In buildings, particularly school buildings, it is necessary to formulate certain design targets at the preliminary planning stages in order that the desired environmental conditions may be attained. The acoustic requirements will vary according to its type and usage, for example “a library and sports hall”. A series of acoustic design maxims should be drawn up for the guidance of all members of the team.This will refer broadly to either noise control of to room acoustics and will be able to maintain optimised speech perception throughout all parts of a lecture room, ensure acoustic privacy for designated offices and to avoid flutter echoes and room resonances in studios.
Vibration of building structures has tended to increase in recent years with the growth in density of roads and rail traffic and the incorporation of extensive mechanical services throughout buildings.At the same time, the construction techniques have tended to move away from the use of massive elements, which tended to dampen to inhibit vibration transmission to encourage daylighting.
Furthermore, the sub-audio frequencies generated in a structure may induce higher frequency noise components where a partition or slab vibrating with high amplitude at a very low frequency will tend to cause fixtures to rattle and re-radiate noise components. This is an important reason to isolate the building structures from all potential sources of excitation and it is therefore necessary to be able to specify permissible limits for structural movement by vibration.
Where human tolerance is of vibration or re-radiated noise from a vibrating surface is not crucial it will still be necessary to ensure that no vibration induced damage occurs to the building.It is generally advised to undertake measurements of structural insulation and room reverberation time to assist in establishing design criteria for a major remodelling of an existing building or as acceptance trials of a complete project.
In the past, sound level meter response was used extensively by acousticians for all types of internal environmental noise studies but it soon became apparent that its advantages, when used during acceptance tests on finished buildings were more than offset by its shortcoming as a design criterion.
It is generally advised that when an acoustical site survey is to be determined, the following points are necessary.
(a) The noise and vibration climate at the site
(b) The tolerance of surrounding sites to an introduced noise source
(c) To assist layout, grouping and zoning onsite in order to maximise natural noise control provided by adjacent buildings and ground topography.
(d) To establish the insulation and isolating performance of existing structures prior to renovation.
(e) To assist designs for room acoustics and sound reinforcement systems in existing areas prior to renovation and renovation and remodelling.
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