# Acoustics toolbox

Published on 14 Apr 2020 - Updated on 09 Mar 2021

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