Thanks for the guidelines, does a corner horn have to be a bass reflex design, or can it be sealed? The ebp for my subs prefers a sealed, though plenty of people build vented boxes for these. I've been reading through lots of the old post, and seems you've had to explain many(!!!) times the size of a theoretical horn for 20 hz performance. I could live with 30 hz for an acceptable frequency limit. I will post more questions as I learn more and model different designs. One quick question, are there any 10pi designs you or others have designed less than the size of a house with 18" drivers that have output to 30 or below hz with high spl levels at those lower frequencies? I am strongly considering some JBL 2241H (I think thats the number) or Eminence Kilomax subs instead of using these car audio subs.Thanks again, randy.