Motorola Vibrasonic, something I don't think I've ever seen, or heard of. They seem to have been used to give a more interesting sound effect to a radio, before Stereo was invented, on vacuum tube single speaker radios

In general the feature seems to give more "distance" and some echo to the sound, and maybe back in the twangy guitar era (Duane Eddy, or slow dance do wop, and the Ventures, surf music, and early Elvis type stuff with a couple electric guitars, and a big ol bass) it made the music really liven up on crummy old paper speakers.

I've read that with the right music, a vibrasonic reverb made it sound like the music was in a church, or concert hall, and up until the 60s gospel sold a lot of records... Aretha and Elvis both were selling gospel albums.

 'Vibrasonic' is just another brand name for the reverb that was popular in that era. Fisher had the 'SpaceXpander'

https://antiqueradios.com/forums/viewtopic.php?f=19&t=291446
https://www.ebay.com/itm/163644281526?ul_noapp=true

Hmmmm, I bet Jalopnik, Hagerty, Old Motor, and who ever else are out there aren't doing goofy articles like this about strange old car stuff no one has anymore... but find interesting anyway