A sealed box rolls off at about 12db/octave below f3, relatively shallow, whereas a ported box rolls off at about 18-24db/octave past f3, pretty sharp. The sealed box will give you alot of usable bass in the very low range, mid 20's and down, where in most automotive ported boxes, this low bass would be diminished or absent. A sealed box almost certainly gives you a smooth frequency response unless built too small, in which you will start gaining a midbass peak, so from a musical standpoint, they sound good because they are predictable, and you won't have a narrow band of a frequencies that are way too loud, or one-note-bass as in the case of a ported box tuned for output. The benefit of the ported box, besides output, is extra energy in the low frequencies, but I wouldent say they play lower. If you design a ported box for low frequency extension, not SPL, you can choose a sub and box to give the system an almost flat response, down to the port tuning frequency, where it drops sharply. In my opinion; a ported box tunned high for SPL. For the flattest response, a ported box tuned low with the correct sub. For the absolute lowest sub-bass frequencies or inaudible notes, the large sealed box. And as for group delay...
