ENVIRONMENTAL ENGINEERING NOISE POLLUTION Definition Noise is defined

ENVIRONMENTAL ENGINEERING NOISE POLLUTION

Definition • Noise is defined as unwanted signal. • To be more specific, noise is referring to unwanted sound. • But, sometimes the word “unwanted” can be subjective. • Two type of noise pollutions: a) Voluntary noise b) Involuntary noise

Classification of Sound • Continuous -An uninterrupted sound level that varies less than 5 d. B during the period of observation. -Example: Noise from household fan • Intermittent -A continuous sound that last for more than one second but then interrupted for more than one second. - Example: A dentist’s drilling • Impulsive/Impact -A sound which last for less than one second. -Example: Noise from firing a weapon

Effect of Noise • Reduction of quality of life; i. e. interfere speech, conversation and sleep. • Physiological effects, i. e. hearing effects. • Psychological effects, i. e learning effect, mental health

Source of Noise can be emitted from: • A point source – electric fan • A line source – moving train

Source of Noise pollution comes from: • Traffic • Industrial equipment • Construction activities • Sporting & crowding activities • Low-flying aircraft.

Noise Control The level of noise can be reduce by using one of three strategies 1 - protect the recipient 2 - Reduce Source of Noise

Noise Control 1 - protect the recipient Using ear plugs for ear protection is not effective for most of noise types. Thus , better to protect the entire ear and protect the ear plugs wearer from the most noise

Noise Control 2 - Reduce Source of Noise The most effective means of noise control is source reduction. Re-design of commercial airplanes has already been mention as an example of noise source reduction.

Noise Control For traffic noise Reduction can be achieved via re-designing vehicles and pavements. Increasing transportation the use of alternative Reducing vehicle speed and encouraging to use alternative routes, through speed control devices or road designs

Sound Power • Sound power (W): the rate at which energy is transmitted by sound wave. • Sound Intensity (I): Average sound power per unit area normal to propagation of a sound. W = ∫A I d. A …. . (1)

Sound Power • In an environment, in which there are no reflecting surface, the r. m. s. sound pressure, Prms at any point is related to I by following equation: I = P 2 rms / ρc …. . (2)

The Decibel • Human ear able hear enormous range of sound pressure. (20 μPa to 1013 for normal people). • Therefore, sound pressure of linear scale is an inconvenient quantity to use. • This also applied to sound power and sound intensity.

Sound Pressure Level, Lp Sound pressure level, Lp is defined as Lp = log 10 (P 2 rms/ P 2 ref) Unit : Bel …. . (3) Or, Lp = 10 log 10 (P 2 rms/ P 2 ref) Unit : (d. B) …. . (4) Pref = 20 μPa. The factor 10 is introduced in above equation as to avoid a scale that is to compressed.

Sound Power Level, Lw Sound power level, Lw is defined as: Lw = 10 log 10 (W/ Wref) where; Wref = 10 -12 Watt Unit : (d. B) …. . (5)

Sound Intensity Level, LI is given by: LI = 10 log 10 ( I/ Iref) where; Iref = 10 -12 Watt/m 2 Unit : (d. B) …. . (6)

Example 3 -1 The sound pressure inside a diesel lorry is 2 Pa. What is corresponding SPL in d. B? (Answer: 100 d. B)

Example 3 -2 If a sound source has a pressure of 1500 Pa, compute: a) The SPL in d. B b) The sound intensity in Watt/m 2 Given; ρ = 1. 185 kg/m 3 , c = 340 m/s

Example 3 -3 What is the increase in d. B that corresponds to a five time increase of sound pressure?