Re: repurposed bookshelf speakers in rear
Go to a car stereo shop and try out many sets of speakers. Let your ears be the judge. Don't be afraid to crank it up and try a few types of music or different head units and amps to test for sound quality differences.
I see so much misinformation or downright WRONG information on this site, its pathetic. I have some $70 Alpine 6x9's in one vehicle that sound every bit as good as a $200 set of components. I have heard literally 100's of speakers to compare... Like I said, your ears should decide before price or spec sheets. I have heard $900 Focals that sound no better than sets running $250...
'65 VW Bus
(2) PG Ti 12's, (2) Aura Sound 8's, (2) SoundStream 6.5 coax, (2) Alpine Type-S 6x9's [rear fill], MBQ DSC1500.1D, RF 501X
'02 BMW 330xi (AWD coupe)
Harman/Kardon 12-speaker System Option - sounds good =)