Noise calc (dB addition/distance attenuation)

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Inputs

Bulk input (comma/line break delimited)

Bulk input of sound source dB

Results

composite noise level

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calculation formula

10log10(Σ 10^(Li/10))

Purpose

Sound level composition of the same index

Level L2 at distance r2

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Amount of change ΔL

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distance r2

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Applicable formula	—
premise	Free field geometric attenuation only (reflections, shielding, ground effects, and air absorption are not considered)

Graph (distance decay mode)

point	distance	level

Premise/Formula/FAQ

Formula used in this calculation

dB addition: Ltotal = 10 log10( Σ 10^(Li/10) )

Distance attenuation (point source): L2 = L1 - 20 log10(r2/r1)

Distance attenuation (line sound source): L2 = L1 - 10 log10(r2/r1)

Assumptions and limitations

This is an estimate assuming a free sound field (no reflections).
A line sound source (10log) is a valid approximation to the sound source length at short distances, and approaches a point source at long distances.
Shielding, ground effects, air absorption, wind, temperature stratification, etc. are not considered.
Please use the same input dB (all dBA, etc.).

Frequently asked questions

What is 60 dB + 60 dB?

Two equal sources add by energy, not by simple arithmetic. The combined level is about 63 dB, which is a 3 dB increase over either source alone.

How much does the level drop when distance doubles?

For a point source in a free field, doubling distance lowers the level by about 6 dB. For a line-source approximation, the drop is about 3 dB.

Will this match a real measurement?

Use it for rough checks and comparison, not for compliance work. Reflections, shielding, ground absorption, weather, and source directivity can all move a field measurement away from the simple model.

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