sub woofer alignment head to head

The title may be a little misleading. Here is the setup: (2) MTX 10" sub woofers. 1 mounted on each side of the vehicle. The 2 subs face each other with approximately 4' of separation between them. The subs are facing the center of the car and the face is parallel to the side of the car. (FYI, this is in the back of a hearse). My question is do these subs cancel each other out? I have been reading other forums, posts, and research on the web, and what I find are answers ranging from a "My god yes they cancel, why did you do it?" to a "Why no, they will be fine as they are. Enjoy." Right now the subs are in phase. Thank you for your help in advance.

Forgot to mention, but I don't think it will make much difference, this is in a 1988 Mercury Grand Marquis Eagle Hearse. These subs are in the casket compartment of the hearse. So air volume in the "trunk" (for lack of a better term) is MASSIVE.

subwoofer cancellation can be independent of whether or not they are in phase. if the distances between each sub are significant, the placement of each sub can be a deciding factor of how much output you get out of them. try unplugging one of the subs and see if the system seems to be louder. sub bass frequencies have long wavelengths so they are very vulnerable to cancellation even if each sub is in phase. it's the same principal that can make or break a ported box design.

Ah. Thanks. I did a little playing around while I was driving the other day, and it *SEEMS* louder when I open the window. But as soon as I can get out of the neighborhood to somewhere I can turn the system up, I will try that. Thanks.There is no devil, only God when He is drinking.