Limiting range of speakers

I have a 2000 Audi A4 with the Bose package.  I took the rear speakers out because of there horrible bass response.  I know you can limit the signal going to the speaker.  I was thinking of putting them back in and placing a capacitor on the units but I am not sure what size to use.  I think they would be a great mid speaker.  The rear doors do a good job but it sometimes sounds a little flat.„h "Simplicity is the ultimate sophistication." Leonardo da Vinci (1452-1519)

Yes, you could do that.  Use a passive crossover.  You could design your own using the links on the left side of this site, or the so-called "bass blockers" available at most car stereo shops will do the trick.