I've had the unfortunate experience of refoaming a pair of BD2 units. Unlike Andy's MD units mentioned in this thread which have a wide magnet gap which does not require precision circularity of the voice coil the BD2 units have the Lowther style 1mm voice coil gap.
This caused unexpected complications. When preparing a voice coil after refoaming for reinsertion into such a gap, it has to be precisely circular to within less than 1/4mm. The way of doing this is with a Lowther jig, a tapered mandrel upon which you force the voice coil down as far as it will go to stretch all give arising from non-circularity so as to ensure that it's as precisely circular as it can be. For good measure, I reverse the cone on the mandrel ensuring the whole voice coil tube is precise.
Using an aluminium mandrel the problem is that this can leave grey or black marks on the paper.
When the bloke saw this, even though it's hidden by a phase plug in normal use, he accused me of devaluing his units. There was a history to his dissatisfaction as the units had presented other problems, worse.
Another problem of refoaming units is that when the foam is really old and brittle, it snaps away from the paper crisply and gives little problem in cleaning. But when the foam is just on the point, it goes like a toffee goo and is a right beast to clean. And you have to clean it perfectly as you can't stick new foam on top of goo. So I use meths to dissolve it. The problem is that once dissolved, it can be carried by the meths on one's fingers and I accidentally left a dark finger-smudge on the cone from the meths in handling the cone whilst cleaning.
Oh dear. As far as I'm concerned speakers are to be heard, to sound, to sound perfect, and visual matters especially of old refurbished units are of secondary importance.
Of course the bloke could have sent them to AER to have them done at four or five times the cost . . . . but I really wonder if when you send a unit to AER for refoaming whether they really do send you back the original cone rather than simply inserting a freshly made one. The problems of removing goo , to say nothing of glue, and get perfect results make me wonder.
In handling a number of Lowther units and seeing how AER have copied them, clearly doing enough to avoid Lowther being hot under the collar, I really wonder what's necessary sonically and what's necessary simply not to be like Lowther, and when I see that claim that AER reproduce up to 80,000Hz, about which I've commented in this thread, I really wonder about everything.
Lowther units don't all have the "Lowther Shout". I think the reputation has been unfairly attributed. The C units which have Ferrite magnets can produce resonant frequencies in the region of the sound of cymbals - but this isn't because of the magnets. It's because there's a short paper cylinder connecting the voice coil to the cone, and resonances between one end of the paper and the other are not damped. This is cured by the A series and DX and EX with Alnico or Neodimium magnets. It's not the magnet that cures the shout but the longer length of paper cylinder connecting the two units and this provides enough disconnexion to interrupt any travelling waves. The paper is a treated paper like the rest of the cone. The foam spider used to be glued on with a brown glue, possibly shellac, which is brittle and often snaps away from the paper. I use Copydex, a latex glue for gluing the spider, which in future will always simply peel away from the paper.
It was coming to the gluing of the spider on the AER that I ran into real trouble. AER use some sort of glue possibly like silicone which can't be peeled off the paper without danger of tearing the paper. Unlike Lowther treated paper, the AER voice coil is on an untreated paper of the consistency of photocopy paper. Not only could I not remove the original glue, and can't imagine how AER can either, upon gluing on the new spider the water content of the Copydex glue simply disintegrated the paper. Inserting it onto the mandrel as a former to keep shape, it simply tore off. This was a surprise and a nightmare beyond contemplation.
Upon consulting an old friend who used to work for Lowther he said that they had this sort of problem from time to time and it was possible simply (not actually) to glue a new slither of paper inside to reconnect the voice coil to the cone and resolder the wires, and which even to my surprise I did successfully. So the unit was in working order again and working well, with no audible difference between the sound of the two newly refoamed units, the other one on which I'd used a thin silicone as glue.
As soon as I had the problem I confessed to the owner and this put him into the blackest of moods.
I'd loaned him a pair of the 97dB Lowther Challenge units available on
eBay, which are rather good. (Perhaps I might talk about those on another thread) When he arrived to collect his AER units I asked him if he had brought my Chinese units back. He hadn't and from which I deduced that the bloke had come merely to haul me over the coals and give me grief.
He complained that I'd devalued his units, but the reality was that I handed back to him two perfectly serviceable newly refoamed working units.
AER charge 560eu each for refoaming (if in the light of what I've seen whether that's really possible) or 1500eu for reconing and upgrading. So for anyone really wanting the latest most improved AER experience an upgrade should be the way to go and to ensure top value is kept in the units.
As he was extremely dissatisfied with the quality of my work, with a mark on one and the other with a repaired voice coil assembly, I didn't charge and I'll be surprised to see my Chinese units back again.
I wouldn't be surprised were he to have intended keeping and using my Chinese units, as they're good, and expecting to sell the refoamed AER units for top whack.
He told me that he'd seen on YouTube how simple it was to replace Lowther foams. Ha ha! I responded that if he'd done his AERs himself he'd have got into a worse mess than I had found myself in, and then not have been able to repair them at all.
Having looked at the AER and the Lowther units, for a number of reasons I know which I'd choose for myself. The roll back surround to the whizzer on the Lowthers needs to be flipped forward to restored to the original vintage format and then the A, DX and EX series are superb.
And for anyone wanting a cosmetic as well as a functional restoration of AER units, please do go to AER. I don't want to be in a situation of dissatisfaction ever again.
Best wishes
David P
