Listener Response to Different Types of Loudspeaker Directivity

Research Student: Dr William Evans
Principal Supervisor: Dr Tim Brookes
Co-Supervisor: Dr Russell Mason
Co-Supervisor: Prof Francis Rumsey
Co-Supervisor: Dr Slawek Zielinski
Supported by: Bang & Olufsen and EPSRC

Start date: 2008
End date: 2012

Project Outline

The directivity of a loudspeaker characterises how it radiates sound into the space around it. Loudspeaker directivity is thought to influence the perception of reproduced sound in a room but the types and magnitudes of its effects have yet to be determined. Theory from acoustics and psychoacoustics literature indicates that changes in the characteristics of direct and reflected sound (as a result of changes in directivity, loudspeaker/listener position and room characteristics) will cause small changes in the perceived attributes of reproduced sound. These attributes include timbre, apparent source width, localisation, loudness, envelopment/spaciousness and distance. Tests using loudspeakers with a variety of directivities confirm that all of these attributes are affected.

In order to more fully characterise and quantify these effects in a controlled fashion, an auralisation system is shown to make an appropriate platform for listening experiments. A series of experiments using such a system with a novel elicitation and analysis technique reveals that: changes in loudspeaker directivity interact with changes in room surface absorption to mostly affect perceived width, loudness and reverberence; a narrowing in on-axis directivity is associated with a perceived reduction in width, brightness, closeness and spaciousness; the perceptual changes caused by variations in loudspeaker directivity and in room surface absorption occur in parallel, along one dimension; the magnitude of effects caused by variations in loudspeaker directivity is reduced with the increased presence of reflections; and classical music is an effective signal to highlight the perceptual differences between different loudspeaker directivities. The influence of listener position can be significant, but the degree of its effect is dependent on the range of positions evaluated, and the magnitude of boundary separation has less effect than directivity on the perception of reproduced sound. Finally, loudspeaker directivity does influence listener preference.