BS ISO 4869-6 pdf free download

BS ISO 4869-6-2019 pdf free download.Acoustics – Hearing protectors Part 6: Determination of sound attenuation of active noise reduction earmuffs.
5 Testing
5.1 Specimens and conditioning
Four pairs of earmuffs shall be submitted for testing. Each indivklual earmuff CU shall be uniquely marked for identification. The power source shall be fully operational.
All specimens shall be conditioned and tested in an environment having a temperature of (22 ± 5) °C and a relative humidity of not more than 85 %.
5.2 Test conditions
Random incidence sound field conditions at the reference point as described in ISO 4869-1 are required for all one-third-octave bands ofthe test signals specified in 5.
5.3 Test signals
5.3.1 Broadband noise for measuring active insertion loss
A broadband noise signal shall he 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 offat 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 anti 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. Ifthe 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 he presented up to an A-weighted sound pressure level of95 dB.
NOTE 2 Test signals up to an A-weighted sound pressure level of I 10 dFl can be necessary if the device incorporates a threshold level only above which the active attenuation is working.
5.3.2 Red noise for testing linear operation
Red noise shall be used with the maximum of the spectrum in the 125 Hz one-third-octave band and one-third-octave-band levels in the 100 Hz anti 80 Hz band of 1 dB and 3 dB less than the maximum. The signal shall be presented up to an A-weighted sound pressure level of 110 d13.
5.4 Test method
5.4.1 General
The measurements described in 5.4.3 determine the active contribution (active insertion loss) to the total attenuation ofthe earmuff. This quantity is derived from two separately measured data sets:
a) the sound pressure level at the wearers’ ears in the active mode,
b) the sound pressure level at the wearers’ ears in the passive mode ofthe ANR earmuff. The difference of these two data sets yields the active insertion loss.
For both measurements a) and b), the microphone-in-real-ear technique (MIRE) with closed earcanals shall be used according to ISO 11904-1. including the requirements for averaging times.
Sixteen test subjects, with separate measurements made on both ears, shall be used. Each specimen shall be tested by four test subjects.
5.4.2 Oscillation and acoustic malfunction
Ifany 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. lithe 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 d13 to 95 d13. 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 d13.
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 85dB to 95 dB, even if switched on.
5.4.4 Maximum sound pressure level for linear operation
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 lIz, 125 lIz and 160 lIz). 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 d13 (with a tolerance of ±1 (IB). The maximum external A-weighted sound pressure level to be applied shall be 110 dB.BS ISO 4869-6 pdf download.