Nice, detailed write-up on upgrading your Crown Vic's front and rear speakers...

http://www.autoclinix.com/Mercury/Rear Speakers.html (http://www.autoclinix.com/Mercury/Rear%20Speakers.html)

http://www.autoclinix.com/Mercury/Front Speakers.html (http://www.autoclinix.com/Mercury/Front%20Speakers.html)

I upgraded front speakers and Head Unit (turned off the rears) on my 96 grand marquis.
Kenwood Heand Unit and Pionner REV speakers, total cost about $250. ~~much better.