I'm thinking about just changing out the speakers, but I'm a newb and don't know if that's even possible. Do you always need an amp? Would swapping out JUST the speakers be possible and/or worth while? My car is pretty loud, windows are often down, etc... so I'm not trying to make it sound like I'm in a concert hall, but I think the front right speaker is gone and if you're replacing one, why not all?
I mentioned in one of my earlier responses that one disadvantage of swapping the OEM speakers out is that almost always the aftermarket speakers are less sensitive than the originals. This means in an A to B comparison, just swapping the speakers but changing nothing else, you'd need to turn the stereo up to a higher number to achieve the same perceived "loudness" vs the old speakers. However, aftermarket speakers almost always sound better than the cheap paper POS speakers that came with the car, so the drop in volume may be offset by the increase in quality.
Do you always need an amp? Not necessarily, but there are several factors that you may want to consider: One, you mentioned that your car is pretty loud, so overcoming the sound of the car can become a challenge with the less sensitive speakers. Two, just turning that knob up may do more bad than good. Because aftermarket speakers take more juice to get them moving, and because they are rated to take more power than the OEM units, many folks have a tendency to just crank that volume knob to 11 and let the tunes fly! However, all audio equipment reaches a point when it begins to clip, or distort. That signal clipping heats the voice coils in speakers, causing them to cook and eventually fail. Many times this distortion is inaudible, but it's still there and still doing it's damage. It is actually easier to kill a speaker by under powering it than it is by over powering it.
By by adding an amplifier, you give yourself some headroom before driving things to distortion. It doesn't even have to be a big amp. Just a small amp, like the ones I've suggested to [MENTION=5193]War_Panda04[/MENTION] with only 45x4 will sound louder and cleaner than any factory (or aftermarket, for that matter) head unit out there.