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Author Topic: Measurements of sound pressure using Earthworks M50 Mic  (Read 605 times)

Ahsan Raza

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Measurements of sound pressure using Earthworks M50 Mic
« on: March 02, 2017, 10:11:30 pm »

Hello Everyone,
I am working on a project in which I have to measure the sound pressure of ultrasound frequency. For this purpose, I am using Earthworks M50 microphone and Quad-Capture USB 2.0 (I have UMC202 as well). Can anyone please tell me how can I record and convert the value on dB scale and how can it be converted into pressure.

Thanks in advance

Regards,
Ahsan
« Last Edit: March 02, 2017, 10:36:32 pm by Ahsan Raza »
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Mac Kerr

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Re: Measurements of sound pressure using Earthworks M50 Mic
« Reply #1 on: March 02, 2017, 11:15:34 pm »

Hello Everyone,
I am working on a project in which I have to measure the sound pressure of ultrasound frequency. For this purpose, I am using Earthworks M50 microphone and Quad-Capture USB 2.0 (I have UMC202 as well). Can anyone please tell me how can I record and convert the value on dB scale and how can it be converted into pressure.

Thanks in advance

Regards,
Ahsan

Do you want the level in a calibrated Sound Pressure Level or do you want it in Pascals? To get a calibrated SPL you need to calibrate your meter, which requires a calibrator which provides a specified SPL, usually 94dB, so you can set you meter to read 94dB SPL at that level. Then you use that calibrated meter and take a measurement. That will give you a number in dB on the A scale, B scale or C scale. You need to know which is required.

To convert to Pascals you need to do some math. Read about it HERE

Mac
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Mark McFarlane

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Re: Measurements of sound pressure using Earthworks M50 Mic
« Reply #2 on: March 02, 2017, 11:24:56 pm »

What frequencies are you measuring? 
What software are you using? 
Do you need absolute pressure readings, or relative readings?  M50's come with individual sensitivity and frequency measurements (and probably an import file suitable for SMAART).


I don't know for certain, but it is possible that the individual sensitivity measurement that comes with the mic could be manipulated to take the place of a dedicated calibration device. Or maybe not, you'd still have to deal with potential variability in the preamp gain.

Is it a brand new mic that has been carefully stored and handled? Earthworks recommends recalibration every 5 years.
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Mark McFarlane
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Ahsan Raza

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Re: Measurements of sound pressure using Earthworks M50 Mic
« Reply #3 on: March 03, 2017, 12:03:50 am »

What frequencies are you measuring? 
What software are you using? 
Do you need absolute pressure readings, or relative readings?  M50's come with individual sensitivity and frequency measurements (and probably an import file suitable for SMAART).


I don't know for certain, but it is possible that the individual sensitivity measurement that comes with the mic could be manipulated to take the place of a dedicated calibration device. Or maybe not, you'd still have to deal with potential variability in the preamp gain.

Is it a brand new mic that has been carefully stored and handled? Earthworks recommends recalibration every 5 years.
I am measuring the frequencies in the range of 50 Hz to 500 Hz and for recording the sound data I am using MATLAB which stores the data into WAV file. And I am seeking to get absolute value of pressure of certain frequency. How can I use the the data of WAV file to convert it into pressure or dB SPL?
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Mark McFarlane

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Re: Measurements of sound pressure using Earthworks M50 Mic
« Reply #4 on: March 03, 2017, 12:29:10 am »

I am measuring the frequencies in the range of 50 Hz to 500 Hz and for recording the sound data I am using MATLAB which stores the data into WAV file. And I am seeking to get absolute value of pressure of certain frequency. How can I use the the data of WAV file to convert it into pressure or dB SPL?


In this case, you need the external mic calibrator as Mac described.  They aren't cheap, but much cheaper than your M50.  If the calibrator puts out 94dB, then run it into Matlab, find the peak value of the wave file and you have a 94dB reference point.  Make sure you have the gain setting on your preamp fixed for every experiment, e.g. glue the knob in place, or leave it at the minimum or maximum value, so it can't move after calibration @ 94dB.

You may also need a second point of reference.  I'm not sure if the voltage output by every mic capsule is perfectly linear with SPL, so I'll leave that for an expert.

FWIW, your initial post said 'ultrasound'.  50-500Hz is NOT ultrasound.  Ultrasound frequencies are above human hearing, i.e. > 20KHz, and typically in the MHz range.
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Mark McFarlane
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Ivan Beaver

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Re: Measurements of sound pressure using Earthworks M50 Mic
« Reply #5 on: March 03, 2017, 07:56:36 am »

Hello Everyone,
I am working on a project in which I have to measure the sound pressure of ultrasound frequency. For this purpose, I am using Earthworks M50 microphone and Quad-Capture USB 2.0 (I have UMC202 as well). Can anyone please tell me how can I record and convert the value on dB scale and how can it be converted into pressure.

Thanks in advance

Regards,
Ahsan
I would be EXTRA careful in what you are reading above 20Khz.  Your interface device and software may not give accurate answers due to the sampling rate.

I did not look into the specs on the rest of your system, but just something to be aware of.

You need to look at the limits of the ENTIRE system.  DO NOT assume that because the mic goes high-the rest of the gear will also
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