Multiple Home Theater Subs, 12's x 4 or 15's x 2? How to measure?
I currently have two BIC F12's and two Polk PSW505's. Obviously budget end of things, but they're good budget subs and still kicking it over 8 years later from purchasing over the years during sales. I'm currently reading about how to best organize them and on Audioholics it shows a best setup being one in each corner of a symmetrical room. Also, from reading, my understanding is that multiple smaller subs will flatten out response and increase output of lower frequencies a little bit so that the overall sound is smoother and more consistent in almost all listening positions in the room.
So my real question becomes.... do I stay with 4x 12's like this, or do I consider trading them out for two 15's (such as Monoliths, HSU, etc). Obviously higher end units than my current budget subs, however, does that even matter for movies and when comparing 4 of them to a smaller number of larger subs? Conventional wisdom seems to be more is better.
Room size is around 22 feet x 18 feet.
I'm curious about resources on how to measure sub response with a microphone too. I've seen others doing this. I'm curious about any easy to follow guides on how to do this so I can take a better look at how well the 4 subs are performing versus just soaking up electricity?