(Please see the following as a philosophical discussion about future measurements
. At this point I've said everything there is to say about the Neumann measurements specifically, but it'd be nice to make things as good as possible for future measurements and not have discussions about remeasuring in the first place).
On the reference axis: I brought this up earlier in the thread, but since we're already 18 pages deep in less than 3 days...
As
@edechamps points out, CTA-2034-A says measurements should be referred to the manufacturer axis unless not specified. Granted, we're not following everything in the document to a tee, but this seems like no-brainer. Although I do understand from Klippel's documents that it's faster doing the expansion from the tweeter axis.
Its effects on KH80 specifically aside, I think it's really important to use the manufacturer- reference axis going forward, because sometimes meaningful, potentially audible differences do emerge. The KH80 is one of the best-controlled vertically-aligned speakers out there, so issues with missing the vertical axis by a few degrees are not major. Others are not so lucky, and audibility aside, it can really screw up people's perception of a speaker's performance if the presented on-axis graph does not reflect the intended reference axis.
Here's is the Buchardt S400 at its reference axis (between woofer and waveguide) in white and just 10 degrees above the reference axis,
which I estimate is roughly close to pointing at the tweeter. In other words, basically the exact same situation as the KH80 EDIT: Brainfart. I forgot the S400 is an upside-down configuration meant to be with the woofer above the tweeter. Nonetheless, errors show up both ways. Here's 10 degrees above the reference axis (aimed at the woofer)
And 10 degrees below the reference (at the tweeter):
Barring a major issue with my measurements in that region - which I doubt is the case - that is a massive difference in the upper mids. It's okay on the KH80 because it doesn't change that much in the first place, but if I saw the blue or puple curve as the on-axis graph for the Buchardt, I'd be concerned. Granted, the listening window would smooth things out a bit, but it would still be significantly worse than the listening window centered around the proper reference axis.
This is a great speaker on the whole and these listening window vertical issues are significantly diminished and balance out in a typical living room setup. But you nevertheless want to get the vertical height right to maximize optimal listening position, especially if you listen from unusually close.
Another example: here's the Focal Chora 806. Being 10 degrees below the reference point (which in this case is the tweeter, as normal) causes a major shift:
Also remember, we do not just hear an even balance of direct sound and reflected sound. Which one we hear more of varies with frequency. The higher in frequency, the more the direct sound matters. In addition, the lower the relative volume of reflections vs direct sound, the more the direct sound matters (obviously).
Per Toole's book:
In the nearfield or a heavily treated room, it is fair to assume the distribution of perception looks more like the bottom cinema hart, as reflections are less audible. In my experience, small changes in vertical position are occasionally audible in the farfield, and sometimes very audible in the nearfield. Changes in vertical position are most likely to manifest in the crossover frequencies and above, where we begin to be more sensitive to the direct sound.