Improving the Bass Response of Schroeder Diffusers

Room acoustic diffusers can be used to treat the acoustics of critical listening environments to improve speech intelligibility and to make music sound better. The development of the modern sound diffuser can be traced back to the pioneering work of Schroeder, who developed the phase grating diffuser. These consist of a series of wells of different depths separated by fins. The order of the well depth sequence is determined by a number theoretic sequence. If the quadratic residue sequence is used, then the diffuser produces grating lobes of similar energy at most integer multiples of the design frequency. Figure 1 shows a cross section through an N=7 quadratic residue diffuser.