Noise Reduction Calculator Formula
Understand the math behind the noise reduction calculator. Each variable explained with a worked example.
Formulas Used
Combined Noise Level
combined = 10 * log10(pow(10, source1/10) + pow(10, source2/10))After Barrier Reduction
after_barrier = 10 * log10(pow(10, source1/10) + pow(10, source2/10)) - barrier_reductionVariables
| Variable | Description | Default |
|---|---|---|
source1 | Sound Source 1 Level(dB) | 85 |
source2 | Sound Source 2 Level(dB) | 82 |
barrier_reduction | Barrier Insertion Loss(dB) | 10 |
How It Works
Combining Sound Levels
Sound levels in decibels are logarithmic, so they cannot simply be added.
Formula
L_total = 10 log10(10^(L1/10) + 10^(L2/10))
This converts each level to linear power, sums them, and converts back. Two equal sources produce a combined level 3 dB higher than either alone (not double). A noise barrier reduces the combined level by its insertion loss.
Worked Example
Two machines at 85 dB and 82 dB with a 10 dB barrier.
- 0110^(85/10) = 316,227,766
- 0210^(82/10) = 158,489,319
- 03Sum = 474,717,085
- 04L_total = 10 x log10(474,717,085) = 86.7 dB
- 05After 10 dB barrier: 86.7 - 10 = 76.7 dB
Frequently Asked Questions
How much louder is a 3 dB increase?
A 3 dB increase doubles the sound power (barely noticeable). A 10 dB increase is perceived as roughly twice as loud. A 20 dB increase sounds four times as loud.
What noise levels require hearing protection?
Most regulations require hearing protection above 85 dB for an 8-hour exposure. For every 3 dB increase, the allowable exposure time halves: 88 dB = 4 hours, 91 dB = 2 hours, 94 dB = 1 hour.
How effective are noise barriers?
Typical insertion loss: solid wall/fence 5-15 dB. Earth berm 5-10 dB. Building facade 20-35 dB. Enclosure around a machine 15-30 dB. Barriers work best for high-frequency noise and when source and receiver are close to the barrier.
Ready to run the numbers?
Open Noise Reduction Calculator