DEVIL PHYSICSTHE BADDEST CLASS ON

CAMPUSIB PHYSICS

TSOKOS OPTION I-1THE EAR AND HEARING

IB Assessment StatementsOption I-1, The Ear and Hearing:I.1.1. Describe the basic structure of the

human ear.I.1.2. State and explain how sound pressure

variations in the air are changed into larger pressure variations in the cochlear fluid.

I.1.3. State the range of audible frequencies experienced by a person with normal hearing.

I.1.4. State and explain that a change in observed loudness is the response of the ear to a change in intensity.

IB Assessment StatementsOption I-1, The Ear and Hearing:I.1.5.State and explain that there is a

logarithmic response of the ear to intensity.

I.1.6.Define intensity and intensity level (IL).

I.1.7.State the approximate magnitude of the intensity level at which discomfort is experienced by a person with normal hearing.

IB Assessment StatementsOption I-1, The Ear and Hearing:I.1.8.Solve problems involving intensity

levels.I.1.9.Describe the effects on hearing of

short-term and long-term exposure to noise.

I.1.10. Analyze and give a simple interpretation of graphs where IL is plotted against the logarithm of frequency for normal and for defective hearing.

Objectives:

Lesson Objectives. By the end of this class you should be able to: Describe the basic components of

the human ear Define sound intensity and the

sound intensity scale based on the decibel

Perform calculations with intensity and the decibel scale

Objectives:

Understand how the ear functions Describe how the ear separates

sound according to frequency in the cochlea

State the meaning of the terms threshold of hearing and audiogram

Introductory Video

Macroscopic View of the Ear

Ear is sensitive to sounds ranging from 20 Hz to 20,000 Hz

At 1000 Hz, the ear can pick up sound vibrations that displace the eardrum by 1/10th the diameter of a hydrogen atom

Outer ear Middle ear Inner ear

Eustachian tube serves to equalize pressure Airplanes Scuba Diving

Semicircular canals do not contribute to hearing

Provide us with a sense of balance

The Ear and Balance

Schematic Diagram of the Ear

Figure I1.2, Schematic Diagram of the Ear

Ossicles are three small bones: malleus, incus and stapes – smallest in human body

Purpose is to amplify amplitude of sound waves by a factor of 1.5

Figure I1.2, Schematic Diagram of the Ear

Area difference between eardrum and oval window increases amplification by 13

Total amplification = 20x Acoustic reflex – muscles limit ossicle

movement Does not protect from instantaneous sound

Figure I1.2, Schematic Diagram of the Ear

Cochlea is where hearing takes place Vestibular, Helicotrema and Tympanic

canals (2cm long) Round window is pressure release point

Figure I1.2, Schematic Diagram of the Ear

Scala media or cochlean duct runs between canals

Covered by the basilar membrane Contains nerve endings which convert sound

waves into electrical signals sent to the brain

Figure I1.2, Schematic Diagram of the Ear

Basilar membrane Organ of Corti responsible for converting

vibrations into electrical signals Different parts are sensitive to different

frequency ranges

Mismatch of Impedances

Sound travels differently in different media

In hearing, sound goes from air to the fluid in the inner ear

The term impedance is used to describe the difference in sound in different media

Acoustic Impedance: ρ is density c is speed of sound

cZ

Mismatch of Impedances

When sound transitions to a new media, differences in impedances will cause some of the sound to be reflected

More sound is transmitted when impedances are matched

Impedance before oval window is 450 kg/m2s

Impedance after oval window is 1.5 x 106 kg/m2s

Mismatch of Impedances

Because of the difference in the impedances, the sound must be amplified by the ossicles and by the differences in area between the eardrum and the oval window

Complex Sounds

Complex Sounds

Any periodic function can be written as a sum of harmonic functions

Complex sounds can be decomposed into component frequencies of the harmonic function

This is what is done in the cochlea The sound is then reconstructed in

the brain

Intensity of Sound

Sensation of Hearing

Hearing does not increase linearly with intensity

It is a logarithmic function Increase in hearing is proportional

to the fractional increase in intensity (Weber-Fechner law)

This give us the decibel scale

Sensation of Hearing

An increase of 10 dB equates to an increase in intensity by a factor of 10

I0 refers to the threshold of hearing, 1 x 10-12 W/m2

Frequency Response and Loudness

The normal hearing range is 20 Hz to 20,000 Hz

The threshold of hearing reduces with age

Frequency Response and Loudness The threshold of hearing of 1 x 10-12

W/m2 is based on 1000 Hz Sounds of greater or lesser intensity

may be heard depending on frequency

Threshold of Hearing Curve

Threshold of Hearing

Threshold of Hearing

Hearing sensitivity can best be understood based on resonance in the ear canal

Think of it as a closed-end tube where the fundamental wavelength is 4L

Threshold of Hearing

The length of the ear canal is 2.8 cm

Hzcf

xL

3036112.0

340112.0028.044

Pitch

Subjective How high or low a sound is Primarily determined by frequency,

but also by intensity

Frequency Separation in Cochlea The basilar membrane decreases in

stiffness along its length (35mm) Velocity of sound is high at the

beginning of the canal and drops along the length

Response by the organ of Corti is greatest to sounds that are resonant

Frequency Separation in Cochlea

Frequency Separation in Cochlea

Hearing Defects

Sensory Nerve Deafness Damage to hair cells and neural

pathways Tumors of the acoustic nerve or

meningitis Conduction Deafness

Damage to the middle ear Blockage (full or partial) of the auditory

canal Bone disease to the ossicles

Hearing tested with an audiogram

Hearing Loss

Aging Gently curved with smaller loss in

decibels Damage

More substantial loss, especially in higher frequencies

Required Amplification

40

5.40

0

1016.3

10

log10

45

xxII

xII

II

dB

Audiogram

Steep curve Large high

frequency loss indicates damage due to over-exposure

Aging would show shallow curve, less overall loss

Audiogram

Circles for air Triangles for

bone Gap between

the two indicates a conduction problem in middle or outer ear

Audiogram

When the bone and air graphs nearly coincide, the problem is most likely a cochlear or nerve problem in the inner ear

Hearing Aids

Used for conductive hearing loss where inner ear is still functioning

Amplifies sound within a limited range Mainly the range of human speech Doesn’t work well for much else

Cochlear Implant

For sensory loss in the inner ear Consists of:

Microphone Signal processor to convert sound to

electrical signals Electrodes surgically implanted in the

cochlea Mimics the function of the cochlea

HAD ENOUGH?

OKAY, I HEAR YA!

Objectives:

Lesson Objectives. By the end of this class you should be able to: Describe the basic components of

the human ear Define sound intensity and the

sound intensity scale based on the decibel

Perform calculations with intensity and the decibel scale

Objectives:

Understand how the ear functions Describe how the ear separates

sound according to frequency in the cochlea

State the meaning of the terms threshold of hearing and audiogram

IB Assessment StatementsOption I-1, The Ear and Hearing:I.1.1. Describe the basic structure of the

human ear.I.1.2. State and explain how sound pressure

variations in the air are changed into larger pressure variations in the cochlear fluid.

I.1.3. State the range of audible frequencies experienced by a person with normal hearing.

I.1.4. State and explain that a change in observed loudness is the response of the ear to a change in intensity.

IB Assessment StatementsOption I-1, The Ear and Hearing:I.1.5.State and explain that there is a

logarithmic response of the ear to intensity.

I.1.6.Define intensity and intensity level (IL).

I.1.7.State the approximate magnitude of the intensity level at which discomfort is experienced by a person with normal hearing.

IB Assessment StatementsOption I-1, The Ear and Hearing:I.1.8.Solve problems involving intensity

levels.I.1.9.Describe the effects on hearing of

short-term and long-term exposure to noise.

I.1.10. Analyze and give a simple interpretation of graphs where IL is plotted against the logarithm of frequency for normal and for defective hearing.

QUESTIONS

#1-9Homework

STOPPED HERE ON 4/4/2013