The second sub should add about 5db to the sound pressure. If you experiment with placement, you can use the second one to even out the response in the room. I think it's best to place a sub about a foot from the nearest wall, and several feet from the nearest wall. If you are splitting the sub output of a receiver that has auto setup, I'd run the sub setups first then receiver. Also try to keep the subs a similar distance from the seating location so that the delay in the receiver will work for both subs, otherwise you will have to work harder to manually integrate them.
I'm using a pair of matching subs between my towers and Television stand to good effect. The are about 5ft from center to center. It evened out the response and added some detail to the bass. I'm only using a single sub out on my receiver split with a Y so Audyssey can correct them together.
I'm using a pair of matching subs between my towers and Television stand to good effect. The are about 5ft from center to center. It evened out the response and added some detail to the bass. I'm only using a single sub out on my receiver split with a Y so Audyssey can correct them together.