Implementing Wave Field Synthesis in an Itu Spec Listening Room Part 2: Bass without Modes

Accurate reproduction of sub-bass in small rooms can be problematic because the low modal density and damping over this frequency range can cause different frequency components to be greatly emphasised or de-emphasised. In addition, at frequencies where one mode dominates sound transmission significant spatial variation will be seen in the frequency response, sometimes ranging over as much as 40dB between locations of pressure maximum and minima, meaning that corrective equalisation (EQ) cannot be globally effective. Finally, the low damping of modes also manifests as a long decay time, adding tonal artefacts which are particular audible with transient sounds such as a kick drum. Traditionally these problems have been treated by carefully choosing room dimensions and installing resonant acoustic absorption. However there has recently been significant interest in designing electroacoustic systems which avoid exciting problem room modes. This paper describes design of such a system and evaluates its performance.