Environmental Technology Noise Assessment & Abatement Module 7.0

Obj 7.1: What is sound? n sound is pressure variations (high and low density) n that are created by mechanical vibrations n and can be detected by the tympanic membrane (eardrum) of humans and animals

How is it transmitted? n sound is transmitted by any medium that is capable of compression and expansion n solid, liquid, gas n concrete wall, water, air, steel, masonry, glass

What are its characteristics? n cycle is distance (wavelength) between peaks n amplitude (loudness) is a measure of pressure intensity n frequency (pitch) is a measure of how many cycles per second (Hz)

What can humans hear? n the average human ear can detect noise between 20 Hertz and 20,000 Hertz

Obj 7.2: Measuring sound.... n most of the sound we hear is transmitted by air, so we measure air pressure n the human ear is capable of detecting extremely small differences in air pressure

Obj 7.2: Measuring sound.... n normal atmospheric pressure is kiloPascals (kPa) n one microbar is one millionth of the standard atmospheric pressure n the human ear is capable of detecting pressures as small as microbars and as large as 2000 microbars without damage

Obj 7.2: Measuring sound.... n A logarithmic scale called the… Decibel Scale...is used to measure sound n dB is the unit of Sound Pressure Level (SPL)

Obj 7.2: Measuring sound.... SPL = 20 x log(P/P 0 ) where P 0 = microbars (baseline) and P = measured sound pressure n calculate SPL if P = n calculate SPL if P = 2000 (painful) n calculate SPL if P = 1000

Obj 7.3: Weighting scale n sound is a combination of amplitude (loudness) and frequency (Hz) n 70 dB at 2000 Hz will seem louder than 70 dB at 500 Hz n for the urban planning field an “A” weighting scale has been created to combine the two measures of sound

Obj 7.3: Weighting Scale n dB is adjusted to dBA to account for frequency n it’s like a wind chill factor used for temperature n find the dBA for 70 dB at 2000 Hz n find the dBA for 70 dB at 500 Hz