the cabinets were quite well built, despite the vinyl wrap, the mid-range drivers having their own separate enclosure to work into. The front baffle is MDF & the remainder of the carcass is of quite good quality chipboard (if there is such a thing!).
The clean-up job took a long time - lots of isoprop' alcohol, delicate work with various craft knives of different sizes and plenty of care and patience.
So, today was the day when things went back together. I glued the inner rims first and gave them an hour to set. After this, I started to get really worried about getting those voice coils properly centred, as whatever I did, I didn't seem able to consistently find the sweet spot.
Then I remembered there was an AoS thread which mentioned using a battery to charge the coil in order for it to pulse and eventually cause it to centre itself.
A quick search found Rob (hoopsontoast) and his 'My bits and pieces' thread, where James said:
Well! This is what I tried and it worked like a dream - not a sign of any rubbing. What an absolutely brilliant piece of advice, thanks a lot James - I owe you one!Originally Posted by istari_knight
So, the work continued:
...........and I ended up with two fantastic looking drive units:
I connected them to the Levinson ML9 and they sounded great. The photo below has them looking fairly small beside the big Mirages but they're actually quite substantial stand mounters at 0.77m tall, with a footprint of just over 33 cm x 33 cm - a 10" woofer and, bloody hell, can they do bass?! I'm actually thinking I may not sell these at all & keep them instead, to use in one of the other house systems instead of some little Tannoys - dropped onto some proper stands, they could be something quite special - we'll see.
Anyway, now I feel completely confident in tackling the SD Acoustic speakers, which was the whole point of the exercise.
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