NOISE POLLUTION Noise Standards : Type of Area Night (dB) Day (dB) Sensitive 40 50 Residential 45 55 Commercial 55 65 Industrial 70 75 Noise : Noise is unwanted Sound . Sound is measured in terms of Sound Pressure Level (SPL) and expressed as decibel (dB) . SPL , L = 20 log10 (P/P0) where , P = pressure in Pa P0 = reference pressure ( 20 Pa ) Sound can be sensed by humans when Sound Pressure Pa Conversion Note : 1 bar = 105 Pa 1 bar = 105 Pa SPL at two positions : L2 = L1 – 20 log10 ( R2 / R1 ) R1 R2 Equivalent Noise and Average Noise : A source (or sources) emitting different sounds at different time periods . Equivalent Noise , Leq = 10 log10