The role of sound in Architecture can be traced back to the development of various arts and art forms that were performed within enclosures and in outdoor spaces like several performing arts theatres during the Roman and Greek civilization. The acoustics of any place was also a very important consideration for Civic buildings and places where large gatherings were addressed; these could be the palace court rooms or even sports arena like the Colosseum. Outdoor or Indoor sound usually needed to either be enhanced or amplified or completely dampened for sound proofing like that in prisons, confidential discussion rooms etc.
Its only in the past 100 years post the industrial revolution, a significant component of outdoor environmental sounds,
“ Noise”; was added to the environmental either by way of machinery, or modes of transportation like cars, buses, planes, trains, trams, construction activities , community and religious celebrations, processions etc. There is recorded scientific evidences on the detrimental effects of noise pollution on the human health. Some of these being, hypertension, hearing impairment, heart disease, annoyance, stress, disturbed sleep etc which has long term implications. A survey by CPCB reveal that Mumbai and Delhi are amongst the noisiest cities in Asia. The decibel levels in many areas are twice the permissible thresholds. While several policy level decisions are being formulated and some implemented at city level; several noise mitigation measures could be considered by designers of the built environment. The understanding of the science of sound travel and behaviour would help.
THE SCIENCE OF SOUND TRAVEL
The science of sound travel has made revolutionary breakthrough since 200 years, in the field of communication, medicine and even warfare. However, we have somehow ignored the detrimental impacts of the ambient sounds that urbanization has been adding steadily over the years. The following can be summarised a basic understanding, that could impact mitigation of noise:
a)Sound travels in the form of waves. It is a form of energy and needs a medium to travel.
b) It travels faster through a denser medium like water than air.
c) The speed of sound travel increases with increase in temperature. However at higher altitudes the speed of sound decreases due to decrease in temperature of air.
d) Concave surfaces and spaces like valley’s gather the sound waves and increase the amplitude, where as convex surface disperse the sound waves and thereby decrease its amplitude.
e) Firm and dense medium transmits the sound faster and in the same magnitude. Porous and lighter media, reduce the speed of sound and also absorb it.
NOISE MITIGATION IN THE BUILT ENVIRONMENT.
NEW DEVELOPMENTS : Noise mitigation for the built environments starts at planning level. The primary strategies could be as follows:
1) Orientation and programming : Zones sensitive to loud sounds like Hospitals, schools, residences, etc need to be separated from noise generating activities in planning or oriented away from the source of noise. In dense urban areas where large buffering is not possible, the habitable spaces can be pushed back by features like balconies, flower beds etc. For habitable spaces facing the source of noise, windows and openings can be oriented in the direction perpendicular to the sound. This will reduce the decibels substantially, and further reduction can be archived by sound attenuation of windows and walls
2) DEFLECTION OF SOUND :
For openings facing the source of noise, sound can be prevented from reaching the openings by deflecting it. Fenestrations or facade can be designed to achieve this.
Fenestrations can be designed with deflectors that can be used, deflect the sound away from the building. This deflected sound can be intercepted by green cover or trees to further decrease the amplification at higher altitudes. Alternatively, the surfaces can be finished with sound absorbing medium that would prevent the deflection, but reduce the amount of noise incident on the habitable room
3) SOUND ATTENUATION :
Higher floor of many buildings facing the roads have amplified sound reaching them, especially near flyovers. Multi-layered vehicular travel has led alleviation of noise and air pollution at higher floors. In existing buildings this can be checked by providing sound attenuation to the walls or modify the glazing in the windows to Insulated glazing. Additionally externally sound absorbing medium can be used on the bottom of overhangs to further reduce the reflected or deflected sound. Unless and until, measures are taken to control the level of noise, the ongoing urbanization and industrialization may complicate the problem so much that it becomes incurable.