BS EN 61669 2016 pdf free download.Electroacoustics — Measurement of real-ear acoustical performance characteristics of hearing aids
6.1 3 Attenuation of probe microphone to external signals
When the probe microphone sound inlet is acoustically sealed and placed in a sound field, the SPL, as a function of frequency, measured by the probe microphone, shall be at least 1 0 dB lower than the lowest level to be measured with the sound inlet open, over the frequency range 200 Hz to 8 000 Hz, for pure tones, or in the one-third octave bands from 250 Hz to 6 300 Hz for broad-band signals. The sound field used for this measurement shall be uniform over the surface of the entire probe microphone and of sufficient level to cause the measured SPL to exceed the noise floor of the probe microphone by at least 1 0 dB.
6.1 4 Analysis characteristics
The equipment manufacturer shall report the analysis type(s) employed by the equipment and shall supply the information listed below for each type. For analysis of a tone-burst test signal, report the integration time of the SPL measurement if different from the ON time of the tone-burst. For broad-band analysis, report the measurement bandwidth and integration time. For spectrum analysis employing a swept filter, report the filter bandwidth and skirt slope. For spectrum analysis employing digital means, report sampling rate, digital resolution, averaging time or number of averages, analysis bandwidth, block length, windowing type, window overlap, method (synchronous, FFT auto-spectrum, FFT cross-spectrum, digital filter), and total frequency range of analysis. For analysis using a digital filter bank, report centre frequencies, bandwidth and integration times. Octave or fractional-octave band filters should conform to IEC 61 260 Class 2. Preferred frequencies are the one-third-octave frequencies specified in ISO 266.
6.1 5 Output indication
The output indicator used shall give r.m.s. value indication within 2 dB of the true r.m.s. value for the type of signal to be measured. If, under certain conditions, it is necessary to use a selective measuring system, e.g. filtering, to ensure that the response of the hearing aid to the test signal can be differentiated from inherent noise in the hearing aid, the use of the selective system should be stated in the report.
NOTE The type of output indicator employed can influence the test results significantly if a non-sinusoidal voltage is being measured. Such non-sinusoidal voltages can be present when making measurements with high input levels to the hearing aid.
6.1 6 Graphical printout It is recommended that frequency response curves be plotted on a grid having a linear decibel ordinate scale and a logarithmic frequency abscissa scale with the length of one decade on the abscissa scale equal to the length of (50 ± 2) dB on the ordinate scale.
7 Test conditions
7.1 Ambient conditions in the test space The operator shall ensure that the equipment has reached a stable operating condition and that ambient conditions in the test space at the time of test are within the ranges specified in 6.2. If other conditions apply, these conditions shall be stated. If the calibration of the measurement system depends on ambient conditions, corrections for such dependence shall be made in accordance with instructions provided by the equipment manufacturer or as determined by the operator.
7.2 Background noise At the field reference point, the signal shall exceed the background noise at every analysis frequency (or in every analysis band) by at least 1 0 dB. Background noise at frequencies outside the analysis range shall not affect measured results by more than 1 dB. 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.BS EN 61669 pdf download.