In §C.12, the theory of multiport scattering was derived, i.e., the reflections and transmissions that occur when digital waveguides having wave impedances are connected together. It was noted that when is a power of two, there are no multiplies in the scattering relations Eq.(C.129), and that this fact has been used to build multiply-free reverberators and other structures using digital waveguide meshes [434,522,147,399,524,525,401,402,404,55,203,324,323,325,426,33].