For the Midterm Flashcards
three things that calibration ensures
1) an audiometer produces a puretone at the specified level and frequency
2) the signal is present only in the transducer in which it is directed
3) the signal is free from distortion or unwanted noise interference
who sells the calibration standards?
the acoustical society of america
three different makers of standards, and who is used in the USA?
ANSI, ISO, and IEC
the ANSI standards are used in the USA
three different parts of puretones which need to be checked during calibration
1) frequency
2) intensity
3) time (both phase and signal duration)
two pieces of equipment that do not yet have calibration standards
ABR and OAE
how often should transducers have their outputs checked?
trimonthly
7 basic pieces of equipment for calibration
1) voltmeter or multimeter
2) condenser microphone (pressure and free-field types)
3) 6cc coupler
4) 2 cc coupler
5) 500g weight
6) mechanical coupler or bone vibrator measurements (artificial mastoid)
7) sound level meter or spectrum analyzer–allows one to read output from an attached microphone input
what is used to check frequency output on an audiometer and how accurate does the audiometer need to be?
- checked using an electric counter (oscilloscope can be used, but is only accurate to 5%
- diagnostic audiometers need to be accurate within 1%, but others need to be only within 3%
how to check linearity of audiometer output
check through transducer by setting to max dB, then reducing in 5dB steps until the output can no longer be read (checks attenuator)
*must attenuate within 1dB
dB allowance for calibrating with artificial ear
- +/- 3 dB from 125-5000
* +/- 5dB at 6000+
under what 2 circumstances when calibrating do you need to have the manufacturer come in to calibrate audiometer
- if the audiometer is off more than 15dB at any frequency
* if the audiometer is off by 10dB at three or more frequencies
what are the two types of noise classifications and the definitions of them
1) transient= impulse of impact noise
2) continuous= noise that remains constant for longer than one second
where is a noise notch?
4kHz but can range 3-6K Hz
what percent of people with noise induced hearing loss are males?
80-90%
what is the walsh-Healey Act and what year was it
1969
*was revised and incorporated hearing conservation into federal law
what and when was the williams-steiger occupational health act
1971
*included te walsh-healey revision, required hearing conservation for all employees in the work force not already covered by walsh-healey
when was the HCA (hearing conservation act)
1983
*stemmed from walsh-healey and is the federal register
what are the 3 fundamental principles all hearing conservation guidelines are based on
- qualify
- abate
- protect
qualify as a fundamental principle of hearing conservation
*evaluate sound exposures in work environments to determine if workers are exposed to sound in excess of what is allowed by federal law
abatement as a fundamental principle of hearing conservation
- is to decrease sound exposures so that guidelines are no longer exceeded
- –must be accomplished before going to the final segment which is protection of personnel
- abatement can be costly and sometimes is economically or technologically infeasible to decrease levels sufficiently to achieve a safe work environment
two forms of abatement
- engineering controls= modification or redesign of equipment. the most effective being elimination at sound source. others include placement of noise shields, baffles, or enclosures
- administrative controls= of noise outputs is impossible to reduce, then it may be appropriate to reduce overall exposure by schedule modification. sometimes this cannot be accomplished due to the need for certain skilled persons at that area
protection as a fundamental for hearing conservation
- if excessive exposure according to the guidelines continues to be a problem after these 1st two steps, then the protection part of the hearing conservation program is put into operation
- worker protection takes two forms:
- –hearing protection devices
- -monitoring audiometry takes place
what is the theoretical maximum for a pure tone?
94dB
describe a c weighted scale
practically linear with virtually no weighting of the spectrum in the largest part of the audible range
describe the a weighted scale
based off a smoothed version of the 40 phon line
describe the b weighted scale
roughly equivalent to the 70 phon line
describe the d weighted scale
- is 90 dB phon curve
- similar to the b scale for the lower frequencies and has an 11dB hump at 2K Hz concurrent with human sensitivity to that frequency area as compared to lower and higher frequencies
what is a similarity between the a and b scales
they discriminate against low frequencies like the ear does
*they are attempts to adjust sound measuring devices to approximate human experience at two levels of stimulation (40 and 70dB respectively)
what is the action level?
85dB
what is the formula to calculate dose?
dose=100 (c1/tc+c2/t2+etc)
c is the duration of exposure at the particular sound level
t is the allowable duration of exposure for that level according to OSHA guidelines
Leq
equivalent level
*composite sound exposure descriptor favored by the federal government since 1975
*a time weighted energy average that represents the total sound energy over a time period as if the sound was unvarying
*example: Leq=75 means that all of the sound integrated over a 1 hour period presented the same energy as an unvarying 75dB sound
(leq is 3dB tradeoff; Losha is 5 dB tradeoff)
what is the Ldn
- day/night equivalent level
- it is utilized for the hours between 10pm-7am
- any intrusive sound is more noticeable during these hours than daytime
- the Ldn descriptor is calculated by adding a 10dB constant to any sound that occurs during this time period
type 1 sound level meter
precision units that meet the most rigorous specs
- used for measures that might be reported/discussed in courts of law
- can typically do things like find TWA and dose
type 2 sound level meter
general purpose meters, adequate for most industrial measurement activities
*will give virtually identical a weighted measures as a type 1 meter
type 3 sound level meter
survey meters for nonprofessional (hobby-type) use
calibrators for sound level meters
- most SLMs have an internal electrical calibration signal to provide checks of the condition of its electronics
- the microphone/transducer is the weakest point in the SLM system and the internal calibration will not check this
- a calibrator produces a known/consistent sound source which is used to check the accuracy of the mic as well as the associated electronic circuitry
- a calibrator is obtained from the slm manufacturer and is a must
basic role of octave band analyzers
- once full spectrum or weighted measures are completed, an octave-band analysis can be done
- –the environment is broken down electronically into a series of bands which have been specifically defined
- –this is done to identify those portions of the spectrum that contain the greatest amount of sound energy
- –noise control action plans are often predicated from octave-band analysis findings
fun facts about impulse/impact noise
type 1 will measure, not in the federal register
- is acoustically different from steady state
- has a rise time that is the first 1/4 wave of a frequency
compare the time/intensity trade and maximum allowable dB level for OSHA vs ISO
- OSHA time/intensity trade is 5dB with max of 115dB A
* ISO time/intensity trade is 3dB with no maximum stated
what does DRC stand for
damage risk criteria
*note this is best done using a TWA of a person’s noise exposure during representative activity (dosimetry)
what is a Standard
a codified set of rules (regulation) developed by ANSI or ISO
what is a regulation
a rule prescribed by the gov (published in the federal register) with compliance procedures and effective dates
what is a law
enacted by congress giving agencies powers to enforce (DOL-OSHA)
two elemental forms of noise reduction strategy:
1) decrease sound output of the source. this is done through engineering controls, proper maintenance, or equipment purchase specifications
2) interrupt the pathway of the sound. this is done with the use of sound barriers or increasing the distance between the source and receiver
how to find wavelength
speed of sound/frequency
*ss=1100ft or 343m
near field sounds
near field means close to the sound source
*the only effective treatment of the soundpath between the source and the receiver is the treatment of the source or the use of a barrier located directly between the sound source and any receivers
define far field
several wavelengths away from the sound source
*acoustical treatment of the room may be effective in decreasing the amount of sound that reaches the person
list the 6 possible strategies for noise reduction
1) reduce sound at the source
2) enclose the sound source
3) place a barrier in the near field
4) place a barrier near the receiver (refers to hearing protectors)
5) enclose the receiver
6) remove the receiver from the sound source
what is the equation to figure out how tall a near field barrier must be
speed of sound/frequency=x
then take 5x
*to create a sound shadow, a barrier must be 5 wavelengths high
what are the requirements for CAOHC (DOUBLE CHECK)
- 20 hour course at least 3 specialists
* renewed every 5 years
calculate percent of hearing impairment in 1 ear (DOUBLE CHECK)
- find average of 500, 1000, 2000, and 3000
- subtract 25dB
- multiply by 1.5 to get the % for that ear
calculate percent of hearing impairment binaural (DOUBLE CHECK)
- find the percent for each ear separately
- multiply the better ear percentage by 5
- add percentage of the poorer ear
- divide by 6
when must you use double hearing protection?
when the 8hr TWA is >105dBA
