The QRD® Diffractal™: A new 1- or 2-dimentional fractal sound diffusor
Peter D’Antonio · The Journal of the Acoustical Society of America · 1990
Number theoretic diffusors, as described by Manfred Schroeder, are characterized by a periodic grouping of a series of wells of equal width, but different depths, separated by thin dividers. Over the past 5 years, the quadratic residue depth sequence has been very useful in over 300 applications, including recording studios, concert halls, worship spaces, conference rooms, music education, and even home listening rooms. The frequency bandwidth is determined principally by the depth of the deepest well, which determines the low-frequency limit, and the well width, which determines the upper limit. Physical manufacturing contraints pose a limitation of approximate 1 in. on the well width and approximately 16 in. on the depth, after which the units become diaphragmatic and defeat the purpose of increasing the depth further. To extend the low-frequency range and bandwidth of the QRD, a fractal diffusor, the Diffractal, has been developed which is in effect a diffusor within a diffusor, each crossing over at different frequencies, much like a multiway loudspeaker. The mid-high-frequency diffusors are placed on the wells of a dedicated stiff and massive low-frequency diffusor. These bandlimited nestled diffusors allow virtually any bandwidth, limited only by the available depth and the surface detail. Two applications of the Diffractal will be described at Peter Gabriel's Real World Studios, Bath, England and INXS' Rhinoceros Recording Studios, Sydney, Australia. A two-dimensional diffractal capable of providing even further low-frequency control will also be described.