Sound Propogation Flashcards
What are spherical spreading losses ?
As the distance from the source increases
Acoustic energy is spread over larger areas.
What are energy changes proportional to ?
Sound pressure
Describe the relationship between sound pressure and distance,
As the distance doubles
Sound pressures halves
Sound pressure level drops by 6dB
Air absorbs sound energy
True or False ?
True.
Air particles interact & we superimpose our sound waves onto them.
Which frequencies of sound are more strongly absorbed ?
High frequencies
Which sound frequencies are used for long range signalling ?
Low frequencies as they are less readily absorbed by the air.
Why do birds sing in the morning ?
Layered atmosphere.
Warmer temp further up, sound wave at top travels faster
Will be reflected off the ground
Increasing acoustic footprint
Also decreased predation risk
What is a layered atmosphere ?
Still air layers of different temperatures.
Describe the disadvantage of birds singing in the afternoon,
Layered atmosphere
Warmer temp at the ground
Sound wave will be angled up and away.
Decreasing acoustic footprint
The speed of sound increases with temperature
True or False ?
True,
Sound waves which are warmer travel faster.
Name the species which can communicate over several thousand kilometres.
Humpback Whale
Song is channelled at 700km (no spherical spreading)
Water has low absorbtion.
What does the speed of sound in seawater depend on ?
Salinity, Pressure and temperature
Where in the ocean is speed of sound impacted least ?
at 700m
Where do humpback whales sing ?
At 700m
Song will remain trapped in this depth (no spherical spreading
What is the advantage to the humpback whale of having sound in a disc rather than a sphere ?
Propagates sound on one plane
Lose far less sound per distance
