1. Sound Intensity = Power / Area (Watts / Meter2)
1 Bel = Log10 (Sound Intensity1 / Sound Intensity2)
10 Decibels (BD) = 1 Bel
Sound Power = Sound Pressure2
Sound Pressure Level (SPL) in DB’s =
10 x Log10 (Power1 / Power0 ) = 20 x Log10 (P1 / P0 )
DB = 0 => P1 = P0
Common Reference:
0 DB = 20 uN/M2 = 20 uPascals = 20 ubars
1000 Hz Pure Tone Barely Audible under Ideal Conditions

2. Equal Intensity Phon
Base 1000 Hz Pure Tone
Second Tone (Different Frequency)
Judged To Be Equal Intensity
1 Phon = Loudness of DB
Example 40 DB same as DB
Since 40 DB = 40 Phon then
50 65 DB = 40 Phon

3. Relative Intensity (Sone)
Loudness of DB = 40 Phons = 1 Sone
Ten Fold Increase Loudness = Double the Sones
Ten Fold Increase Loudness (Increase by 10 DB) = 2 Sones