Hi all,
I have been very busy this year (trying to make enough money not to let our company go bankrupt due to covid consequences) but now I finally have some energy again to pick this awesome topic up.
I thing I am starting to gain enough understanding to start doing some coding in Matlab to try and replicate your results NTK.
What would be helpfull is to get some intermediate resultas from your calculations so I can check my results step-by step
I can read and understand (mostly) your code, but I dont have python skills (and really no time to learn yet another language at this time)
I hav also been pondering on a hardware setup and have come up with something that might work and be easy and cheap to implement.
I was thinking along these lines (see attachd drawing):
-lasercut a 2.5mm steel double ring with gear teeth already cut in in the outside ring for stepper motor 2
-add 16x mems pdm mic on the half inner circle in 10degree steps
-add 16x mems pdm mic on the half outher circle in 10degree steps
https://nl.mouser.com/ProductDetail/Knowles/SPH0655LM4H-1/?qs=/ha2pyFaduhvp7CqAAKzBBNK2rEwhn0N%2B8ibYkFktxzfMhqYbHKVqA==
-use 2x minidsp mchstreamer to convert the pdm signals to usb
https://www.minidsp.com/products/usb-audio-interface/mchstreamer
-attach stepper motor 2 on the axe of stepper motor 1.
-the ring (it will be lightweight, approx 3,5 kg) rests on the gearwheel of stepper motor2
stepper motor 1: this is the horizontal rotationand will make all angles possible
- use stepper motor 2 to roll the complete semi circle +-10degree, this will make alle vertical angles possible
to perform the amount amir does (ca. 1100) will take the time of 34 measurements, so should take approx: 5 seconds sweep for high dynamic range+5 seconds movement=10*34=340seconds =~5minutes
to perform a full 5 degree resolution dual layer sphere measurement (35*71*=4970measurments) , will take the time of 155 measurments =~25minutes
I have tested the mems mics (8 pieces so far) ; they are fantastic in consistency and live up to the specs, to even further improve calibration measurements can be performed for every mic.
I am highly critical in this topic; part of my daytime job is developing type1 soundlevel meters and I own a bunch of different type1 measurement gear.
estimated BOM costs are approx.
2x mchstreamer = 230 dollar
32x mems mic=32
steel lasercut ring=200 (checked with supplier)
steel structure=200
2x stepper motor=100
cabling and a rest material=200
Total = approx. =~ 960 dollar
of course the semi circle could also be a full circle so you coul use only 2 mics, but I really dont see an advantage in that since the mems are so good .
@ NTK; would this be the most optimum mic placement (the consistent r values)? I thought I could conclude that from your part 5 post but don't know if I fully understood
Let me know what you guys think!
Cheers,
Kees