Sure, I think that the method mentioned a couple of posts before this one is fine. Something else you could do to test the limitations of your subwoofer, in your room, would be to perform a compression test. That would actually be a little simpler to perform using REW. I am linking Data-Bass test results for your subwoofer, performing long-term output sweeps.
Where some frequencies stop getting louder (compressing) in relation to other frequencies, your subwoofer is running out of headroom. You will note that the graphed frequency responses show the graph lines getting closer together, at about 100db (2m outdoors) especially at lower frequencies. The lowest frequencies are where most subwoofers exhibit the earliest indications of compression. This is a pretty easy test to perform. You just keep increasing the volume, in 5db increments, to determine where you start to run out of headroom.
But, there is something missing from both of these tests. And, that is the human element---you
, in other words! The tests will show you the limits of your subwoofer, at that position, in your room. But, the tests still won't tell you whether or not you need
an upgrade, because you may or may not actually listen at the volume levels required to produce distortion or compression for your subwoofer. Knowing your subwoofer's limits is only helpful if you ever actually reach those limits.
This is an important point that I have tried to make to you before. If you are satisfied with your current subwoofer performance (perhaps including confirmation that your sub is not distorting or compressing at your normal listening levels) then there is no reason to consider an upgrade, purely from the standpoint of output. But, the key is still your
listening levels, in relation to your subwoofer's output limitations, and your
satisfaction level. If you are truly satisfied with your current subwoofer performance, then why worry about this at all?
If on the other hand, your curiosity about an upgrade persists, then the only real way that you will know whether an upgrade would be worthwhile for you would be to try a better and more powerful subwoofer. You don't know what you don't know! Until you compare something else to what you have now, you will never know whether or not you are actually missing anything, especially with respect to the frequencies under about 20 or 25Hz, because that's where the PB12-NSD really starts to roll-off.
In that case, as previously stated, I would recommend an SB3000, or a PB3000 if you can afford it, because either version will be a better subwoofer in every respect than the one you have now. In my personal opinion, there really isn't a better answer to your question about whether or not you need
PS: As a personal note, like many SVS owners, I started with a PC12-NSD as my first "good" subwoofer. And, I enjoyed it! It was only when I became curious about what I might have been missing with respect to the lowest frequencies that I started to upgrade. And, in my large room, on concrete, I found the differences to be profound. But, that is really a YMMV issue.
There is no reason to even consider an upgrade, if you are truly satisfied with your current performance, or unless you are truly curious about whether you are missing anything. And, there is only one way to satisfy that curiosity about whether you are missing anything. That is to try something else to compare to what you are used to.