Sweet Room - Kill those room modes

[Confused]

@Confused ,

The differences in frequency between measured and predicted for your modes (eg 27.4 Hz measured vs 28 Hz) can be due to one or two things. There could be an inaccuracy with the meter or the AMcoustics software but the most probable cause is that there's some flex in your walls which means that the mode is actually going to be slightly lower than a prediction based on length because the walls bulge out under pressure, increasing the length of the room axis slightly.

As for the 54.5 Hz mode being less offensive than predicted, that also could be due to one or two things but since it's harder to absorb sound as the frequency lowers and since walls//ceilings/floors do absorb some sound, it could just come down to your walls being more effective absorbers at 54.5 Hz than they are an octave lower at 27.4 Hz.

Your software tool will give you an idea of what the frequency of your modes are, and of their severity, but room construction and materials are going to modify what's actually happening in the room to a slight degree and the only way of really knowing how the room actually behaves is to measure what it does. Feeding room dimensions into a mode calculator will not give accurate results because your room surfaces aren't perfectly rigid.

I agree that a feeding room dimensions into a mode calculator will not give perfect results, there are two many variables as you mention.  (although in my case with a rectangular room there is perhaps a surprising degree of correlation.)

However, this does distract from the key point I was trying to convey.  REW is actually measuring the room, so will take all of the above into account.  

The REW measurements indicate that my most offensive room mode is at 54.5Hz, whereas the room mode at 27.4Hz (also measured by REW) is subjectively and audibly by far the worst, this is the key point.  This is based on measured results, listening to tones that correlate to the measured results, and hence is completely unrelated to how AMcoustics Room Mode tool is calculating anything.  As for the difference between 27.4Hz and 28Hz, the mode sounds much the same at 27Hz as it does at 28Hz, so I do not think a 0.6Hz difference is much to worry about in practice.