This is myth, not fact.Im my eperience, (limited for the last few years), a sealed box tends
to have a tighter response where as a ported one will extend the low-end.
As far as output, i think a ported one will produce more "percieved" volume
due to the extended low frequency response.
It all goes back to " what the listener preferes". I like rock and sealed boxes.
For my clients who like rap, ported all day long..
It is a simple formula for me, but it has worked.
I am sure there are more knowledgeable responses to follow.
I like to keep it simple.