here is some usefull info, I got this from a different forum
Sealed vs Unsealed subs
"I find it interesting that people are still making the old 'sealed v ported' equals ' music v movies' comparisons.
Virtually every person in this thread (where they are honest enough to state their kit list) is running ported speakers and yet there is no question of their speakers 'musicality' as being lacking as a result. Why is porting assumed to be a purely subwoofer issue?
The truth is that where subs are concerned there are four basic factors that affect 'musicality':
1. A flat in room response. The naturally falling response of a sealed sub may make this easier when balanced with room gain, but a well positioned/EQ'd ported sub can deliver this too. A flat response is important as changes in frequency response result in phase shifts that effect timing. A badly positioned sealed sub that suffers large peaks in the resonse will sound less tuneful and slower than a well positioned/EQ'd ported sub.
2. Impulse response; How quick a sub starts and stops. Remember that above the port tuning frequency a ported sub is effectively sealed due to the ports resistance, so arguments about sealed subs stopping quicker are specious. A ported sub only becomes an open box below the port tuning frequency and if the sub is large enough, then this point is well below 20Hz and only a church organ fetishist will count as being within the musical band. Being ported is not a problem unless the tuning of the port is way below the natural tuning of the box/driver. As a result the attempt to stretch the frequency response of the sub will result in large phase shifts and possibly high distortion too. Good ported subs don't do this.
3. Phase coherence or if you prefer group delay. This is about phase (again) which is the most consistently misunderstood technicality on this forum. As noted, it results from optimistic port tuning, non flat in room frequency response or (and this is a biggy) for some uber sealed sub owners; Internal EQ. No sealed sub delivers a flat response. Below the natural system resonance, the response will tail off at 12dB per octave. If it doesn't, then there is serious internal EQ being applied and this is no better than an optimistic port tuning. External EQ of the subs response can't help either, because it can't compensate for the sub's internal EQ.
4. Distortion. A lot of so-called 'musical' subs produce a hat full of harmonic distortion which sounds (and feels) like a bigger, deeper version of speaker bass. Thus, subs that don't 'sound' like this are dismissed as wrong. People are used to hearing 20Hz as a collection of 40, 60 & 80Hz, second, third and fourth harmonic distortions all of which (being higher frequencies) start and stop quite quickly. A pure 20Hz note by comparison takes 1/20th of a second to even register as a note and thus sounds quite slow. The fact is that low distortion bass sounds immediately like something has gone missing (the distortion you're used to) and slow because it actually is. This alone takes some readjusting and the time should be taken to do so, because this is accurate.
So, to recap; The ideal sub is low distortion, offers a flat in room response, has a deep frequency response without hopeful port tuning or internal EQ and has a smooth phase response. The eagle eyed will have spotted that these are the same requirements for great music or movie reproduction and thus doing one well, does not exclude the other.
These qualities are not the exclusive preserve of sealed or ported subs."
AVF Hardware Reviewer
Here are 2 more linkshttp://www.kicker.com/ported_Enclosure_Pros_and_Conshttp://www.kicker.com/Sealed_Enclosure_Pros_and_Cons