Audiometer and Testing Environment - KSU

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.