Acoustics toolbox

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Published on 14 Apr 2020 - Updated on 25 Jun 2020

This page provides useful information on acoustic domain. Goal is to help to plan sound level and describe how to measure.

Reference documents

ISO 11201:2010 : Acoustics - 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

Useful formulas

Convert sound power to sound pressure

$$L_p=L_w-|{10.log_{10}(\frac{Q}{4 \pi r^2})}|$$ \(L_p\) is the sound Pressure in \(dB_A\)
\(L_w\) is the sound Power in \(dB_A\)
\(Q\) 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 acoustic measure depending on background noise value delta. It shall be substracted from measured sound pressure or power
$$ K_{1a}=-10.log(1-10^{0.1\Delta_L}) $$ \(\Delta_L=\)A-weighted measure - A-weighted background noise
If \(\Delta_L > 15 \medspace dB_A\) then \(K_{1a} = 0\)

Measure deviation

If \( \Delta_L > 10 \medspace dB_A \) then measure is Grade 1. Deviation is \( \pm 0.5 \medspace dB_A \)
If \( 6 \medspace dB_A \leq \Delta_L \leq 10 \medspace dB_A \) then measure is Grade 2. Deviation is \( \pm 1.5 \medspace dB_A \)
If \(6 \medspace dB_A < \Delta_L \) then measure is not compliant with ISO standard. Result is an estimated upper value

Sound Pressure differences

  • Every \( 3 \medspace dB_A \), sound pressure level doubles
  • Every \( 10 \medspace dB_A \), human feels the noise double