Magnepans were around in the '70s. (That's about 5 decades.)
I had investigated some kind of "planar"
speakers at a iocal "hi fi" shop and wasn't impressed. I'm pretty sure they were electrostatic, not magnetic.
By then I had settled in with my two bass ultraflex speakers (as above) and was dinking around with reel-to reel tape decks. I had a Sony TC-560, I believe it was*. The trouble with deep bass speakers was I could not find or afford a record turntable where the turntable rumble didn't come through, so I was moving to tape. At one point I was getting pretty sure much of the turntable rumble was from the original record cutting lathes since it seemed to vary from record to record.
I had my own rifle range at that point in life and I began to drift away from achieving audio perfection since my own hearing was drifting away from perfection --muffs and plugs notwithstanding.
Terry
*ETA Yes it was. Best "portable" (ha!) tape recorder of the time:
"Sony TC-560 Reel to Reel Tape Recorder Four track stereo and mono recorder 7 1/2 ips (19 cm/s), 3 3/4 ips (9,5 cm/s), 1 7/8 ips (4,8 cm/s)
20-21.000Hz at 7 1/2 ips 20-15.000Hz at 3 3/4 ips 20-8.000Hz at 1 7/8 ips Power output 5W per channel 56 transistors and 26 diodes."
They averred they had some kind of super dooper oober doober technique for keeping the recording head gaps extremely small which allowed the great high end response.