Really depends on the speakers. I used to have the first generation of Apogee Centuars with Stage ribbon and 8 inch enclosed woofer. Used two on each enclosure and it made a huge difference in reducing the obvious problems with the non-ribbon part of the speakers. Now, this is because the enclosures left a lot to be desired in terms of design and probably construction as well (Apogee later did better with the Slant6/8 series. I would imagine that the effects are highly speaker dependent, but it solved my problem. As I recall, reviews at the time these came out said that effects were less noticeable with better speakers and more noticeable with those of lesser build quality. Have esl's now so boxes are a non-issue.
