INTRODUCTION TO PURE
TONE AUDIOMETERY
(AUDIOMETER & TESTING
ENVIRONMENT)
By Mrs. Wedad Alhudaib with many
thanks to Mrs. Tahani Alothman
Topics : This lecture will incorporate both
theoretical information as well as practical demonstration on the following topics:
What is the audiometers and its components
Audiometer basic types
What is the concept of Hearing level and how does it correlate with Reference Equivalent Threshold Sound Pressure Level
Audiometer Calibration
Testing environment
INTRODUCTORY POINTS
The main disadvantage of TFs tests
is that they fail to quantify the hearing
loss
The purpose of hearing test is
Help to find the type and extent of
hearing loss
Develop habilitative and rehabilitative
plan to deal with the impact of this loss
To meet this purpose, accurate
performance and interpretation of
hearing tests are essentials
Reliability of any test is depend on
collaboration between different factors
like calibration of equipment, patient
performance and examiner difficulty
Pure tone hearing tests performed
using Audiometer
AUDIOMETER
It’s the basic tool used to evaluate the
auditory function of the patients.
It’s an electronic device that produces
and delivers sounds to the patient.
It allows precise knowing of what
presented to the patient and ensures the
consistency of the sound presented.
BASIC AUDIOMETER COMPONENTS
Power switch:
Controls the electrical supply to the
instrument, usually there is an
indicator whether the device is on or off
(light ).
Interrupter:
The button that presented the tone to
the patient, this should be either in on
or off mode.
Stimulus dial:
Button for presenting the stimuli once. It should be pressed manually.
Frequency control (dial ):
It allows sweeping between different frequencies for testing.
Most audiometers include the frequencies
125, 250,500,750,1000,1500,2000,3000, 4000, 6000 and 8000Hz.
Stimulus or tone mode switch: Used to change between different tone
types (continues, pulsed or warble “frequency modulated”).
Masking control: Allow introduction noise needed for
masking
Attenuator or hearing level control: Controls the intensity of the test signal.
Unlike the volume control, the attenuators are calibrated I.e. each level correspond to specific SPL .
For example, setting the attenuator at 45 dB HL, means sound coming out of the earphone have a SPL that stands for 45 dB HL.
Most audiometers have attenuators that are calibrated at 5 dB steps.
The intensities range from as low as -10 dB HL up to 120 dB HL for air conduction and about 50-70 dB HL for bone conduction.
The output selector or transducer:
To direct the signal to the Right or Left
ear or to bone conduction vibrator.
Transducers are either supra-aural
earphones, insert earphones or
bone conduction vibrator.
TRANSDUCERS
1. Supra-aural earphones: It known as that because the earphone/ cushion combination is worn over the ear.
2. Inserts: It has an elastic earpiece that can be inserted into the external auditory canal.
3. Bone vibrator: It is usually held against the mastoid process by spring like headband.
AUDIOMETER TYPES BASED ON NUMBER
OF CHANNELS
Audiometers can be either a single-
channel or two channels. Tow
channels is more common.
In two channels audiometer, the
second channel used to generate the
noise whenever masking needed.
AUDIOMETER TYPES BASED ON ITS
FUNCTIONS
1- Pure tone Audiometer
It’s able to produce pure-tones at certain
frequencies.
It contains the basic Audiometer
components.
It’s easy to move from one place to
another (portable)
It’s widely used for screening purposes
PURE TONE AUDIOMETER
2- Clinical Auidometer (Diagnostic)
It includes all features of Pure-tone
audiometer plus additional collections to
perform more sophisticated tests using
tone or more varied signals.
It also includes microphone, inputs for
tape and CD players that used to present
recorded tests, patient’s responding mic ,
an intercom system, a patient response
signal, computer interface….etc
It provides higher frequencies testing in the 8000 to 16000Hz range , known as (Extended high frequency audoimeter).
It provides a wider variety of output transducers:
1) Right/ Left supra-aural earphone
2) Right/Left inserts
3) The B/C vibrator
4) Loudspeakers and
5) Any combination of these.
CLINICAL AUDIOMETER
HEARING LEVEL
Our actual hearing sensitivity in decibels
of SPL is not the same at each frequency.
For example, a normal hearing person
needs 26.5 dB SPL just to hardly hear a
250 Hz tone. However, 7.5 dB SPL to just
hear a 1000 Hz tone.
Refer to the table below to see the normal
threshold SPLs.
NORMAL HEARING LEVEL IN SPL
These values considered as normal
reference values or more technically
Reference Equivalent Threshold
Sound Pressure Levels (RETSPLs).
They are the physical intensities needed
by the normal people to reach the
threshold of hearing.
So, the person with hearing loss needs
higher SPLs than the normal ones to just
hear the sound; the more threshold
deviation from these values, the greater
hearing loss the patient has.
Since It’s difficult to have different values
at different frequencies like those SPLs,
there should be a reference values
instead.
As all of these values indicate that the
sound just barely audible, they are
equally audible, they heard the same, so
we can say they have same hearing level.
SO, WHAT IS THE HEARING LEVEL?
As these reference values are the softest
sound that can be heard, they are
corresponding to the hearing level (HL) of
Zero ( Reference SPL = 0 dB HL)
For instances,
At 250 Hz >> 26.5 dB SPL = 0 dB HL,
At 2000 Hz >> 11 dB SPL = 0 dB HL.
As a results all of these reference values
are built in the audiometer circuit so,
when any value dialed in dB HL, the
audiometer automatically adds these
reference values to produce the intended
intensity.
For example, presenting a 55 dB HL
tone at 500 Hz means ( 55 + 13.5 = 68.5
dB SPL ) was dialed.
SENSATION LEVEL
The intensity level above the threshold level
For example, if tone presented at 30 dB SL , means 30 dB above patient threshold
If patient threshold is 10 dB HL and we need to present a tone at 10 dB SL, the presentation level is 20 dB.
AUDIOMETER CALIBRATION
o Calibration is necessary to ensure
that:
The audiometer is producing a pure tone
at the specified frequency and intensity
The stimulus is present only in the
earphone to which it is directed
The stimulus is free from unwanted noise,
the interference, and distortion
CALIBRATION TYPES
Four types of audiometer
check/calibration schedules:
Daily listening check
Psychoacoustic check
Periodic electronic calibration
Exhaustive electronic calibration
1.Daily Listening Check
Routine and subjective tests
They should be carried by someone with
sufficiently good hearing to detect any
faults.
They should be carried out in a normal
test room with the equipment set up as
installed.
These checks should be recorded.
If any faults noted, the equipment shall
not be used until the fault corrected.
STEPS FOR DAILY LISTENING CHECK
In the morning after warm up (10 min)
Signal is checked at various intensities (
High = 60 dB for AC and 40 dB for BC,
Low = 10-15 dB for both) and at all
frequencies
Look for transient clicks or distortion
(undesired acoustic signal)
Ensure that signal is delivered to the
correct earphone
No cross talk is present
Cross talk: when the signal intended for
exclusive routing to one earphone is also
routed to the other
2.PSYCHOACOUSTIC CHECK
It’s done at least once per month
The output from the audiometer is
checked
This process is done either with:
A. Psychoacoustic (biologic) check
B. Electro-acoustical calibration check
with a sound level meter
A. PSYCHOACOUSTIC (BIOLOGIC) CHECK
Obtain baseline thresholds on 3-5 normal
hearing individuals who will be available
for comparison testing throughout the
year
If on the monthly check, a threshold
difference > 5 dB HL is found for one of
the individuals for any test frequency
between 500-6000 Hz, the other subjects
should be checked
If a shift > 5 dB HL in the same
direction is confirmed, an electronic
calibration of the audiometer is required
Monthly results should recorded in a
form
B. ELECTRO-ACOUSTICAL CALIBRATION
CHECK
Performed with sound level meter and
real-ear coupler
Measurements are obtained directly from
the audiometer earphone at a fixed
attenuator setting and compared with
the expected ANSI 1996 reference
equivalent threshold SPL value
If the difference is > 3 dB, the
audiometer would require electronic
calibration
TERMS
Sound level meter:
An electronic instrument designed to measure sound intensity in dB in accordance with an accepted standard
ANSI(American National Standards Institute):
An association of specialists, manufacturers, and consumers that determines standards for measuring instruments, including audiometers
3.PERIODIC ELECTRONIC CALIBRATION
It should be done at least one time each
year
To make sure that the audiometer is
meeting the minimum standards defined
by ANSI S3.6-1996
4.EXHAUSTIVE ELECTRONIC
CALIBRATION
It’s done Every 5 years
More comprehensive than the periodic
electronic calibration
Includes testing of all settings on the
frequency and intensity dials
Replacing switches, cords, earphone
drivers and cushions
TESTING ENVIRONMENT
Noise Level
Noise level needs to be low enough to
allow the threshold measurement down
to 0 dB HL at each tested frequency by
both air and bone conduction.
SOUND-ISOLATED CHAMBERS
Audiological tests are performed in
specially constructed, sound-treating (
isolated ) chambers known as booth or
anechoic chambers.
Audiological booths are either
Single room
It’s either just the patient inside the
booth while the examiner and the
equipments outside
OR
Both the examiner and the patient in
the same sound-treated room .
One room setup
ONE ROOM SETUP
Two-room, patient room and control room.
The patient room needs to be as large as possible, important for sound field and paediatrics testing.
The tester’s room needs to be large enough to fit the equipments, tester and an observer.
Windows provide visual communication between both rooms
Electrical connections are essentials to
direct the signal from audiometer to
the transducers
Talkback system with microphone,
amplifier and speaker or earphone is
important for examiners to hear their
patients when they speak
Two room set up
TWO ROOM SET UP
CONT. TESTING ENVIRONMENT
Room dimensions should account for
door opening and closing and wheelchair
access.
The room walls are usually either single
walled or doubled wall with dead air
space in-between and it gives more
isolation.
The window between the patient and the
tester should be made of multiple pans of
glass with dead air spaces in between
and moisture observing materials .
A sound-muffled ventilation system used
to allow air entrance and escaping.
Condescend light is preferable to use to
avoid any noisy sound. However,
fluorescent light could be used if it’s
noise source built outside the booth.
Subject face shall be clearly visible to the
examiner.
The ambient noise shall not exceeds 35
dB (A), otherwise test should not be
conducted.
dB(A), it’s a measurement that
excludes the effects of lower frequencies
and are especially useful in noise level
measurements.