properties of sound Flashcards
what is sound
the propagation of a local perturbation in molecular density
what is ultrasound
extremely high frequency sound (>100 kHz)
advantage: reflects back very detailed information
what is infrasound
extremely low frequency sound (below 5 Hz)
advantage: carries great distances
how is infrasound used by elephants
sound from underground is a sign of danger far away so they don’t move away immediately
if sound is above ground, it signals danger is nearby so they move more quickly
how is ultrasound used by bats
using echolocation and chirping gets more frantic when prey is nearby
what is a free field and does it exist
a place with no echoes, it doesn’t exist
what is the calculation for relative amplitude (dB)
20log10(Pmeasured/Preference)
the decibel measurement is always relative
what is a period
duration of 1 cycle (T)
what is a phase
relative shift between peaks
how do you get noise cancellation
an 180 degree shift; reducing noise when 180 degrees out of phase
what is frequency
cycles per second; reciprocal of a period (f)
f=1/T
what is wavelength
measure of distance
wavelength = Tc
what is c
sound of speed
what does wavelength depend on
medium
what is near field
net displacement of particles
what is far field
no net displacement of particles
what is the doppler shift
object is moving slower than the speed of sound
wavelengths shorter (higher frequencies) in front of moving object
what is the pressure inverse law
pressure decays with distance
how does frequency affect sound absorption
higher frequencies lose energy faster than lower frequencies
acoustic impedance
resistance of a medium to transmitting sound
what is formula of acoustic impedance
Z = pc
Z=acoustic impedance
p=density of medium
c=speed of sound
why does acoustic impedance matter
impedance determines how sound reflects
what does R^2=0 mean
total absorption
what does R^2=1 mean
total reflection
what does R^2 < 1 mean
partial reflection and partial absorption
what does R depend o
ratio of Z2/Z1
greater the difference between medium 1 and 2, greater the reflection
