It would seem that there are days when I can neither read or count. My advice remains the same. Think of it this way, if your VR 4s actually are flat to 25Hz then there is a very good chance that you have fairly uneven bass response. The single sub operated out of phase at the rear of the room can go a long ways towards evening out the bass response.
If it has a 24Db/oct. roll off that is variable in frequency, you can experiment with the crossover point and try to flatten out the bass response below 150Hz, which is generally about where room induced problems start manifesting themselves. You should be able to run the rear sub at a greatly reduced level compared to the front mains and still flatten out bass response in the room. The Bass Optimizer can be set for the higher frequency subsonic filter.
Ideally when the sub is on operating out phase at the rear of the room you shouldn't even be able to tell it's on from the listening position if its level is set right. The sub isn't being used to augment the bass you have, but rather is being used to equalize the pressure in the room in the bass region. You can get away with running it at a lower level than the mains because you are only trying to cancel out bass energy headed towards the rear wall and the bass wave has been attenuated on its way by absorption by room boundaries.
Scotty
