In Reply to: Replacing speakers, posted by Dave on January 09, 2000 at 19:53:48:
I assume you're in need of more bass when you ask about frequency response. In that case I would not even mess with increasing the size of your rear deck speakers as going to a 51/4 in won't be significant enough a gain. Instead, get someone to build you a custom sealed box with a very high quality driver mounted in it and stash it in your trunk. Get a good high powered amp with as high a dampening factor as you can afford.Wire up a speaker level to line level converter to supply a signal to your amp.
This is assuming your system is stock except for the MB's you're installing. Basically, you want to have larger speakers reproducing your bass not small drivers they just can't physically do the job cross'em over bass block'em do whatever it takes but keep high powered low frequencies away from small drivers.
note: the most accurate bass reproduction generally comes from sealed enclosures. They're not as loud but sound a whole helluva lot better than boomy band pass or ported boxes. They require more power too (less efficient)
Hope this helps