Pure tone audiometry is used to determine the hearing thresholds of a patient across different frequencies. It involves presenting pure tones through air conduction and bone conduction headphones to measure the softest sounds a patient can detect. The results are plotted on a graph called an audiogram. Interpreting the audiogram can provide information about the type, degree and configuration of any hearing loss. It is an important diagnostic tool but does not assess all aspects of hearing. Masking noise is sometimes used to isolate testing of one ear. Proper technique and interpretation are required to obtain accurate results.

1. PURE TONE AUDIOMETRY
Dr.A.GANESH BALA M.S ENT
ASSOCIATE PROFESSOR
VMMC - KARAIKAL

2. DEFINITIONS
 SOUND- It is a form of energy produced
by vibrating object.
 PURE TONE SOUND- sound produced by
a sine wave at a single frequency.
 FREQUENCY- It is a number of cycles per
seconds & is measured by HERTZ.
 PITCH- It is a subjective sensation
produced by frequency of sound.

3.  INTENSITY- It is the strength of sound which
determines its loudness & is measured in DECIBELS.
 LOUDNESS- It is subjective sensation produced by
intensity.
 HEARING THRESHOLD- The lowest sound pressure
level ,at which under specified conditions, a person
gives a predetermined percentage of correct responses
on repeated trials.(minimum sound that a subject may
hear for a given tone or frequency)
 DECIBEL – 1/ 10 of bel.

4. AIMS
 Whether the subject has any definite auditory
disorders.
 Whether the hearing loss is conductive,
sensorineural or mixed.
 The degree of hearing dysfunction.

5.  The results plotted graphically is called pure tone
audiogram.
 Instrument used to measure is called pure tone
audiometer.
 The range of normal human hearing is 20- 20,000 HZ.
 The graph plotted in x –axis frequency in hertz are
250,500, 1000,2000,4000 & 8000 (cycles per second
).
 In y –axis hearing loss in decibels from -10 to 110 db.
PURE TONE AUDIOGRAM

6. PROCEDURE - AIR CONDUCTION
TEST
Calibration of the instrument.
A reasonably noiseless test environment.
Position of headphones
Instructions to the patient.
Technique of air conduction test- First is Conventional

7. CALIBRATION OF INSTRUMENTS
 ISO – 1964 Specifications for calibration
 Electronic calibration – atleast once in 6 months
 Biological calibration – should be done each day
before the audiometer is used.
 Micro-processor based audiometers are used
nowadays.

8. A REASONABLY NOISELESS TEST
ENVIRONMENT
 Level of Test Environment < Level of Masking
Sound
Cause A Threshold Shift In Normal Hearing
Subject
 ISO / DIS 8253 – maximum permissible ambient
noise for the different frequencies required for air and
bone conduction tests.
 Air Conduction - 25 - 30 db
 Bone Conduction - 10 -15 db

9. POSITION OF HEADPHONES
 Diaphragm of headphone – over the opening of
EAC ( >15 db)
 No wax , discharge , cotton in EAC
 Collapse of ear canal – supraaural earphones /
headphones are placed over ear – Cause small Air-
Bone gap.

10. INSTRUCTION TO PATIENT
 Test needs should be thoroughly explained.
 Little time spent in getting acquainted with the
patient and his problems prior to the test , helps in
establishing a rapport.

11. TECHNIQUES - CONVENTIONAL
METHOD
 A detailed clinical history & examination should
precede the test.
 Better ear is tested first, start with 1000 Hz & then
2k,4k,8k,10k,then 500 , 250 Hz.
 If difference is more than 20 db then half octaves is
to be tested.
 Tones are lowered in 10 db steps and increased in
5 db steps.

12. TECHNIQUES - CONVENTIONAL
METHOD
 Second ear – may start with last frequency used to
test the first ear ( no need to start with 1000 Hz )
 5-up-10-down ( tones are lowered in 10 db steps
and increased in 5 db steps )

13. STEP 3 - RAISE SOUND BY 10 db (i.e 60 db)
RESPONSE PRESENT –
PROCEED TO STEP 5
RESPONSE ABSENT –
PROCEED TO STEP 4
STEP 2 - RAISE SOUND BY 20 db (i.e 50 db)
RESPONSE PRESENT –
PROCEED TO STEP 5
RESPONSE ABSENT –
PROCEED TO STEP 3
STEP 1 - START WITH 30 db HL SOUND
RESPONSE PRESENT –
PROCEED TO STEP 5
RESPONSE ABSENT –
PROCEED TO STEP 2
METHOD OF ASHA

14. STEP 6 - RAISE SOUND BY 5 db
RESPONSE PRESENT
– PROCEED TO STEP
7
RESPABSENT - RETURN TO STEP 6 ,
I.E RAISE SOUND BY 5 DB TILL
RESPONSE IS PRESENT THEN
PROCEED TO STEP 7
STEP 5 – LOWER SOUND BY 10 db
RESPONSE PRESENT – REPEAT
STEP 5 , I.E AGAIN LOWER TILL
RESPONSE ABSENT THN
PROCEED TO STEP 6
RESPONSE ABSENT –
PROCEED TO STEP 6
STEP 4 – RAISE SOUND BY 10 db STEPS TILL
RESPONSE PRESENT AT
A PARTICULAR STEP –
PROCEED TO STEP 5
MAXIMUM OF AUDIOMETER
BUT NO RESPONSE
OBTAINED – RECORD AS NO
RESPONSE OBTAINED
METHOD OF ASHA

15. METHOD OF ASHA
STEP 7 – 6 STIMULI PRESENTED AT SAME LEVEL
3 RESPONSE CORRECT –
RECORD AS HEARING
THRESHOLD FOR THAT
PARTICULAR FREQUENCY
LESS THAN 3 CORRECT
– RETURN TO STEP 6
STEP 6 – SOUND RAISE BY 5 DB
RESPONSE PRESENT –
PROCEED TO STEP 7
RETURN TO STEP 6 , I.E RAISE
SOUND BY 5 DB TILL
RESPONSE IS PRESENT THEN
PROCEED TO STEP 7

16. BONE CONDUCTION
COMPRESSIONAL / DISTORTIONAL BONE CONDUCTION
Vibratory energy ( Sound ) reaches the cochlea
Alternate expansion and compression of cochlear shell
(due to flexiblity of round window memb and cochlear
equeduct)
Movement of cochlear fluid
Displacement of basilar membrance
Leads to changes that result ultimately in sound being
heard

17. BONE CONDUCTION
INERTIAL BONE CONDUCTION
Vibratory energy ( Sound ) strikes the skull
Sets the skull into vibration
Ossicles in middle ear lag behind & do not move due to
inertia of ossicles
Sets up relative motion b/w footplate of stapes & cochlear
fluid deep to oval window
Vibration of cochlear fluid

18. BONE CONDUCTION
OSSEO-TYMPANIC BONE CONDUCTION
Vibratory energy ( Sound ) reaches the skull
Skull starts vibrating
Sets into vibration the column of air in EAC
Partially transmitted to TM
Thro’ the ossicles in the middle ear
To Cochlear fluid of inner ear ( like air - conducted sound)

19. PROCEDURE - BONE
CONDUCTION
 Calibration of instrument
 Reasonably noiseless test environment
 Placement of bone conduction vibrator
 Instructions to the patient
 Technique – same as air conduction.

20. PROCEDURE - BONE
CONDUCTION
MASTOID PLACEMENT OF BONE VIBRATOR
 Tension of spring metal headband over the mastoid -
500 gm / sq.cm
 Should be free of hair as possible , should not touch
the pinna
 A constant sound is given and B.C vibrator is moved
over the mastoid – till a point of maximum
sound is heard.
When ears without any conductive pathology are
covered by earphones or occluded by any
apparatus , there is a false increase in the bone

21. PROCEDURE - BONE
CONDUCTION
FRONTAL PLACEMENT OF BONE VIBRATOR
 Adv : less variation of the amount of tissue b/w bone
conduction vibrator and skull bone & lesser
artifacts
 Correction factor has to be subtracted
15 db for 250 - 500 Hz
10 db for 1000 - 4000 Hz

22. LEFT RIGHT
AIR CONDUCTION SOUNDS ARE HEARD
UNMASKED
MASKED
BONE CONDUCTION
UNMASKED
(MASTOID)
MASKED
MASKED (
FOREHEAD)
AIR CONDUCTION SOUNDS NOT
HEARD
UNMASKED
MASKED
BONE CONDUCTION
UNMASKED
(MASTOID)

23. MASKING
Noise presented to the non-test ear to prevent it from
responding to a signal presented to the test ear
WHEN TO MASK ?
- All bone conduction
- When interaural attenuation is more than 45 db .
- When air conduction more than 45 db HL
- Cross – hearing in air conduction if
AC ( test ear ) – BC ( non test ear ) > IA
HOW TO MASK ?
For bone conduction
- minimum masking = B t +( A m – B m)
For air conduction
- minimum masking = At – 40 + (Am – B m)
Maximum masking = B t + 45

24. MASKING
STEP 2
Obtain unmasked threshold by AC in both ears
STEP 1
For BC tests always mask the contralateral ear .
For AC tests always mask contralateral ear if test ear is
comparatively poorer ear & sounds of 45 db or more are
being used for the AC tests.

25. MASKING
Subject Hear Test Tone Subject does not
hear test tone
Actual Threshold Proceed To
Step 4
STEP 3
Present masking sound in non-test ear at 15 db
above AC threshold of non-test ear & present the
test- tone at unmasked threshold in test ear

26. MASKING
Subject Hear Test Tone Subject does not
hear test tone
STEP 4
Raise test tone by 5 db
Raise masking noise by 5
db
Raise masking noise by 2-3 steps
of 5 db till subject hears tone &
then proceed step 5
Raise masking sound by 2-3 more
steps of 5 db. If subject still hears –
Actual Threshold. If doesn’t hear -
Go back to step 4
Subject hears tone --- Subject
does not hear tone
Go to step 5

27. MASKING
STEP 5
Alternately raise test tone & masking sound in 5 db
steps till subject continues to hear the test tone in
spite of 2-3 consequetive increments of 5 db of
masking noise. This is actual threshold.

28. MASKING
 Over masking
If the masking sound used is so loud thai it crosses over
from the non-test ear and obliterates or mask the test
signal in test ear , the subject will not hear the test
signal in the test ear until it is much above the actual
threshold.
 Under masking
 Undermasking leads to false A-B gaps and is usually
the result of operator inexperience or a failure to follow
masking rules.

29. MASKING
 MASKING DILEMMA
 In pts with b/l moderate to severe CHL ( large AB Gap ) ,
the plateau in Hood’s plateau method of masking may be
unidentifiable.
 Max and Min masking may be equal (or) min masking may
become more than max masking

30. SOUNDS USED FOR MASKING
 WHITE NOISE
Broadband or wideband noise ( equal amt of sound
of all frequencies , starting from low to very high
frequencies )
NARROW BAND NOISE
Narrow band of noise centered on test tone freq.
with 100 – 200 Hz above and below that freq.
 COMPLEX NOISE
Low freq. fundamentals plus the multiples of that

31. INTERPRETATION OF AUDIOGRAM
0-25 db - Normal
26-40 db - Mild deafness
41-55 db - Moderate deafness
56-70 db - Severe deafness
71-90 db - Very severe deafness
Above 90 db - Profound deafness

32. % of Handicap
 Formula for calculating % of handicap for unilateral
deafness – { [( a+b+c+d)÷ 4 ]- 25} x 1.5
%
 Bilateral – [ (5x +y) ÷6 ]%
Pitfalls
- Vibrotactile stimulation
- Faulty response in bone conduction tests at 3 k
& 4 k Hz.

33. PITFALLS

34. DISADVANTAGES
 Improper technique
 Improper test condition
 Improper test instrument
 Improper examiner
 Subjective & time consuming test
 Does not assess main features of hearing- frequency
discrimination & temporal resolution of sound.
 Does not identify nature of the pathology
 Bone conduction test does not assess true sensoneural

35. CLINICAL TESTS WITH PTA
WEBER’S TEST USING BONE VIBRATOR
 TO identify the better ear in SNHL and the ear
with larger AB Gap in suspected CHL
 BC vibrator is placed in centre of pt’s forehead
and a 1000 Hz sound of 0 db is presented
 Above 1000 Hz is avoided – resonsce in skull
may blemish the results
 Above 10 db above threshold is not used – may
heard by air conduction

36. CLINICAL TESTS WITH PTA
BING TEST OR OCCLUSION TEST
 BC Vibrator is placed over mastoid process
 BC threshold at certain freq. b/w 250 – 1000 Hz
ascertained twice , once with EAC open & EAC
occluded.
 No change in BC thershold – Conductive
deafness
 Hearing threshold found better with EAC
Occluded – No Conductive deafness

37. CLINICAL TESTS WITH PTA
GELLE’S TEST
BC Vibrator is placed over mastoid process of test ear
Audiometer ear phone is placed over the other ear
Masked BC hearing threshold of test ear is determined at air
pressure of -400 , 0 , +400 mm of water pressure.
In normal middle ear - the BC hearing threshold is found to
become poorer at -400 & +400 as compared to 0.
In stapes fixation - no change in BC threshold

38. STENGER TEST
May be used to identify unilateral or asymmetrical
functional hearing loss.
When both ears are stimulated simultaneously by a
tone equal in frequency and phase, the auditory percept
is lateralized to the ear with better hearing.
When speech stimuli are used, the test is called a
Speech Stenger test or a Modified Stenger test.

39. NORMAL

40. MILD CHL

41. MODERATE SNHL

42. VERY SEVERE MIXED DEAFNESS

43. CHL SHOWING LARGER AB GAP -
OME

44. CHL WITH VERY LARGE AB GAP –
OSSICULAR DISCONTINUITY

45. CARHART’S NOTCH - OTOSCLEROSIS

46. FLAT AUDIOGRAM – SNHL
STRIAL PRESBYACUSIS

47. DESCENDING AUDIOGRAM – SNHL -
OTOTOXICITY

48. SNHL – DIP IN 4OOO HZ –
ACOUSTIC NEUROMA

49. SNHL – MOD DEGREE IN LOW FREQ –
EARLY ENDOLYMPHATIC HYDROPS

50. TROUGH SHAPED – CONGENITAL
SNHL