Noise_2009 - Introduction to Noise Randall Guensler Chris...

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1 Introduction to Noise Randall Guensler Chris Grant Rob Dell-Ross The sensation produced in hearing organs by pressure variation or vibrations in air. EFFECTS ON HUMANS: • Masking of unwanted sounds • Auditory fatigue • Hearing damage • Irritation • Startling noises • Infrasonic vibration Sound
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2 Spontaneous Independent of previous activity Independent of future activity No residual evidence is left behind Transportation Noise Emission, Transmission, and Reception of Noise Source Media Receptor
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3 • Temporal Distribution • Magnitude • Cyclic Frequency • Time-Variance Other Important Aspects • Time of day • Day of week • Month of year Temporal Character of Noise
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4 Each sound wave produces a pressure variation measured in microbars (one dyne/cm 2 ) or 1 millionth of normal atmospheric pressure 10 microbars = 1 Pascals (Pa) Common noises can range from 20 to 2,000,000+ μ Pa Sound travels by vibrating individual particles back and forth in the direction of the propagating wave Magnitude COMMON OUTDOOR NOISES Jet Plane at 500m Gas Lawnmower at 1m Diesel Truck at 15m Noisy Urban Daytime Commercial Area Quiet Urban Daytime Gas Lawnmower at 30m Quiet Urban Nighttime Quiet Suburban Nighttime Quiet Rural Nighttime Sound Pressure ( μ Pa) Sound Pressure Level (dB) 80 70 60 50 40 30 20 10 0 90 100 110 200,000 63,246 20,000 6,325 2,000 362 200 63 20 632,456 2,000,000 6,324,555 COMMON OUTDOOR NOISES Rock Band at 5m Inside Subway Train Food Blender at 1m Normal Speech at 1m Shouting at 1m Large Business Office Dishwasher next Room Small Theater Library Bedroom at Night Threshold of Hearing
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5 Decibels (dB) • A division of a uniform scale based on 10 times the logarithm of the relative intensity • Dimensionless unit that logarithmically relates two like quantities of different magnitudes SPL= 10 log 10 (P/P o ) 2 = 20 log 10 (P/P o ) P = root mean square sound pressure, n/m 2 P o = reference pressure, 2 x 10 -5 n/m 2 (0.0002 microbars) (threshold of hearing) (SPL, Sound Pressure Level as measured in dB) Magnitude 0 dB The sound pressure equals the reference pressure 100 dB The sound pressure equals 20 microbars, or 100,000 times the reference pressure of 0.0002 microbars Decibels SPL= 20 log 10 (P/P o )
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6 COMMON OUTDOOR NOISES Jet Plane at 500m Gas Lawnmower at 1m Diesel Truck at 15m Noisy Urban Daytime Commercial Area Quiet Urban Daytime Gas Lawnmower at 30m Quiet Urban Nighttime Quiet Suburban Nighttime Quiet Rural Nighttime Sound Pressure ( μ Pa) Sound Pressure Level (dB) 80 70 60 50 40 30 20 10 0 90 100 110 200,000 63,246 20,000 6,325 2,000 632 200 63 20 632,456 2,000,000 6,324,555 COMMON OUTDOOR NOISES Rock Band at 5m Inside Subway Train Food Blender at 1m Normal Speech at 1m Shouting at 1m Large Business Office Dishwasher next Room Small Theater Library Bedroom at Night Threshold of Hearing • Highway-generated road noise is 50 to 95 dB Typical Traffic Noise Levels
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7 Number of times per second that the sound pressures repeat, measured in Hertz, Hz 1 Hz = 1 cycle/second Audible range of human hearing: 20 to 20,000 Hz Cyclic Frequency Traffic 100 - 4,000 Hz Engines 100 - 250 Hz • Humans respond differently to sound pressures at different
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This note was uploaded on 06/07/2009 for the course CEE 4620 taught by Professor Gensler during the Spring '09 term at Georgia Institute of Technology.

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Noise_2009 - Introduction to Noise Randall Guensler Chris...

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