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SPL readings in silent room 8 years 8 months ago #8038

  • JohanW
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Hello

I have tested to measure the SPL in "silent" room using UMIK-1 with the "SPL Meter" in REW5.
The noise floor of the microphone will probably give false readings.
I was supprised anyway that the "SPL meter" readout was so high.

db(z): ~65
db(c): ~57

I noticed a peak at 1khz(with over tones) in the RTA window (see attached picture).
Could the peak be from a clock in the microphone?
Another peak could be seen around 9 Hz.
I have tried to put the microphone in a box and wrap fabrics around the box to block away sound in the room.

Is my microphone ok?
My calibration file is 700-0199.

Thank you


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Re: SPL readings in silent room 8 years 8 months ago #8039

  • JohanW
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I noticed that all calibration files(checked maybe 6) have the same sensitivity factor: -21.1dB.
Is this really correct?

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Last edit: by JohanW. Reason: spelling

Re: SPL readings in silent room 8 years 8 months ago #8041

  • john.reekie
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That seems odd. The REW signal generator isn't turned on by any chance? Or something else running on the computer. (Best to ask/check, to eliminate all variables :) )

I didn't notice anything like that when I did a similar test but will try some more later tonight.
I am not miniDSP support.

"You must ask the right questions." - Dr. Alfred Lanning's hologram.
-> Have you read the User Manual??
-> Have you drawn and posted a diagram?
-> Have you posted a screenshot?
-> Have you posted your config file?

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Re: SPL readings in silent room 8 years 8 months ago #8045

  • adolfotregosa
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I noticed the same thing yesterday. The noise level is high and on rew waterfalls I can see constant noise at some frequencies, 1khz I'm 100 % sure and I remember something going into 20khz.

So we lose 44.1khz sampling rate and 15khz calibrated measuring, we have bad floor noise level and and all mics have the same sensibility factor (also noticed that), yeah right. I'm starting to regret this buy..

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Re: SPL readings in silent room 8 years 8 months ago #8054

  • doclike
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Could u guys give a short hint how u do that tests? I want to contribute my files too ;) (I am bit new to this stuff)

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Re: SPL readings in silent room 8 years 8 months ago #8057

  • JohanW
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Could u guys give a short hint how u do that tests? I want to contribute my files too ;) (I am bit new to this stuff)


I am quite new to this as well. I don't know if this noise floor is anything to worry about.
Maybe this isn't an issue with higher SPL levels when you do real measurements.
The test is very easy to do.

1. Connect the microphone
2. Start REW.
3. Press the RTA icon on top of the screen.
4. In the RTA dialog box press the settings icon (rightmost icon on the top of the dialog).
5. Copy the settings from the first post in this thread.
6. Press the red icon to start the measurement.
7. Wait until the FFT graph is stable and export the picture(camera icon).

You can change the scaling of the graph when you press the icon with two arrows.

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Re: SPL readings in silent room 8 years 8 months ago #8063

  • doclike
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Here are my measurements:


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Last edit: by doclike.

Re: SPL readings in silent room 8 years 8 months ago #8068

  • victoryengineer
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I sure hope this isn't going to be a problem because I just ordered my UMIK-1 and all the forums here and elsewhere are saying the same thing you are. Is there something wrong with the calibration and will a new calibration file be made available soon to correct these issues?

Also in both the 7000190 and 700049 calibration files, they demonstrate 0db @990Hz and 1002KHz. Is this correct?

I sure hope miniDSP and the Devteam get on these issues real fast because there are many forums where their name is quickly turning to mud. If people can't trust the readings then they have no use for the product. I'm on your side miniDSP and wish you the best of success but please correct these issues.

Previously, many people got turned off because the mic was advertized as working down to 15Hz when in fact it cannot. After they purchased the site was changed to reflect 20Hz to 20KHz. I'm not concerned about this because I don't need to go that low but I do expect it to work as advertized and be able to trust the readings.

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Re: SPL readings in silent room 8 years 8 months ago #8070

  • JohanW
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Also in both the 7000190 and 700049 calibration files, they demonstrate 0db @990Hz and 1002KHz. Is this correct?


I think all calibration files are normalized at 1KHz.

The sensitivity factor is very strange though.
The new batch all have the factor -21.1 which is about 6dB lower than the old batch.
If the sensitivity factor is correct for both batches something must have changed in the hardware between the two batches. This is my conclusion.

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Re: SPL readings in silent room 8 years 8 months ago #8090

  • devteam
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This reading sounds like its showing a peak generated by the internal/PC. We'd have to investigate to see what's the issue/Cause. Something we'll look into definitely.

Down to the measurement in an actual real scenario, with the current microphone sensitivity and rating for high SPL (127dBSPL), the mic is actually low in sensitivity by nature as you'll learn when you actually make some real measurement to be used for say tuning of a room with a DSP/Acoustic. Meaning that in general, even without a spike, you'd want to measure above 60dBSPL to make sure you're the overall acoustic background noise of a room isn't affecting your measurement.

DevTeam
miniDSP, building a DSP community one board at a time.

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Re: SPL readings in silent room 8 years 8 months ago #8091

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Btw. the sensitivity values got fixed/changed.

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Re: SPL readings in silent room 8 years 7 months ago #8250

  • mvs0
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I see the same 1KHz (with over tones) in the signal at 45 dB (with REW) and -95dB (audacity recording).

Any solution for this?

Marinus

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Re: SPL readings in silent room 8 years 7 months ago #8251

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Just recorded this tonight in our basement theater... water heater, furnace and fan were running on the other side of the wall.
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Re: SPL readings in silent room 8 years 7 months ago #8308

  • miki_ada
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Dear DevTeam,
I'm very interested in your UMIK. I've read throught the web about the issues in the calibration files and I'm happy to see that the files are now OK. Are there some news about this minor issue? Just to know if in the next days you are going to release a new mic without this issue or if it's a long and complicated thing.
Many many many thanks for your support.

Michele - ITALY

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