I'm not a box expert, but you can't generalise with "ported enclosures" as the tuning frequency makes a massive difference to have the driver reacts. I don't know how to explain it but there is more pressure inside a ported box. Also, ported subwoofers have handle more power around the tuning frequency as the cone and port "react" to create the sound and the cone excursion is reduced to virtually nothing but the sub will be at it's loudest and highest power handling. Ask on Termpro or CAA forums... There are alot of people who will KNOW the answer, but still a few who will be guessing and repeating crap they've read.
They are different types of distortion occuring....Stone is correct in saying that there is more resistance inside a sealed enclosure. It's pretty simple really. When the cone is moved back it pushes the air inside the back around. Now, that air has to go somewhere right? Wrong. It's an airtight enclosure remember? What the driver has to do is COMPRESS the air inside the box. It can do this...but it also makes it a lot harder for it to move back to where it's supposed to be. Thus causing an alteration in the repoduced signal. So, what about when the driver moves forward? Well, then the box effectively tries to create a vacumm! When that happens..you have the power driving the driver forwards but the vacumm effect pulling it back in. Once again, you alter the sound reproduction. So, with all that said, why use a sealed enclosure at all? Because when all is said and done the right size and SHAPE allows the driver to use that effect to it's advantage. Hence why sealed enclosures are known for their tightness. It's because of this factor that sealed systems generally handle more power then ported...theres more resistance keeping everything in check. Now, onto the port side of things. When that speakers is pulled back....it does try to compress the air. Instead, it forces it all the port tubing...then when it moves forward, it SUCKS the air back inside the box. So, for all intent purposes, the pressure on the inside of the box is equivalent to the pressure on the outside of the box. But, because of this equal LOW pressure system in the front and back the driver is MUCH more inclined to start distortion and reaching it's Xmax long before it max power handling has been reached as there is nothing pushing out when it wants to go in and nothing sucking back when it wants to go out.... But because of this, there is less coloration added into the music signal being reproduced making for a more pleasant and smoth response curve. But, don't forget, that it can easily become unstable at higher power (not neccessarily higher volume) did that make sense at all?
