Range of human hearing, Loudness, Decibel scale and Doppler Effect.

Range of human hearing,
Loudness, Decibel scale and
Doppler Effect.
Range of voices & hearing in animals
The human ear is built
to sense pressure
changes above and
below normal
atmospheric pressure.
It will sense changes
in the 20Hz –
20,000Hz range.
(# 1 to 5)
Ultrasonic and infrasonic sounds
6 - Frequencies above 20
kHz (20,000 Hz) are
called Ultrasonic
frequencies,
Dogs, cats, bats and
dolphins can hear these
sounds
7 - Frequencies below 20 Hz
are called Infrasonic
frequencies.
Whales, elephants,
hippopotamuses, rhinoceros,
giraffes and alligators are
known to use infrasonic sound to
communicate over distances—up
to hundreds of miles in the case
of whale sounds.
How do we measure the volume
of a noise??
8 - Sound intensity is measured
in watts / m2 (power/area)
9 - The minimum sound intensity the
average human can hear is
1x10-12 W/m2
10 - A sound that is 10 times louder than this minimum
would be is 1x10-11 W/m2
11 - A sound that is 100 times louder than this minimum
would be is 1x10-10 W/m2
12 - The intensity of sound varies inversely with the
square of the distance from the sound source.
Jim and Jane go very early to a
concert with festival seating.
Jim sits 20 feet away from the
speakers. Jane thinks this is way
too close and decides to move
back to 80 feet away from the
speakers. After the concert
Jane tells Jim “I told you it was too loud that close” but
Jim’s ears are ringing so badly he temporarily can’t hear her.
How many times louder was the sound Jim heard?
Answer : The intensity of sound varies with the
square of the distance from the sound source.
Moving four times closer increases the sound
intensity by 42 or 16 times
Inverse square relationship
#13
1/4
1/9
Sound intensity is measured in watts / m2
this is not a very convenient scale for many people because
the numbers are so small and require use of exponents
14 - For example the sound intensity for a typical library is
10-8 W/m2
Decibel (dB)Scale – sound intensity level
15 - The decibel scale is a logarithmic scale of sound
intensity level (pressure) on the ear drum.
16 - With a logarithmic scale, every increase of 10 decibels
(dB) results in a ten times (10X) increase in pressure on the
ear drum.
Zero dB is considered the minimum sound intensity level
humans are capable of hearing and this is equal to
1x10-12 W/m2
.
Table of sound intensity level (dB) and sound intensity (W/m2)
(#17)
Decibel (dB) Scale
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..
19 - 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.
Some common pressure & dB ratings
Doppler Effect
23 - 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.
24 - There is a higher
perceived frequency for
an object approaching
and lower perceived
frequency for an object
leaving.
What
do I
hear?
What
do I
hear?
Doppler Effect
# 25