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@mtg90 - I have an extra BMS4550 - Would that be useful for your testing, or are you already tripping over CD's? :LOL: (You can keep it as long as you need - it's literally a spare)
 

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Discussion Starter · #222 ·
HexiBase did a video recently about the new umik-2:


Interested to see if you see any measurement differences between the csl calibrated umik-1 vs the minidsp umik-2.
Both arrived the other day. I haven't tested the UMIK-2 yet and only a basic verification that the frequency response of my original CSL UMIK-1 with the distortion issue matched the new one from CSL. To my relief the measured frequency response was practically identical, I was worried the response on my older umik-1 was going to impacted by whatever caused the distortion issue.

I haven't done more testing because I didn't realize the UMIK-1 had switched from micro USB to USB-C at some point and 2m cable included is too short to be useful when connected to my PC so I am waiting for some longer cables so I can actually position the mic where I need to.

I too am interested to see how the UMIK-2 compares to the UMIK-1 in terms of noise floor (supposedly improved) and how close its response matches that of the CSL calibrated UMIK-1.
 

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I would suggest testing the cable against the supplied cable. I ordered a long micro USB to work with my umik-1 and it caused all sorts of weird issues. It was a super cheap cable though.

It would be cool if you could get a TAD TD-2001 to test. Just for the fun of it.
 

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Discussion Starter · #224 · (Edited)
Well I've been busy with other projects but got around to doing some quick tests with the new mics and I'm really disappointed.

The new UMIK-1 measures almost identical to the older UMIK-1, same issue with 2nd harmonic distortion creeping up as you get above ~90dB masking the real distortion from the driver/speaker being tested.

I am however even further disappointed in the UMIK-2. Not only does it exibit the same issue with climbing 2nd harmonic distortion but the internal preamp seems to clip as you approach 105dB! 20dB less then what the mic is rated rated for. I opened the mic up and it doesn't have the dip switches to adjust gain like the UMIK-1 either. I'm going to try updating the firmware but I'm not sure how to fix the gain settings if that is even the issue.

So far the UMM-6 measures the best of the bunch in regards to distortion, but I'm not sure how much it can be trusted either. I'd have to test more with a better driver to determine how much better it really is.

But at this point I'm worried I'll have to pony up for something like an earthworks and external preamp.

Here is a comparison between the two CSL UMIK-1's (matched almost identical), the UMM-6 (treble response slightly more elevated) and the UMIK-2 (totally clipped at this level). This was just a random compression driver/waveguide I had sitting used to run the test. Note measurements were taken at 10" from the screen on the compression driver.
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Now the comparison of 2nd harmonic distortion, The UMIK-2 is not included here because of the compression/clipping. The older UMIK-1 is on top with the newer one just below, UMM6 is at the bottom. You can see the curves converge near 1khz where the level drops enough (and the driver's distortion rises) that the UMIK-1 mics are picking up the driver's actual distortion instead of this self generated distortion.
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Dropping the level to 100dB:
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Distortion at 100dB (UMIK-2 measures similar to new UMIK-1 but UMM-6 still measures the lowest practically at it's noise floor limits there):
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90dB test:
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90dB distortion (pretty much all into the noise floor 1.5k-6k but the UMIK-2 does have lowest noise floor so it measures lower by a small amount):
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Matt,
How does one tell if distortion comes from the measuring device rather than from the thing being measured?
I could kind of follow your logic when comparing multiple measuring devices but how did you tell your original UMIK went bad?
 

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Discussion Starter · #226 ·
I was doing some close mic measurements on a driver and noticed the distortion (and only 2nd harmonic) jumped way up compared to a far field measurement at the same drive level. The only thing that changed was the microphone distance and I took several more tests at different levels and distances to verify this was the case. So something in both the UMIK-1 and UMIK-2 is generating high 2nd harmonic distortion at high SPL levels, I don't know if it's the capsule or the preamp. The Dayton UMM-6 doesn't show this increase in 2nd harmonic at higher SPL levels or at least not to the same extent as the other mics.
 

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Discussion Starter · #228 ·
I'll take and post some more graphs with a nicer driver that show the rise in distortion it better, I just got frustrated that both new mics showed no improvement (and in a lot of ways worse with the UMIK-2) that I stopped messing with it. That was >$300 I could and should have put towards a nicer mic setup but at least it allowed me to rule out any damage to my original UMIK-1.
 

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Discussion Starter · #229 · (Edited)
Here is a better test more clearly showing the rise in 2nd harmonic distortion with increases in SPL I'm getting from all three of my the MiniDSP mics.

Using the Celstion CDX1-1731 in the Titan 818 HF waveguide (No crossover, only an L-pad to drop noise level hiss from the amp) and taking measurements at 40" - 20" - 10" - 5" (roughly 1m, 50cm, 25cm, 12.5cm). The speaker output level remains constant only the microphone position is changing.

SPL/response measurements from the two mics at these four positions:
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UMIK-1 2nd harmonic distortion overlay.
Note the rise in distortion as SPL increases at the closer distances. The microphone hits 1% distortion at just over 105dB:
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UMIK-1 3rd harmonic distortion overlay.
No real increase in distortion as should be expected, some weirdness at the 5" mark I think that is approching the mic preamp limit in the 18dB setting, as a test at 2.5" clipped the preamp:
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UMM-6 2nd harmonic distortion overlay.
Only a very minor increase seen at the closer distances (high SPL), not anywhere near as bad as the UMIK-1.
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UMM-6 3rd harmonic distortion overlay.
Again little change as should be expected, distortion actually drops a little at the closer measurements due to an increase in the SNR:
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