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Is Dirac software restricted to UMIK-1 ? 6 years 10 months ago #17005

  • ergo22
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Skylinestar, if you are calibrating a 2 channel stereo system then point the microphone to the center between the speakers and use the 0deg calibration file. The error will be very small as both speakers are within +/- 45deg where the microphone calibration is still reasonably valid.

The 90deg calibration is meant for a situation where your sound sources are on side or back compared to measurement mic. Then one would point the microphone towards the ceiling and use the 90deg cal file as then the result is more accurate. It's especially the high frequencies where the measurement microphone would otherwise have a small drop due to it not being perfectly omnidirectional.

***
As for accuracy of the stock calibration file. I did re-measure/recalibrate mine with my own tools (I have access to anechoic room and lab grade microphones from G.R.A.S). The deviation was below 1 dB until about 10kHz and deviated only by +/-1dB above that.

I have also done a cross-check for the EMM-6 mic I bought from Cross-Spectrum. The agreement I got in my calibration process with Herb's was very good.

Mind you that 'having a microphone calibrated' is a very tricky topic. In the range from 5...20kHz the mounting of the microphone to the mic stand will have an effect that can be several dB. Also it will be different if a 'replacement method is used' where Reference mic is put in sound field, then removed and replaced with the mic to be measured or if both of them are is sound field at the same time..... So unless the lab you make calibrations at are willing to share all these details and you replicate the mounting same way every time it is unlikely that the file you get is any more accuracy in your result.

Ergo
Tallinn, Estonia

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Is Dirac software restricted to UMIK-1 ? 6 years 10 months ago #17008

  • stephenting99
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Hi Stephen, the advantage of the 90 degree cal file is that it will give you a consistent measurement across all speakers (in a conventional 5.1/7.1 system). That is what Dirac Live needs. What you get then is a starting point. Per the manual, you will then want to tweak the target curve to suit your own system and personal preference. You can do that BECAUSE you have a reasonable 90 degree cal file.

If the question (to me) is what is the specific +/- X dB tolerance on the calibration? I could guess on a specific number, but I feel that it would be pointless. I don't know if CSL provide a guaranteed +/- X dB number but again, there's your go-to if you actually need a specified tolerance.


Hi john,

For the CSL calibrated UMIK-1 mic, they produce a mic report that shows a table and graph indicating the error and linearity of the mic over the frequency range. From the graph, one can see how much the mic deviates from a flat response. For me, the 90 deg file has the best flat response and this is what's normally used in REW for measurements.

It would vary with each individual mic by some amount, i.e. not every UMIK-1 would have the same curve.

I was trying to find out what the absolute error is for the stock standard UMIK-1 mic provided by MiniDSP with the 90 deg file. Without a reference mic to compare it against, it will be very hard to determine this.

From ergo22 response, it's 1dB up to 10kHz. This is close to what the CSL mic report says - happy to report back. Above 10kHz, the error goes pear shape. Trying to understand why.

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Is Dirac software restricted to UMIK-1 ? 6 years 10 months ago #17011

  • ergo22
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The slight rise of high frequency rise is common in small diameter ECM capsules and varies from 2..4dB rise at 15kHz to as much as 8..10dB raise depending on the capsule model and the production tolerances.

Getting the response perfectly flat is VERY complex. The laboratory grade mics that achieve that cost >1..2kUSD, use different power etc. These will have a very finely engineered cover in front of the diaphragm that in end compensates the raise and end response is flat. That is just not feasible for price range asked for UMIK.

When you enter the calibration file into Dirac software it will be deducted from the measured response - so even if your mic is up by +5dB at 15kHz for example the SW will compensate that. That is the purpose of having the cal file...

Look at these pages for interesting info and samples of various mic cal results
www.htguide.com/forum/showthread.php?345...e2&highlight=ECM8000
realtraps.com/art_microphones.htm
www.hifizine.com/2012/09/dayton-emm-6-me...cross-spectrum-labs/

and if very serious look at the theory by B&K.
bksv.com/doc/be0089.pdf
bksv.com/doc/bv0054.pdf

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