Yeah I don't really have much experience with enclosure design, but my basic understanding is that a ported box will be 50-100% louder at the tuning frequency than a sealed box, but basically the bass isn't as accurate as a sealed box.
I guess my question is how much of audible difference is there between a good ported box and a sealed box in terms of accurate bass reproduction both at tuning frequency and way outside of it?
Would a ported box (even a good one) mask the attributes of a good sound quality sub?
Subwoofer SQ is almost exclusively about frequency response. Anyone that says different is wrong, that's the honest truth. Generally in a car for sq your looking for a fairly flat response from the midbass to subbass, generally down to 40hz or so. From 40 and down you actually want a rising spl, around around 6-12db/octave. Not super exact, but those curves generally sound the flattest to the ear and won't be missing anything. Despite what many think, you do NOT want RTA flat for SQ, even in competition. Outside competition, the curve I described still sounds VERY good, but most people will bump the whole subbass region up, so the flat transition from midbass to subbass might have a bump, how much depends on what you listen to. The curve i described is basically what the sub itself should be doing between 80 and 20hz, how much louder you want all that vs the rest of the music is up to you.
Anyway sealed boxes tend to produce good frequency response in most cars without a lot of guess work. Is it perfect, no, no setup is, but it'll get you in the ballpark as long as your box is appropriately sized for the vehicles cabin gain and you used a good sub for a sealed enclosure.
Now if you have equalization, ported becomes a better choice all around. Ported has some inherent SQ advantages. Since the sub moves less during tuning and is more effecient overall, distortion is reduced. A ported sub playing anywhere near tuning has less distortion than a sealed sub playing the same note. The issue is again, the frequency response, which is the most important thing and what tends to make many ported boxes not sound as good. Anyway, if you have an EQ you can simply reduce the frequencies that your ported box is playing too loudly, then your getting great effeciency since your ported, lowered distortion AND good frequency response.
Lastly, some subs work better in some boxes than others. A high fs high q sub isn't going to have good sq in a sealed box in a large car, it's going to lack too much low end. Even with EQ, you may have mechanical or thermal limits to take into account. That sub, may however, do very well in a large car if it's in a large box tuned low.. A higher q lower fs sub would be the opposite, it'll be fairly flat in a sealed box, but in a ported box would be very loud and boomy wherever you tune it. For example, my last subs were very low q AND low FS. Somewhat unusual pairing, but they EXCELLED in a small ported box. 3-3.5cubes tuned to about 25-30hz has great frequency response in most cars. Better than a sealed box would have been in most cases and certainly more accurate than a larger ported box, unless it's a suv, then you'd want to go a bit bigger.
So it's not really all in the box as some say.. Really, it's all in the box that the combination that sub and vehicle dicatate works best. If you only have 5 cubes to play with a sub that will need a ported box of at least 6 cubes to play flat, isn't a SQ sub for that vehicle.