Implementing wave field synthesis in an ITU spec listening room part 2: Bass without modes

In recent years various sound reproduction systems have been proposed which attempt to use multiple transducers to tame the modal behaviour often prominent in rooms at low frequencies. Of particular interest is the Controlled Acoustic Bass System (CABS) proposed by Celestinos and Nielsen, and it was decided to install a permanent system in our ITC spec. listening room. A number of constraints had to be considered, not least positioning the subwoofers so as not to compromise the existing passive acoustic treatment. A system comprising eight subwoofers was implemented and rear delay and attenuation were fine tuned to minimise deviation from a flat frequency response over the listening area. The result was a significantly more uniform frequency response and the elimination of the most prominent tonal artefacts. This allowed corrective equalisation to be applied giving the system a nominally flat response over its operating frequency range of 30Hz to 120Hz