fowler:can any one who owns some atc 11s tell me how to clean the drive units on them ?
Unfortunately there's no safe way to clean the dust off. The advice of jaxwired is sound, in that it would be best to leave them alone.
However, I bought a second-hand pair of (original) SCM-7's some years ago, these had clearly been used without the grilles in place and dust had collected onto the sticky "doped" surface of the cone and voice coil dust cap. ATC were happy to send me a pot of their doping solution (for a cost) to enable me to recoat (as thinly as possible) the drive units. They now look pristine!
Of course to avoid a similar build up of dust in future, it'd be best to leave the grilles in place and remove them only when you're listening, if you prefer the sound without the grilles on!
Regards
Lee.