Noise basics

Sound is a pressure wave; noise is unwanted sound. Because the ear responds to a huge range of pressures, sound level is measured on a logarithmic scale in decibels. A-weighting, dB(A), adjusts for the ear's lower sensitivity at low and very high frequencies.

Logarithms change the arithmetic. Two equal sources together are only 3 dB louder than one. A 10 dB rise sounds roughly twice as loud. From a point source in open air, the level falls by about 6 dB each time the distance doubles; from a long line of traffic, by about 3 dB.

Construction and traffic are major urban noise sources. Controls work at the source (quieter equipment, enclosures, timing), along the path (distance, barriers, landscaping) and at the receiver (insulated facades and windows).

In India the Noise Pollution (Regulation and Control) Rules, 2000 set ambient limits for industrial, commercial, residential and silence zones, separately for day and night.

On construction sites, noise is managed with a plan: measure baseline levels, predict levels at the nearest homes, schedule noisy work in permitted hours, and monitor during work.