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Noise Control
Industrial Audiology
42
Audiology
Graduate
06/14/2018

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Cards

Term
What is the goal of noise control?
Definition
To treat the dominant noise sources that add to TWA exposures of 85 dBA and above
Term
What is the biggest challenge of noise control?
Definition
IDing the primary noise source
Term
How much can time weighted averages be reduced & what is the associated cost?
Definition
Typical attenuation from HPDs is about 10 dBA. Cost depends on the type of industry.
Term
Benefits of Noise Control:
1. reduces the potential for ____
2. may reduce ___ of other parts of the HCP
3. may reduce ___ & legal costs
4. improves ___; requires less vocal effort
5. ___ accidents/injuries/absenteeism
6. may reduce ___ ___ disease
7. Reduces ___ and increases productivity
Definition
ONIHL; costs; compensation; communication; reduces; coronary heart; errors
Term
Costs of noise controls depend on the type of ___
Definition
industry
Term
-When workers are exposed to hazardous noise levels above 90 dBA TWA, OSHA requires using feasible ___ or ___ noise controls.
-Impulse or impact noise should be controlled so it does not exceed ___ dB peak SPL
Definition
engineering; administrative; 140
Term
What professions are involved with noise control?
Definition
occupational health professionals, plant engineers, and noise control engineers
Term
What are some common sources of noise?
Definition
mechanical impacts, high velocity air flow (air valves), high-velocity fluid flow (pipelines), and vibrating machine surfaces or products (food processing or glass manufacturing)
Term
Ways to Treat the Path:
-Use ___ enclosures or barriers since reflections from walls, floors, & ceilings can increase levels generated by a source
-Effectiveness of an enclosure is related to its ___; materials with higher mass are better (reduce more noise)
-Barrier used depends on the ___ content of the noise
Definition
acoustic; mass; spectral
Term
What is an example of a barrier or shield?
Definition
A lead curtain
Term
A higher sound transmission class (STC) means ___ sound is blocked
Definition
more
Term
You can treat the source of sound by ___ ___
Definition
modifying equipment
Term
devices put into the path of a flowing medium (e.g. air) to reduce sound levels.
Definition
Silencers
Term
What is an example of a silencer?
Definition
A muffler can decrease noise from vehicles’ exhaust pipe
Term
What are the 3 types of silencers?
Definition
Dissipative, reactive, and combination
Term
Dissipative Silencer/Muffler:
-Dissipative/absorptive: use ___ materials to absorb sound
Definition
porous
Term
Reactive Silencer/Muffler:
-Reactive/reflective : use big changes in ___ & sound ___ to decrease noise in a pipe
-Ex: Inlet pipe of the silencer has lots of tiny holes, then sound goes to the expansion chamber. When the sound goes into the
bigger cavity, the waves reflect off of the sides of the shell & ___ with incoming sound waves (fig. 3.2)[image]
Definition
impedance; reflection; interfere
Term
Combination Silencers:
-Combines ___ & ___ components
-Includes a layer of ___ on the outer shell of the reactive silencer
-More noise abatement ___ frequencies
-___ applications
Definition
dissipative; reactive; fiberglass; across; Limited
Term
Active noise cancellation may be used with passive silencers:
-Provide good ___ frequency attenuation; not good for sounds above ___ Hz
-Works well if air has ___ and/or particles
Definition
low; 1000; moisture
Term
Outer surface of pipe is wrapped in sound absorption material then covered with a barrier material; used when silencers isn't an option
Definition
Acoustic pipe lagging
Term
___ ___ operations can reduce noise. Ex: ??
Definition
Proper machine; follow directions on how to operate it and running it at a lower speed than recommended can reduce noise
Term
What are some materials with high absorption coefficients?
Definition
Heavy carpet on foam rubber, polyester urethane foam (1 inch thick), and sprayed on cellulose fiber on timber lath
Term
Examples on treating the receiver?
Definition
Enclosures, hearing protection, administrative noise controls (rotate work force to decrease total noise exposure for individuals), and provide adequate break times
Term
pressure fluctuations of a medium that has elasticity and viscosity
Definition
Sound
Term
pressure (p) variations above & below ambient atmospheric pressure; amount by which instantaneous pressure varies from atmospheric pressure
Definition
amplitude
Term
-pressure oscillation (in air) is ___ ___
-oscillation (in solids) is ___
Definition
sound pressure; vibration
Term
Sound pressure can be generated by....
Definition
-Impact
-Pressure fluctuations in turbulent fluid flow
-Vibrating surfaces
Term
distance traveled by sound wave during one pressure cycle
Definition
Wavelength
Term
physical number of oscillations in a wave
Definition
frequency
Term
SPL decreases by 6 dB when the distance from the source is ___
Definition
doubled
Term
What does p stand for and Pref stand for?
Definition
p=measured sound pressure and Pref=reference pressure=20 uPa
Term
What is the equation for SPL?
Definition
20log(p/Pref)
Term
Pressure:
-#dB=20 X log (__/__)
Definition
Po/PR
Term
What does Po and Pr stand for?
Definition
Po=pressure output and Pr=pressure reference=20 micropascals
Term
logarithmic unit that describes a ratio
Definition
decibel
Term
The Decibel:
-The ratio may be in ___ or ___ (intensity)
Definition
pressure; power
Term
A measure of total noise radiated by equipment in all
Definition
sound power level
Term
Power per unit area is Intensity:
-Acoustic power is ___ distributed over a sphere when it is radiated from a point source
-The resulting sound power per unit area of sphere is ___ (in watts/m^2)
-There is no practical way to directly ___ sound power
Definition
evenly; intensity; measure
Term
Units of Measure for Power & Pressure:
-Sound power (W) is the ___ ___ ___ from a source in watts (w)
-reference level for power (intensity) is ________
-Sound pressure (p) is a force per unit area expressed in ____ or (N/m2)
-reference level for pressure is ___ microPascals
Definition
total acoustic output; 10^-12 watts/m2; Pascals (Pa); 20
Term
The Decibel in Measurements from a PO WER Reference:
-#dB IL = 10 * log __/__
Definition
Wo/Wr
Term
What does WO and WR stand for?
Definition
Wo=watt/cm^2 (power) output
Wr=watt/cm^2 (power) reference
Term
Start on slide 54
Definition
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