BS/EN 61669-2016 pdf download.Electroacoustics Measurement of real-ear acoustical performance characteristics of hearing aids.
NOTE Background noise at frequencies outside the analysis range can activate automatic gain regulating circuitry or cause saturation in the hearing aid under test.
7.3 Acoustical properties
The physical size and absorption characteristics of the test space influence the accuracy of real-ear measurements. The extent of this influence depends upon the test signal used, the working distance, the method of sound field equalization, subject movement, and the type of hearing aid being tested. In order to minimize errors due to reflected sound, the field reference point should be chosen such that the distance from both the field reference point and the sound field source to the nearest reflective surface is at least twice the working distance.
7.4 Sound field characteristics
The environments in which measurements are made can vary considerably. A free sound field is preferred but a quasi-free sound field may be used. The type of sound field used shall be stated. The test space shall allow the test signal level to be controlled to within 3 dB of the desired test signal level.
7.5 Calibration
Pretest calibration of the test equipment shall be carried out directly, using a calibrator complying with IEC 60942. or indirectly following the manufacturer’s instructions. Any setting- up procedures should also be performed in accordance with the manufacturer’s instructions.
At least annually, the calibration of the reference microphone shall be verified by coupling it to a calibrator complying with IEC 60942 using a suitable adapter supplied or specified by the equipment manufacturer.
7.6 Equalization
7.6.1 General
The test system shall be equalized prior to a test, and as otherwise indicated in 7.6.2 to 7.6.4,
using one of the methods of this subclause. The equalization method used shall be stated.
7.6.2 Substitution method
Following the equipment manufacturer’s instructions, record the test signal at the test point with the subject absent. The recording shall be updated whenever there is a change in the acoustic environment This method requires a free sound field such as can be achieved in art anechoic chamber.
Sound outflow from a large vent or open fitting can interfere with the concurrent equalization process. In this case, It can be necessary to employ stored equalization with the hearing aid switched off or muted during the recording of the test signal. The manufacturers instructions in this regard should be followed.
7.7 Test signal level
The test signal level shall be chosen with concern for subject safety and comfort, the ambient background noise and the characteristics of the hearing aid under test. The level used shall be stated.
Special consideration shall be given to hearing aids with automatic gain control circuitry or which apply other non-linear signal processing techniques. When it is desired to test hearing aid performance in the linear operating region, the lowest possible test signal level should be used. Linearity should be verified by observing that over the frequency range 200 Hz to 8 000 Hz, or as otherwise desired, a change in test signal level causes the same change at the measurement point. The frequency range used shall be stated.
NOTE The SPL presented to the hearing aid microphone can significantly exceed the test signal level because of
the locahon of the hearing aid microphone and subject position.
7.8 Location of the subject
The subject shall be located in the subject test position during all measurements except the initial Sound field recording of the substitution method. A minimum working distance of 0,5 m, an elevation angle of sound incidence of 0° and an azimuth angle of sound incidence of 0° or 45° are recommended. Working distance, elevation and azimuth angles of sound incidence shall be stated.
7.9 Location of the tester
The tester shall remain at least 1 m from the test ear during testing and during equalization if
using the method of 7.6.3.
7.10 Location of the field reference point
This point may be recommended by the manufacturer or dictated by the physical construction of the equipment. The results of the measurements (REUR, REUG, REAR, REAG, REOR and REOG) depend upon the choice of field reference point. For these measurements, the exact location of the field reference point is to be specified by its perpendicular distance (in mm) from the surface of the head, and its distance (in mm) forward of and above or below the centre of the ear canal entrance. For devices operating linearly, REIG is independent of the field reference point. When concurrent equalization is used, care shall be taken to ensure that the presence of the hearing aid during the aided measurement does not alter the signal being produced by the sound field source.BS/EN 61669-2016 pdf download.
BS/EN 61669-2016 pdf download
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