Noise pollution

Noise pollution

undesirable sound that harms the health of humans and wildlife alike

which one of sound and noise has a varying pitch

Noise-sound has a constant pitch

units of noise and sound

Decibels and Hertz respectively

periodic motion

Sound has regular periodic motion and noise has no regular motion

Wavelength

distance between pressure peaks

Frequency

number of wavelengths that appear to pass a fixed point in 1 second [Hz]

Amplitude

heights of the peak which represents the pressure intensity and is related to the volume or loudness

Speed of sound in steel,water and air

5000m/s in steel, 1500m/s in water, 340 m/s in air

fomula to determine the speed of sound

v=lambda * frequency, v is the spped of sound-Speed of sound is constant so the frequency and wavelength is inversely proportional.]

important defintions

decibel scale (dB) - a ratio of two pressures

Sound Pressure Level (SPL) - expresses the magnitude of sound (dB) 

Sound Intensity (W/m²) - is proportional to the square of the root mean square (rms) value of a sound pressure or SPL

(Note :for every 10 dB increase in SPL, there is a 10 fold increase in sound intensity.)

optimum noise level as prescribed by WHO

45db by day and 35db by night

hazardous db level for noise

80db

effects of noise at different decibel levels

Sources of Noise pollution

Household sources like lawn mowers
social events like a hip hop concert
commercial and industrial activities
vehicles like trains and airplanes

Threshold of hearing

0.00002 Pa

Threshold of pain

200 Pa (Rocket liftoff)

abbreviation for OSHA

Occupational Safety and Health Administration

L_eq concept

L₁₀ is the level exceeded for 10% of the time. For 10% of the time, the sound or noise has a sound pressure level above L₁₀

L₅₀ is the level exceeded for 50% of the time. It is statistically the mid-point of the noise readings. It represents the median of the fluctuating noise levels

L₉₀ is the level exceeded for 90% of the time. For 90% of the time, the noise level is above this level

what is L_eq

It  is  equivalent  continuous  noise  level  in  dB (A)  over  a  given  period  for  measuring  it

L_eq is that statistical value of sound pressure level that can be equated to any fluctuating noise level

Silence zone

an area comprising not less than 100 m around hospitals, educational institutions and courts

CPCB(Central Pollution Control Board) standards of noise levels in db

Ambient level of noise in various zones

controlling noise pollution at the source

Design new machines to replace noisy ones

Proper lubrication and better maintenance of machines

Installing noisy machines with sound absorbing materials

Using Silencer to control noise from automobiles etc.

Control of noise pollution at the receiver end

For people working in noisy areas ear protection aids like ear plugs, muffs, noise helmets, head phones etc., should be provided it to reduce occupational exposure

Legislative measures to control noise pollution

Minimum use of loud speakers, near silence zones

Banning Pressure horns in automobiles

Framing a separate noise pollution act

Zoning

Increasing distance of noisy areas (like bus stand and railway stations) between source and receiver away from silence zones near residential areas, educational institutions and hospitals

Example of efficient noise absorber

A green belt of trees

Sound Insulation

Sound insulations can be done by constructing windows with more than one panes of glass and filling the gap with sound absorbing material

Acoustical tiles, perforated plywood can be fixed on wall, ceilings, floors to reduce noise