In talking to blaser, he pointed out that I didn't explain too well in my last or original post the reason why an equalizer is helping the decay of the resonance and needed further explanation how this is done electronically?
Well, in my reading about 2nd order biquad filters, poles and zeros, and minimum phase systems, some of the assertions by the author of REW do make some sense in that regard.
I tried to explain this in my original post, but probably fell short since perhaps I don't fully understand it myself.
The modal response of a room acts exactly like a 2nd order filter and matches the BFD generated filters in all aspects. At modal frequencies, a room resonates in gain and Q exactly as if you fed a sub signal through a 2nd order parametric filter. This fact allow us to fashion an identical 2nd order filter with the opposite gain and bandwidth that matches the room mode so it will completely disappear (at the point of measurement).
This doesn't apply outside the low frequency range where signals are no longer considered minimum phase, where primary reflections (second order) from the walls, ceiling and floor arrive at the listening position anywhere in the room with a phase shift of quite a bit less than a cycle. So, the effective limit here of about 80Hz-100Hz is reasonable for equalization in most rooms...(an 80HZ signal has a wavelength of about 14ft)............
I suppose I could also add here that REW may also not suggest a filter for a peak that you think it should have tried to correct. This may be a result of the peak not having the attributes of a modal resonance (this is what REW is looking for). You'll likely find that if you examine the waterfall at that peak that REW ignored, there would be no ringing out in the time domain. There's nothing stopping you from adding your own manual filter into REW and then into the BFD. It would be wise to examine the waterfall after that though.
There also may be modal resonances very close together, perhaps as a result of equal lengh and widths in a room or other reflections. REW could have trouble finding these, so you may have to do it manually. It's tricky and requires a back and forth measurement and tweaking as you watch the waterfalls.
JohnM may refute any of my ramblings in this thread if they are misleading or plain dumb....
brucek