Human range of hearing,
Loudness, Decibel scale, Beats,
Doppler Effect.
Human Range of Hearing
• Remember: The
human ear is built
to sense
pressure
fluctuations
above and below
atmospheric
pressure. It will
sense
fluctuations in the
20Hz – 20,000Hz
range. Check out
other organism’s
hearing.
Decibel (dB) Scale
Measurement of a decibel is tricky, 0dB
is the equivalent of an inaudible sound,
10dB is a 10 times larger pressure
amplitude than an inaudible sound and
20dB is 100 times more than an
inaudible sound. This is a logarithmic
scale.
Most people perceive a 10dB increase
in sound level as about twice as loud
as the original level.
0 dB to 10dB
10 times greater
pressure than the
reference
amplitude.
0 dB to 20dB
10X10=100 times
greater pressure
than the reference
amplitude.
A decibel, or one unit of sound
(abbreviated as dB,) is used
to measure the intensity of a
sound wave.
Decibel (dB)Scale
• The decibel scale is a
logarithmic scale of
sound pressure.
• Since it is logarithmic, an
increase of 10 dB results
in a ten fold (10X)
increase in pressure on
the ear drum.
• Zero dB is considered
the Threshold of Human
Hearing.
• Sound intensity at this
point is 1x10-12W/m2
Some common pressure & dB ratings
Ha Ha!!!
Above and
Below
• Frequencies above
20 kHz (20,000 Hz)
are called Ultrasonic
frequencies,
• And those
frequencies below 20
Hz are called
Infrasonic
frequencies.
Beat Frequency
• When sound waves from
two different similar
frequency sources
overlap, interference
occurs, both constructive
and destructive.
• A beat frequency is heard
based on how often the
sound waves interfere.
• The more beats heard,
the greater the difference
between the two sound
sources.
•
•
Used to tune instruments.
http://www.acs.psu.edu/drussell/De
mos/superposition/superposition.ht
ml
Beat Frequency
The beat frequency is the frequency of a
sound which is created from two similar
sound sources interfering.
Example:
If two tuning forks are set into vibration
side to side, and the frequencies of each
are 100Hz and 105Hz, the two waves
will cause constructive and destructive
interference and the beat frequency will
be 5Hz.
Check the math!
Beat Frequency (Hz) = │F1 – F2 │
Where the beat frequency is equal
to the absolute value of the
difference between the frequencies
of the two tuning forks.
The frequencies of the red and
blue sound waves are slightly
different and their constructive &
destructive interference
determines the beat frequency,
shown by the green wave.
Doppler Effect
• When either a
sound source is
moving or a person
hearing a sound
source is moving,
there is a perceived
shift in frequency for
the listener.
• Higher perceived
frequency for
approaching, lower
perceived frequency
for leaving.
What
do I
hear?
What
do I
hear?
Simulations
•
•
•
•
•
http://www.youtube.com/watch?v=eo_owZ2UK7E
http://www.youtube.com/watch?v=h4OnBYrbCjY
http://www.youtube.com/watch?v=Ude8pPjawKI
http://www.youtube.com/watch?v=17tqXgvCN0E
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600:
:/sites/dl/free/0072482621/78778/Doppler_Nav.swf
::Doppler+Shift+Interactive
• http://www.youtube.com/watch?v=uENITui5_jU