It's your lack of familiarity that's apparent, a lack which you position as everyone else's (or my) problem. This entire thread is about the operation of the NFS. For a single quick example of validation of ASR results I provided extracted on axis data from the hemianechoic measurmements of S&R, and Neumann's own. The results are very close. There is no smoothing applied. If you want to understand measurement conditions of S&R you have explanatory articles published by Dr. Anselm Goertz, who is responsible for them. For Neumann's I haven't found a good source explaining conditions, but they are among the most transparent manufacturers when it comes to sharing performance data. For ASR, this is one of the best threads on the subject, and if you want more for the KH80 specifically you can read the not one but three threads dedicated to it alone.
Again, claiming general knowledge or deflecting the burden of proof are not valid methods in scientific circles (which this website / forum implies by its very name).
If a person cannot provide clear concise well documented evidence, it is almost always because they have none. I strongly assume you cannot provide said documentation, like Anselm's S&R measurement methodics. If so, you would have simply quickly linked to them, instead of taking forever to try to explain the topic away.
As I've stated myself first, close correlation of multiple sets of data itself implies accuracy. But this is a simplification, and it's not actually even necessarly about accuracy. Different measurement methodics and environments, even hardware and software, do by definition produce different results. If we would know them, we could associate them - "this measures differently because this and this".
As for smoothing, you don't even have to apply dedicated smoothing (which actually seems to have been done, as I suspected, as crtl just indicated) for the measurement to have a different resolution. Varying FFT sizes alone make a huge difference. For example, load up a measurement in ARTA, switch between the default 4K and let's say 32K FFT, and compare the difference.
Level of documentation depends on application. A defense contractor may have to produce hundreds of pages of documentation on some system. They get paid to produce such documentations that may have to comply with many laws and standard. Likewise someone researching into a new field, would need to have extensive documentation and database of results.
What we do here is none of that. Heck, companies can't even be bothered to product a simple frequency response.
Agreed. I actually explicitly specified the level of documentation that would be needed, and it wouldn't be something that fills a few hundred pages; probably not even one. Problem is, Curvature provided none, except vaguely naming the source.
Also agreed on the problem of manufacturer data. I have probably seen hundreds, but never seen one single properly documented manufacturer measurement. The most you're getting in some cases is information like "2,83V, 1m half space", which is better than nothing, but tells us nothing about the measurement environment and its influence etc. - for example, simply stating "anechoic" tells you next to nothing, since every anechoic chamber is different in size, length, shape, material of its damping elements, etc., and has a different lower "corner frequency".
As for the rest of your statements that I haven't quoted, please don't put words into my mouth. Never at one point did I criticize or even refer to your measurements or their accuracy, or even the Klippel NFS' accuracy or a supposed lack thereof.
We could simply conclude that these measurements are within a reasonable margin of error and that it's probably all okay and simply let it rest at that. That's probably okay for most purposes. Again though, we are 11 pages into a thread full of intricate technical discussion in a forum that names itself Audio
ScienceReview - and suddenly we're getting too technical? Yeah, right. But, if you as the owner say so, I am happy to not get further into the discussion.
For the record, I / we, in a German DIY community, are currently organizing a measurement comparison with a fixed DUT with multiple participants, that includes an NFS, free field measurements, and many more . Here's a timelapse of our DUT in the NFS:
If all goes well we'll arrive at some 10 data sets. We have some preliminary results so far. Once the project is complete I think it would be interesting to compare and diagnose the results vs. those presented here, less in a sense of "right vs wrong", but "which factor / variable influences the measurement in which way". Even the size and shape of the DUT alone might play an important role. Like someone else stated in the course of this thread, also, there hasn't been a single KH80 tested here, but multiple devices - series deviation / production spread is a reality. Etc. The more (well documented) data is available, the more accurate the conclusions that can be drawn.
BUT, again, I am happy to stop at this very point, if this kind of technical discussion and sharing of data is not wanted. I am posting in various other audio forums and am happy there. I do not have to post here.
To get this information you only have to browse the
KH80 Thread No.3.
If you want to get the comparison of Amir's NFS measurement compared to different sources right away,
you can find a summary here.
There I compare the measurement of the KH80 from Amir (newest and older measurement via NFS) with the measurements from Neumann and
S&R (both use anechoic chambers to my knowledge).
Thank you! As usual, Anselm is very thorough in his documentation:
"Der Klasse-1-Messraum erlaubt Messentfernung bis zu 8 m und bietet Freifeldbedingungen ab 100 Hz aufwärts. Alle Messungen erfolgen mit einem B&K 1/4″-4939-Messmikrofon bei 96 kHz Abtastrate und 24 Bit Auflösung mit dem Monkey-Forest Audio-Messsystem. Messungen unterhalb von 100 Hz erfolgen als kombinierte Nahfeld-Fernfeldmessungen."
It would be relevant to name the method for SPL matching of the near field measurements of the low frequency sources (membrane and port). In the original documentation of this measurement method,
Low-Frequency Loudspeaker Assessment by Nearfield Sound-Pressure Measurement, D.B. Keele, AES, 1973, the author names a formula for doing so - square root of sd/sv. Another known method is SPL matching by hand at a frequency of appx. 1/2 fb. I believe I remember though, from another of his tests, or maybe from a personal conversation with him, that Anselm uses the latter - so, question answered.
