Chapter 4 – Calibration

Why calibrate?

-required by ______and ______

-ensures that results are as accurate as possible (eliminate equipment variations)

-necessary to ensure the audiometer produces a pure tone at the correct frequency and specified level via the selected transducer

-ensure that the signal is not distorted and is free of unwanted noise interference

Parameters of Calibration

-follow standards and procedures outlines in the equipment’s manual

-do regularly scheduled tests

-do listening tests

Basic Equipment

-basic calibration equipment for checking output levels:

  • voltmeter or multimeter
  • condenser ______
  • 6-cm3 coupler
  • 2-cm3 coupler
  • ____ gram weight
  • mechanical coupler for bone vibrator measurement
  • ______meter or spectrum analyzer
  • also possibly:
  • oscilloscope
  • graphic level recorder
  • electric counter
  • frequency analyzer
  • distortion meter

Checking the Calibration of Puretone Audiometers

-basic signal

  • read the instructions

-biologic test

  • listen to the signal at different settings and through each tranducer

-frequency check

  • use an electric counter to tell the exact ______of the output

-linearity check

  • Change ______from highest dB level and check each step down individually

-distortion check

  • distortion appears as a lack of linear attenuation
  • presence of energy at other frequencies
  • more common at high output levels

-rise-fall time

  • put output directly into a storage ______
  • ______time is the time between pressing the button and the signal being at its intended strength
  • ______time is the time it takes from the stopping of the signal presentation for the level to return to its steady value

Ear Phone Calibration

-generally, the ear phones are tested on a group of people using real-ear methods

-can also use a coupler method which acts as an “artificial ear”

Bone Vibrator Calibration

-more difficult than ear phone because a ______cannot be used as the pick up device

-preferred method the “artificial ______procedure” which uses a coupler

Speech Audiometers

- very similar to pure tone checks

-check linearity and level

-match output ______of the oscillator to input ______of the audiometer

Monitoring (VU) Meters

-monitoring meters indicate ______and are found on the face of most audiometers

-calibrated relative to the input it is monitoring (not an ______value)

-on a speech audiometer it is used to monitor the speech signal and lets audiologist adjust the input ______tone for recorded speech materials

Sound Field Testing

-check any ______“hum”

-check internal ______of loudspeaker

Calibration of Ancillary Equipment

-masking generator

  • there are standard definitions for white ______, weighted random noise for masking of speech, and ______noise for masking of pure tones.
  • it is important to first do an electronic check of the ______since they vary greatly. This verifies that any variation in the bandwidth is due to the transducer rather than the ______itself.

-Compact disc and tape players

  • Follow instruction manual that comes with the specific piece of equipment for general maintenance
  • Important to calibrate these as recorded speech testing is an integral part of audiometric testing

- Other equipment that requires calibration:

- Auditory ______Response Units (ABR)

- ______Emission Devices (OAEs)

-Acoustic ______Devices

  • Measure frequency activator
  • Be sure air tube is connected properly
  • Check the reflex activating system

Test Room Standards

-Ambient______must be below a standard level ( referred to as MPANLs or Maximum Permissible Ambient Noise Levels)

-Different for _____ conduction testing than bone conduction or sound field testing

-check the room using a ______meter to verify that this standard is met

-important to check testing booths as well since fans, transducer hum, etc can affect testing