By Jian Kang
Acoustics is an enormous problem in lots of lengthy areas, corresponding to highway or railway tunnels, underground/railway stations, corridors, concourses and concrete streets. the explicit difficulties of such irregularly formed areas, starting from noise toxins in streets and tunnels to bad speech intelligibility of public tackle platforms in railway stations will not be handled through vintage room acoustic theory.
This state of the art exposition of acoustics of lengthy areas provides the basics of acoustic thought and calculation formulae for lengthy areas in addition to giving guidance for functional layout
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Extra info for Acoustics of long spaces : theory and design guidance
The modulation transfer function in room acoustics. BruÈel & Kjñr Technical Review, 1985, 3, 3ÿ12. HOUTGAST T. and STEENEKEN H. J. M. A multi-language evaluation of the RASTImethod for estimating speech intelligibility in auditoria. Acustica, 1984, 54, 185ÿ199. STEENEKEN H. J. M. and HOUTGAST T. RASTI: a tool for evaluating auditoria. BruÈel & Kjñr Technical Review, 1985, 3, 13ÿ39. HOUTGAST T. and STEENEKEN H. J. M. A review of the MTF concept in room acoustics and its use for estimating speech intelligibility in auditoria.
9. 5. Validation To validate the above theory, comparison was made between calculation and measurement in a corridor and in several underground stations in London. 16). 83 m, respectively. The boundaries of this corridor could be considered as geometrically re¯ective. 1 appeared to be an appropriate estimation of the average absorption coecient of the boundaries at 500±1000 Hz. 5 at 500± 1000 Hz. 5 m from an end wall. The receivers were also along the centre of the cross-section. 10. 16), by considering ten image source planes.
2 are applicable to long spaces with acoustically smooth boundaries. If there are irregularities on boundaries, diuse 48 ACOUSTICS OF LONG SPACES re¯ections should be taken into account. 21]. It is assumed that the sound energy re¯ected from a boundary is dispersed over all directions according to the Lambert cosine law, namely, I l $ cos l , where l is the angle between the boundary normal and a re¯ection. 1. The main steps of this model are: (a) (b) (c) (d) (e) divide each boundary into certain amount of patches; distribute the sound energy of an impulse source to the patches Ð the patches can then be regarded as sound sources, which are called ®rstorder patch sources below; determine the form factors between pairs of patches; re-distribute the sound energy of each ®rst-order patch source to every other patch and, thus, generate the second-order patch sources Ð continue this process and the kth order patch sources can be obtained (k 1 F F F I); this process is `memory-less', that is, the energy exchange between patches depends only on the form factors and the patch sources of the preceding order; and calculate the energy response at each receiver by considering all orders of patch sources, from which the acoustic indices can be derived.