Audiometers, Calibration
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Transcript 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
CD recordings
Microphone - Speech
Tones
Masking
Components - Diagnostic
Additional components
Menus for setting up
Response indicator
VU meter
Talk over
Special test features
Transducers with Audiometers
Air Conduction
Supraural earphones
Insert earphones
Speakers in soundfield
Bone conduction
Vibrator
Air Conduction ( AC )
Performed via
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
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
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?