BS ISO 4869-6:2019 pdf download – Acoustics – Hearing protectors
5.3.1 Broadband noise for measuring active insertion loss
A broadband noise signal shall be used to determine the diffuse-field related sound pressure levels. The test signal at the reference point shall be a broadband random noise in each one‑third‑octave band centred from 50 Hz (or 100 Hz) to 10 000 Hz, and shall be at least 3 dB down at the one‑third‑octave bands below and above these limit bands, and roll off at least 12 dB/octave for the bands below and above that. Adjacent one‑third‑octave‑band levels shall not differ by more than 3 dB. The difference between the maximum and minimum one‑third‑octave‑band levels shall not exceed 10 dB from 50 Hz (or 100 Hz) to 10 000 Hz. NOTE 1 Pink noise is a suitable broadband noise signal. If the total attenuation is to be determined for the frequency range from 63 Hz to 8 000 Hz, the test signal shall extend from 50 Hz to 10 000 Hz. If the test signal is only available for 100 Hz and above, the total attenuation can only be determined from 125 Hz upwards. The measurements described above shall be conducted with a WS2P or WS2D microphone (working standard, ½ inch, pressure field/random incidence) according to IEC 61094‑4. The use of digital pseudorandom white and pink noise sources is restricted to measurements of passive hearing protectors. Some FFT analyzers with internally generated digital pseudorandom white and pink noise sources with known statistical characteristics, i.e. wide sense stationary, can potentially overestimate the active insertion loss with some ANR hearing protectors. The sound pressure level measured under the hearing protector (occluded condition) in each one‑ third‑octave band with the test noise on shall be at least 10 dB higher than the sound pressure level measured under the hearing protector with the test noise off. The test signal shall be presented up to an A‑weighted sound pressure level of 95 dB.
5.4.2 Oscillation and acoustic malfunction
If any subject reports sustained oscillations or acoustic malfunctions when the ANR system is switched on, the subject shall be asked to switch the ANR system off, remove the earmuffs and then refit them, according to the manufacturer’s instructions. If the oscillation persists when the ANR system is switched on again, the specimen should be rejected and replaced by a new one. If the malfunction is caused by some characteristics of the subject, the subject may be replaced. In any case, the occurrence of sustained oscillation or acoustic malfunction shall be reported.
5.4.3 Active insertion loss
For the two measurements in the active and passive modes from which the active insertion loss is calculated, the broadband noise as described in 5.3.1 shall be set at an overall A‑weighted sound pressure level in the range from 85 dB to 95 dB. The timespan between the two measurements shall be as short as possible and the test conditions shall be unaltered, especially the fitting of the earmuff and the positions of the microphone in real‑ear. The measurements shall be performed with the same test subjects as the measurements of the passive sound attenuation according to ISO 4869‑1. The spectra in active and passive mode shall be determined for the one‑third‑octave bands between 50 Hz (or 100 Hz) and 10 000 Hz. For each of the 16 test subjects, the difference between passive and active mode shall be calculated to derive the active insertion loss as per 5.5. For devices that incorporate a threshold level only above which the active attenuation is working, the measurements are to be carried out 5 dB above that threshold (specified by the manufacturer), but not lower than 85 dB or above 110 dB. NOTE This option exists with some devices that combine level‑dependence and active attenuation. For these and other devices, it is possible that active attenuation will not function at A‑weighted sound pressure levels as low as 85 dB to 95 dB, even if switched on.