Sound pressure level (Lp)
Is a measure of the sound energy emitted from a source of noise, expresses in decibel or dBA
Sound power level (Lw)
Is the above but measured in predefined conditions
The sound power level is independant on:
- the location of the equipment
- the environmental conditions, and
- the distance from the measurement point
The sound power level can be considered as the more precise of the two. The sound power will have a higher value than the sound pressure, bon't be mislead by this.
The impact of decibels:
| Lp dB(A) | Perceived loudness | Sound |
| 0 | Treshold of hearing | - |
| 20 | Extremely soft | Rustling leaves, quiet room |
| 40 | Very soft | Refrigerator humming |
| 60 | Moderately loud | Normal conversation, restaurant |
| 80 | Very loud | City traffic, lorry |
| 100 | Extemely loud | Symphonic orchestra, farm tractor |
| 120 | Treshold of feeling | Jet taking off |