Originally Posted by Audiokarma
Initially, the HD series had two digits, such as HD77 and the top model HD88. They replaced the Imperial line but still retained the foam grills. They were superceded by the 3 digit series such as HD770 and top HD880 which went to even nicer cabinets and cloth grills. Similar driver configuration. Soft dome tweeter and super tweeter. I believe they still had the removable foam plug for the port, as you mentioned. Not sure who made the drivers, although my speaker repair tech had a reference book that said the woofers were made by Oxford. They are in for refoam right now. The woofers do have decent size magnets and I believe a 2" voice coil but are stamped steel, not cast aluminum, like JBL's. :( Don't recall seeing the DS series...will keep an eye out just so I can see what they look like.