http://www.avrev.com/home-theater-loudspeakers/subwoofers/the-svs-sb-2000-subwoofer-review.html
There are differences and advantages to sealed and ported designs. According to SVS, "sealed subwoofers typically have a smaller overall cabinet size and footprint, allowing easier integration into the listening environment with minimal visual impact to the décor. A properly designed sealed subwoofer will typically exhibit less phase rotation, lower group delay, and reduced ringing in the time domain. These characteristics make the sealed subwoofer a natural choice for critical music applications, and are typically described by enthusiasts as sounding tighter and more articulate, with less perceived overhang.
A sealed subwoofer naturally has a shallower roll-off slope than a ported subwoofer. SVS takes this concept one step further by employing sophisticated DSP equalization to tailor the overall shape of the frequency response and roll-off slope, in order to take maximum advantage of available ‘room gain’ so common in small to mid-size rooms. The end result is much deeper in-room extension than the quasi-anechoic frequency response would otherwise suggest.With each successively deeper octave, cone excursion quadruples in a sealed subwoofer in order to maintain the same sound pressure level. In addition, the equalization required to tailor and optimize the quasi-anechoic frequency response consumes amplifier power. As a result, a sealed subwoofer will typically have considerably lower dynamic output limits <40 Hz than a larger ported subwoofer in the same family/price range.
In a ported subwoofer design, a relatively large enclosure size is required in order to achieve both a deep system tuning frequency, and sufficient port area to minimize chuffing artifacts at high drive levels. A larger enclosure also greatly enhances system efficiency in the deeper octaves, with no need for additional EQ boost to achieve naturally deep extension.
The result is 2-4X more peak dynamic output in the 18-36 Hz octave as compared to a sealed subwoofer in the same family/price range. This makes the larger ported SVS subs a natural choice for system applications with larger rooms (where less room gain is present) and IMAX-like playback levels, particularly on demanding Blu-ray action and sci-fi movies with strong LFE tracks."