Ch 3 (MIDTERM) Flashcards
Speed of Sound
343m/s or 1100ft/s
What is speed of sound NOT affected by?
Frequency, wavelength, period
What is speed of sound affected by?
Medium’s density, elasticity
Temperature/altitude
Speed of sound & Elasticity of medium
DIRECT relationship
If medium has high elasticity, more tightly packed, more force repelling each other when compressed, more speed since disturbance is carried onward faster
Speed of sound & Density of medium
INVERSE relationship
If medium has more density, greater mass, slower vibration
Speed of sound & Temperature of medium
Higher temperature, faster sound (more kinetic energy)
Lower temperature, slower sound (less kinetic energy)
Speed of sound & Altitude
Higher altitude, slower sound
Lower altitude, faster sound
Think: higher altitude, colder, slower sound
Periodic Wave
Each cycle takes the SAME amount of time
Pattern, symmetrical
Aperiodic wave
Each cycle takes different amount of time
Asymmetrical noise
Diffraction
BENDING of sound as it encounters a barrier
will either:
a.) pass around barrier
b.) go through a hole
If sound passes around a barrier…
Greater wavelength than barrier, better diffraction, sound wave long enough to wrap around barrier and be heard
Lower wavelength than barrier, lower diffraction, sound wave not long enough to wrap around barrier and not be heard
If soundwave goes through a hole…
Opening acts as the new origin of sound/sound speaker
Head shadow
Wavelength lower than head (higher freq): cannot wrap around, bounces off (reflected)
or, it creates a head shadow where it cannot be heard in both ears because it doesn’t wrap fully around head
Wavelength higher than head (lower freq): wraps around head and can be heard in both ears
Think, whistle vs. horn
2 cues for localization
Intensity
Time of arrival
Higher frequency uses which cue?
Intensity cue
Lower wavelength will not full wrap around head, one ear will hear it louder, that’s where sound came from
Lower frequency uses which cue?
Time of arrival cue
Higher wavelength will fully wrap around head, both ears will hear it at around the same intensity
but one ear would have heard it earlier/faster
Anechoic chamber
Closest we can get to a sound proof room
Barrier with absorbing layer and reflecting layer, increasing transmission loss
Kemar (mannequin for hearing aid)
When sound wave approaches barrier, it can either:
be reflected
absorbed
transmitted
diffract
Incident wave
Sound wave striking object
Coefficient of absorption
Ratio of sound absorbed to sound reflected
Different material are better at absorbing
Materials better at reflecting
Hard, dense
smooth
i.e. window, sound tiles
Materials better at absorbing
Soft, fricative
rough
i.e. carpet
Sound proof room…
More sound absorption, less reflection
no reverberation
good for understanding speech because there is less overlap
Reverberation time
Sound lasts longer due to incident wave reflecting off and going back into eardrum
If sound wave arrives at ear again when its still vibrating, its REVERBERATION
Small distance
Sound never stops
Echo
When sound wave reflected and reaches ear again when ear drums have stopped vibrating
Substantial distance
Sound stops then is heard again
Doppler effect
When something moves towards its compression wave, lower distance between each consecutive wave, higher frequency
i.e. train
as train moves closer, higher frequency
as train moves farther, lower frequency
Sonic Boom
Plane’s doppler effect
As plane reaches the speed of sound, has a barrier of compressed air constantly in front of it
as plan goes faster than speed of sound, leaves behind a trail of compression waves that is heard as sonic boom on Earth
Interference
Combination of waves that can either enhance or delete sound
Constructive interference
Enhances sound
Amplifies it by adding up amplitudes of both waves
Destructive interference
Deletes sound
Waves combine (areas of compression and rarefaction) and decreases resultant amplitude by subtracting both amplitudes
possibility of complete dampening if exact match
