Originally Posted by DanFrancis
It seems that it is a sympathetic resonance; the amplitude remains steady throughout the measurement while the energy at most other frequencies dies out relatively quickly. Isn't your house constructed with a large amount of concrete? My personal guess would be that the length of your room is pretty close to 22.3 feet, and that the front and back walls are ultimately made of thick concrete.
Though it does ring at 24+ db below your initial signal, and you're 10 db down at 120 ms. I'd say you're not "hearing" that ring at all- and processing can only do so much. Pretty cool that you can see that through the measurement, though.
You would be right, the room length is just about 22 feet and yes the whole room . walls ,ceiling and floor are thick re-enforced concrete. In my last listening position before I moved it I was getting bad modal ringing around that frequency, but you are right I am not really hearing it at all now.
And I have no idea what is going on around the 800hz mark??? And Dirac seems to make it worse, or my setup is not allowing Dirac to do its job. Is it possible to have a 800hz null? I wonder if I could use the PEQ in Dirac to bring that up? Or is that not advised?
This is my previous listening position after Dirac applied and I could really hear the ringing here.
Originally Posted by Roger Dressler
It could be that whatever it is that is sympathetically resonating at 25 Hz is not linear. It may be able to vibrate to certain excursion and then the material becomes less elastic, as in a speaker cone that has reached the limit as the surround and spider run out of range. In the non-linear range the resonance cannot return the full level of the excitation, but after the excitation stops, it decays at its own rate like a tuning fork, and at some point you can see it.
I wonder if a high Q notch filter would be able to help. I have seen John Mulcahy discuss this in p.107 of the REW Help doc
Roger , I do have a boxed 18" sub that is not being used sitting in the room, I wonder if that is the cause?
Carl, Is using the PEQ EQ on top of Dirac a bad thing?