With a ported enclosure you have well... a port. That is basically an open hole of known surface area and length which tunes a box of known volume to a specific frequency. The resistance of the tuned port is very high above tuning and near/at tuning it resonates increases the amplitude at those frequencies. Below the tuning it unloads and simply becomes a "hole" in the box. This is a problem as the speaker is now essentially functioning in free air. Not a problem when its below its max limits, but still not yielding appreciable output vs its excursion levels... so why run things so hard for so little output. At the same time, people are often beating on their system HARD when this occurs and when they end up playing a track below tuning things REALLY go wild and unload. This will mechanically damage the speaker due to over excursion. Ripped/torn parts, fatiguing the lead wire... all sorts of bad. So, we place a sticker on the front of the box telling useful tips on setting up your system... and to me one of the biggest ones (if not the biggest) is to set the subsonic filter properly for ported systems. This is true of all subs. Not just ours. Now if you have a decent mechanical excursion sub with relatively no Xmax, it isnt as much of a problem simply due to the fact it has little linearity vs the high mechanical excursion. But on most modern subs where Xmax is closer to 75% of mechanical limits... you can power it linear right up to the point where it wants to break itself. Do yourself and the sub a big favor and set the filter a couple of Hz below tuning. If you are unsure of where that is, err on the side of caution and set it higher than needed. You can eventually back down when things break in and you "know" the system a little better. Learning curves are our friends. Thanks, Scott