To expand, All subs have a natural Frequency at which they are most efficient. If a port is tuned above that frequency (too short) or below that frequency (too long) it wont be as effecient as tuning the port to that woofer's optimal tuning frequency.

As far as port area (size of opening), this is tuned to the box not the woofer (in most cases). Generally, optimal port area should be calculated (roughly) at 15-16 sq inches for each cubic foot of net box volume. Some woofers can vary a bit from these numbers, but generally, when using this formula you get a tuned ported box that has a wide frequency response from high pass cutoff to low pass rolloff.

When a ported box is tuned properly, it is ALWAYS louder than a sealed box. That said, the comment about across frequency range the summed SPL of a sealed box would be technically louder, which is great, but show me one competition series that rates SPL across the frequency range. The Ported boxes that beat hard at one frequency and then suck on the rest are the prefab, Best buy special boxes. these are made to pound at (give or take) 40hz, which is where most hip hop songs play. A truly tuned ported box with the right matched sub or subs will beat across any USEABLE frequency range (30hz- about 50-60 hz). Not trying to argue with anyone, just throwing out some facts.

As far as Bad Apples work, dude does sick shit. Thats coming from another Shop owner with 15+ years experience in the industry.

Colin
AW