Favorite obsolete formats.....

Somewhat surprised that no stories of a Quadraphonic system have emerged. Maybe they weren’t that popular?I remember the Simpsons episode where young Homer was trying to hang out with the cool kids that had a Quadraphonic setup in their van only to be turned away. 

cd318 got it right.

 "The sound of some of those cassette car units (1980s/1990s) seemed to be a lot better than what I now hear in many car CD players.

That could just be my memory but there's no doubt that there were some very good car units back then."

The Alpine 7347 (circa 1985) skyrocketed the high-end car audio industry with some of the best sounding car audio systems to date. Of course, great amps and speakers played just as important of a role.  Even though the CD player offered a better signal to noise, the analog sound from the cassette was consistently smoother sounding.  DAC was only in its infancy back then so grainy sound was what you got with the CD.  High-end car audio systems today can be really good.  However, the industry has shrunken due to how cars are made with the OEM system being integrated into vehicle functions.  The audio enthusiast, however, will still pursue the products that integrate with the OEM designs and build some very impressive car audio systems.  Listening to a top flight car audio system is really a great experience. 

It wasn't a medium, but a source.....the lowly hand-held transistor radio that only played AM, but introduced many of us to the world of modern (for that time) music. Elvis, Chuck Berry, Little Richard, Fats Domino, Little Eva, along with many others that kept us up way past bedtime until the battery died. The fancy ones had leatherette cases, the sound was as low-fi as you could get, but it was a passport to rock 'n roll nirvana and cool personalities called DJs.

Edison wax cylinder, of course!

I add a vote for multichannel SACD.