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Do calibration files for measuring Mic's matter?

Snarfie

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#1
Spoke sometime a go an sound engineer who is working for a company which does measuring in the music industry like studio's live events but also boardrooms, canteens etc but most work is done for infrastructure like sound walls for absorbing/deflecting traffic noise and other environment projects where sound is involved. He told me that the measuring Mic's they us has to be as linear as possible. They use calibration files but he noted frequently the Mic's has to be re-calibrated to make or measurings legit. Now the change after recalibration is minimal but after a few years it is getting a bit larger. For the use of high end audio/room correction in his opinion using a old/original calibration file does not make much sense if the Mic is already more than 3 or 4 years old you have to recalibrate it if you want the best result. However he doudt that you can hear any difference.

I also did a test with mine one Superlux an a self made calibration file based on the enclosed graph (here under) that was included in my Superlux box. As you could see the Superlux graph is already quite linear without calibration file. When I measure them both (with and without calibration file) the graph are barley changed an I really can't hear a difference between the two.






Are their forum members who did for instance a measuring with a UMIK-1 Mic with and without calibration file an could you hear a clear difference. Who is recalibrating their Mic if so after how many years.
 
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Pio2001

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#2
For what it's worth, here is an MMM measurement made three times in a row with three different Umik-1 microphones. The curves were drawn taking each microphone's respective original calibration file.

The upper graph shows all the frequency range. The lower graph is a zoom in low frequencies.

The small deviations everywhere are probably caused by the MMM method that doesn't give 100% reproductible results.

The suspect deviations are the 3 dB that are missing at 28 Hz with Ohl's micro, the 3 dB in excess above 10 kHz with Igor's micro, and the tiny peaks at 50 and 100 Hz with mine (the mains are 50 Hz in Europe).

Comparaison micros en MMM.png
 

Blumlein 88

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#3
While not the same thing here are some condenser microphones used for music recording. I recorded a sweep from a speaker which is the source of the up and down graph, but you can see if different mics are the same or not. I would imagine measurement condensers or electrets would stay the same better than these larger diaphragm music microphones.

If you have a cal file I'd use it, and I would think they'll stay consistent over time unless abused. Or at least close enough for the purposes of using to tune our audio systems the differences will be inaudible.

Three Audio Technica AT4033 purchased used at various times.
1596637435535.png


A pair of Aventone CK1's.
1596637521070.png


Three Shure KSM32 microphones. 10 years between oldest and newest. The green one has a different mesh cover.
1596637614848.png

A pair of CAD M179's purchased 6 months apart.
1596637681494.png
 

RayDunzl

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#4

solderdude

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#7
When a sensor or measurement device is used professionally and needs to be accurate in an absolute sense it is customary to check calibration.
Time intervals can be determined by the manufacturer or by the user/company of the product.
At work all (essential) measuring equipment and tools that needs calibration checked is sent in (or done on site such as temp chambers.
Lots of things never need adjustments, some do.

A Dayton iMM-6 started to loose the lowest frequencies gradually over time and didn't catch it immediately. Only after results seemed 'off' I noticed.
It's not really a problem as its mine but mics do seem to get 'worse'. If you need absolute accuracy maybe mics need calibration as well.
 

Chromatischism

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#8

dasdoing

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#9
you can see they all use the same Panasonic wm(xx) capsules. my first "calibration mic" I build with one and a straw, my Dayton, my SPL meter...all use the same capsules.

also this is relevant to the question if those mics get worse. SPL meters need to be calibrated once a year in my country for example to be valid as proof. again, they all use the same capsules
 

Chromatischism

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#11
I want to make a graph like this of my correction file, but it's too many data points (1500 offsets) for Excel to handle. I might have to bin the data first.
Found a way. Here is my UMIK-1's response, obtained by inverting the offset values in the calibration file.

CSL UMIK-1.png
 

dasdoing

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#14

ctrl

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#15
Do calibration files for measuring Mic's matter?
This depends on the microphone capsule used.

If the microphone capsule meets the "Class 1" specification in frequency sensitivity or is even "Class 1" specified (very expensive), then the measurement errors of 40-4000Hz are already very limited.

Nevertheless, even with "Class 1" mic capsules, the tolerance in sensitivity is so high that only calibrated measurement microphones are suitable for reliable audio measurements.

Since each microphone capsule is different, each microphone must be calibrated individually. There is no "standard calibration file" for a microphone model.


1596709006289.png



if the Mic is already more than 3 or 4 years old you have to recalibrate it if you want the best result
This might depend on the microphone capsule used. With my measuring microphone, it says:
This microphone is a maintenance free product but could require a recalibration in case of a mechanical impact or periodical temperature cycling/use at the min and max working temperature
So, when used in normal ambient temperature, no recalibration should be necessary.
 

Bamboszek

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#16
Electret microphones are much less stable than non-prepolarized condenser microphones.
Once I talked with professor at my university about Superlux ECM999. They have been using lots of them to build microphone matrix.
He said that initial accuracy is good, especially considering price but they tend to differ much with changing humidity and temperature.
 
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