Resonance and RT60 : how to analyse low frequencies ?

Hi everyone,

First, let me introduce my situation : I'm a french student who works on a project dealing with acoustics in water infrastructures.
I thus have to compare 2 solutions that could provide to reduce the RT60 in these infrastructures.
However, I tested these 2 solutions (stretched canva / Helmholtz resonator coupled with a special hydrophobic insulator) in a small room of 33m^3, by a impulse response, and there are thus problems with modal resonances.
When I try to show the RT60 graph, data before 200Hz seems inacurate, and I thus want to know how to get better results for RT60 at low frequencies, without considering modal resonances.
Maybe I should use other graphs like RT60 Decay or Spectrogram, but I am not a pro in REW and I havent a lot of time to learn how it works...
I attach here the graph of RT60 (T30) and the mdat file.

Thanks in advance for your help !

Thank you very much for replying so quickly !
I agree with you, I should use this tool of REW to understand much more what I analyse, and it saddens me to be a beginner with this software when I realise all the possibilities it offers...
However, is there really a way of obtaining RT60 values for this room at low frequencies (before 200 Hz), without taking into account the big variations initially there because of modal resonances ?

John Mulcahy said:

That's not possible to say with any certainty since you have not posted a measurement of the room alone, only of the room plus the equipment whose behaviour you are measuring. In general RT60 can only meaningfully be measured in a frequency range where the underlying assumption of a diffuse soundfield is valid. That becomes the case above the room's Schroeder frequency, which for that room looks to be about 850 Hz, so it is wholly unsuited to measuring RT60 at lower frequencies.

Click to expand...

Ok, thank you for your answer !! I'll try to mesure RT60 in a bigger room.