ib can sound nice and efficient, as mentioned. aside from the needed wave separation issue, look at it more this way: the driver needs a certain amount of compliance to perform well. to assist in this, ib or fee-air subs tend to have a low moving mass, and also a real stiff suspension. typically, the enclosure will help move the cone back to center so it can be pushed by the next part of the wave, so it can "comply" with the signal. another aide in this, is the use of a class a amp. all other classes do not really pass much power through the sub at idle/neutral. a/b amps pass a small amount, but not much. the large amount of power, again, helps to hold the "neutral" point in travel. these are not too common ways of doing things, even less lately, so i would not venture to say that most setups will sound good at all.
on another note, there is a great deal of success that can be had using the opening in the deck as a passage for the port to fire from a 4th order.
