Adding up noise
Sound pressure levels are measured on a logarithmic scale, so they cannot be added arithmetically, they must be converted
back to a linear scale. The total sound pressure level of incoherent sources can be calculated using the following equation:
dBtotal= 10 · log10 · (10dB1/10 + 10dB2/10 + ··· +10dBn/10)
If there are two sound sources of 50 dB each, then the combined sound pressure level will not be 100dB, but only
This equation can be used only for the general case in which the sources have different frequencies and random phase relation (incoherent sources).
However, if the sound comes from sources with the same frequency (coherent sources), above equation cannot be used, phase needs to be considered.