sound propagation

Question 1

what is global attenuation

Answer 1

frequency spreading loss (freq fading)

Question 2

how does global attenuation affect in air

Answer 2

lose 6dB in pressure per doubling of distance

Question 3

what is pattern loss

Answer 3

receiver of sound may perceive sound differently than what was originally sent out

Question 4

what does plant vibrational attenuation look like

Answer 4

sound is measured at different distances from the sender and there is a resonance frequency at which the plant wants to vibrate at (~2kHz)

Question 5

what is scattering loss

Answer 5

sound can be scattered by irregular surfaces like leaves

sound scattering can cause 2-35 dB attenuation per 100m distance

Question 6

what are boundary effects

Answer 6

in terrestrial environments sound propagates as a direct wave, as a reflected wave off of the ground, and as boundary waves

Question 7

what frequencies can boundary waves be detected

Answer 7

only carry low frequencies and are only detectable when sender and receiver are both close to the ground

created when direct and reflected waves interfere negatively

Question 8

what is the rule of thumb for boundary waves

Answer 8

the shallower the water and the softer the bottom, the higher this cutoff frequency. animals in shallow water must use higher frequencies or none at all

Question 9

in air, temperature goes ___, density ________, and the speed of sound _______

Answer 9

up, decreases, increases

Question 10

relationship of speed of sound in air of temperature vs velocity

Answer 10

as temp increases, velocity increases

Question 11

what happens when sound travels faster in a given medium

Answer 11

when sound travels faster, in a given medium, it loses energy more rapidly

why? because some of this energy is wasted as heat

Question 12

when does sound travel farther

Answer 12

when it travels slower, less energy is wasted

Question 13

in terrestrial environments when does sound propagate further

Answer 13

-when the ground is colder than the air
-when the caller is below the canopy of a higher forest
-when the caller is upwind of the receiver (in front of the wind, relative to receiver)

Question 14

what is sofar channel

Answer 14

zone of low sound velocities that is 1200m deep at mid latitudes (sound fixing and ranging)

Question 15

how does noise affect signals

Answer 15

obscure them

Question 16

how does reverberations affect sound

Answer 16

echoes off of objects en route to a receiver result in different versions of the same signal arriving with very slight delays. this generates distortion in the overall waveform received

Question 17

which birds suffer from reverberation problems and which don’t

Answer 17

birds living in forests suffer from reverberation while birds living in open grassland don’t

Question 18

what factors limit signals

Answer 18

-sound production
-sound absorption
-boundary effects
-refraction
-noise

Question 19

what is the optimal range for birds to receive sound the best

Answer 19

1-4kHz