Sound Physics Flashcards
1
Q
Sound
A
- a form a physical energy
- caused by pressure variations from a source
- a vibration that moves air and molecules and generates pulses of increased pressure that radiate from a source in a pressure wave
2
Q
Noise
A
- any annoying or unwanted sound
- not recognized as harmful until hearing loss occurs
3
Q
Pressure waves
A
- can travel for long distances
- occurs in moveable or elastic mediums like air, water or solids
- the rate at which a pressure wave repeats itself determines the sound’s frequency
- the faster the cycles, the higher the pitch of the sound
- when simple pressure changes occur the resulting sounds are pure tones b/c the pressure variations occur at only one frequency
4
Q
Sound frequency
A
- measured in cycles per second (cps)
- also called Hertz (Hz)
5
Q
Pitch
A
- psychological perception of sound frequency
6
Q
What frequency range can the young, healthy, human ear perceive?
A
- 20Hz - 20,000Hz
7
Q
What tones do audiometers produce?
A
- 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz
8
Q
Frequency
A
- measured in Hz
- psychologically interpreted as pitch
- perceived as low, medium, and high
- the way that pressure waves repeat themselves
9
Q
Amplitude or intensity
A
- measured in decibels
- psychologically interpreted as loudness
- perceived as low, soft, moderate, loud, high
10
Q
Time
A
- measured in Ms, S, Min, Hrs, etc.
- psychologically interpreted by duration
- perceived as short and long
11
Q
Intensity
A
- pressure/strength of a sound wave
- the greater the pressure = the more intense the sound level = louder we perceive sound
- measured subjectively as loudness and objectivity as sound level or sound pressure level
12
Q
Decibels
A
- an expression of amplitude
- the units that measure sound pressure are newtons/ square meter (N/m^2) or Pascals (Pa)
- the smallest sound pressure the ear can hear is 0.00002N/m^2
- 20N/m^2 is harmful
- anchored to an arbitrary 0 of 0.00002N/m^2 at a frequency between 3000 and 4000 Hz
- based on ratios which expresses the range of sound pressures we can hear in a few numbers
- scale increases in decibels of 10 = increasing the intensity 10X
13
Q
Decibel ratio scale
A
- based on ratios which expresses the range of sound pressures we can hear in a few numbers
- Scale increases in decibels of 10 = increasing the intensity 10X
- Ex. 20 Db is 10x more intense as 10 Db
- Ex. 1,000 relative energy intensity = 30 Db
- scale is logarithmic so decibels cannot be added
- Ex. two machines that are side by side each produce 90 Db would NOT produce a sound level of 180 Db, because of the scale they would produce around 93 Db together
14
Q
A-weighting scale
A
- used to measure sound to filter out different sound frequencies
- excludes some low frequencies and some very high frequencies
- is closest to the frequency response characteristics that the human ear is most sensitive to (250-8000Hz)
- expressed as an A after the decibel level
15
Q
Damage Risk Criteria
A
- standards established to protect the majority of workers from noise induced hearing loss
- can be met through engineering or administrative controls or through the use of personal protective equipment
16
Q
The trading relationship/ exchange rate
A
- reflects the relationship between the permitted exposure levels and exposure durations
- If permissible noise exposure begins at 85 dBA for 8 hours, a 5 Db increase to 90 dBA is permissible if exposure time is reduced by half, to four hours.
- the 5dB trading relationship is based on temporary threshold shift and on the theory that the ear rests between exposures
- Less TTS occurs from intermittent noise exposure than from continuous noise
- TTS is NOT a valid indicator of permanent threshold shifts
17
Q
Damage risk criteria in Alberta
A
- a 3dB trading relationship or exchange rate based on equal energy theory
- equal amount of A-weighted energy results in equal amounts of hearing loss, regardless of the type of exposure.
- an 8 hour limit of 85dBA could accommodate a 3dB increase (to 88dB) if exposure time is reduced by half to four hours
- results in equivalent exposure b/c when intensity is doubled the sound pressure level is increased by 3dB.
- If decibels increase by 3 and exposure time is halved there is a equivalent exposure level or Lex
- If decibels increase by 3 and exposure time is halved there is a equivalent exposure level or Lex
- Lex expresses equivalent exposure level , averages a workers total exposure to noise over the entire work day and adjusts it to an equivalent 8 hour exposure
- Section 219 of the OHS code requires employees to do a noise exposure assessment if they are going to be exposed to noise over 82 dBA Lex
18
Q
Identifying Threshold
A
- the worker’s threshold of hearing at each frequency can be determined
- want to identify the softest sound they can hear at each frequency
- to determine if a threshold has changes, there has to be at least 2 hearing tests to compare it to
19
Q
Threshold shift
A
- when hearing is affected and some hearing is lost, the thresholds can shift
- a threshold change at any frequency is a shift
- usually the results of hearing loss and an increase in dB
- a shift is a change of at least 15dB
- changes of 5dB or 10dB is too small to be considered a shift
- can occur still when there is no actual change in hearing
20
Q
Pure Tones
A
- sounds that only occur at one frequency
21
Q
3dB trading relationship
A
- Based on equal energy theory
- Equal amounts of a-weighted energy cause equal amounts of hearing loss regardless if the exposure is constant or intermittent or impact vs. Steady state
