Acoustical effects of columns, beams and furniture on sound fields in small enclosures
In acoustic design of small enclosures, it is a considerably important matter to control eigenmodes at low frequencies, so that many researches have been done on the effect of overall shapes of rooms on the eigenmodes, such as optimization of room dimensions ratio. However, overall room shapes are usually restricted to rectangular forms due to easy construction, therefore it is desirable to improve sound fields only by changing partial elements in rectangular rooms. In the present paper, the effects of additional elements, such as columns, beams and furniture, on the sound field in a small rectangular room are investigated through wave-based numerical analysis. Supposing a room for listening use with a loudspeaker, the effects are evaluated regarding the flatness of frequency response and the uniformity of spatial distribution in a listening area. The results show that: the effect of columns is small but more than beams; that of closed-type shelves is relatively large but not so much as open-type shelves; the size and the arrangement of every element have unnegligible effects. It is also seen that the additional elements generally lead to positive effects in flatness of frequency response and special uniformity even at low frequencies, although in a specific case.
Experimental study of wood acoustic absorption characteristics
Abstract The objective of this study was to determine normal impedance on the surface as well as sound absorption coefficients for several wood species from Europe and from the tropical zone. The mathematical models of Miki, Attenborough, and Allard – dealing with acoustic properties of porous materials – have also been compared. The air flow resistivity exhibits a distinct link between fiber dimensions and wood porosity. The highest sound absorption coefficient was found for oak, ash, sapeli, and pine woods at 2 kHz frequency. The Attenborough model provides results closest to laboratory measurements, although it still requires significant improvements. The Miki and Allard models have some drawbacks and should be applied with reservation for the determination of wood acoustic properties.
Air-Borne Sound Insulation of Single Walls at Low Frequencies: A Discussion on the Influence of Boundary and Mounting Conditions
A theoretical analysis of the air-borne sound transmission through a single wall at low frequencies is presented. The wall is assumed to be surrounded by orthogonally mounted partitions. The results are compared with those presented previously for a wall mounted in a baffle. The comparison shows that the presence of the orthogonal partitions can substantially increase the transmission due to the forced response at frequencies around and below the critical frequency. The magnitude of this effect depends on how the wall is mounted to surrounding constructions; it can be large for certain cases. The analysis also shows that the transmission due to the resonant response increases by 6 dB at frequencies below the critical frequency in the region where the edge radiators are predominant.