As far as I understand the alpine type-r's are very good for their price range. You might consider going up to two 12's. Or, if you are just looking for loud you could consider the Kicker L7 or Audiobahn which I believe are in the similar price range just more focussed on spl. You may also consider a more powerful amplifier or a larger ported box. Lots of options to consider, good luck =)
Mike