To both Russell and IronGiant,
I've done a bit more investigating.
Although it's not something I'd ever need, two of the phono inputs are 'Line Left' and 'Line Right'.
These are for stereo pre-out connectivity and are routed through the same filter that handles the Hi-Level.
So he could have used one of these.
(But then why didn't he use the unfiltered LFE in his graphs, marked as 'bypass' like he's done with other subs? Or he clearly doesn't understand how to operate this sub properly.)
Regarding the 'scary' hamonic distortion graph mentioned before, since it goes exponentially off-scale long before it gets down to 20Hz, to me he must have been doing something wrong -- like overdriven input etc.
Using the following basic rule:
input*gain=output
So if he hadn't set the gain high enough to start with (and the factory default is a v low '30'), then the input voltage he would have needed to apply would have been be incredibly high in order to reach the amp's max output level for his test.
In my use of the sub, I set the gain to around '60' to get the oomph that I want (regardless of the input). With a 30 setting you could feed whatever you like to the input, and you'd never get the richness & dynamics that I get when the gain is around 60.
The other thing is if you read from the manual, there are many paragraphs on how to position this sub in order to corectly 'pressurise' the room. Move it a couple of feet in the wrong location, and you can lose all the real-sub bass (i.e. 15-20Hz).
Also, since REL's spec makes it absolutely clear that 16Hz
is realisable, then that off-scale graph posted earlier must have been caused by something going seriously wrong with his test procedure. Input saturation/overload/clipping, cone flapping, safe-set triggered etc. And certainly there is no room to 'pressurise' at his chosen outdoor testing location -- an important point which the manual goes into great length about. Moreover, it's not just a function of it's sealed cabinet design (as you implied earlier). Rather, 'Zero-Q loading' also involves active intelligent bass circuitry inside to tune the output in realtime.
Anyway, see this:
Quote from review
". . . the REL Storm 5 drops effortlessly past where the PV1 stops . . ."
http://www.homecinemachoice.com/files/reviews/HCC/092_HCC_118.pdf
FWIW, in some cases the cone is hardly moving, but you can feel deep bass all the way across the room. It's uncanny how it manages it, but that's what happens in reality.
In short, there are so many variables at play here (and so much inconsistancy between this test and the ones for other subs) and so little he's stated in the way of test assumptions and
nothing about testing methodology! Moreover, if I would have handed in something like this to my engineering professor at Uni, he'd have certainly put a line through the whole thing and required me to re-run and fully document the aforesaid test.