The 2 systems that I will never get out of my head. Ive searched for that experience ever since.
1st was a shop Astro van for a local shop. Shop was really have in high end home audio and brought car audio in for a couple of years. They used all Infinity Beta except the tweeters which were the Infinity kappa ribbon tweeters.
4 Beta 12's, 6 Beta 6's (3 in each front door in pods), Beta 4s in the dash, and Infinity Ribbons in the A pillar, All US Amps with I think was a Denon head unit. That thing was loud and crisp. My cousin and I sat in the front seats and both our jaws dropped. He played a bunch of music but once he put that Deathrow cd in, it was over.
2nd car was a Cadillac Deville a shop just finished. Car was like 92 body style. Installer took me out to the bay to listen to it because they were surprised by it. All I remember was a 4th order with 4 12 round solobarics ported through the rear deck. The one thing that I never forget is it sounded like music. It hit hard, but was musical not just bang. The other thing was it didn't have any rattles. They open and shut the doors a couple of times and it basically sounded like bass with door open and vault with the door closed.