Different readings from the SPL meter and RTA when measuring room background noise.

[solo541]

Hi John, could you please explain the situation? I have a calibrated USB microphone (UMIK-2) with a 90-degree calibration file for measurements. When measuring the room's background noise, the SPL meter and RTA show different readings. The Adjust RTA levels function is turned off. What could be the problem?

 

[John Mulcahy]

Are you comparing readings with the same weighting?

 

[solo541]

 

[John Mulcahy]

Your concern is the difference between 33.2 on the meter and 34.4 on the RTA?

 

[solo541]

Yes

 

[solo541]

Maybe need to change the window from HANN to Rectangular?

 

[John Mulcahy]

You have the meter set to Fast, so much less filtering than 2 averages of 64k zero overlap FFT. For a more stable meter reading use Slow or Leq, and for more stability on the RTA use exponential averaging, e.g. 0.97.

 

[solo541]

Ok, I'll try. Thank you.

 

[John Mulcahy]

You should also use overlap for the FFT.

 

[solo541]

Ok.

 

[solo541]

What value should be optimal in Max Overlap: 50% or 93.75%?

 

[John Mulcahy]

Doesn't much matter, 50% is OK, higher overlaps will give more frequent trace updates.

 

[solo541]

Ок.