Physics of Sound Flashcards
sensation that results from the stimulation of the auditory mechanism by pressure variations in any “elastic” medium
sound
unwanted sound
noise
requirements for sound
1st- sender
2nd- medium
3rd- receiver
source of vibration and source of energy
sender
carries the pressure change
medium
auditory mechanism to receiver and interpret the signal
receiver
causes alternative pressure changes in the air molecules
vibration
molecules of the medium forced together causing high pressure
compression
molecules of the medium separate causing low pressure
rarefaction
a series of compression + rarefactions
sound wave
what does speed depend on
depends on the medium, the denser the medium, the faster sound travels
1,100 feet per second
air
4,500 feet per second
water
15,000 feet per second
steel
graphical representation of the compressions and rarefactions
sine wave
horizontal axis
time
vertical axis
molecular vibrations
frequency is also known as
pitch
sound frequency is quantified in terms of
hertz (Hz)
human ear is sensitive to frequencies as low as ___Hz and as high as ___Hz
20
20,000
speech hearing range
250 Hz - 4000 Hz
consonant sounds
high frequencies
vowel sounds
low frequencies
human ear is MOST sensitive to sounds in the range between ___Hz and ___Hz
1000
4000
human ear is LEAST sensitive in
low frequency range
what determines intensity or loudness of a sound
pressure or energy exerted at the source of the sound
human ear’s perception of amplitude
loudness
intensity is expressed in
decibels (dB)
range intensity range for human ears
0-140 dB
represents the average we can hear
0 dB
where serious and immediate damage can occur
140 dB
background noise begins to interfere with communication
50 dB
level of average speaking voice
60 dB
hazardous continuous noise
80 dB
hazardous impact noise
140 dB
possible tissue damage
170-180 dB
possible death
180+ dB
if you need to shout to be understood from 3ft away, you are in a potentially hazardous noise environment
three foot rule
last longer than one second
continuous noise
large differences in sound level occur during the day, with periodic interruptions of relative quiet periods
intermittent noise
noise levels that vary in intensity with no significant quiet periods
varying noise
very short burst of noise lasting less than one second
impulse noise
noises are slightly longer in duration than impulse noises
impact
combination of sound waves with a mix of frequencies, with varying intensities
complex tones
simplest form of sound and represents one frequency
pure tone
microphone to measure sound pressure level (SPL)
sound level meter (SLM)
is the amount of sounder energy in the atmosphere
sound pressure level (SPL)
the decibel scale is
logarithmic
scale used by BE
mimicking of the human ear
dBA SPL
A scale
captures more of the low frequency sounds and slightly more of the high frequency sounds than the A-weighting filter
dBC SPL
C scale
very loud, fast sounds (impulse noise)
dBP SPL
P scale
hearing test derived by testing a large group of young, normal hearing people
comparing frequencies over time
HTL scale
when a noise source is doubled the noise level will
increase by 3 dB
example: two machines running at 90dB, overall sound level is 93dB
doubling the distance from a sound source the intensity of the exposure will
inverse square law
decrease by 6dB
when ___ are used, high frequency sounds are attenuated more than low frequencies
barriers
amount of time a worker is exposed to hazardous noise over the work day (8-hr day)
time-weighted average (TWA)
percentage of an allowable noise exposure the worker experiences through the work day.
noise dose
noise dose takes into account two factors:
permissible exposure limit (PEL)
exchange rate
8 hour time-weighted average exposure at which point 100% noise dose is reached
permissible exposure limit (PEL)
OSHA and most U.S. government regulations use ___dBA as the PEL standard
90
DoD sets the maximum PEL at ___dBA
85
the amount of decibel increase/decrease in the TWA noise exposure causes the noise dose to double (or cut in half)
decibel exchange rate
when the steady sound level is increased, what happens to the duration
cuts in half
examples: 85 dBA increased to 88dBA the duration goes from 8 hrs to 4 hrs
