BS ISO 4869-6:2019 pdf free

BS ISO 4869-6:2019 pdf free.Acoustics – Hearing protectors – Determination of sound attenuation of active noise reduction earmuffs
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.
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 each subject and each ear, the linearity in the active mode shall be checked in the 125 Hz octave band (calculated from the three one-third-octave bands 100 Hz, 125 Hz and 160 Hz). Red noise as described in 5.3.2 shall be used. The sound pressure level at the subject’s ear shall be monitored, starting at the overall sound pressure level set for the measurement of active insertion loss (see 5.4.3) and increasing the sound pressure level in 5 dB steps. It shall be checked that the sound pressure level at the ear also increases by 5 dB (with a tolerance of ±1 dB). The maximum external A-weighted sound pressure level to be applied shall be 110 dB.BS ISO 4869-6 pdf free download.