Hi All,
I had good luck using REW to set up my previous sub over a year ago. I'm now using it (with the latest version) to set up a (new to me) used SVS PB12-plus/2. Please take a look at the graph and let me know why you think the response is dropping so low at 40 hz.

The crossover on my receiver is set to 80 (I've also tried it at 100 with no real difference), the PEQ on my sub is disabled (and set to 120hz just in case) and I've tested it enabled and set to 40hz so it does work. I've tried several different locations in the room, and the curve looks very similar above 40hz in all of them.
Red is 25hz tune, green is 20hz tune, and blue is 16hz tune.
It almost looks like there's something wrong with the sub's amp or EQ. Any thoughts?
Thanks,
Alex