c 11 sound propagation

8/12/2019 C 11 Sound Propagation

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Sound PropagationReflection, refraction,

diffraction


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What do we know about soundpropagation?

Speed of sound in air

Speed of sound insolids/liquids/gases

343 / 0.6*( 20) /v m s T m s Sequences

of compressionand rarefaction

v f


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Classification

Growing frequency

20 Hertz

20 000 Hertz=20kHz

Audible range3000 Hzbest hearing

Infra sound

Ultra sound

Growing

Wave length?

Earthquakes, heavy traffic

Medical imaging, dogwhistles, bats


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Wave lengths of the audible range

20 kHz:

20 Hz:

20000 340 /

340 /0.017 1.7

20000

v f Hz m s

m sm cm

Hz

20 340 /

340 / 1720

v f Hz m s

m s m Hz

Width ofa finger

Width of

a house

Objects in our environment are of the same order of sizeas the wave length of sound waves.


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How can we represent sound inspace?

Surfaces of equal compression = planes

Direction ofpropagation

Wave fronts

Rays

Plane waves


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How can we represent sound inspace?

Direction ofpropagation

RaysSurfacesof equalcompression= spheres

Sphericalwaves

How many raysare there?

Where doyou measure

the wavelength?


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ComparisonPlane waves spherical waves

Parallel raysRadial rays

Wave fronts are planes Wave fronts are spheres

Amplitude is constant Amplitude diminisheswith distance from source

Rays are perpendicular to wave frontsRays straight lines


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Waves encountering a surface

Will all these raysbe reflectedback to the person?

Can the blue person hearthe echo?

Reflection


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SpecularReflection


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DiffuseReflection


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How can the two people hear eachother?

Each of the rays traveled different lengths of way

Each of the rays used a different amount of time


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Variable speed of soundCool air = low speed

Warm air = high speed

Wave front

Plane waves atconstant speed

Rays are bent awayFrom surface!

Refraction

Wave fronts if the air iswarmer at the ground


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Variable speed of sound

Cool air = low speed

Warm air = high speed

inversion

Rays are bent towardsurface!

Wave fronts if the air iscooler at the ground

Refraction


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Variable speed of sound

wind

sound

Resulting motionof sound waves

Resulting motionof sound waves

sound

wind

The rays are bentupward upwind of

the source.

The rays are bentdownward downwind of

the source.

Refraction


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Reflection and refraction

Reflection: At solid obstacles, a sharp change of

direction Echo, ringing effect in halls

Refraction: Inhomogeneous speed, gradual change

of direction Air layers with different temperatures,

windReflection is of more importance to us than refraction.


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Why can we hear around a corner?

Reflection ?


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Sound waves at obstaclesTop view:

Diffraction


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Diffraction at small openingSmall: d


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Diffraction at large openingSmall: d>> Wavelength small compared to opening

Shadow zone

Shadow zone

Diffraction bendsthe wave frontsonly lightly at

the edges of a large

obstacle.


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Where can we observe diffraction?

Speak to a person, but not directly: Mouth: 5 cm


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Outdoor Music

Problems: Waves propagate away from source (no

wall reflections) Deadness (no overlap from secondary

reflections) Uneven distribution over a large

audience


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Possible solutions

Shell behind the performers

Audience


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Possible Solutions

Roofed outdoor pavilions:

Traps sound

Not good for outside audience


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Possible Solutions


Helps audience

Band members can hardly hear each other


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Possible Solutions


compromise

Okay for band and audience


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PHYSICS O F SOUN D


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What is Sound?

The sensationresulting from

stimulation of theauditorymechanism by airwaves or other

vibration


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Graphic fr om Jay Rose website athttp://www.dplay.com/book/sample.html

Source of vibration(such as vocal folds)

Source of energy ( suchas lungs)

A medium (to carry thevibration, such as air)

A receiver (such as the

human ear)

Requirements For Sound...


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What is Noise?

Any unwantedsound

Varies fromperson toperson!


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Transmission of

SoundSound travels in waves, leaving point oforigin in a spherical pattern (in air) series of compressions and rarefactions

Usually depicted as a sine wave One complete vibration cycle, 360 degrees

of motionSpeed of Sound increases with density of the

medium 1100 ft/second in air 4500 ft/sec in water 15,000 ft/sec in steel
http://www.digital-recordings.com/hearing-test/ht-products.html


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Horizontal Axis : time in seconds Vertical Axis : molecular movement Compression : upward movement Rarefaction : downward movementAmplitude: height of wave; intensity

The Sine Wave (Pure Tone)


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FrequencyPitch/Hz

Perceived as Pitch . Equal to the number ofcomplete cycles that occurin one second. one cycle = one

compression and one

rarefaction.Measured in Hertz (Hz).


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Human Hearing

Human range: 20-20,000 Hz

Human ear is most sensitive inthe 1,000 - 4,000 Hz range.Less sensitive in lower

frequencies.HL Scale was developed &normalized to represent humanhearing.


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IntensityLoudness/dB

Perceived as Loudness. Intensity is expressed as the soundpressure level (SPL), which is a functionof distance the vibrating object isdisplaced (amplitude), which depends onenergy applied.Measured in decibels (dB). One dB is

1/10 th of a bel.Decibels are logarithmic units. Thereference used is .0002 dynes/cm2 ,roughly the smallest pressure that will

move the TM.


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Intensity (cont.)

Why logarithms?To compress the very large range ofpressure our ears can hear in to asmall range of numbers forconvenience.0-140 dB represents a sound

pressure range of 1:1,000,000,000units (a ratio of 10 million to 1!)


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Intensity(cont.)

0 dB is typically the softest volume thatcan be heard, but sound energy is alsopresent below 0 dB.Human intensity range is 0-140.140 dB is the threshold of pain.170-180 dB causes tissue damage.

180 dB+ can cause death!


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INVERSE SQUARE LAW

Doubling the distance from asound source decreases intensityby 6 dB.


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Doubling the Noise Source

A combination of two differentnoise sources of equal loudnesswill increase the intensity by 3dB For example, if noise source A is

93 dBA and noise source B is 93dBA, the combined result of A and

B is 96 dBA.


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DurationTime

Perceived as Time . Can last from thousandths of a

second, to several hours or allday!Occupational noise exposurevaries over time.Can be constant or intermittentwith continuous (steady-state)or impulse noise.


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SpectrumQuality

Perceived as the Quality of sound. Varies from a simple puretone to a complex mix ofmany frequencies andintensities; such as thehuman voice.Range is infinite.

d l


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Hazardous Noise LevelsDefined As

Continuous or steady state noise > 84dBA Generator, Aircraft Noise, etc.

Impulse/Impact noise > 140 dB peakSPL Explosions or weapons fire Two or more objects hitting together

Intensity and duration are the two mainfactors that determine if a particularsound is hazardousIf it is loud enough for long enough,most people will suffer hearing loss.

Often takes many years!


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Sensitivity of the Human Ear(Review)

Frequency Range: 20 - 20,000 HzIntensity Range: 0 - 140 dB SPL Referred to as the dynamic range

Sounds >140dB lose tonal qualityPrimary speech frequencies: 500 -4000 Hz Frequencies above and below add quality to

speech, but little intelligibility Consonant Sounds Primarily high freqs,

convey 80% of meaning of speech Vowel Sounds Primarily low freqs, convey

80% of energy of soundsThreshold = The lowest intensity thatthe human ear can hear


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ANY QUESTIONS?

oun aves an


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oun aves anHearing

Standard 8-6.5Explain hearing in terms of the

relationship between sound wavesand the ear.


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Three Basic Parts of the Ear

Outer Ear

Funnels sound waves or collectswaves

Middle Ear

Transmits the sound waves inward

Inner Ear

Converts the sound waves into a format that your brain canunderstand.


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Three Basic Parts of the Ear


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Outer ear (sound collector) Sound waves are gathered by the

outer ear.

Made up of the ear, the ear canal,

The outer ear is shaped to helpcapture the sound waves (energy

transferred in particles of air) andsends them to the ear canal, whichtransfers them to the eardrum.

Middle ear (sound amplifier)


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dd e ea (sound amplifier) The middle ear amplifies sound waves. It consists of the eardrum, which is a small,

tightly stretched, drum like membrane. The vibrations of air particles cause the

eardrum to vibrate.

-Contains the three smallest bones inthe human body.

Hammer, Anvil Stirrup


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-Vibrations from the eardrum are transmitted to thethree small bones which transmit the vibrations tothe inner ear.

Inner ear (converts sound waves so


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(converts sound waves sobrain can understand) The inner ear transmits vibrations from

the bones of the middle ear to a cavityfilled with liquid ( cochlea ).

Vibrations in the liquid cause tiny hairs to

vibrate.- The tiny hairs in the inner ear vibrate as the liquid vibrates.

- The vibrating tiny hairs transmit the energy to nerves attached to the hairs.

- The nerve impulses are transmitted to the brain and interpreted as hearing.


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How we hearSound is collected by the visible part of the ear and

directed through the outer ear canal.The sound makes the eardrum vibrate, which in turn causes a series

of three tiny bones (the hammer, the anvil, and the stirrup) in themiddle ear to vibrate.

The vibration is transferred to the snail-shaped cochlea in the innerear.

The cochlea is lined with sensitive hairs which trigger the generation of nervesignals that are sent to the brain.


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d d h


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Sound and PitchPitch distinguishes between the highness

and lowness of a sound.The pitch of a sound depends on thefrequency of a sound wave.

The keyfarthest to theleft on thepiano isattached to thelongest string.This key playsthe note withthe lowest

pitch.

L Pi h


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Low PitchLow Pitched sounds: Vibrations follow each other slowly (low

frequency) Low pitch = Low frequency

Examples: Tubas, base piano keys andengines of heavy trucks.

Hi h Pi h
http://www.purdue.edu/UNS/images/tuba.hail.jpeg


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High PitchHigh Pitched sounds: Vibrations follow each other more

rapidly (high frequency) High pitch = High frequency

Examples: Ambulance as it passes,birds singing and smoke alarms.


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VOLUME WHAT IS IT?


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Sound waves with large amplitudes push on theeardrum with more force and are heard as loudsounds.

Sound waves with small amplitudes push on theeardrum with less force and are heard as softsounds.

VOLUME WHAT IS IT?


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IN YOUR JOURNAL, ANSWER THESE QUESTIONS IN A


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PARAGRAPH FORM.

1. Explain the difference between PITCH and VOLUME. Be

sure to include information on what is pitch and howsound waves travel. (use the words frequency andamplitude in your info)

2. In a step-by-step format, if you heard a lion roar right

now, explain how the sound ends up recording inyour brain. Start with sound waves traveling throughthe air and hitting your ear.

FINISH THIS ASSIGNMENT


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What is an Audiologist?

A professional holding a Mastersdegree in Audiology, as well as aprofessional license or certification,who is educated in the areas ofhearing measurement, hearingdisorders, aural rehabilitation,

amplification, & hearing conservation Otolaryngologist ~=

Opthalmologist Audiologist ~= Optometrist


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Who Needs Audiologic Testing?

Infants, children, and adultspeople known to be at risk throughgenetics, noise exposure (ongoing orepisodic), oto-toxic drug exposure,aging, related health issues ortrauma, those who are concerned

about difficulties hearing (orfriends/family are concerned abouttheir hearing)

age = birth - 130 years

The Basic (Adult)


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The Basic (Adult) Audiologic Evaluation

history, reason for referralotoscopytympanometrystapedial reflexespure tone audiometry

air and bone conduction; maskingspeech testing (speech audiometry)


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Tympanometry

tympanometry = an objectivemeasure of eardrum compliancechange as air pressure is varied inthe external ear. An assessment ofeardrum mobility. Also calleddynamic compliance

tympanometric curve = pressure-compliance function


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The Tympanogram

Measured on an impedance bridge A tympanogram will give anindication of the status of the middleear, in terms of compliance is the middle ear system stiff or floppy

what is the pressure in the middle earspace

is the eardrum intact

Tympanometric Norms


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Tympanometric Normsfor Compliance

typically ~ 0.3 cc - 1.5 cc WNL foradults; ~ 0.2 - 1.0 cc for childrenlower than this indicates highimpedance, higher than this indicateshigh compliance low compliance may indicate middle ear

effusion or stiffening (otosclerosis) high compliance could indicate TM

scarring (flaccid monomeric areas),ossicular discontinuity

Tympanometric Norms


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Tympanometric Norms -from Margolis &Heller, 1987

Compliance Vol.Width

(mmho or cc) (cc) (daPa) ADULTS0.3 - 1.4 0.6 - 1.5 50 - 110(X = 0.8) (X=1.1) (X= 80)

CHILDREN (age 3 - 5 years)0.2 - 0.9 0.4 - 1.0 60 - 150(X = 0.5) (X = 0.7) (X= 100)

Liden Jerger Classification


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Liden-Jerger Classificationof Tympanometry

categorical classification oftympanogramsthe most commonly used ofclassification systems; uses

alphabet category names

normal tympanogram (normalcompliance, pressure,morphology) is Type A


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Type A with Subscript

Type Adeep (Ad) denotes atympanogram with a peak and normalpeak pressure, but increased

compliance e.g. peak pressure + 15 daPa, compliance

1.9cc

Type Ashallow (or As) denotes atympanogram with a peak and normalpeak pressure, but reduced compliance

e.g. peak pressure - 25 daPa, compliance


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The Flat Tympanogram

A flat or type B tympanogram canindicate occlusive obstruction in the ear canal

look for smaller EAC volume; otoscopy a TM which is not moving due to high

middle ear impedancelook for normal EAC volume; otoscopy

a perforated TMlook for large volume; otoscopy

Type C Tympanogram


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Type C Tympanogram- Negative Pressure

When peak pressure is lower than -150 daPa this is a Type Ctympanogram

indicates negative middle ear pressure;usually associated with eustacian tubedysfunction

compliance may be normal or reduced type C can be concomitant with, a

precursor to, or occur during resolution of

middle ear effusion

Stapedial Reflexes


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Stapedial Reflexes(aka Acoustic Reflexes)

Loud acoustic stimulus will causebilateral contraction (reflex) ofstapedius muscles

measured on an impedance bridge loud stimulus delivered to one ear,can measure reflex response on theipsilateral or contralateral ear -measurement of both ipsi and

contra gives best info


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Acoustic Reflex Pathways

START: outer ear -> middle ear ->inner ear -> VIII nerve -> cochlearnucleus -> ipsilateral superior

olivary complex THEN IPSI - ipsi facial nerve - > ipsi middle

ear OR

CONTRA - contra superior olivarycomplex -> contra facial nerve ->contra middle ear

Stapedial Reflexes


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Stapedial Reflexes(aka Acoustic Reflexes)

use to detect non-organic hearingloss, investigate facial nervefunction, investigate possible

retrocochlear pathologyreflex can be also be absent due tomiddle ear dysfunction or severe

hearing losslook at reflex threshold normscompared to hearing levels


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Reflex Decay

reflex decay test - present stimulustone 10 dB higher than the patientsreflex threshold for 10 seconds; 500

or 1000 Hz stimulusmeasure the amplitude of the reflexfor 10 seconds, if it is reduced 50%

or more in this time period this is reflex decay

suggestive of retrocochlear pathology


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Pure Tone AudiometryTypically tested frequencies include 250Hz - 8000 Hzhumans can hear ~ 20 Hz - 20 000 Hzbut this tested range of frequencies isthe area of our most sensitive hearingand the frequencies most used inhuman speechmay include ultra high frequency testing(>8000 Hz) if monitoring high riskindividuals (noise, cisplatin exposure

etc.)


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Pure Tone Audiometry

A calibrated audiometer is requiredto ensure that the presented soundsare the proper frequencies and

intensitiescalibrated earphones required todeliver the sounds

quiet testing area required to ensuredetection of sounds is not masked


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Earphones

Earphones are sound transducersCommon styles or earphones include supra-aural earphones circumaural earphones insert ear phones

bone conductiontransducer/headbandspeakers for sound-field presentation


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Advantages of Insert Earphones

reduces chance of collapsing earcanalsbest reduction of environmentalnoiseimproved comforthygiene - usuallydisposable/cleanable tipsincreased inter-aural attenuation less need for masking


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Pure Tone Testing

Typically used protocol is abracketing technique, beginning at30 dBHL when thresholds unknown,

or ~10 dB above known thresholdsif no response at 30 dB, go to 50 dBbracket 10 down & 5 up e.g. response at 30, go to 20, response

at 20, go to 10, no response at 10, goto 15; recheck 2-3x


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Pure Tone Testing

good idea to test better ear firstif there is an asymmetry in hearingof over 60 dB when using insertphones, or 40 dB using supra-auralphones, you may have problems withcrossover and inadvertently

stimulate the non-test ear inter-aural attenuation ~60 dB w/ insert

earphones, ~ 40 dB w/ supra-auralheadphones


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Crossover

E.g. - thresholds of 10 dB left andthresholds over 50 dB right willrequire masking w/ supra-aural

headphonese.g. thresholds of 10 dB left andthresholds over 70 dB right will

require masking with insertearphonesif you do not mask, the sound will

cross over via bone conduction


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Crossover

To prevent getting responses fromthe non-test ear in these situationsyou must use masking noise

for pure tone testing use narrowband noisefor speech testing use speechweighted noiseremember crossover is by boneconduction even if stimulating via air

conduction

k


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Masking

Various equations used - examplehereFor masking for air conduction threshold of non-test ear, plus 15 dB want to plateau 15 dB to ensure real

threshold

ideally want 30 dB effective maskingremember that masking can also crossover, so you dont want to overmask andelevate threshold of test ear- remember

-

k l


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Masking Example - AC

E.g. threshold left ear 10 dB, right75 dBbegin with masking left 25 dB,present tone again right - if responseobtained from right, increasemasking 5 dB, if no response,

increase presenting level to test earby 5 dBfollow this until you are able to

increase masking three times in non

B C d i


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Bone Conduction

Bone conduction testing uses a vibratingsound generator held to the head tostimulate the inner ear ~ directly

bypasses outer and middle ear systems usually test 250 or 500 - 4000 Hz with BCusually use pure tone stimulitypical placement on mastoid, (nottouching pinna) can use forehead, teeth,nose

B C d i


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Bone Conduction

Use bone conduction when airconduction thresholds are elevated &want to differentiate b/w conductive

and sensorineural hearing lossconductive hearing loss - hearingloss due to pathology of outer or

middle ear systemsAC thresholds elevated, BCthresholds WNL = conductive hearing

loss

Ai B G


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Air-Bone Gap

The difference b/w the AC and BCthresholds is called the air -bonegap, or the conductive component

e.g. AC threshold 45 dB, BCthreshold 5 dB air- bone gap, or conductive

component 40dB this indicates normal function of theinner ear and auditory CNS, problem

OE or ME

C d i H i L


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Conductive Hearing Loss

Conductive hearing loss associatedwith otitis media

otitis externa TM perforation ossicular discontinuity

otosclerosis occluded ear canal/stenosed ear canal

S i l H i L


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Sensorineural Hearing Loss

if elevated AC and BC thresholds arethe same (or very close, 5 dB,together) then the hearing loss is

sensorineurale.g.AC threshold 45 dB, BC threshold45dB

OR AC = 45 BC = 40 no air-bone gap, bypassing the OE and

ME does not improve threshold, so

hearing loss is sensorineural - due to

S i l h i l


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Sensorineural hearing loss

Called sensorineural since can besensory or neural: typically sensory,due to IE/cochlea

popular but incorrect, nerve deafness Sensorineural hearing loss associatedwith

noise exposure -retrocochlearpathology

aging -illness (e.g.meningitis)

ototoxic drugs -labyrinthitis

Mi d H i L


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Mixed Hearing Loss

if there is an air-bone gap, but theBC thresholds are not WNL, then it isa mixed hearing loss

the degree of hearing loss is partlydue to OE or ME and partly due to IEe.g AC threshold 75 dB, BC 40 dB air-bone gap 35 dB, BC threshold

elevated out of normal range (>25 dB)

Mi d H i L


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Mixed Hearing Loss

MHL has a component of CHL andSNHLMixed hearing loss can be associatedwith: otosclerosis SNHL with otitis media,

SNHL with cerumen occlusion SNHL with TM perforationSNHL with overlay of etc. etc. etc.

post-surgical e.g. cholesteatoma

S h R ti Th h ld


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Speech Reception Threshold

SRT - lowest dB HL at which (closedset) speech can be understoodusually obtained by presentingdescending levels of spondaic words(spondees) until only 50% score isobtained

use a list of 10-15 familiarized wordsspondee - two syllable word withequal emphasis on both syllables

(e g hotdog)

S h R ti Th h ld


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Speech Reception Threshold

SRT is usually within ~ 6 dB of thepure tone average (PTA = averagethreshold using 500, 1000, and 2000

Hz)if hearing loss is steeply sloping orhas a notch SRT may be lower

than PTA, closer to best threshold quick reliability check - if SRT betterthan thresholds would indicate - ?

test validity

S h Di i i ti T ti g


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Speech Discrimination Testing

Present a list of publishedphonetically balanced words, usually25 - 50 words at a level allowing

good audibility and comfortusually ~ 35 - 40 dB over PTA/SRTNU-6, W-22

PBK for kindergarten age children modify for special needs (board,write etc.)

Hearing Sensitivity


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g yvs. Hearing Clarity

speech discrimination testing givesan idea about the clarity of hearing patients with identical audiograms(thresholds/sensitivity) may differsignificantly in their functionalauditory abilities depending on their

speech discrimination abilitiesunusually poor or asymmetric

discrim can suggest retrocochlear

pathology


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Young Children


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Young Children

Age ~ 2 1/2 - 5 years use playaudiometry usually with earphones, condition child to

respond to perceived sounds with a playresponse such as dropping a block in abucket or putting a sticker in a bookcan usually accomplish some speech

testingchildren/adults with younger functionalages can be tested in this manner as well

Amplification?


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Amplification?

people with hearing loss affecting thefrequency/intensity ranges of spokenlanguage will often benefit from

amplification (hearing aids or othervarieties of amplification)good speech discrimination allows

better amplified performanceensure appropriate hearing aidprescription

Other Audiologic Tests


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Other Audiologic Tests

ABR/BAERECOGOAEsCAP testingtinnitus counselling

Re Cap


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Re-Cap

otoscopytympanometrystapedial reflexespure tone audiometry air and bone conduction; masking

speech testingother tests as needed to follow up

Abbrevations Used


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Abbrevations Used

EAC = external ear canalWNL = within normal limitsTM = tympanic membrane (eardrum)SRT = speech reception thresholdPTA = pure tone average

OE = outer earME = middle ear

Abbrevations Used


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Abbrevations Used

SNHL = sensorineural hearing lossCHL = conductive hearing lossMHL = mixed hearing lossABG = air bone gapAC = air conduction

BC = bone conduction

c 11 sound propagation

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