It's difficult I have 'heard' the REL is more musical, AKA, articulate then SVS. I am new to mesurements but there's more to reproduction than db at particular frequencies is there? Articulation and speed HAS to be a factor at the driver level ?
Some drivers are better suited to the task than others, sure. But it's more than the driver. The driver needs to be paired with the right enclosure volume and sealed or vented based on its T/S parameters. It's a system and it all needs to work together. Then there is DSP which needs to be applied after the best location is found in the room for the sub and your seat because the room will distort its sound no matter how good the sub is. It almost doesn't even matter if DSP was applied at the sub-level to achieve a flat response outdoors because you won't get that. You hear the sub + the room.
Beyond that, generally light and very stiff is preferred in drivers, and there are many ways to get there. PSA uses a hardened paper. JTR uses a paper/kevlar blend. Rythmik uses aluminum. Whatever is chosen affects the T/S parameters, along with the excursion or linear travel, which dictates enclosure volume and makes some drivers better for vented and some better for sealed, and sensitivity which affects amplifier pairing. As far as one sounding better than another if frequency response is the same, I'm not sure. Frequency response is what we hear, so if that is held flat you won't be able to hear differences at these frequencies where there is no difference in dispersion width unlike smaller speaker drivers that have audible differences due to how they create different reflections in a room. At subwoofer frequencies, all of the sound you will hear is coming from all around you – the ceiling, the floor, and the walls. The pressure emanates from the sub and expands in all directions simultaneously.
With all of that said, I do believe subwoofers sound different between brands, but I think that is mostly because you can't keep all of the variables constant when comparing them. When you swap out a sub, you are changing the driver and the enclosure, which gives a different tuning frequency. Some alignments and port locations change how it interacts with the room. Some will be using DSP to shape the frequency response differently which has a huge impact on the sound. In addition, some designs will cause more vibrations and give more of a tactile feel while others will be more stealthy. None of this has anything to do with driver material, though.
Larger is generally better. To achieve the same SPL, a 15" driver will only have to move a very small amount compared to an 8" driver which will lead to much lower distortion and cleaner playback. Vented reduces distortion further by increasing efficiency by using the back wave of the driver to produce SPL in phase within a certain frequency band, best optimized at 20 Hz and below. My 15" vented subs are much, much cleaner than any 8" sealed box on the planet for these reasons. At the same time, if you call upon them, they have huge output capability that a sealed 8" can't even dream of. What they can not do as well as the 8" boxes is hide from the spouse. But life is all about trade-offs
