I just bought a second sub. the first is a smaller Yamaha, the second a larger 12 inch down firing JBL. I've currently got sone one on one side of the room (to the listener's right approx. 7 ft. away), the other is placed to the left (in a corner approx. 7ft. away) They would be firing across at one another, but the JBL is downfiring. Any suggestions for placement? Putting a sub behind the listener is impossible in this situation.