Favorite obsolete formats.....

Transcription discs....'course, they need a tone arm the length of your forearm, but Hey....*L*

Oh, and a platter the size of a large pizza....

@yogiboy ...my brother had a later version of a 'car record player', bright chromy underdash trash.
I suppose it would work acceptably if your suspension allowed one to float on down the highway, but this didn't in his 56 Chevy....
It could do broadjumps with a minor road wrinkle.
No clue as to how many grams it didn't work at...

Your memory test:  'Vibrasonic delay units'?
A set of long springs within a equally long metal box?
Gave the sound that 'echo' that was novel....

Until you hit a good sized bump....

The sound elicited by those springs hitting the inside of that box was 'memorable'...*L*