It is said that it takes about 250ms signal to get those room modes ringing. Here (bottom) they actually show a formula for this. Trise = 0.32 T60 So it's about third from T60 time. If a good decay is say 600-800ms then that 250ms would be quite correct. Now we come to TrueRTA and it's Quick Sweep. QS takes about 1500ms and it goes 10Hz-20kHz. If it's linear each major third (1/3 oct) should take about 50ms or less (1500ms/31). Even less for each minor and so on. This indicates that QS would be too fast for room to response and therefor room modes should't be built. In the TrueRTA help John L Murphy says "There is gating but it is sufficiently wide that it does not exclude room reflections on the acquired sweep. Because of the wide gate, room reflections will influence measurements when testing indoors." I have measured with both ways, QS and pink noise and the results are the same, so Murphy is of course right. So is that 250ms correct or where is the problem? How fast signal we need to exclude those room modes? Am I confusing room modes and normal reflections?