Quadratic diffusion is a technology that does require proper distance from the diffusor
surface to the listener. This distance is required because it takes distance to give the
diffused energy waveform, if you will, time to fully form. A little more distance is
required if one is using two dimensions of quadratic diffusion.
Due to your
smaller space, I would consider sound redirection devices such as ones that have curved
surfaces. They are commercially available and some have absorbing properties built in.
Focus on the low end first in your room. People do not know how much low frequency
energy harms our musical presentation. Low frequency issues smother and blur major parts
of our critical hearing bands and managing low frequency pressure issues is a must in any
small room environment. If low frequency energy is properly managed in your room, notice I
said managed, not controlled,it is almost impossible to control a 30 and 40'
wavelength,your sound stage and imaging will have more focus and definition.
Next, deal with side wall reflections to assist with image centering and instrument and
vocal separation. Use absorptive technologies that have a smooth rate of absorption.
Acoustic foam technology will work well in side wall locations. Diffusion or sound
redirection devices could be considered later for the rear wall.
low frequency absorption solutions. Listen to the music without hearing the room!