Acoustic Measurements

[NI-Bongo]

Hello Imperial-aero,

The conversion is just as you suspected.  The mV/Pa sensitivity of the microphone is the proper conversion factor to get Pa from a voltage measurement.  Calibration is not required for this step.  Depending on your application, a calibration may be required.  If you are measuring multiple signals from different sources, you may need to calibrate your microphones to a reference.  Let me know if you need more details on this.

[imperial-aero]

Hi John,

Thanks for your reply.

I'm using 8 tie-clip microphones placed around the cirumference of a large tube to measure the sound waves generated by a loudspeaker. The manufacturer of the microphones only specifies the sensitivity in dB (-65 dB +/- 3dB). I was told that it's probably best to calibrate it. I wanted to know whether there are simple devices to calibrate such microphones.

[NI-Bongo]

Hi again Imperial-aero,

There are simple microphone calibrators that output a few fixed frequencies and sound pressure levels.  You can take data with the microphone in the calibrator and calibrate your sensitivity to get the appropriate values in your acquisition.  The Sound and Vibration Toolkit for LabVIEW provides microphone calibration VIs to make the software part of it easy.  NI does not make microphone calibrators, but you can find a vendor online.  Here is a list of microphone/accelerometer/pressure transducer manufacturers.  You may find one from one of them.

Major Vendors for Accelerometers, Microphones, and Other Transducers for Sound and Vibration Measurement Applications
http://digital.ni.com/public.nsf/allkb/0B55060DDD1FF3E986256CE5005FDA04

NI Sound and Vibration Software
http://www.ni.com/soundandvibration/software

I hope this helps!

[jchrisj]

SL in T wrote:

" Have Sound and Vibration Toolkit Version 3.1. Once I replaced the standard FFT with the one from SVT I now get correct/matching dB levels for both FFT and Octive Analysis. >> Problem solved!"

 

Hi I have also had some problems making acoustic measurements with a microphone and I do not have the SVT. Are you saying that there is a problem with the FFT in the standard signal processing kits that the SVT fixes?  I am trying to follow an ASTM for a two microphone method of testing acoustic absorption, but I have hit a wall.  I seems that all the calculations are correct,  leading me to think that there is a problem with a labview VI.

Does anyone know if there is a problem with the standard FFT VI in labview?

Thanks in advance 

[rathib]

I have a wav file constisting of a recorded calibration signal, the signal is a recorded tone with a sound pressure level of 93.9 dB (~0.99 pascal) at 1000 Hz. The equipment I used to record the file "calibration.wav" has a sensitivity of around 53.49 mV/pascal. After performing 1/3 octave analyses on that wav file it should show 94 db for 1000 hz but it is below that. Is there any way to fix it? I'am also using SVT and tried to scale the signal EU units, didn't help. Any suggestions? 

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@jchrisj