RT 60 measurements "not reliable" (orange). Why

[ReDRuM]

Hello,

I'm wondering what influences the "not reliable" parameter for RT60 measurements. I'm testing some panels, and am noticing that while testing the empty room, RT60 measurements are rarely labeled as "not reliable", but with panels added, many more values are flagged. The sweep is fairly loud (I had it even louder for "treated" measurements), so I doubt it's the noise floor.

I know RT60 measurements don't really apply for small rooms... If that's the reason for the unreliable measurements (pushing the Schroeder frequency lower), I would really appreciate a bit more detailed explanation, especially if I can improve reliability in some way.

Thank you!!!

P.

 

[John Mulcahy]

Values are flagged based on the correlation factor of the Schroeder curve, i.e. how linear the decay curve is. In a large space the decay curve is very linear to the point it reaches the noise floor, in smaller spaces the statistical conditions for a linear decay are not met, more so the lower the frequency gets. The panels remove some of the reflected energy and, presuming they are not evenly distributed around the space, make the soundfield less diffuse and increase the deviations from linearity.

 

[ReDRuM]

Thank you