Last updated on May 15th, 2024 at 08:20 am
Hearing is one of man’s most important communication channels, perhaps only second to vision. But, whilst the eyes can be shut when there is too much light or an unwanted scene to view, the ears are open throughout life to unwanted noises as well as to wanted sounds.
Protection, if necessary, will have to be provided in the environment.
Noise is the term used for any unwanted sound, thus the definition of noise is subjective. One man’s sound is another man’s noise.
In rural life sounds rarely become noise: partly because they provide a sense of participation in the social life of the community and partly because they hardly ever reach intolerable levels.
Urbanization brings about a rapid increase of noise sources (industry, traffic, aircraft, radio, etc.) but also a change in social attitudes:
In a village, one knows everyone else, and every sound originates from a known source and conveys some meaningful information; but a town is full of strangers and unidentified noises, for which we have little tolerance.
The low density of rural areas ensures a greater distance between the noise source and listener, thus reducing the disturbance, while in high-density towns there are more potential noise sources in a given area also the distances between sources and listeners is much less.
As the noise sources multiply, the problems increase and defensive measures must be followed.
What are the various effects of noise of different levels? Explain in detail.
Noises of various levels may produce both psychological and physiological effects:
65 dBA up to this level noise or unwanted sound may create annoyance, but its result is only psychological (nervous effects). Above this level
physiological effects, such as mental and bodily fatigue, may occur.
90 dBA many years of exposure to such noise levels would normally cause permanent hearing loss.
100 dBA with short periods of exposure to this noise level, the aural acuity may be impaired temporarily, and prolonged exposure is likely to cause irreparable damage to the auditory organs.
120 dBA causes pain.
150 dBA causes instantaneous loss of hearing.
The acceptable level of noise depends not only on objective, physical factors but also on subjective, psychological factors.
Whether noise is disturbing or not depends on the state of mind or expectation of the listener.
In a sleeper train the monotonous noise, even at 70 to 80 dBA, will not be disturbing; but in a quiet home if the listener is badly ‘tuned; even the ticking of a clock at 20 dBA may cause great annoyance.
Noise may adversely affect noise concentration, particularly if the noise or unwanted sound has some information content.
Furthermore, as habits, expectations, and attitudes depend on the socio-cultural environments, the noise tolerance of people may vary with the kind of society of which they are a part.
Discuss in detail about the noise in free field with the help of suitable example?
The inverse square law is applicable only to noise free field conditions, where there is no obstruction, no solid objects from which the sound could be reflected. Open air conditions approximate the theoretical free field.
According to the inverse square law, every doubling of the distance will decrease the intensity to one-quarter.
Due to the logarithmic relationship, in sound level, this will correspond to a reduction of 6 dB for every doubling of the distance, regardless of the magnitude of intensity, e.g.:
What do you mean by the term noise What is the affect of noise in our daily life
A sound at 1 km from source: I’= 0.01 w/m²
At 2 km: I”=0.0025w/m²
Distance also affects sound by the molecular absorption of energy in the carrying medium. This molecular attenuation in air is only significant for high-frequency sounds. For every 300 m distance, this reduction is:
1 dB at 1000 Hz
40 dB at 9000Hz
Hence loud noises from a great distance (e.g. thunder) are heard at a lower pitch than from nearby: the higher frequency components have been filtered out by the air.
What are the various means of noise control? Discuss in detail?
From the point of view of a building which is to be designed, it is useful to distinguish:
a) external noises
b) internal noises
Against external noise, the following means of protection are available to the designer
1. distance
2. avoiding zones of directional sound
3. screening
4. planning: using non-noise-sensitive parts of the building as barriers
5. positioning of openings away from the noise source
6. noise insulating building envelope
Against noises generated within the building, the designer can take the following measures:
I. reduction at source
ii. enclosing and isolating the source, or use of absorbent screens
iii. planning: separating noisy spaces from quiet ones, placing in different areas in between basement)
iv. placing noisy equipment in the most massive part of the building (e.g. in a
v. reduce impact noises by covering surfaces with resilient material
vi. reduce noise in the space where it is generated by absorbent surfaces
vii. reduce airborne sound transmission by airtight and noise-insulating construction
viii. reduce structure-borne sound transmission by discontinuity
What are the various requirements for control of the noise?
Statutory requirements for noise control are few and far between in tropical areas.
The choice is left to the designer, but this also increases his responsibility.
Today, noise sources are less, and generally noise level is lower than in industrialized societies. Human tolerance is greater; aural privacy requirements are less exacting.
So for both reasons, the requirements for noise control performance are less.
This is just as well because the available means of noise control are also less effective. In the future, the noise is likely to increase. The improving standard of living and changing social patterns will bring about increased demand for aural privacy.
Then the designer will face a very serious challenge, a problem much greater than the problems in moderate climates.
The shelter, the building envelope, should give a satisfactory performance in controlling heat and light, as well as sound.
In tropical climates, the aural and the thermal requirements may clash. The contradiction cannot be resolved in physical terms.
Firstly: rural and thermal factors must be weighted. The relative importance of good thermal and good aural conditions must be established.
Clearly, this will be a function of building use. Generally in the tropics, thermal factors will outweigh sonic ones, unless the activity housed imposes strict aural requirements (as in a lecture room).
Time and duration exposure conditions may help this weighting, e.g. if the outdoors is noisy all day, and overheating occurs only after 15.00 hours, the noise control requirement may become more important than the thermal control.
Secondly: the economic implications must be considered in relation to the weighted requirements.
To continue the above example: if an inexpensive shading device could overcome the afternoon overheating, both aural and thermal requirements would be satisfied. If, however, it is found that thermal as well as aural comfort can only be ensured by full air conditioning, the cost of such an installation must be weighed against the benefit of full comfort and indeed, against the capital available for investment.