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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 
0Treshold of hearing-
20Extremely softRustling leaves, quiet room
40Very softRefrigerator humming
60Moderately loudNormal conversation, restaurant
80Very loudCity traffic, lorry
100Extemely loudSymphonic orchestra, farm tractor
120Treshold of feelingJet taking off

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