I have two after market speakers i installed in the rear of my chevy aveo . they fit up by the back window, there is nowhere in the door for speakers in back. So these speakers can be seen from the trunk. that being said they have all that air space in the trunk, would it be better to build a little box to cap the back end of the speakers for sound?
Absolutely, boxing them will help out with the bass response. If you have the thiele small parameters you could even build the enclosures to exact specs then you will have the best possible frequency response.
Car speakers are generally designed to be used without an enclosure (with the exception of subwoofers). You don't need to build a box for them, and it won't improve the sound quality if you do. It's important that the top of the speaker is completely separated from the bottom, so that the sound waves produced by the two sides of the speaker don't interfere with each other. If there are any holes or gaps in the rear deck, it might help to seal them up. Also, it's important that the speakers are mounted in a very rigid and stable surface, that won't vibrate as the speaker cone moves back and forth. Dynamat or other damping material can help you there.
