Might be all understood and redundant, but looking at what has been done can be useful I think:
https://www.klippel.de/fileadmin/kl...ld Measurement of Loudspeaker Directivity.pdf
https://www.klippel.de/fileadmin/kl...ld Measurement of Loudspeaker Directivity.pdf
That information has already been shared and talked about, but yeah here once more again. 
Seeing how accurate steppers are these days, especially with a additional rotary encoder, I find the argument for the position accuracy weak.
Calibrating the mics relatively is also not a big deal.
Seeing how accurate steppers are these days, especially with a additional rotary encoder, I find the argument for the position accuracy weak.
Calibrating the mics relatively is also not a big deal.
2020 Aluminum extrusion should be sufficient and light weight. 5 feet is a little over 1.5 pounds and it’s not expensive:
https://www.amazon.com/SANTIE-Aluminum-Profiles-Extrusion-European/dp/B09WD48RXX/ref=sr_1_21?dib=eyJ2IjoiMSJ9.2wmXsUKMJFfg9uknxuSFdo1uKNBOTX6N-yJqkH1xz1S_zrQD5dgA3WMF7WwZWwLHMEUpzpuYt674QYbKLCyeIWZCy7QsL9yGJvrNah5Ol5_Mgm8c5rOJ3rar9kvB7pvUXrWnY2QEOXYCd_VVzUZCpxwvjgThxahlAEx1v0C4DE-jbaTYcbuBp7KBfIwAc74mupOY6j-oJbm1i928TfDQCV5VbJVf5I1yq0nZ8OyqpuU.RhhWybcokEi84qwxKCpOSnDvLvzimAsXyYy6lmibaXg&dib_tag=se&hvadid=580777321859&hvdev=c&hvlocphy=9027676&hvnetw=g&hvqmt=e&hvrand=9628773940960510187&hvtargid=kwd-844742577115&hydadcr=8685_13501823&keywords=2020+extrusion+1000mm&qid=1710874657&sr=8-21&th=1
Guide plates are also cheap:
https://www.amazon.com/IdeaFormer-A...27e-9a13-647e6a75f5eb&pd_rd_i=B09TQDZWWW&th=1
https://www.amazon.com/SANTIE-Aluminum-Profiles-Extrusion-European/dp/B09WD48RXX/ref=sr_1_21?dib=eyJ2IjoiMSJ9.2wmXsUKMJFfg9uknxuSFdo1uKNBOTX6N-yJqkH1xz1S_zrQD5dgA3WMF7WwZWwLHMEUpzpuYt674QYbKLCyeIWZCy7QsL9yGJvrNah5Ol5_Mgm8c5rOJ3rar9kvB7pvUXrWnY2QEOXYCd_VVzUZCpxwvjgThxahlAEx1v0C4DE-jbaTYcbuBp7KBfIwAc74mupOY6j-oJbm1i928TfDQCV5VbJVf5I1yq0nZ8OyqpuU.RhhWybcokEi84qwxKCpOSnDvLvzimAsXyYy6lmibaXg&dib_tag=se&hvadid=580777321859&hvdev=c&hvlocphy=9027676&hvnetw=g&hvqmt=e&hvrand=9628773940960510187&hvtargid=kwd-844742577115&hydadcr=8685_13501823&keywords=2020+extrusion+1000mm&qid=1710874657&sr=8-21&th=1
Guide plates are also cheap:
https://www.amazon.com/IdeaFormer-A...27e-9a13-647e6a75f5eb&pd_rd_i=B09TQDZWWW&th=1
As long as stiffness is high enough, and there isn't more than the allowable amount slack in fixturing elements. We are cantilevering this thing 1-1.5 Meters at max extension. Using cable stays like Klippel is probably a good idea.
True. But are you understanding the actual size of these extrusions versus what is used on the Klippel system?
8020, 8030 and probably 5050. That adds up quickly especially when you factor in the required lengths.
Last edited:
We need some torsional rigidity so 2x 2040 for horizontal and one for vertical is probably a good idea.
I'm also thinking V-slot and OpenBuilds plates.
Then we need referenced sources on doing this calibration properly no?
I might have a few. The systems I have used did not require calibrating the two mics. But I think you are right. It will indeed need calibration if two mics are wanted.
Calibration of the microphones is indeed not a big deal these days (I am referring to the acoustics, not the positioning). Some microphones already come with a calibration file, and you can always send your mics to someone who does the calibration for you (I offered this service for a while, but I got lazy and stopped doing this). The main problem with mic calibration I see is that cheaper microphones (like Behringer ECM8000 and similar "entry level" measurement mics) tend to drift quite a bit over time, so they'd need re-calibration from time to time. I did not have this problem with quality microphones like Isemcon or Earthworks. I can't see how someone would take all the effort of building a Klippel sound field scanner and then skimp on the microphone quality.
You will need phase calibration to allow two mics to be used as references. SPL is as you say easy.
It is not always the case that you require expensive mics. I have many. But as an example the Speaker tester pro system will use a Behringer ECM8000 and give you very accurate values as long as the SPL/Pa is accurately known. For this you need a mic calibrator.
If SPL is easy (it is!), phase is too. Mics are minimum phase, so phase can simply be determined from the SPL curve. I think I explained this already a few posts back.
The measurements are only accurate if the calibration is accurate. The calibration is only accurate as long the microphone does not drift away from it's calibration. That's not necessarily the case with Behringer ECM8000 and similar mics (mine certainly had drift problems).
Also, it's not just about the sensitivity spec (V/Pa number), but also about the shape of the transfer curve.
I attached the documentation of how I did the microphone calibration back then (it's in German, but it may still be useful with a bit of Google translate, DeepL or ChatGPT).
No, since it's about relative calibration, they just have to perform well relatively to each other.
Meaning; pick one mic the be the master and calibrate all slaves accordingly.
Source is not important, again because they need to be relatively accurate, not in absolute terms.
I wouldn’t do it like Klippel (mechanically; with large extrusions)
The inward/outward axis (x) with 4 2020’s (x 1000mm) in a box-frame with interior cross-bracing. Estimate of about 9 pounds for axis frame + (V) slot guide braces (3 of the 4 1000mm extrusions) and on the third extrusion a run of light weight gear rack to direct-drive that axis (which looks like what Klippel used).
gear rack ex.:
https://bulkman3d.com/product/ct0001/
The vertical might need a single 2040, though if the acceleration/deceleration isn’t to fast then a single 2020 should suffice.
Last edited:
Agreed. My German is rusty, but I will understand some, and use the translators as you mentioned. I have 12mm Neutrik mics, and 6mm from Hangzhou Aihua Instruments. They manufacture as tight a tolerance mic as B&K. In fact they make measurement mics for many of the European brands. I also use 1/2 and 1 inch lead zirconate-lead titanate ceramic mics that are exceptionally stable. And yes a few Behringers, and a UMIK. And I agree that the Behringers drift. So I use a microphone calibrator that uses 6 different tones to get a wide band calibration.
For most measurements the UMIK is pretty much the same as the very expensive mics. Only when I am chasing low distortion measurements or very low frequency, or very high SPL measurements do I use the larger or much more expensive mics.
Attachments
Oh I like this! Very nice idea Scott. You might have me onside here! In Canada lots of times it's cheaper to get this stuff via China. I have never seen that kind of a rack. This really makes sense.
You are engineering this with some great ideas. I'll see what I can find also.
Mark
Thank you Matthias. It took quite some time, I managed to translate it through some of my limited German and a few of the machine translation programs.
Mark
Wow, thanks! That's pretty impressive, especially in light of your signature line ;-)