Introduction to Noise Control Environmental Science Ithan B. Zimmer, Ph.D., P.E.

Basic Noise Control Environmental Noise Studies Other Studies: Industrial, Theoretical, Mechanical Environmental Impact Statements (EIS) –You need to understand the language –You can participate in an EIS –More background means it is harder to fool you

Famous Authors Leo Beranek Cyril Harris (handbook) Karl Kryter (Effects) Charles E. Wilson (NJIT)

Basic Noise Control Noise = unwanted sound –pollution is redundant –wasted energy What defines noise is subjective Environmental noise generally is transient

Possible Effects Hearing Loss Annoyance – Quality of Life Issues Physiological Disorders Psychological Disorders

Noise Measurement Decibel scale (dB) Logarithmic, use common log, base 10 log xy = y log x log (xy) = log x + log y log (1/x) = - log x log (x/y) = log x – log y log 1 = 0

Sound Pressure Level (SPL) SPL (dB) = 20 log (P/P 0 ) –P = rms sound pressure –P 0 = reference pressure 20 μPa Threshold of Hearing = 0 dB Threshold of Pain = 140 dB

Combining Noise Measurements (Fig 14.4) SPL DifferenceAdd to the Higher > 100

Equation for Total Sound Pressure Level SPL T = 10·log (10 L1/ L2/10 + … + 10 Ln/10 ) L1, L2 … are noise measurements in dB Examples using table or equation

Loudness An average individual perceives an increase in sound level of ~10 dB as a doubling in loudness.

Frequency Weighting There are multiple weighting systems A-weighting is, by far, the most common It is the best for environmental and community applications because it reflects human response. Abbreviated dBA, see Fig 14.5 Humans hear 20-20,000 Hz –Most sensitive from ,000 Hz

Metrics – Cumulative Noise Levels L X – noise level exceeded X% of the time L 10 L 50 – median noise level L 90 – background noise level Transit/Highway applications

Equivalent Sound Level - L eq Average over a period of time Equations on the board Day-Night Level: L dn or DNL –An L eq for 24 hours with a 10 dBA penalty for night noise (10pm to 7am) –Used in community noise, especially airports –Airports must mitigate to below DNL 65 –EPA outdoor to DNL 55, indoor DNL 45

Basic Noise Control Elements SourceReceiver Path Environmental concern: air path, also structure Sources: surface traffic, trains, aircraft, fans, machinery Receiver: people

Noise Mitigation and Control Reduce at the Source – almost always the best method Increase or block the Path Protect the Receiver

Noise Mitigation and Control Source: engine design, exhaust control, friction reduction, # of vehicles Path: noise barrier, increase the path, Land Use Management Receiver: home treatment, hearing protection

Line Source vs. Point Source Double Distance = ? SPL 1 – SPL 2 = 10 log (r 2 /r 1 ) SPL 1 – SPL 2 = 20 log (r 2 /r 1 )

Any Questions?