Interesting comment here on how subwoofer coupling will give you extra db's just by putting them side by side

subwoofer coupling

kind makes you wonder if the verticle EP800 is better than two seperate EP500s'

Troy, although the linked article didn't mention it, the general requirement for two drivers playing simultaneously to "couple" and result in as much as a 6dB level increase(varying somewhat with room acoustics)is that their cone centers be within about 1/4 wavelength of each other. At 80Hz 1/4 wavelength is about 3 1/2'(1130/80/4). The EP800 drivers are already configured that closely, but two EP 500s could be arranged horizontally or vertically closely enough to satisfy the requirement.

Although the extra level increase by being located closely(as much as 6dB rather than the usual 3dB from any two drivers playing simultaneously)can be had, possibly more important overall would be locating separate subs widely apart(e.g., midpoints of opposing side walls or front and back wall or diagonally opposite corners)to partially cancel room modes and lead to smoother bass response.

thanks John.

I currently have two Enegry ESW10's was thinking if I had a EP800 up front centre wall under the VP180 and put two of the Energy's in each rear corner. Probably upgrade to the Verita 10"s
Reason is they are also a very good sub and more compact the the EEP500.
Just space is at a premium, my front rear walls are 11ft wide

room is now going to 21.5 long under 2000sq ft and four EP500 are over kill heck other than smoothing out frequencies two EP500 are a lot.