Dear @aainpb : Not from the 70's but I own and am the original owner of a marvelous ADS L2030 ( heavy tweaked by me, you can read here:
https://systems.audiogon.com/systems/3080 ).
Those are acoustic suspension and exist other two models: the L1230 and the L1530. This one along the 2030 were used as speaker monitors by Telarc recordings.
Even today my speakers are a true challenge for almost any speaker. Those ( especially. ) main silk made midrange and tweeter drivers are just extraordinary by any today standards.
https://gear.discogs.com/gear/68646-ads-l2030
this is a restored pair not tweaked ones:
https://audiokarma.org/forums/index.php?threads/ads-l2030-restoration.801968/
http://sportsbil.com/ads/l-2030-brochure.pdf
Why today exist only a few acoustic suspension speakers design? I really don't know.
Btw, M.Kelly was the ADS L2030 designer whom years latter founded Aerial Acoustic speakers and his today designs are not acoustic suspension but ported one: ? ¡ ? ¡ ?
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.