this is dependent on your setup. running mono, i always run a common chamber enclosure, i seem to always be able to get much more efficiency this way. when running in a stereo configuration, always run separate chambers. with stereo configuration, some music doesnt play the same from left channel to right channel. with common chamber in a stereo configuration, the left channel playing while the right channel isnt would cause the right channel subwoofer to act like a passive radiator, and the left channel subwoofer would unload. passive radiator in itself isnt bad if thats the type enclosure your going for, but a floppy sub in a ported box is never good.