Regarding port area comments, the math tells us what port area we need with a given sub at a given frequency. And that's not some special math, it's the same math we use to calculate box volumes, port lengths, et al. And port area is not volume dependent, it's xmax and tuning dependent. We just use the x port area per cube because it's easy... and 99% of people look for the easy way to do something before they look for the best way.
I run ¼ wave transmission lines in everything I can, because they're the most efficient alignment you can put a driver in when you consider all factors. And just to clarify, the ideal "port" area of a ¼ wave t-line is 100% of Sd. So for one entry level, 150 watt ten that's ~54in² of port area regardless of tuning. It's also the same port area for a 1500 watt competition level ten... provided the subs share the same amount of piston area.
In my truck, I have a line for two 15s and the "port" area is ~250in². And, in my truck, Let My Beat Pound, White Girl and Woofer Cooker are my favorite low note demo songs, because those notes below 30 are not only felt, but heard. With the drops in Let My Beat Pound and Woofer Cooker, the bass is audible when the subs look like they're moving in slow motion, although with Woofer Cooker the drops do become inaudible but, only because they reach below the threshold of human hearing. I can also throw Bad on the system and you can feel the upper sub bass in that song and I can play Ride Across the River and the kicks hit you right in the gut. I don't have to change ports, add or remove mass, fiddle with settings or put my elbow in my ear. I only have to change songs.
And yes, t-lines aren't ported boxes but all loudspeaker systems seek roughly the same end goal and all of them must conform to the same laws of physics.
