Improving the bass response of Schroeder diffusers

Room acoustic diffusers can be used to treat the acoustics of critical listening environments. A Schroeder diffuser is a popular type of diffuser which has the property of producing grating lobes of similar energy at most integer multiples of the design frequency. However at the critical frequencies, all the wells re-radiate in phase, so the diffuser appears to reflect sound like a flat surface. Space utilisation is also an issue for Schroeder diffusers, with a significant amount of the diffuser volume being unused. Folding the longest wells allows the diffuser to be packed into a smaller space, thereby making more efficient use of the space and allowing more bass diffusion. While well folding has been suggested before, it appears not to have been thoroughly investigated. A 2D Boundary Element Method is used to model the scattered energy from folded and normal versions of a Schroeder diffuser. This prediction model has been previously validated against measurement. At low frequency the diffuser with folded wells mimics the performance of a standard Schroeder diffuser. At high frequency there is an apparent change in the well depth sequence, which can be exploited to reduce the effects of critical frequencies