Paper cone woofers died in 1962 .... a look back

@lastperfectdaymusic, the ESS Transtatic put the KEF B139 in a transmissionline enclosure (hence the "trans" part of the name; the "static" for the RTR electrostatic tweeters). That enclosure was very similar to that of the IMF Monitor, which also had a B139 woofer. Irving Fried (IMF were his initials) was a fan of transmissionlines.

I heard a Leak loudspeaker with a "sandwich" cone woofer in 1971---it was excellent, the best speaker I had heard until hearing my first ESL later in the year. That year I also heard the ESS Transtatic I, which had three RTR ESL tweeters and the legendary (with good reason) KEF B139 woofer, itself having a sandwich cone with a flat front face of Styrofoam and a butyl surround. I currently own a pair of the Transtatics, and their B139’s are still operating perfectly, as are the KEF 5" B110 Bextrene midrange drivers (the first commercially available Bextrene-coned driver) and the RTR tweeters.