Low frequency room excitation using Distributed Mode Loudspeakers

Conventional pistonic loudspeakers excite the modes of an enclosed sound field in such a way as to introduce modal artefacts which may be problematic for listeners to high-quality reproduced sound [1]. Their amelioration may involve the use of highly space-consumptive passive absorptive devices or active control techniques [eg 2,3,4]. Other approaches have concentrated on the design of the driver used to excite the room. Distributed sources ranging from the dipole [5] to more complex configurations [6] may be expected to interact with the room eigenvectors in a complicated manner which may be optimised in terms of the spatial and frequency-domain variance of the soundfield. Recent interest in distributed sources has centred on the Distributed Mode Loudspeaker (DML), and this paper reports an investigation into the interaction of DMLs with modal soundfields. It is shown that large DMLs may be expected to modify the low-frequency soundfield. Producing useful low-frequency control remains difficult but may be achieved in some circumstances.