Higher distortion in the 50-120 Hz range can't be the reason for favouring sealed subs because smaller sealed will have more sensitivity/output (not much but 0.5-1 dB) than larger sealed/ported and therefore has less distortion in that range. Below ~40 Hz that would be correct.Yep, it's the same reason why some prefer the sound of a sealed sub using the same driver and why you'll see a few Avalanche 18 LLT owners at a different forum wanting to build dedicated sealed subs for the 50-120hz range - they favor the artificial oomph or kick that comes along with higher distortion. The car or club bass sound is what they are after, as most people don't really get exposed to clean bass in life. They get used to the artificial oomph and that's what they take a liking to.
I haven't measured an AVA 18" or 15" but I'm pretty it's pretty similar to the MK1 Tumult when it comes to distortion figures, meaning quite high upper bass distortion. It doesn't have a shorting ring? And only 8" spider?
More about the XBL^2 in a few days... Before that a rhetorical question: did Adire Audio ever provide even a single real world measurement that the XBL^2 reduces distortion? If they did, please show it to me.