Originally posted by: Extrarius
Originally posted by: TuxDave
You want a nice formula, ok....
10*log(base 10) of [10^(db1/10) + 10^(db2/10) + .....]
This is the correct way to 'add' decibel values - you convert from the logarithmic scale back to linear, add, then convert back to the logarithmic scale
Decibels are a logarithmic system: db = 10 * log10(value)
Thus, to undo it, Value = 10 ^ (db / 10)
Then you add up the values to the the sum. To convert that back into decibels, db_sum = 10 * log10(value_sum)
Or, for the question of 8 * 25db fans:
value = 10 ^ (25/10) = ~316.23
value_sum = 8 * value = 2529.84
db_sum = 10 * log10(value_sum) = 10 * log10(2529.84) = 10 * 3.4 = 34 db
All this only works if all the db values are relative to the same base. Also, this is only in an ideal environment where they all add perfectly and no dampening or amplification occurs. In reality, the total noise should be somewhat lower or higher.