Reference documents

  • ISO 11201:2010 : Accoustics - Noise emitted by machinery and equipment – Determination of emission sound pressure levels at a work station and at other specified positions in an essentially free field over a reflecting plane with negligible environmental corrections
  • ISO 7779:2010 : Acoustics – Measurement of airborne noise emitted by information technology and telecommunications equipment

Convert sound power to sound pressure

L_p is the sound Pressure in dBA
L_w is the sound Power in dBA
Q is Directivity factor (1=full sphere, 2=half sphere, 4= quarter of sphere)
r is the distance in meter

Compute background noise correction factor

K_{1a} is a correction factor for accoustic measure depending on bakground noise value delta.
Formula is the following :
Where :
Delta_L=A-weighted measure - A-weighted background noise
Delta_L > 15dBa then K_{1a}=0

Measure deviation

If Delta_L > 10dBa then measure is Grade1. Deviation is pm 0.5dBa
If 6dBa <= Delta_L <= 10dBa then measure is Grade2. Deviation is pm 1.5dBa
If 6dBa < Delta_L then measure is not compliant with ISO standard. Result is an estimated upper value

Sound Pressure differences

  • Every 3dBA, sound pressure level doubles
  • Every 10dBA, human feels the noise doubles
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