I've picked out $10 worth of dollar store parts to treat my 4200ft^3 space. Poster board and string to make cylindrical diffusers, shelf liners and paper lanterns for ceiling diffusers and floor mats for wall and ceiling absorbers. All strategically placed per MATLAB solutions of the wave equation.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated