Problem of Sound Pressure Level and decible.

[n96111346]

I am currently encountering some issues with sound decibel measurements. I am using a USB-4431 DAQ along with an MI-1432 microphone. I have created a VI from the LabVIEW example.I would like to know the dB level of the generated sound. To validate my data, I have used a decibel meter, but the values are completely different. I don't understand why my acquisition is not working. I have attached my VI. Maybe I have hardware issues or my VI is not functioning correctly? You're welcome! If you have any more questions or need further assistance, feel free to ask. Good luck with resolving the issues you're facing!

[PalanivelThiruvenkadam]

No Attachment

[altenbach]

dB is based on a ratio to a reference sound level (typically 20 micropascals), so maybe your reference is incorrect. (see also).

We can help more once you include the promised attachments. 😄

---

@n96111346 wrote:

To validate my data, I have used a decibel meter, but the values are completely different.

---

There are billions of way to be "completely different" so you should be more specific. Are they too high? To low? Off by a constant offset? Off by a constant factor? Nonlinear?Reciprocal? etc.... 

How does it look if you graph the two readings for a few different sound pressures on an xy graph?

[santo_13]

---

@n96111346 wrote:

I am currently encountering some issues with sound decibel measurements. I am using a USB-4431 DAQ along with an MI-1432 microphone. I have created a VI from the LabVIEW example.I would like to know the dB level of the generated sound. To validate my data, I have used a decibel meter, but the values are completely different. I don't understand why my acquisition is not working. I have attached my VI. Maybe I have hardware issues or my VI is not functioning correctly? You're welcome! If you have any more questions or need further assistance, feel free to ask. Good luck with resolving the issues you're facing!

---

Ensure you're doing these,

• Configure DAQmx task as Sound Pressure input
• Configure the sensitivity of the mic in DAQmx task
• Enable IEPE current if your Mic requires
• Now, all DAQ measurements are in Pascals
• Find the amplitude of the frequency of interest using FFT and rms scaling
• Convert Pascals to dB SPL using the formula 
  dB SPL = 20 * log (Value in Pascal rms / 20 e-6)

[Henrik_Volkers]

Assuming you  have setup your DAQ and Mic correctly.

Now you want to do a calibration (a comparision with your reference).

Your reference is your decibel meter.

Usually one use a stable sound source and an Anechoic chamber and replace the reference with the DUT.

Depending on the frequency range even in the (not perfect) anechoic chamber the correct positioning is essential.

In sloppy practical measurements 10 db difference is nothing to wonder about 😉