Which Is Louder (2) 10 POINTS!!!!?

ok you lost me a little bit there, but for a ported box it shouldnt be more than 20 dollars DIY, medium density fiberboard works great, 18s and 15s are similar, you wont hit any lower b notes with an 18 than a 15, but it will be a bit louder and possibly better sound quality. You want to go by RMs becuase max only means thats the most the speaker can handle without completely being destroyed.