I remember a white paper from Dunleavy on multi way speakers and his statement said that the only drivers that should be ported ( hi q) are the biggest ones. Does it make sense that you wouldn't want ported monitor and a sealed sub? idk Or does that only apply to mono amping?
Dunlavy believed in low Q or critically damped designs.
In very large speakers they tend to put very powerful woofers with massive motors (overdamped, Q = 0.5 or less) - in this case the Q can still remain critically damped (Q=0.71) with the addition of the port which also acts to protect the woofer (reduxes excursion and distortion) as well as boosting efficiency by 3 db.
In very small monitors the port is used to increase bass extension and the use of a prototypical small woofer with a small motor means that you are often ending up with a Q of 1 to 1.2 (under-damped). The woofers will tend to have large excursions below port tuning and sometimes visibly popping out by up to an inch in a highly uncontrolled manner which means you get lots of distortion. The roll-off below port tuning is very steep (24 db per octave) so the usable energy below port resonance is very very little.
In a sub - since you are dealing with frequencies from 10 to 90 Hz then it makes little less sense to to have a port tuned at 25 or 30 Hz as the sub will be behave uncontrollably below this port resonance and easily become damaged (even if it sounds louder this way - some subs may have electronic circuits to limit this problem at ultra LF). Better subs are very large and critically damped and have a port tuned extremely low - say at 15 Hz which can be quite effective and gain some SPL without too much risk of sloppy behavior or woofer damage. A critically damped sub (Q=0.71) will work much better with the room (which plays an enormous role below 40 Hz). A sealed critically damped sub will be the most protected from ultra LF (such as 10 Hz) and will sound the tightest or most musical (lowest group delay, lowest distortion and best match to the natural room boost of 12 db/octave in LF), however, it will have LESS SPL output than a ported or under damped design...
Many designers incorrectly assume that because our ears have a lot of difficulty hearing even 20% distortion at 20 Hz then it is OK to have large amounts of distortion in the bass of their speaker or sub wooofer designs. This is a false assumption because you only have to look at an equal loudness curve of our hearing to observe that a mere 1% distortion at an 80 Hz harmonic from a 20 Hz fundamental will sound equally as loud at the original 20 Hz note (even though it is 100 times smaller our ears will pick it up due to their increased sensitivity at 80 Hz).
