The Octave Band Method (OBM), performs the calculations concerning the personal hearing protectors (PHPs) by separately considering each octave band. The first data to insert is the spectrum of the source, which must be provided as sound pressure level (dB) in octave bands ranging from 125Hz up to 8000Hz; the insertion of the 63Hz band is optional.
Then, the user must insert the mean sound attenuation for each octave band (Mf), determined under laboratory conditions in accordance with the testing methods described in the ISO 4869-1 standard, and the corresponding standard deviation sf. The values can be inserted by the user or selected from the PAF database. In order to enter the data from the database, the user can search for a specific brand or model, sort the PHPs for the appropriate type, brand, model or derated SNR, that results from the SNR declared by the manufacturer multiplied by theβ factor corresponding to the chosen type. In case of manual entry, the user must choose the β factor to apply to the calculated attenuation depending on the type of PHP as defined in the following table:
Type of PPE
The first three data are declared in the UNI 9432 standard, whereas the user has the possibility to use a different value or to perform the calculation with the laboratory theoretical attenuation by choosing β =1.
Finally the user is asked to select the value of α: this represents the coverage factor that provides the assumed protection value APVf of the hearing protector for a desired protection performance on the tested population:
Value of α
Protection performance x
The value of α given in the instruction manuals by the manufacturers producing hearing protectors and used for calculating the assumed protection value APVf is α =1. For the sake of caution the procedure allows to select even higher values.
At this point, by pressing the appropriate button, the procedure performs the effectiveness calculation. The “Results” section displays:
The assumed protection value APVf corresponding to each octave band defined as:
The assumed protection value obtained when considering the β factor: APVf * β
The attenuated spectrum of the source resulting from the assumed protection value when considering the β factor:
The C- and A-weighted total sound pressure levels of the non attenuated source : LeqC and LeqA
The sound pressure level of the attenuated source L'eqA
The assessment of the effectiveness of the hearing protectors