REW RT60 Data Panel

[camscottie]

Hi,

I'm currently looking at the RT60 data panel in REW and I noticed that occasionally there are missing values:

Could anyone explain why this happens?

Thanks
Cameron

 

[John Mulcahy]

The values will be blank if there wasn't enough data in the filtered response to generate a result at the frequency. The orange values indicate poor line fit, so the results seem to be problematic through much of the low end. If you attach the mdat file can have a look at it.

 

[camscottie]

Thank you for your speedy response, here is the mdat containing the measurement recorded twice, which have very different line fits. This may have been due to traffic noise, as the microphone was placed in a room that was beside a busy road, but I'm open to your thoughts and opinions on why they may be so different, aswell as any thoughts you have about my first post.

Thanks,
Cameron

 

[John Mulcahy]

In those measurements there are a couple of blank values for the 50 and 63 Hz octave fractions. That is because there is not enough decay curve to analyse before it reaches the noise floor. For the 63 Hz band in measurement 2, for example, the noise floor is reached after only 22 dB of decay. The minimum to generate data is 25 dB.


The room also does not look large enough for RT60 to be meaningful at frequencies that low, the decay is far from linear as it is dominated by the behaviour of individual modal resonances. The results are more consistent above a few hundred Hz, where the assumption of a diffuse soundfield which underlies RT60 measurement starts to become valid. At lower frequencies the modal behaviour will cause the results to vary significantly with the position of the microphone and the source.