Appendix 2 - Free Field Calibration Procedure
A2.1 Assurance of Calibration
The following is a brief description of the equipment and procedures to be
used with the Amplivox Model 260 audiometer as a means of performing
free-field calibration.
However it must be emphasised that it is the responsibility of the
equipment operator to ensure that correct free-field calibration has been
achieved, and it is recommended that the standards for free-field &
speech testing & calibration (e.g. ISO 8253-3 & ISO 389-7) and other
appropriate reference works are consulted.
It is assumed that the room, speakers and listening position have been set
up in conformance with the relevant standards and that the required
calibration equipment, operating procedures and trained technical staff are
available to perform this operation. Once calibrated, items should not be
moved, removed, or added to the room without re-calibration.
A2.2 External Amplifier and Loudspeaker
The following external equipment is specified for use of the Amplivox
Model 260 audiometer in free-field modes of operation:
Amplifier: Interacoustics AP70
Loudspeaker: Interacoustics ALS7
A2.3 Calibration Overview
The following calibration should be performed before any free-field tests
are performed, and repeated if any changes to equipment positions or
settings are made, or if there are other changes to the room (e.g. furniture
moved). Place the speaker(s) in the desired position(s), at least 1.5
meters from the subject’s listening position. Refer to the specification for
the test to be performed for correct loudspeaker and subject alignment(s).
For calibration, the measuring microphone of a sound level meter (SLM) is
placed at the reference point (the point that the subject’s head will be
located).
The procedures outlined below cover calibration for both speech and
warble tone modes of audiometry. If both modes are to be use then
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