Industrial Lectures Page 3
Card number_____ 1
card fld "card field id 3"
Ramazzini in 1700, "De Morbus Artificium Diatriba"
morbus:
"disease"
artificium:
a trade or profession
diatriba:
•a discourse or dispute
•also, a wasting away
"Those hammering copper had their ears so injured by that perpetual din that workers of this class became hard of hearing and, if they grow old at this kind of work completely deaf."
-noise exposure results in hearing loss
-damage is a function of exposure level and duration
-correlation with aging
Some terms:
-NIHL: chronic exposure; most exposures are ≤ 100 dBA. Exposures.
-tinnitus: common symptom associated with NIHL, often a symptom of temporarily or permanently damaged sensory or neural tissue.
-acoustic trauma: brief duration exposure
-occupational hearing loss: NIHL from employment, "boilermaker's deafness"
-sociocusis: hearing loss from non-occupational noise exposure (music, airplanes, subways, firearms, lawnmowers, powertools, snowmobiles, etc.)
-presbycusis: hearing in the elderly, hearing loss associated with aging; primary variable confounded with NIHL. The issue of
◊employer culpability
◊combination of factors affecting handicap
-nosoacusis (GR nosos, disease): hearing loss from accident, trauma, ototoxicity, etc.
For an introduction to the main components of a hearing conservation program, click HCPs
card fld "Info…"
Towards the end of the semester, some concepts…
•Be sure you are very familiar with the OSHA regulations for occupational noise exposure.
◊I will be picky & specific
-go card Regulations
•The story of the Mabaan tribe and presbycusis
-regarding hearing loss: maybe its not growing old per se, but how we grow old
-go card Mabaan
•Calculating the fence (onset of material impairment) or %HL for each ear and binaural weighting (5:1)
-go card Fence
•Probability of crossing the fence from exposure to the PEL
-29% without noise exposure ammendment, 5% risk with Jan '81
-go card Risk
•Interaction of pre-existing permanent hearing loss with daily TTS
-more hearing loss, less TTS
-go card TTS
•Cochlear electrophysiology and mechanics
-go card Cochlea
•Major theories regarding mechanism of hearing loss from noise exposure
-go card Effects
•Dose and TWA calculation
-Done for you by the dosimeter
-go card Dose
•For a pink noise exposure, which formula, HPD attenuation, paragraph (j), predicts greater HPD attenuation (or estimated A-level TWA exposure, Est-A)?
◊Est-A = A-weighted TWA - (NRR - 7)
◊Est-A = C-weighted TWA - NRR
-go card Regulations
•Ambient noise in test suite can affect validity of the baseline audiogram
-this limits ability of the annual audiogram to detect changes in threshold produced by noise exposure
-go card Ambient
card fld "HCPs"
•Administration
√Initial
√Ongoing Evaluation & Re-evaluation
•Exposure Measurements
√Initial Survey
√Noise Monitoring
•Noise Controls
√Administrative
√Engineering
•Hearing Protector Devices (HPDs)
•Audiometry
√Baseline
√Annual
•Training & Education
•Medical Evaluation
Card number_____ 2
card fld "Stressor"
•increased noise levels produce peripheral vasoconstriction
•resulting in increased heart action,causing increased blood pressure
•increased secretion of corticosteroids (adrenal steroids, catecholamines)
•fight or flight mechanism
card fld "Performance"
•vigilance tasks boring, may help
•hinders more complex tasks
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•Noisy jobs generally less attractive, more dangerous
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card fld "Elasticity"
An elastic deformation: a deforming force causes a body to change shape. When the deforming force is removed, body returns to original size.
•eg, a spring moving a distance when a mass is suspended from it
•stiffness: the ratio of the applied force to the displacement
•compliance: the inverse of stiffness
card fld "Pascal"
Blaise Pascal (1623-1662)
French philospher and mathematician. Invented an adding machine, developed modern theory of probability, worked in field of hydrodynamics.
•Physical unit, Pascal
•Programming language
card fld "Ambient"
Ambient denotes "resting" or "initial" conditions, i.e., of the atmosphere which (usually) serves as the propagating medium…
•The molecules of the atmosphere are uniformly distributed.
•Each molecule (particle) is connected to its neighbor. If one particle is disturbed, its neighbor is disturbed, as if they were connected by springs (i.e., elastic elements).
Statistics about the atmosphere
•The ambient density (ro) is…
1.21 kg/m^3
0.00121 gm/cm^3
•The ambient pressure is…
1 atmosphere (atm)
101,300 N/m^2
1,013,000 dyne/cm^2
14.7 psi
760 mm of Hg
almost 30 inches of Hg
•1 N/m^2 is 1 Pascal (Pa)
•A Pascal is a relatively large unit. The softest sound we can hear is about 2*10^-5 Pa (0.00002 Pa), so units expressed in millionths of a Pascal are common (µPa)
2*10^-5 Pa = 20 µPa
•Sound waves propagate as tiny fluctuations above and below atmospheric pressure
•For example, the typical rms** pressure in average conversational level speech is about 0.036 Pa.
ACL = 101,300 Pa ± 0.036 Pa
**more about rms later
•Fluctuations in atmospheric density (r) create fluctuations in pressure
Pressure = r * c^2
•Fluctuations in atmospheric pressure (p) create fluctuations in sound intensity
Intensity = p^2 / (ro* c)
card fld "Power"
Sound Power
•Power has the units of "Watts." Power is the rate at which energy is being used, or consumed.
•1 Watt = 1 joule/s
Sound Intensity
•Intensity is measured in Watts/m^2. Intensity is the "rate at which energy is being radiated over a given surface area."
Intensity = Power / m^2
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Card number_____ 5
card fld "Speed"
The tine of the tuning fork moves to the right:
•compressing the atmosphere (increasing density & pressure)
pressure = r * c^2
•when the tine moves to the left it expands or "rarefies" the atmosphere (decreasing density & pressure)
•each molecule influences its neighbor
•causing the area of compression (or rarefaction) to propagate away at the speed of sound, c
Speed of sound is influenced only by the physical properties of the propagating medium (not by the characteristics of the vibrating body, such as frequency):
•temperature
-increased T increases c
•density
-increased density reduces c
•elasticity
-increased stiffness increases c
•Generally, sound travels faster in solids, slower in liquids, slowest in gases
-mainly due to differences in stiffness (not density)
•At room temperature the speed of sound is about 344 m/s
Sound waves are longitudinal
•Each particle oscillates back & forth in the same direction that the wave travels; each particle…
-moves very little
-with a relatively small mean velocity
Card number_____ 6
card fld "SHM"
Simple harmonic motion…
•Motion with one degree of freedom; repetitive, cyclical motion
Examples…
•Tine of a tuning fork (produces a pure tone, a tone of a single frequency)
•A swinging pendulum, a metronome, the pendulum on a cuckoo clock
•A mass on the end of a spring
•Beavis swinging a dead rat on a string about his head
•The diaphragm of a headphone while its delivering a 1000 Hz tone during a hearing test
•A spinning top, water swirling through a lavatory
•The spinning wheel of a bicycle
•The air inside your mouth while you are whistling
Cycles, phase, period, frequency
•After 1 complete cycle, the vibrations associated with SHM are repetitive, like going around a circle (0° to 360°)
•Phase describes what part of the cycle the vibrating body is in…
-or where in the cycle it begins, or
-the difference between two bodies vibrating simultaneously
•The duration of one complete cycle is defined as the period (T)
-seconds
-milliseconds (1000ths of a second)
•Frequency (Hz, named after Heinrich Hertz) is defined as the number of cycles completed in 1.0 second (f)
-Hz (cycles/sec)
-kHz (1000nds of cycles/sec)
Amplitude
•Instantaneous amplitude is the displacement from the position of rest at any instant in time.
•Peak amplitude (Ap) is the absolute value of the maximum deviation from the position of rest (to either the right or left, + or -).
•Peak-to-peak amplitude (Ap-p) is the absolute value of the deviation between the maximum excursions (right to left, or + to -).
Card number_____ 7
card fld "Concepts"
Harmonic Motion Stack
•Illustrates SHM via a simple spring-mass system (a mass oscillating on the end of a spring)
•Shows the linear projection of the SHM into a sine wave
•Shows the analogy between projected SHM and circular motion — projected uniform circular motion
•Describes why the waveform is called a sine wave — the anatomy of a triangle is defined.
Oscilloscope Stack
•This stack allows us to synthesize pure tones by defining the frequency, amplitude and phase.
•We can define complex tones (i.e., sounds that have more than one frequency)
•Illustrates how complex tones are built from simple tones by addition
•Tones of the same frequency can be added, but phase is important
-A 180° phase difference ("out of phase") causes cancellation.
-A 0° phase difference ("in phase") causes reinforcement.
•Periodicity, the repetitiveness of complex, periodic waves is illustrated.
•Defines period and wavelength relative to the waveform
•Describes the mathematical relationships between period, frequency, wavelength, and speed of sound
•Defines peak amplitude (Ap), peak-to-peak amplitude (Ap-p), instantaneous amplitude (ai), and the rms amplitude (Arms)
•Defines the relationship between Ap and Arms.
And…
When complex sounds are composed of frequencies that bear simple numerical relationships to one another, the result is aesthetically pleasing. Nice visual and auditory patterns result, as in Leonardo da Vinci's ideas of beauty in symmetry.
card fld "Ordinate"
The ordinate of the graph can represent…
•The instantaneous displacement of the vibrating body (relative to "0," its position of rest)
•The corresponding changes in density, pressure, or intensity occurring in the propagating medium
•A measured analog of these changes, like voltage on an oscilloscope)
The abscissa of the graph, for example, when displaying density…
•Can represent time. Changes in density occurring at a point in the atmosphere as a function of time (as the wave moves through).
•Can represent distance. Strike the tuning fork, allow a few cycles to propagate, "freeze" time. Changes in density in the atmosphere can be plotted as a function of distance from the sound source.
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Card number_____ 10
card fld "Info…"
•A 10 volt peak sine wave delivered to a resistor, causes the resistor to generate heat (i.e., energy).
•The same amount of heat would be generated by delivering a 7.07 volt dc signal to the same resistor.
•The rms value measures the amount of energy contained within the signal.
Card number_____ 11
Card number_____ 12
card fld "Decibel"
The decibel scale
•Decibels are "dimensionless" units. In the process of calculating dB, the units cancel. So always specify the type of dB, i.e., dB SPL, dB IL, dB HL, etc.
•All decibel scales have a reference. The reference defines what 0 dB is. The reference for the hearing level scale (dB HL) is the average sound pressure needed to reach threshold for normal hearing people. This pressure varies with frequency.
•The reference for the SPL scale is…
CGS 0.0002 dyne/cm^2
2*10^-4 dyne/cm^2
MKS 0.00002 Pa
2*10^-5 Pa
20 µPa
Note: These are the same pressures, just expressed in different units
•The reference for the dB IL scale is…
MKS 10^-12 Watt/m^2
•A sound with a pressure of 20 µPa has an intensity of 10^-12 Watt/m^2. This means that the dB SPL for a sound will always equal its dB IL.
Procedures for calculating decibels
Sound pressure
1. Identify the sound pressure that you wish to convert to a sound pressure level.
2. Divide the pressure by the reference to obtain a ratio. Choose the reference that has the same units.
3. Take the logarithm of the ratio. Multiply the logarithm by 20 to get the dB SPL.
Intensity
1. Identify the intensity that you wish to convert to an intensity level.
2. Divide the intensity by the reference (10^-12 Watt/m^2) to obtain a ratio.
3. Take the logarithm of the ratio. Multiply the logarithm by 10 to get the dB IL.
Constant Proportions
•Every time the pressure increases 10 times, the SPL increases by 20 dB.
•Every time the sound pressure doubles, the SPL increases by 6 dB.
•Every time the intensity increases 10 times, the IL increases by 10 dB.
•Every time the intensity doubles, the IL increases by 3 dB.
•Every time the sound pressure doubles, the intensity increases 4 times. The SPL increases by 6 dB, and the IL increases by 6 dB.
Finding dB differences
•You can find the dB difference between any two values, provided they have the same units.
•Example: What is the dB difference between a pure tone that has an Ap = 7 Volts, and one that has an Ap = 3.2 Volts?
dB = 20*log( 7/3.2) = 6.8 dB
Should I multiply by 10 or 20?
•For pressure, force, voltage multiply the ratio by 20.
•For intensity, power, energy multiply the ratio by 10.
Card number_____ 13
Card number_____ 14
card fld "card field id 1"
0 Softest audible sound
10 Normal Breathing
20 Rustling leaves
30 Very soft whisper
40 Quiet residential community
50 Department store
60 Average speaking voice (65 dB)
70 Inside moving car
80 Loud music from radio
90 City traffic
100 Subway train
110 Loud thunder
120 Amplified rock band
130 Machine gun fire (close range)
140 Jet engine at takeoff
180 Space rocket at blastoff
Card number_____ 15
card fld "Spectrum"
The sound spectrum
•The sound spectrum is…
-a description of which frequencies are contained within a sound, and the dB level of each frequency
-a plot of amplitude as a function of frequency (amplitude spectrum), phase is usually ignored