In an attempt to cope with the problem of providing suitably quiet dwellings in noisy urban environments, it has sometimes been suggested that the lower floors of high-rise buildings might be used for offices (or other noise-insensitive uses), while the upper, presumably quieter, floors could be used for housing. This paper suggests that the proposal is not practical since, in many urban areas, the upper floors of buildings are exposed to almost as much noise as the floors near street level.
NOISE LEVEL VERSUS ELEVATION
For outdoor sources of sound, the sound level generally decreases in a more or less continuous manner with increasing distance from the source. This contrasts with the behaviour of sound indoors, where, beyond a certain distance from the source (that depends on the furnishings of the room), the sound level tends to remain fairly constant throughout the room.
Even outdoors, however, under certain circumstances sound may exhibit propagation characteristics that resemble indoor behaviour, such that the attenuation rate is less than would normally be expected in the open. Two phenomena have been observed in built-up urban areas where low attenuation rates in the vertical direction arise from two quite different causes: (1) in city canyons (and even in less fully enclosed regions) the noise of local street traffic is confined,just as in a room, and the sound level fails to decrease significantly with increasing elevation above the street until the top of the buildings is reached; and (2) in low-rise areas, as 231
Applied Acoustics (12) (1979)--~i~) Applied Science Publishers Ltd, England, 1979