Decibel is a logarithmic unit used to describe the ratio of the signal level - power, sound pressure,voltage, intensity, etc. Decibel is a logarithmic unit used to describe the ratio of the signal level -power, sound pressure, intensity or several other things.The decibel can be expressed as:
Decibel = 10 log (P / Pref)
Where
• P = signal power (W)
• Pref = reference power (W)
Note! Doubling the signal level increases the decibel with 3 dB (10 log (2)).
Adding Equal Sound Power Sources
The sound power and sound power level is commonly used to specify the emitted noise or sound from technical equipment as fans, pump and other machines.
The logarithmic decibel scale is convenient when calculating resulting sound power levels and sound pressure levels for two or more sound or noise sources.
Lwt = 10 log (n N / N0) = 10 log (N / N0) + 10 log (n)
= Lws + 10 log (n)
Where
• Lwt = Total sound power level (dB)
• Lws = Sound power level from each single source (dB)
• N = sound power (W)
• N0 = 10-12 - reference sound power (W)
• n = number of sources
Note: Adding two identical sources will increase the total sound power level with 3 dB (10 log (2)).
Adding Equal Sound Pressure Levels
The resulting sound pressure level when adding equal sound pressure can be expressed as:
Lpt = Lps + 20 log (n)
Where
• Lpt = total sound pres sure (dB)
• Lps = Sound pressure level from each single source (dB)
• n = number of sources
Adding Sound Power from Sources at different Levels
The sound power level from more than one source can be calculated as:
Lwt = 10 log ((N1 + N2 ... + Nn) / N0)
