I think maybe I didn't explain the point very clearly...Of course modes are usually detectable in inadequately treated rooms. But how significant relatively?
It's not an issue of weather or not modes are detectable, but rather the simple fact that the modes themselves (not the ringing! Just the mode...) are what shape the frequency response of the entire room, and the entire spectrum. Absorption is largely irrelevant here, since it doesn't change the modal response: it just damps the ringing.
I'm not sure if you have Kleiner and Tichy's book on small room acoustics, but they explain the issue quite clearly:
The overall steady-state frequency response is determined by the modal response. And damping doesn't do a lot to change that:
Even with high damping (lower graph) the frequency response is not getting flat: In other words, the modes are still there still making their effect "present", even though the might be highly damped, and not ringing at all. The modes are "detectable", regardless of weather the treatment was "adequate" or not.
Hence, there's no such thing as "no modes in a room". It's certainly possible to have a room where the modes don't ring: that can be done in any carefully designed room of reasonable size). But the modes are still there: the modal response still has a large effect on the overall frequency response of the room, even if the time-domain response is smooth, with no modal ringing.
In the second graph above, I'd say that the remaining modal "ghosts" (to coin a term" are very much significant, despite the damping: there's still wild swings on SPL, over a range of 30, 40, and even 50 dB.I wouldn't hazard a guess as to what level of mode is 'significant'
Yup! For sure! You can get more of the spectrum above the Schroeder frequency, and into statistical territory. That's always a good thing....bigger is generally better, particularly as it can include treatment.
Yup. Many first-time studio builders greatly underestimate the effect of the rear wall, and can't understand why you need a meter or so of treatment back there, wanting to put up one inch of foam instead...the Back Wall is typically the biggest factor at play, and most often inadequately treated.
Yup! If only architects would be back to building ten foot ceilings in houses, or at least 9 foot ceilings! It would make things a lot easier. Or maybe persuade engineer to start mixing while crouching down low, sitting on a 6" kiddie chair... or sitting way up high on a bar stool!the almost absurd practice of placing the listener Mid Width AND Mid Height.
Not much we can do about side-to-side, but vertically it would be nice to have more options.- Stuart -
. For decoupled room within a room you build two free standing rooms. The outer frame has 4 walls and roof trusses/joists sitting on it. The inner frame has 4 walls and ceiling joists sitting on it, and doesn't touch the outer framing at all, at any point. 
that was an old design before I had researched properly. My door is in the side and I didn't install windows, I'm putting a window in the door though.