SPL is pretty much all out bass and SQ is sound quality meaning very clear. I suggest checking on crutchfield or
www.sounddomain.com and find the speakers that you want. Then head over to Ebay and run a search on that speaker and find the cheapest. Your best route (if its a front speaker that blew) is to go with a component set. Its got the speaker you will need (6.5" or whatever) plus a tweeter (small 1"-2" speaker for hi tones) and a crossover to "clear-up" the music.
Personnally I love Infinity (reference or Kappa series), but there are tons of great companies... kicker, JBL, Rockford Fosgate, MB Quarts, just to name a few. good luck and were here if u have any more questions.