Sound Absorption at Low Frequencies: Room Contents as Absorbers

A description is given of sound absorption in small-furnished rooms at low frequencies. The objective of the work was to characterise room absorption due to contents such as furniture and to develop a model of absorption appropriate for a modal description of contained sound fields at low frequencies. In this paper, a study of the influence of furniture on low frequency room response was performed by introducing idealised contents into an enclosure which previously had been numerically modelled. The contents were solid objects with absorbent coverings and wholly absorbing objects. A real item of furniture also was measured and modelled for inclusion in the room model. Eigenfrequency shifts and selective modal damping were observed throughout the frequency range of interest, 20-200 Hz, and the numerical model was able to take these effects into account, showing overall good agreement with measurements. It is shown that when a solid or absorbing item is introduced into a room there is little effect on the room frequency response for frequencies below 50 Hz. Between 50 Hz and 200 Hz the effect is more pronounced and the influence of location becomes apparent. Contents placed along a wall or in room corners will produce a greater change in room response, when compared with a central location.