Clearly one can tell the difference even at low notes between bass with just one sub woofer and with two.

I think that the cut-off for being in the nearfield is the point where the size of the frequency actually matches the room size.

But I thought I saw a note by Jim that below 600 there is not much point in trying for a woofer line array except for much higher sensitivity.

Of course if you cross at 150, then the comb filtering doesn't start until the c-to-c distance of the woofers is 7.5 feet, so one at the top and one at the bottom would work. The nearfield is roughly 3 times the length of the line. So without some modification based on frequency, a line of 2 at the top and the bottom would put most listening rooms in the nearfield for the bass portion.

Of course if you cross at 500, then the woofers will need to be about 27 inches apart and you will then need three of them. Crossing at 100 is 135 inches, and is higher than the average room. So perhaps when you get below 150, you only need one woofer to stay in the nearfield.

Just a few thoughts.

Marlboro