Hi again,That may not be enough to solve the problem, but it can't hurt. The only disadvantage to angling the walls and ceiling is that you can no longer calculate modes reliably. You need finite element analysis - which is way beyond me.
Diffusion is probably not going to do much - you need to think in terms of wavelength, not frequency.
To get an idea of scale let's look at ISO 1/3 Octave Centers:
20.0 Hz 56.50 ft
25.0 Hz 45.20 ft
31.5 Hz 35.88 ft
40.0 Hz 28.25 ft
50.0 Hz 22.60 ft
63.0 Hz 17.94 ft
80.0 Hz 14.13 ft
100.0 Hz 11.30 ft
125.0 Hz 8.97 ft
160.0 Hz 7.06 ft
200.0 Hz 5.65 ft
250.0 Hz 4.48 ft
315.0 Hz 3.53 ft
400.0 Hz 2.83 ft
500.0 Hz 2.24 ft
(apologies for using Imperial measurements)
But you can see that a diffusor would have to be VERY large to affect energy even at 500 Hz.
To manage (you don't really control) the room modes you need to use absorption and reflection, and again the scale of the absorber is problematic. Look into a device called the Tube Trap. I no longer remember why they work, but they do, they are not snake oil. And they still won't solve the problem but they can help.
It isn't about failing, or succeeding! It is about getting as far as you can on your own, and then inviting someone with more experience to help you get further. That is an important distinction.
I most likely need to use some time tuning the room properly. I will off course do whatever I could to my self first before I contact ppl for help.
What you think of the psi audio Avaa c20?