MNSR 29 - Sound Amplification

Question 1

Intensity formula

Answer 1

Power/Area

Question 2

what unit is intensity measured in

Answer 2

Wm-2^

Question 3

how does sound propagate

Answer 3

it propagates outwards from the source as a spherical wave

Question 4

Intensity formula including radius

Answer 4

Power/4(3.14)r2^

Question 5

what is the human ears dynamic range

Answer 5

10-12^Wm-2^ to 1Wm-2^

Question 6

What unit is used to measure human hearing

Answer 6

Sound intensity level decibel

Question 7

sound intensity level formula

Answer 7

10log(10)(I/10-12^)

Question 8

what is the relationship between intensity and distance

Answer 8

intensity reduced quadratically with distance r

Question 9

will sounds of different frequencies and same intensity sound differently?

Answer 9

yes?

Question 10

unit of loudness

Answer 10

dBHL or Phon

Question 11

relationship between unit of loudness and sound intensity level

Answer 11

dBHL = dBSIL multiplied by a function that mimics the frequency sensitivity of the ear

Question 12

what causes the threshold of audibility to rise with age

Answer 12

Presbycusis

Question 13

mechanical levers

Answer 13

ossicle

Question 14

function of ossicle lever

Answer 14

transform low force high amplitude vibrations to low amplitude, high force vibration in oval window.

Question 15

basilar membrane function

Answer 15

acts as a resonance structure - property of structure to move at a preferred frequency

Question 16

when the intensity is doubled (in regards to SIL formula) how is the SIL value changed?

Answer 16

the SIL does not double it increases by 3 decibels or dB

Question 17

if the value of I in the SIL formula is mWm how do you insert it in the formula?

Answer 17

I x10-3

Question 18

Describe the first mechanism of sound amplification in the ear drum

Answer 18

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

Question 19

2nd mechanism of sound amplification in the ear drum and ossicles

Answer 19

Ossicles act as mechanical levers to convert vibration in eardrum to vibration in oval window. Decreases amplitude but doubles the force.

Question 20

3rd mechanism of sound amplification in the ear drum and ossicles

Answer 20

Area of ear drum is 20 times greater than oval window - amplification of intensity is increased by a factor of 20

Question 21

calculate total amplification gain from the 3 mechanisms of sound amplification in the ear and convert it to 3 decibels.

Answer 21

2 x 2 x 20 = 80 times 19dbSIL

Question 22

features in cochlea in relation to oval window

Answer 22

round window
basilar membrane(between bone shelf)
bone shelf
helicotrema - tip

Question 23

the perilymph fluid in the cochlea swings depending on what?

Answer 23

swings at different locations depending on the frequency of the sound

Question 24

where does the perilymph fluid swing at low frequencies and where does it swing at high frequencies?

Answer 24

Low freq - resonates towards apex

high req - resonates close to oval window

Question 25

why is sound detected at different parts of the cochlea.

Answer 25

basilar membrane acts as a resonance structure and it has different resonance frequencies depending on that line/