# UMIK-1 SPL reading in silent room



## JohanWa (Feb 12, 2013)

Hello

I have just started to test my microphone. The first I did was to test SPL readings in silent room (not possible to get it 100% silent).
I know that I will get wrong results because of the noise floor of the microphone.
To my suprise the readings was much higher than expected (~65db(z) and ~57db(c)).
The reason for the high values seams to be a peak at 1KHz(with over tones). Could this peak be from a clock inside the microphone?
I put the microphone in a box and wrapped the box in fabrics to block any 1KHz signal in the room.
The result was the same.

The calibration file for the microphone is loaded(700-0199).
Is my microphone ok?

Thank you


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## Zeitgeist (Apr 4, 2009)

Those peaks look awfully high. Assuming it's not an issue with your computer -- you might want to contact MiniDSP to ask.


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## adolfotregosa (Feb 2, 2012)

here's mine...


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## JohnM (Apr 11, 2006)

1kHz harmonics indicate pickup from the USB data. Worth trying different USB cables (the one that comes with the mic works well for me, nothing visible at all at 1kHz on the spectrum) and different USB ports on your computer, if available.


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## JohanWa (Feb 12, 2013)

adolfotregosa said:


> here's mine...


Your frequency response almost looks like a copy of mine. I will post the same frequency range later.
I am not sure this is a problem for real measurements.
I will check if the peaks disappears if a pink noise is played at higher SPL.

I have checked old calibration files and it looks like old files have sensitivity factor around -15dB.
New files have a factor of -21.1dB. Both old and new files have zero compensation at 1KHz (normalized).
It's a 6dB difference between the two batches.


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## JohanWa (Feb 12, 2013)

JohnM said:


> 1kHz harmonics indicate pickup from the USB data. Worth trying different USB cables (the one that comes with the mic works well for me, nothing visible at all at 1kHz on the spectrum) and different USB ports on your computer, if available.


I will try with a new cable later today (if i manage to find one).
I have tried with a laptop(battery powered) and my stationary computer with the same result.
Tested with different USB ports.


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## adolfotregosa (Feb 2, 2012)

I have tried all of the suggested and it comes from the mic itself.


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## JohanWa (Feb 12, 2013)

adolfotregosa said:


> here's mine...


and mine with the same frequency range.
changed cable also but with the same result.


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## larft (Jan 30, 2013)

My initial reaction was the same as yours JohanWa but I am new to doing this kind of testing. My results are similar and show a somewhat different curve, but the harmonic peaks are still present:









For me it's all a learning experience and what at first looks like a problem will hopefully turn out to be normal. My guess is that the power supply to the soundcard in the microphone should have more filtration, but as I said that's just a guess.


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