1. Equipment for Measuring Hearing and Calibration
Lecture 4

2. Outline Equipment: Audiometers Calibration Types Components
Reference Level
Calibration
Purpose

3. Audiometers: Screening units

4. Components Power source Frequency selector dial Hearing Level dial
Ear Selector
Stimulus selector

5. Audiometers: Diagnostic Unit
2 channel audiometer
Stimuli
CD recordings
Microphone - Speech
Tones
Masking

6. Components - Diagnostic
Additional components
Menus for setting up
Response indicator
VU meter
Talk over
Special test features

7. Transducers with Audiometers
Air Conduction
Supraural earphones
Insert earphones
Speakers in soundfield
Bone conduction
Vibrator

8. 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

9. Parameters for testing with AC
Parameters vary depending on equipment
Upper Limits for AC: maximum output ranges between 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

10. 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

11. Parameters for testing with BC
Placement is on the skull
forehead or mastoid
Upper limits for BC : maximum output ranges between dB HL
Limit depends on frequency
Lowest limit for BC: dB HL
Standard frequencies tested: 250, 500, 1000, 2000, 4000 Hz

12. “Think-pair-share” Calibration
What is calibration?
Why is calibration important?

13. 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

14. See Table 4.1

15. Calibration
If signal too strong, then hearing assessments will be ______________
If signal is too weak, then hearing assessments will be ___________________

16. 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

17. 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

18. 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
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)

19. Calibration Process
Coupler that
connects with
earphone

20. Earphone placed over coupler
Earphone remains
connected to
Audiometer
SLM used to
Measure actual SPL values

21. Weight to hold
earphone in place

22. Procedure to calibrate and example
Signals sent from audiometer to earphone and read by SLM
Each frequency from 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?

23. ANSI Standard Output of signal measured Frequency of signal measured
+/- 3 dB SPL is defined as “within calibration”
Output of
signal measured
Frequency of signal measured

24. Calibration sheets All information is recorded on calibration sheets
Units MUST be calibrated annually.
NO EXCEPTIONS !
Critical documents

26. 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 ? ? ? Etc.

27. 1 minute evaluation What can you apply when you leave this room?
What was the most important thing you remember learning today? What one question would you like reviewed related to what was discussed ?
What can you apply when you leave this room?