RT60 for low frequencies

[simbo_saheed]

Hi,
I measured response (while doing calibration - output connected to input) of my sound card (Focusrite scarlette 2i2 2nd gen) and i noticed that RT60 values are rising up with lower frequencies up to 0,4s for 50Hz, is this normal for such situation and for regular room measurement this effect does not happen? Frequency response is perfectly flat, this is the only odd thing that boggles my mind.
Thank you guys

 

[srossi]

For the RT60 to increase with decrease in frequency is expected and somewhat desired. The main factor for this is the decrease in absorption coefficients at lower frequencies for typical rooms (i.e. non-anechoic). From a subjective point of view this increase (as long as is not to drastic) can give the room 'body'.

 

[John Mulcahy]

I measured response (while doing calibration - output connected to input) of my sound card (Focusrite scarlette 2i2 2nd gen) and i noticed that RT60 values are rising up with lower frequencies up to 0,4s for 50Hz, is this normal for such situation and for regular room measurement this effect does not happen? Frequency response is perfectly flat, this is the only odd thing that boggles my mind.

You are seeing the effect of the group delay of the fractional octave filters used to generate the figures for each frequency. It can be reduced by using the time reversed filtering option (see the help) although the effect on room measurements is typically much smaller than for a near perfect impulse as obtained from a loopback measurement. Alternatively the RT60 Decay graph is immune to this particular issue.

 

[srossi]

My apology I did not read your post in detail. I answered thinking the measurement was in a room. I defer to John Mulcahy's answer.