MNSR 29 - Sound Amplification Flashcards
Intensity formula
Power/Area
what unit is intensity measured in
Wm-2^
how does sound propagate
it propagates outwards from the source as a spherical wave
Intensity formula including radius
Power/4(3.14)r2^
what is the human ears dynamic range
10-12^Wm-2^ to 1Wm-2^
What unit is used to measure human hearing
Sound intensity level decibel
sound intensity level formula
10log(10)(I/10-12^)
what is the relationship between intensity and distance
intensity reduced quadratically with distance r
will sounds of different frequencies and same intensity sound differently?
yes?
unit of loudness
dBHL or Phon
relationship between unit of loudness and sound intensity level
dBHL = dBSIL multiplied by a function that mimics the frequency sensitivity of the ear
what causes the threshold of audibility to rise with age
Presbycusis
mechanical levers
ossicle
function of ossicle lever
transform low force high amplitude vibrations to low amplitude, high force vibration in oval window.
basilar membrane function
acts as a resonance structure - property of structure to move at a preferred frequency
when the intensity is doubled (in regards to SIL formula) how is the SIL value changed?
the SIL does not double it increases by 3 decibels or dB
if the value of I in the SIL formula is mWm how do you insert it in the formula?
I x10-3
Describe the first mechanism of sound amplification in the ear drum
sound travels from ear canal to tympanic membrane (ear drum) - area of tympanic membrane is half the size of the ear opening. This means sound intensity increases by a factor of 2.
Intensity = Power/ Area
2nd mechanism of sound amplification in the ear drum and ossicles
Ossicles act as mechanical levers to convert vibration in eardrum to vibration in oval window. Decreases amplitude but doubles the force.
3rd mechanism of sound amplification in the ear drum and ossicles
Area of ear drum is 20 times greater than oval window - amplification of intensity is increased by a factor of 20
calculate total amplification gain from the 3 mechanisms of sound amplification in the ear and convert it to 3 decibels.
2 x 2 x 20 = 80 times 19dbSIL
features in cochlea in relation to oval window
round window
basilar membrane(between bone shelf)
bone shelf
helicotrema - tip
the perilymph fluid in the cochlea swings depending on what?
swings at different locations depending on the frequency of the sound
where does the perilymph fluid swing at low frequencies and where does it swing at high frequencies?
Low freq - resonates towards apex
high req - resonates close to oval window
why is sound detected at different parts of the cochlea.
basilar membrane acts as a resonance structure and it has different resonance frequencies depending on that line/
