Jafant asked I relay what Rob Gillam might know.
Rob replied quickly that these are indeed model 4 and that the bottom element is a passive radiator. He added rebuild kits are available for the tweeters but that the woofer and passive radiator are no longer available ( mine all are good happily).
Rob also attached a model 4 marketing sheet contained specifications, and an owners manual in pdf format. Thanks Rob. Great service for a product bought at a garage sale.
When I got them, the passives surrounds were crumbling. The tweeter and midrange were intact. They must have used different material on the passive.
I ordered a surround replacement kit from Simply Speakers and that worked out perfect. First time I EVER replaced a surround. They include special glue, excellent quality surrounds and complete instructions.
Highly recommended.
Cheers