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Appendix 2 ‒ Free Field
Calibration Procedure
1. Assurance Of Calibration
The following is a brief description of the equipment and proce-
dures to be used with the Siemens SD 270 audiometer as a means
of performing free-field calibration. However it must be emphasi-
sed that it is the responsibility of the equipment operator to ensure
that correct free field calibration has been achieved and it is recom-
mended that the standards for free-field & speech testing & calibra-
tion (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.
2. External Amplifier and Loudspeaker
The following external equipment is specified for use of the
Siemens SD 270 audiometer in free field modes of operation:
• Amplifier: Interacoustics AP70
• Loudspeaker: Interacoustics ALS7
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).