What is sound pressure/sound power?

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