Higher order loudspeakers for improved surround sound reproduction in rooms

Holographic surround sound systems aim to accuralcly reproduce a recorded field in a small region of space around one or more listeners. This is possible at low frequencies with well-matched loudspeakers and acoustically treated rooms. At high frequencies the region of accurate reproduction shrinks and source localisation is compromised. Furthermore in typical rooms reflections compromise quality. High quality reproduction therefore requires large numbers of loudspeakers and the use of techniques to reduce unwanted reverberation. This paper considers the use of higher-order loudspeakers which have multiple modes of radiation to offer an extended frequency range and zone of accurate reproduction. In addition, if a higher-order microphone is used for calibration, room effects can be effectively removed.