I don't know why you & some others in this thread have a problem pointing out flaws in the speaker,...
I find the speaker very interesting for personal reasons, because I had followed its genesis - the idea is older.
The measurements and evaluation also show anomalies that call themselves into question - in a positive way.
Bass: as clarified, it is to be seen as in free-field, and then it is simply perfect. When I adjust for good, rich bass reproduction in the room at home, I regularly measure a slope in the bass in the near (~free) field that has a similarly decreasing amplitude. Studio monitors with a flat, then kinking response are held against it. These are delivered with maximum output down to the reflex resonance, and expect a room adjustment, i.e. a regular reduction of the bass by the studio technician.
However, you could also consider whether the in person listening test could be supplemented with a brief measurement of the actual in-room frequency response.
The mids show these ripples that no other loudspeaker does. They are strange. It's not too far-fetched to suspect that the NFS has its problems here. A relatively small loudspeaker in a large baffle. At the frequencies in question, the NFS has to rely entirely on the mathematical development (modelling) of the effective sound field in Hankel functions. The pitch is too low to supplement/replace the Hankel mechanics with gated measurements. It's a wild guess, logically. I don't see this kind of waviness in other measurements of the same loudspeaker. I see nothing in the design, that could be accused to generate it.
The very wide omnidirectional radiation could have influenced the subjective evaluation, which is made with only one loudspeaker (mono). Could it be that the strong diffusion of the sound played an excessive role here? To me, a single, rather narrowly radiating loudspeaker always seems a little thin, sometimes even sharp, and also washed out. A more indirect dispersion eliminates these disadvantages. The design could therefore call into question the rule that loudspeakers are best tested in mono. At the very least, the variable directivity should be taken into critical account. (I am aware that in typically non-optimized rooms, the even worse bass reproduction in mono also plays a role).
Nice looking, the best invention since sliced bread for many, too expensive for a few, anyway a good testbed. Once my Steinway D will be delivered, I'm going to mate it with these ;-)
