hell why not mix subs. 1 18 goes great with 1 8 inch sub. sh.it throw a 10, 12 and 15 in with them and you will bump louder than anyone in your neighborhood. gotta mix it up as much as possible for optimum SPL and quality lol.
b/c the larger sub will play all freq. louder than the smaller sub, essentially "canceling" out the sounds from the smaller sub, making it useless.
brand-wise, not all subs are the same. some will play louder than others, and some will play higher/lower etc. Not every sub plays the same freq. the same. 40hz in a kicker might sound different with another sub. some subs are more efficients. and some might not work as well sealed/ported. etc.
thats why i put a smartass answer. cuz i figured you knew what you were talking about. but actually if you tuned everything exactly perfect you could get away with a 12 and a 15 probably or something like that. running on differnt amps of course.
Well the one way I feel mixing subs works is to cover different frequency ranges say a 12 for 20 hz to 60 hz and a smaller sub for say 61 hz to 80 hz. I see no reason why this wont work fine as a matter of fact im doing something along those lines on my next install
