Download Audiometers, Calibration

Equipment for Measuring
Hearing and Calibration
Lecture 4
Outline
 Equipment: Audiometers
 Types
 Components
 Reference Level
 Calibration
 Purpose
 Types
Audiometers: Screening units
Components
 Power source
 Frequency selector dial
 Hearing Level dial
 Ear Selector
 Stimulus selector
Audiometers: Diagnostic Unit
 2 channel audiometer
 Stimuli
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CD recordings
Microphone - Speech
Tones
Masking
Components - Diagnostic
 Additional components
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Menus for setting up
Response indicator
VU meter
Talk over
Special test features
Transducers with Audiometers
 Air Conduction
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Supraural earphones
Insert earphones
Speakers in soundfield
 Bone conduction
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Vibrator
Air Conduction ( AC )
 Performed via
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TDH-39 headphones – placed over pinna
Can also use with insert earphones in the ear
canal
Through loudspeakers
 Checks validity of entire ear system
 Tests one ear at a time (ipsilateral) if using
headphones or inserts
Parameters for testing with AC
 Parameters vary depending on equipment

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Upper Limits for AC: maximum output ranges
between 90-110 dB HL
Lower Limits for AC: -10 dB HL
 Standard frequencies tested:
250, 500, 1000, 2000, 4000 and 8000 Hz
test interoctaves if >20 dB difference between octaves
Bone Conduction (B/C)
 Bone vibrator placed on mastoid process
(behind the pinna) OR forehead
 Checks validity of inner ear (cochlea)
 Reflects the condition of the better
Parameters for testing with BC
 Placement is on the skull

forehead or mastoid
 Upper limits for BC : maximum output ranges
between 50-80 dB HL

Limit depends on frequency
 Lowest limit for BC: -10 dB HL
 Standard frequencies tested: 250, 500, 1000,
2000, 4000 Hz
“Think-pair-share”
Calibration
 What is calibration?
 Why is calibration important?
Calibration – defined
 Checking the accuracy of the output of a
measuring instrument
 Electroacoustic of psychoacoustic
determination that an audiometer is
performing properly in terms of its acoustic
output, attenuator linearity, frequency
accuracy and distortion
See Table 4.1
Calibration


If signal too strong, then hearing assessments
will be ______________
If signal is too weak, then hearing
assessments will be ___________________
Types of calibration
 Electroacoustic Calibration – completed by a
licensed specialist at least annually

Formal paperwork provided to document
completion
 Biological (Human) Calibration – can be
completed by clinician whenever equipment
used
Biological Calibration
 ID power button
 Visually inspect headphones
 Look/feel for frays/breaks in cords
 Perform Listening check
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Ear accuracy with an audible signal
Attenuator function
Ear phone cord – with a continuous stimulus
Electroacoustic
Calibration Process
Earphone (from audiometer) placed over “an
artificial ear” that simulates an ear canal volume.
A microphone is placed on top of the artificial ear
1.
2.
A.
B.
3.
4.
5.
6.
The artificial ear is connected to a sound level meter
The earphone is connected to the audiometer
A signal is sent through the earphone from the
audiometer
The output of the signal is measured from the SLM
that connects to the artificial ear
Audiometer is set at 70 dB HL
Output values obtained at SLM are compared to
standards for each frequency tested (Table 4.1)
Calibration Process
Coupler that
connects with
earphone
Earphone placed
over coupler
Earphone remains
connected to
Audiometer
SLM used to
Measure actual
SPL values
Weight to hold
earphone in place
Procedure to calibrate and example
• Signals sent from audiometer to
earphone and read by SLM
• Each frequency from 250-8000 Hz is
measured with a 70 dB HL input signal
• Output at each frequency measured
 During calibration what should the recorded
SPL be when the sound level meter is
measuring 1000 Hz?
ANSI Standard
 +/- 3 dB SPL is defined as “within calibration”
Output of
signal measured
Frequency of
signal measured
Calibration sheets
 All information is recorded on calibration
sheets
 Units MUST be calibrated annually.
 NO EXCEPTIONS !
 Critical documents
Self Assessment questions
calibration
 What are the typical limits of audiometers for
AC and BC?
 Why are there limits?
 Can I explain the need for calibration ?
 Why is there a difference between SPL and
HL?
 At 70 dB HL, what should the SPL value be
on the sound level meter if the audiometer is
at 1000 ? 2000 ? 4000 ? Etc.
1 minute evaluation
 What can you apply
What was the most
important thing you
remember learning
today?
What one question
would you like
reviewed related to
what was discussed ?
when you leave this
room?