RT60s and waterfalls

[IWC Doppel]

I am wondering why the waterfalls show an apparently heavier decline than the the TR60'd these are plots of my centre channel. Is this because the cut off on the waterfall is the noise floor and the RT60's are gussing how long a 60db drop might be ?

 

[John Mulcahy]

RT60 is the time it takes for sound over the selected frequency span to decay by 60 dB. For a higher resolution view the RT60 Decay graph is more useful.

 

[IWC Doppel]

RT60 is the time it takes for sound over the selected frequency span to decay by 60 dB. For a higher resolution view the RT60 Decay graph is more useful.

John thanks, so I assume the RT20 is a 20db estimate on a linear basis amp the TR30 30db ? I assume the differences are calculation and accuracy differences ?

 

[John Mulcahy]

T20 and T30 are both estimates of the RT60 value using different portions of the Schroeder integral, as explained in the help.

 

[IWC Doppel]

John, thanks, I think my 300ms target is not so good below 1k, nearer 400ms below 350 Hz and 'terrible' in the lower registers ? (<100Hz)

 

[John Mulcahy]

RT60 targets aren't meaningful below the room's transition frequency, which is around 250 Hz in a domestic-sized room, as the density of modal resonances is not sufficient for the RT60 result to be valid. At those lower frequencies individual resonances need to be targeted by changing placement (to reduce or avoid excitation of the modes), applying treatment (tuned absorbers, for example) or applying EQ to target the individual resonances.

There is more about RT60 times and targets here.

 

[IWC Doppel]

Reading that was helpful John and it seems that between 250-4k my plots are perhaps not too bad. Reasonably consistent across that range and reasonably close between T20 and T30, plus in the desired range. I did a fair bit of A-B listening and whilst the plots looked quite close between 2-4 panels in the room, I didn't like the sound with 4.