SEALED VS PORTED
One of the most persistent myths in the audio industry is that ported subwoofers perform poorly on music. This reputation was largely earned by the public suffering through decades of small, ported boom boxes so common in HTIB systems and brick/mortar retail outlets. These subwoofers don’t sound bad on music because they are ported; they sound bad on music (and movies too) simply because they are bad subwoofers.
SVS ported subwoofers have a flat frequency response, low distortion, excellent bandwidth linearity and a very deep tuning frequency (typically 20 Hz or deeper). The deep system tuning frequency shifts port-induced phase rotation and associated group delay below the typical music bandwidth, where we are relatively insensitive to it.
Below is a graph of the SVS PB13-Ultra group delay curves for the 20 Hz ported, 16 Hz ported and Sealed operating modes. Note the group delay curves for all three modes are coincident from 120 Hz-30 Hz (which covers the typical music bandwidth), only diverging at the very deepest frequencies. While Sealed mode unquestionably has the lowest overall group delay, the two ported modes also have exemplary time domain behavior >30 Hz and can deliver excellent sound on music, as well as stellar movie performance.
https://www.svsound.com/blogs/svs/75367747-sealed-vs-ported