if i understand correctly my audi came with 4" components. so if i want to go aftermarket speakers i need to convert to a 5.25" component. how is everyone doing this? is there a write up, or do i need to order a speaker adapter kit and from where? thanks for the help.

 

or could i just say screw it and get something like this alpine

 

go to www.crutchfield.com and enter your car info and it will tell you what size to buy adn what size your car has from the factory.

 

I just used dynamat and whatever screws would line up... but yeah.
Make sure you amp the speakers... do you have bose right now?

Put a big amplifier to those bose, and you won't want new speakers. I promise.
EDIT: and I don't recommend those alpine's that somebody linked too... I had the SPX-137R's... and although their high's were awesome, the mid-bass sucked. I was giving them 150 watts RMS each... and they DID take all that power, so props to them... but yeah, no mids, awesome highs. Those alpines are even smaller, so would have even less midbass...

seriously, just start with an amp, and stock speakers... I recommend a JL 300/4, or 300/2 (just amp the fronts). But please, take this advice... amplify your speakers no matter what! And buy the amp first... because I truly believe you won't want new speakers after amping the stocker's. I've used amped bose, and amped symphony... both sounded great.
The stock stuff has great mid bass, and really soft highs... like soft... but "real" ... I dunno, I liked them. I have focal polykevlars now... the mids are the best I've ever heard, the tweets suck my ***!