Seems that if you want to create a riot in the streets of ASR, all you have to do is show a non-ruler flat response of Neumann KH80 DSP professional monitor (speaker). Not knowing that, that is precisely what I did in my first review of
KH80 DSP:
This was one of the earliest speakers I measured with the Klippel Near-field scanner. So naturally (or not), there were a lot of suspicions that it could actually recreate anechoic chamber measurements such as provided by the company:
After what seemed like a hundred pages and numerous attacks from every corner on validity of measurements including me not even being dressed right to measure speakers, I decided to test a second KH80 DSP monitor sample that another member was kind enough to offer. Was that the end of it? Of course not. As I said, if the measurements were not ruler flat, folks were not satisfied and this is what we had:
A sin was committed once more with the same dip around 80 Hz or so. Protests ensued and library books burned in streets with assertion that ASR measurements were flat wrong.
After some 25 pages of posts, folks seemed to forget about the fight and thread went dormant. Until... we heard back from Neumann which had asked Klippel Germany to measure an identical sample to what they had measured in anechoic chamber. While there were some differences between the two measurements, they were closer to each other than mine was. So folks went for the jugular this time. Nothing short of repenting on my part and accepting that my measurements were bogus would satisfy. The proof as they said, was right there.
When someone kindly suggested to fund the purchase of a third sample, I decided to not make it the community's problem and purchased that myself. Meanwhile
@GuyLayfield reached out privately to me offering that we work together to see what is going on. Suspicion quickly went after the temperature difference for when I tested mine (in winter) and theirs (temperature controlled at 21 degrees C). Guy showed me a couple of useful slides from Klippel indicating changes in speaker parameters based on temperature:
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Meanwhile my sample arrived and measured it. And what do you know, the low frequency dip had disappeard:
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We still had to verify the problem was temperature. So Guy put a unit in the fridge overnight and then made measurements in the morning every 3 minutes as the speaker and its components warmed up. Here are his results, normalized to 21 degree C (black line):
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As we see in the bottom blue line, lower temp most definitely created the dip around 80 Hz and gradually disappeared as the speaker warmed up. This then showed that my measurements are indeed accurate but were simply impacted by the lower temperature at the time.
Guy, knowing you all, wanted to still investigate some variations in measurements, some of which were also in Klippel Germany measurements. As it happens, they have measurements for each speaker sold and that included my sample. So we set out to try to reduces differences.
The guilty party here appeared to be the microphone protection cage that I use. This is a sensor shroud around the mic with micrswitches that detect any impact to any object (e.g. speaker) and instantly shuts down the system. It avoids banging an expensive microphone against an expensive speaker! Quite a while ago I had noticed that it was causing some comb filtering due to reflections. I experimented with absorption around it and got it under control. Still, we thought maybe it is at fault.
So I took out the cage and sadly as soon as you do that, all alignment of the system is gone. So while I was at it, I re-adjusted everything better than ever before, and even worked on optimizing the signal processing for least amount of error. Here is that measurement:
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Yes, it looks the same! It is a bit flatter in bass but I think it has tiny variations here and there. According to Guy, we are now with +-0.6 dB from their measurements.
We don't know if the variations are because my measurements are wrong, or theirs. There is no gold reference here.
Frankly, I am sick of it at this point so told Guy that we are done and I should just post the results. People need to remember that every measurement system has variability and there is fair bit of that between anechoic chambers as well. For the purposes of evaluating speakers, what we have is more than good enough and far, far better than anything any reviewer is producing.
Importantly the moment the speaker is put in a room, nothing remotely flat comes out of it. So we need to keep that in perspective.
Conclusions
The main variable in our measurements not quite matching Neumann's was temperature. Whether this impacted just this speaker or the others, I don't know. If I get some time (yeh right), I will go back and remeasure a few of the other ones I still have and see what difference there may be. Come this winter, I will heat up the measurement room to get it closer to spring weather at least. Fortunately it never gets that cold here and hopefully we will find that other speakers are not affected as much.
Beside temperature, I have also fine tuned the system, using averaging for example to reduce noise level, deploying more optimal parameters to get the high frequencies right, etc. These have been in place for months so the bulk of what we have measured are accurate as they also enjoy warmer temperatures.
@MZKM has a new score for this speaker which he will post. New spin data is enclosed.
Be on notice that I am not measuring this speaker again so don't even think about asking me to do that. As it is, I have to now rip the system apart again and put the cage back on it and re-align it all.
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As always, questions, comments, recommendations, etc. are welcome.
As you can tell I am quite grumpy because of this ordeal. Fortunately it is not something where a few hundred dollars won't fix. So please
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