Health Effects Lecture 7: Noise - Part 1 (01.04.2020) Mark Brink - PowerPoint PPT Presentation

[701-0662-00 V] Environmental Impacts, Threshold Levels and Health Effects Lecture 7: Noise - Part 1 (01.04.2020) Mark Brink ETH Zürich D-USYS Homepage: http://www.noise.ethz.ch/ei/ D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 1

Topics of the next six lectures Hearing Sound & Noise Emission Perception Immission Effects Rating of noise Assessment Noise abatement Limitation Noise regulation (policy) D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 2

Overview of today’s lecture ► Physical basics of sound ► Sound generation, propagation, and perception (short intro) ► Frequency and wavelength ► Types of waves ► Sound pressure and sound pressure level ► Time and frequency domain ► The Decibel (dB) ► Physiological basis of hearing ► Anatomy of the ear ► Outer ear, middle era, inner ear ► Theories of auditory perception ► The cochlea ► Perceptual organization of sound D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 3

Physical basics of sound D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 4

Sound generation, propagation, and perception What is sound? • Sound is a disturbance that propagates through a medium that has properties of inertia (mass) and elasticity. • The medium by which the audible waves are transmitted is air or water, or even solid bodies (e.g. a wall, a window, the ceiling of your apartment...) • Sound propagation is simply the molecular transfer of motional energy (Hence: sound cannot pass through a vacuum). D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 5

Sound generation, propagation, and perception How is it generated? • By mechanical motion, e.g. from a loudspeaker membrane, from a vibrating string... etc. • If the motion is periodical, the sound has (one or more) distinguishable frequencies waveform of one second of sound waveform of 12 seconds of sound D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 6

Sound generation, propagation, and perception Why can we hear it? • Because the energy contained in a sound wave puts the eardrum into vibrational motion • the eardrum translates the energy of the wave trough the ossicles of the middle ear onto the cochlea in the inner ear and the cochlear hair cells • the hair cells produce neuronal action potentials which travel through the auditory nerve to the brain • ... the brain interprets these action potentials as "sound" • ... more about auditory perception will follow soon.. D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 7

Sound generation and propagation Sound as longitudinal compression wave D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 8

Sound generation and propagation Wavelength and frequency pressure change place x c Propagation speeds:   C Air ≈ 340 m/s f C Water ≈ 1400 m/s standard pitch 'A' (440 Hz) → λ = 0.77 m (in air) D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 9

Sound generation and propagation Summary movement movement of air molecules of tines sound propagation low pressure high pressure medium (air, water) tuning fork sound pressure atmospheric pressure place wavelength ( λ, lambda) D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 10

Types of sound waves (in the time and frequency domain) Sound pressure Pure tone ("Reinton") 440 Hz 880 Hz 4 8 12 16 20 31 125 500 2000 8000 Terzbandpegel [dB] Schalldruck [Pa] Sound pressure Complex sound ("Klang") 4 8 12 16 20 31 125 500 2000 8000 Sound pressure Noise ("Rauschen") white: pink: 4 8 12 16 20 31 125 500 2000 8000 Zeit [ms] Frequenz [Hz] Time [ms] Frequency [Hz] D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 11

Time domain: one wave 4 Wave #1 3 2 1 Sound pressure 0 -1 -2 -3 Time -4 D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 12

Time domain: two waves 4 Wave #1 Wave #2 3 2 1 Sound pressure 0 -1 -2 -3 Time -4 D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 13

Time domain: three waves Wave #1 4 Wave #2 Wave #3 3 2 1 Sound pressure 0 -1 -2 -3 Time -4 D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 14

Time domain: the sum signal Wave #1 4 Wave #2 Wave #3 Sum signal 3 2 1 Sound pressure 0 -1 -2 -3 Time -4 D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 15

Frequency domain: the spectrum of the sum signal FFT spectrum of the sum signal Wave #3 Wave #1 Magnitude Wave #2 Frequency D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 16

Demo-Excel sheet download at www.noise.ethz.ch/ei D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 17

Range of frequencies audible frequency range D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 18

Sound pressure - time course Sound pressure fluctuations are very small in relation to the standing atmospheric pressure Sound pressure p in Pa atmospheric pressure (ca. 100‘000 Pascal [Pa]) 1 Pa = Force of 1 Newton per square meter = 1 N/m 2 Time t D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 19

Root Mean Square (RMS) value = a measure of energy of a sound wave Root mean square value P eff = Effektivwert = Root mean square (RMS) Sound pressure in Pa ger. “Effektivwert” Atmospheric pressure atmosphärischer Luftdruck Sound pressure in Pa Schalldruck p i zum Zeitpunt t i in Pa Zeit t 1 for a sine wave: RMS = 2 D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 20

Transmission, Reflection and Absorption D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 21

Anechoic chamber (A lot of absorption, no reflections) D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 22

Echo chamber (No absorption, a lot of reflections...) Echo chamber at Empa in Dübendorf D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 23

Sound pressure and sound pressure level Sound pressure: Pressure fluctuations in the air that occur in a point in space as the sound pressure waves travel Unit: Pascal (Pa) = 1 N/m 2 → depending on the location of the receiver relative to source Sound power: Sound energy that a sound source produces per time unit Unit: Watt → Independent of the location of the receiver D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 24

Sound pressure level Sound pressure level L p [in dB]: is a logarithmic measure of the sound pressure of a sound relative to a reference value. It indicates “how many times” larger is the measured sound pressure relative to the pressure at the hearing threshold Unit: Decibel [dB] Reference pressure p 0 : 0.00002 Pa (= Hearing threshold @ 1000Hz) Threshold of pain: 20 Pa   2 p   L 10 log   [dB] 10 2 p   0 Note: p is the RMS value in Pascal D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 25

Calculation of the sound pressure level Namesake: A. Graham Bell Bel Deci-bel Sound Reference sound Ratio of Logarithm Level pressure [Pa] pressure [Pa] squares [dB] 0.00002 0.00002 1 0 x 10 = 0 0.0002 0.00002 100 2 x 10 = 20 0.002 0.00002 10000 4 x 10 = 40 0.02 0.00002 1000000 6 x 10 = 60 0.2 0.00002 100000000 8 x 10 = 80 2 0.00002 10000000000 10 x 10 = 100 20 0.00002 1E+12 12 x 10 = 120 200 0.00002 1E+14 14 x 10 = 140 Hearing threshold Threshold of pain D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 26

Decibel scale Source: Effects: 1000 160 2000 Firecracker Acute irreversible damage 200 140 100 Sound pressure level Jet taking off 20 1 120 Threshold of pain Sound pressure Rock concert Sound intensity 2 0.01 Mp3 player 100 Rehearsal room Danger to hearing Jackhammer 0.2 80 10 -4 Noisy road traffic 0.02 60 Speech understandability 10 -6 Conversation 0.002 10 -8 40 Concert hall (empty) 0.0002 20 10 -10 Whisper 0.00002 10 -12 0 Hearing threshold [ Pa ] [ W/m 2 ] [ dB ] D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 27

Decibel arithmetic 80 dB 0 dB + 0 dB = 3 dB + 80 dB = 83 dB   N     0.1 L L 10 log 10 Summation:  n  10    n 1   N   0.1 L 10 n        Averaging: L 10 log n 1 10  N      D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 28

Changes of sound pressure level Qualitative perception Change of level Perception 1-2 dB barely recognizable change 2-5 dB recognizable change 440 Hz, each tone 1 dB lower 5-10 dB well recognizable change 10-20 dB large, convincing change 440 Hz, each tone 3 dB lower > 20 dB very large change 440 Hz, each tone 5 dB lower D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 29

Physiology of hearing D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 30

Anatomy of the ear bone conduction equilibrium organ Cochlea air conduction ear canal eardrum Eustachian tube D- USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 31