Audition Flashcards
How do sound waves form?
object vibrates, compressing air and withdrawing it creating pressure waves of compressions and rarefactions
What is the relationship between frequency and pitch?
log relationship
double frequency increases pitch by 1 octave
what is the relationship between amplitude and loudness?
double amplitude increases loudness by 6 dB
What are broadband vs narrowband sounds?
broadband: contain energy across a large range of frequencies
narrowband: most energy concentrated within a small range of frequencies
describe the structure of the outer ear
composed of the cartilaginous pinna + external auditory canal
it is separated from the middle ear by the timpanic membrane
what is the function of the outer ear?
collects and funnels sound
filters sounds, with some features being attenuated and some amplified, depending on the direction from which the sound enters the ear
which frequencies are most boosted by the pinna?
sound with frequency 2-4kHz
How can you discern where sounds come from?
sounds off to one side arrive earlier at one ear than the other and are louder (ITDs and ILDs)
What is the composition of the middle ear?
air filled cavity between timpanic membrane and the inner ear, connected to the back of the throat
what is the function of the middle ear?
transmit sound from timpanic membrane to inner ear in a way that minimises the loss of energy
how does the middle ear accomplish the transmission of sound from air to water?
impedance matching
what is acoustic impedance?
[measure of opposition to acoustic flow]
a measure of the opposition that a system presents to acoustic flow resulting from an acoustic pressure applied to it
why is impedance matching necessary in the middle ear?
the acoustic impedance of water = higher than air so water requires more energy to vibrate it using sound waves
amplification is required
how does the middle ear achieve impedance matching?
collects the sound pressure of a large area of the timpanic membrane (60mm^2) and concentrates it on the much smaller area of the stapes (3mm^2)
the lever arm of the malleus is longer than the incus, causing a further pressure increase of 1.3x
what is the order of transmission of vibration from the eardrum to through the ossicles?
eardrum -> malleus -> incus -> stapes -> oval window of inner ear
how do the ossicles protect the ear from continuous loud sounds?
stapedius reflex
there are 2 small muscles (stapedius and tensor tympani) connected to the malleus and stapes that, when they contract, reduce the mobility of the ossicles
they can transmit less of the vibration from the eardrum to the inner ear
why can the ossicles not protect the ear from sudden loud sounds
the reflex is too slow
what is the composition of the inner ear?
fluid filled chambers
semi-circular canals = vestibular system
cochlea = coiled tube enclosed in bony shell
what happens to the frequencies detected when the source of the sound is 45 degrees above the plane of the ear?
lower frequencies amplified more
higher frequencies attenuated
differences are large enough to for us to use them to localise sound along elevation dimension (spectral cues)
what are the 2 fluids of the cochlea?
what else does the cochlea contain?
endolymph and perilymph
very sensitive neuroreceptors : hair cells
Where is the perilymph found?
scala vestibuli and scala tympani
what is the composition of perilymph?
contains Na+
where is the endolymph found?
scala media
describe a cross section of the cochlea
top compartment of perilymph = scala vestibuli, Na+
Reissner’s membrane
middle compartment of endolymph = scala media, K+, +80mV
Basilar membrane
bottom compartment of perilymph = scala tympani, Na+