Decibel Addition Calculator
Calculate the combined sound level when two noise sources are added together.
Results
Decibels add logarithmically because they represent sound intensity on a log scale. Two equal 80 dB sources combine to 83 dB, not 160 dB. Adding a second source that is 10 dB quieter has almost no effect. This calculator is essential for noise assessments, speaker system design and environmental acoustics.
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Frequently asked questions
10 × log10(10⁸ + 10⁸) = 10 × log10(2 × 10⁸) = 83.01 dB. Two equal sources always produce a 3 dB increase, regardless of the level.
Decibels are logarithmic. 80 dB means 10⁸ intensity units. Two sources give 2 × 10⁸, and log10(2 × 10⁸) = 8.301, so 10 × 8.301 = 83 dB. The math prevents simple addition.
A 3 dB increase is barely perceptible to most people. It doubles the sound intensity but humans perceive a 10 dB increase as roughly twice as loud. So 83 dB sounds only slightly louder than 80 dB.
Adding 70 dB to 80 dB gives 80.41 dB - an increase of only 0.41 dB. A source 10 dB below another adds less than 0.5 dB and is inaudible in practice.
Convert each to intensity, sum them, convert back. Three 80 dB sources: 10 × log10(3 × 10⁸) = 84.77 dB. Each doubling of identical sources adds 3 dB: 2 sources = +3, 4 = +6, 8 = +9 dB.