BS 61669:2016 pdf download – Electroacoustics — Measurement of real-ear acoustical performance characteristics of hearing aids Measurements of real-ear acoustical performance characteristics of hearing aids which use non-linear or analytical processing techniques are valid only for the test signals and conditions employed. These measurements should be performed in accordance with the hearing aid manufacturer’s recommendations, as they can require specific test signals or test conditions outside the scope of this standard. 6.4 Sound field source When using the substitution method, the sound field source shall consist only of coaxial elements. In order to avoid reflections, the frontal surface of the sound field source enclosure shall be covered with a suitable absorbing material. When using the modified pressure method these restrictions do not apply. 6.5 Coupled sound source The magnitude of the acoustic impedance of the coupled sound source used in the measurement of the RECD shall be at least 3.1 6 times that of the occluded test ear and of the 2 cm 3 coupler. 6.6 Test signal range Narrow-band test signal levels shall cover the range from 50 dB to 90 dB at a working distance of 0,5 m in an anechoic environment, with a maximum step size of 5 dB. 6.7 Test signal level indication For the range of levels indicated by the equipment manufacturer, when measured at the inlet to the reference microphone, the indicated test signal level as a function of frequency shall be accurate within 4 dB. 6.8 Equalization In an anechoic environment, equalization shall allow the test signal to be controlled, as a function of frequency, to within 4 dB of the intended test signal level at the field reference point at a working distance of 0,5 m. 6.9 Frequency The frequency, or components, of the test signal shall cover the frequency range from 200 Hz to 8 000 Hz (i.e. covering the one-third octave bands from 250 Hz to 6 300 Hz). The indicated frequency of a narrow-band test signal or the indicated centre frequency of the analysis bands for a broad-band test signal shall be accurate within 3 %. 6.1 0 Harmonic distortion For a pure-tone test signal in an anechoic environment, the total harmonic distortion of the test signal at the field reference point at a working distance of 0,5 m shall not exceed 3 %. 6.1 1 Probe microphone measurement For the measurement range indicated by the equipment manufacturer, the...
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