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.

0 dB to 10dB 0 dB to 20dB

Most people perceive a 10dB increase

in sound level as about twice as loud

as the original level.

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.

A decibel, or one unit of sound (abbreviated as dB,) is used to measure the intensity of a sound wave.

10X10=100 times

greater pressure

than the reference

amplitude.

10 times greater

pressure than the

reference

amplitude.

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

http://www.acs.psu.edu/drussell/Demos/superposition/superposition.html

Beat FrequencyThe 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.

http://dictionary.reference.com/browse/Doppler effect

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.mcgraw-hill.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

http://www.youtube.com/watch?v=eo_owZ2UK7Ehttp://www.youtube.com/watch?v=h4OnBYrbCjYhttp://www.youtube.com/watch?v=Ude8pPjawKIhttp://www.youtube.com/watch?v=17tqXgvCN0Ehttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600::/sites/dl/free/0072482621/78778/Doppler_Nav.swf::Doppler+Shift+Interactivehttp://www.youtube.com/watch?v=uENITui5_jU