On the DM7 front, I am about to let mine go, and as with the above DM5s, I think the ferrofluid needs replacing.
Sad to see them go, despite Charles' opinions on them I happen to think they have a lot going for them.
On the DM7 front, I am about to let mine go, and as with the above DM5s, I think the ferrofluid needs replacing.
Sad to see them go, despite Charles' opinions on them I happen to think they have a lot going for them.
Location: Portsmouth, UK
Posts: 503
I'm Steve.
Ye Gods, what is all this fretting about ferrofluid! And its viscosity.
When it dries out, your tweeter clogs up and stops working. It's happened to me. It's a mixture of iron oxide and oily kerosene.
http://www.bluearan.co.uk/index.php?...e=manufacturer
That's enough for about 5 tweeters. Clean out the old from the magnet gap and put in the fresh usually. Ocasionally you need to unsolder the voicecoil leads, but this is rare.
It has a 2dB damping effect at either extreme and partially controls the low frequency resonance and provides some cooling to the voicecoil.
Location: Cambs
Posts: 9
I'm Frank.
Still retain DM7 mk.1 from 1978. Always driven by Meridian 105's.
This speaker caused endless grief.
The original Tweeter would 'blow' (wire-stress when threaded through the doped fabric diaphragm?) - and had a c.5kHz resonance (identified by Peter Tribe when visiting the factory).
The Bass cone assembly would slap into the chamber rear & concertina/unravel the former/coil. The roll surround also originally too shallow.
The ABR initially had a metal slug connector - spider to foam - it would detach/unglue itself - replaced by a flanged plastic version.
Later took the precaution of getting 10 treble diaphragms (mk.2 polyamide - still mostly unused)- & noted some variation in coil windings (B&W considered that had no effect..). A residual problem was the kapton former could 'bubble' due to heating and attaching to the pole-piece (treble disappearing). There was no ferrofluid in the Mk.1 tweeters; wasn't aware it was in the mk.2.
The Bass unit was rather a mass of coloration - later production had doping applied to the cone rear - though the source mostly resided behind that..
Applying a thin epoxy 'veneer' from v/c winding end to cone eliminated much, and improved 'detail' (also has prevented further v/c buckling); but the bass unit is inherently 'sluggish' due to v/c mass (+ plastic former under the dust cover).
By comparison a modern QUAD kevlar bass unit is a Revelation for detail/lack of coloration.
Splitting the x-over had some advantage - as did slightly adjusting the treble resistors for output (the mass of bell-wire leading to the upper rotary adjuster being disconnected).
After all that, it became relatively trouble-free; but driver replacements had easily added 50% to the original (20% discounted) price.
Location: Wales
Posts: 3
I'm Howard.
I've been using Yamaha C2/B2 combo since the late '70's. Only amps I could find to do the job properly.
Location: London/Durham
Posts: 6,882
I'm Lawrence.
Nice thread resurrection.
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