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Rough comparison of two measurement mics

RayDunzl

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#1
To satisfy some mild curiosity:

A pair of visually (very) similar condenser microphones.

RTA of music, over about an hour, as seen simultaneously by:

miniDSP UMIK-1, USB microphone, 24/48 signal (but running at 24/96 in REW)

Behringer ECM8000, with UMC-202HD for conversion to digits running at 24/96.

No correction file applied to either (since I only have one for the miniDSP)

upload_2018-3-3_11-58-53.png


Looks pretty close.

Noise floor slightly different, but inconsequential for in-room measurements.
 
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RayDunzl

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#3
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Blumlein 88

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#4
Here is a comparison between a Umik 1 and two recording omnis. The hot pink graph is the Umik. These are measuring a speaker nearfield btw. I put the mikes in the same positions as closely as I could.

The blue graph is a CAD M179 multi pattern LDC set to omni.

The green graph is an Avantone CK1 pencil condensor with omni capsule.

1/6th octave smoothing. Not exactly the same, but not terrible.

There is a little secret however. I used the frequency response graphs for the recording mikes to create a calibration file for each. As much as I always thought those graphs were drawn by marketing, apparently they are actually correct. I used WebPlotDigitizer for this. Takes an image of a graph and turns it into a .csv or other files that REW can use. I didn't do any fine tuning otherwise. Obviously you could tweak the cal files some more if you wished to do so.

BTW, I had a pair of each recording mike. I only show one graph because they created the same exact result. Manufacturing tolerances of even cheap condensers are apparently pretty good.
The only large differences are above 15 khz.

Umik1 CAD M179 CK1 omni.png
 
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Guermantes

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#6
The Avantone looks quite good. Is it a copy of the AKG C451 + capsules? I see the three capsules are included in the one price.
 

Blumlein 88

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#7
For comparison here are two cardioids. They work nicely above 200 hz. A little droop to them at lower frequencies.
The Shure KSM32 in bright green
The Audio Technica AT4033 in blue-green.

I had the speaker in an inside out corner. One side of the corner opens into a large room and hallway. The other opens into a large room. The idea was no surfaces for several feet in any direction for hopefully more consistent measurements. The opposite of your normal corners. I wonder if such calibrated use of cardioids might help us eliminate some reflections for cleaner measurements above 200 hz in room.

Umik1 KSM32 AT4033.png
 

Blumlein 88

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#8
The Avantone looks quite good. Is it a copy of the AKG C451 + capsules? I see the three capsules are included in the one price.
I don't know. I've read which Chinese capsule it uses. One of the more common ones that is a copy of an older European design. Do note I used calibration to compensate for non-flat response of the microphones. Here is a small graph from Avantone. I used the same graph, in larger image size for the calibration. If calibration were perfect you would have a flat line. It looks like you get close assuming the calibration files for the UMIK1 are good since that is the reference in my above graphs.
 

DonH56

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#10
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Blumlein 88

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#11
For what its worth, since developing those calibration curves and seeing they have validity, I've gone back and applied them to recordings I have made. This results in an improvement. Beyond response is directivity with microphones. But frequency response is important and reduces the worst attributes of microphones. That also means I can apply cal curves to cause my mics to mimic classic, expensive, Euro mikes. It is somewhat successful at times. I doubt if any simulation is fully equal to the real deal, but this sort of simple minded thing gets you more than halfway there. Proving once again, 85% of hifi is frequency response.

One more graph here. Three Shure KSM 32 microphones. From construction details and serial numbers these span 11 years. The two closest are the oldest and newest. That is what I call quality control. I believe all the difference is from me being unable to precisely precision each one in the same identical spot at better than an 1/8th inch deviation.

ksm32 .png
 
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