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Late reply, but I thought I would add some facts for reference.=20

Asbestos fiber was used in a wide range of materials, such as insulation, f=
looring, siding, mastics, caulking, fiberboard, cloth, plastics, gaskets, w=
ashers, etc. Even though some asbestos containing materials and some types =
of asbestos fiber are more hazardous than others, all of them are potential=
ly hazardous.=20

I own a pair of early AR3s, and I would be very surprised if they did not c=
ontain some form of asbestos. The black caulking used to seal the woofers i=
s almost certainly Dum-Dum brand, which was widely used and contained asbes=
tos. But the fibers used as a binder in caulking and similar products pose =
little if any risk. The problem is with loose, dry asbestos, or friable asb=
estos.=20

With respect to the AR3's the only real concern would be the loose fiberous=
packing behind the cabinet. Asbestos packing was commonly used to insulate=
circuit boxes, and because of its fire-resistant properties and relatively=
low cost at the time, I would say that there is a pretty good chance that =
AR and/or other manufacturers would have used an asbestos blend as an insul=
ator/dampener.=20

Having said that, the only real risk of exposure would come from opening up=
the speakers. If you are concerned about exposure, I would recommend that =
you open the cabinets outside or in a garage, and wear appropriate respirat=
ory protection.=20

Most studies indicate that asbestosis and mesothelioma are caused by prolon=
ged and repeated exposure to asbestos. Nevertheless, it's a good idea to ta=
ke some precaution when working with any type of fiberous material, whether=
it is fiberglass, mineral wool, polypropylene batting, or asbestos. Inhali=
ng fibers can cause scarring of the lungs, which, over time, can contribute=
to respiratory problems.=20

tl;dr- Closed speakers are safe, but take some precautions when working ins=
ide the cabinet.