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D-0126050 rev 1 - 270+ Operating Manual
8. APPENDIX A - FREE FIELD CALIBRATION PROCEDURE
8.1. GENERAL
The following is a brief description of the equipment and procedures to be used with the Model 270+
audiometer as a means of performing freefield calibration.
The following calibration should be performed before any freefield tests are conducted, 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). The procedures outlined below cover calibration for both speech and warble tone modes of
audiometry. If both modes are to be used then speech calibration must be carried out first. If only warble mode
is to be used then only the warble part of the calibration procedure may be carried out.
However, if speech mode is required later (and a speech calibration is performed) this will invalidate any
previous warble calibration which would then need to be repeated. If warble tones are to be used as a means
of equalising the frequency response in the speech calibration then this will invalidate any previous warble
calibration which would then need to be repeated when warble tone testing is required.
8.2. ASSURANCE OF CALIBRATION
It must be emphasised that it is the responsibility of the equipment operator to ensure that correct freefield
calibration has been achieved, and it is recommended that the standards for freefield & 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.
8.3. EXTERNAL LOUDSPEAKER
The SP90A Active Loudspeaker by RadioEar is specified for use of the Model 270+ audiometer in freefield
modes of operation.
8.4. CALIBRATION SET-UP
Place the speaker(s) in the desired position(s), at least 1 meter from the subject’s listening (head) 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).
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