Sound Absorption at Low Frequencies: Room Contents as Obstacles

Abstract

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 preliminary study of the influence of furniture on low frequency room response was performed by introducing a "reference obstacle" at three positions within an enclosure which previously had been numerically modelled. 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 large solid 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. Obstacles placed along a wall or in room corners will produce a greater change in room response, when compared with a central location.

Sound Absorption at Low Frequencies: Room Contents as Absorbers

“…Also, while the fourth room mode at 58 Hz was shifted 2% downwards in frequency with little level reduction for the uncovered box, in the case of the covered box the same room mode is shifted 6% downwards and reduced by 8 dB. The modelling of the covered box was more complicated than in a previous study of hard obstacles [2]. The challenge was to correctly incorporate the covering absorption.…”

“…In previous papers an investigation was described of the influence of room surfaces and hard contents on the acoustic properties of enclosures at low frequencies [1,2]. However, hard-surfaced objects do not exclusively compose real furniture inside rooms.…”

“…Above this frequency the average is 12 dB ±4 dB. The FE model of the test chamber, described previously [1,2], was modified to simulate the case of 100% floor covering. This result is shown with the corresponding experimental measurements in Figure 6 predicted room response are presented as one-twelfth octave values in Figure 7.…”