Ok, so i'm re-doing my stereo, new head unit and speakers. Should I build enclosures for the speakers. They are 6 1/2" coaxial. Will it make a noticable difference in sound quaility?
It depends on where they mount. Are you talking about putting the speakers in independent boxes or replacing in the original locations? If they mount into a bulkhead that is exposed to the hull (making a large cavity between the bulkhead and hull) can give you lots of bass but pretty muddy or unresponsive. Enclosures should tighten up the mids and bass while not changing the highs. Got any pics of the locations? That could help others to respond with suggestions.
You won't notice much if any of a difference. Don't bother especially with such small speakers. I experimented with trying to build enclosures behind a set of my 6x9s, and it sounded worse.. they love how they are now..