My first gobsmack moment was hearing a K-Horn mono tube system around 1959 in a large room playing X-MAS music and popular vocalists of the time.
My second GS moment was hearing 2 K-Horns in stereo (same room) the following year (think we were invited over for an impromptu indoor Halloween party as it had started raining around dinner time and it was cold).
I don't remember exactly what my parents played music on @ the time, but I do recall a foreign short wave radio and I had a Red/Yellow Tiny Tim crystal radio with an ear plug (still have it).
DeKay