EAT M.
Loud speech is audible but not intelligible through a wall with a TL of 35-40 db.
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correct environment for occupancy use. A flat-dweller does not wish to hear and understand what is happening in his neighbour's flat primarily because it disturbs him to realise that his own situations can be heard. Simi- larly, if telephone conversations can be heard in the next office it disturbs a person's feeling of freedom and securi- ty. It is not necessarily the noise inten- sity itself that causes problems, but what it conveys. In other words it is not so much the quantity of noise as the quality of it.
In some situations an unobtrusive continuous background or masking' sound (acoustical perfume) within an environment will provide an accept- able condition without the require- ment of adding extra noise-control construction.
Hoisé ℗ 70db
Normal speech is inaudible and very loud speech is only a faint noise through a wall with a TL of 40-45 db. If there is some masking round in the room, such as a radio, nothing can be heard.
more intense noise was relatively short and the percentage of the population exposed was small. Today we face almost constant high noise levels as open areas decrease, city centres become masonry canyons and the vehicles-per-inhabitant graph points skywards. High external noise levels throughout the working day affect a large percentage of our population.
External noise considerations
a) In site analyses, site planners and architects should consider the rough layout and foundation orienta- tion in relation to the optimum acous- tical performance at lowest cost commensurate with other factors.
b) A noise level survey at the site will point out the attenuation required for exterior construction of roofs,
70db
25db AUDIBLE NOISE
45db WALL
45db
25db INAUDIBLE
30db or MASKING SOUND ABBED
should be made with the following local agencies:
Airfield or air control at the airport for flight patterns for landings and take-offs under varying weather con- ditions;
Highway commission for future main road developments;
Planning commission for zoning requirements. It may be possible to plan a noise shield in the form of a narrow row of shops, professional offices with parking, or garages be- tween the road and the main building.
e) Air is the carrier of sound waves. Sound energy dissipates itself at a rate of approximately 40 per cent (6db) with the doubling of the distance between the source and the receiver. If building location on site permits, add distance between noise sources and the building.
f) To reduce noise at the building, a screen such as another building, a unit of the complex, a sound fence or a mound of earth can be placed be- tween the noise source and the build- ing. This noise barrier can be of re- latively light construction, but must contain no openings to destroy its value.
The advantage of background or masking sound
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To any one construction problem there are a number of solutions. This truism applies equally to acoustics acoustical problems cannot be held responsible for poor design. For ex- ample, a room finished in hard sur- faces will be reverberant and therefore if it has to be employed say as a staff dining room a considerable amount of sound absorbency will have to be add- ed to make it acceptable.
Turning to noise from outside a building, this should now be a prime design consideration. A decade ago we could consider averaging our noise levels, as the time of exposure to the
walls, windows and doors.
c) Noise problems on built-up streets are accentuated between high rise buildings through sound reflec- tion. This problem can be reduced by locating acoustical, buffer zones such as corridors, lifts, equipment rooms, stores or typists pools on the noisy sides of the building.
d) Where site selection is possible, especially for residential, school, hos- pital and specialised buildings such as studios, a full noise survey should be made at several times during the day and night, and over a number of days. When selecting a site, a check
Traffic noise on built up streets is accen- tuated by sound reflection between high-rise buildings
Far East BUILDER, June 1970
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