Noise Propagation Distance Calculator

Work out noise propagation distance instantly with clear inputs, formula shown and shareable results.

About Noise Propagation Distance Calculator

A point source spreads spherically, so level falls 6 dB per doubling of distance; a line source such as a road spreads cylindrically and falls only 3 dB per doubling. Atmospheric absorption adds a small further loss that becomes significant over hundreds of metres, particularly at high frequency.

Formulas

Point source

Lp = Lw - 20 log10(distance) - 8 for hemispherical radiation

Line source

Lp = Lw - 10 log10(2 pi x distance)

Worked example

With the default values below, Noise Propagation Distance Calculator returns Sound Pressure Level At Distance of 56.500. Change any input above and every figure here is recalculated in your browser.

Inputs used

Sound Power Levelminimum 0 dB: 105 dB
Distance From Sourceminimum 0 m: 100 m
Source Typeone of Point source, hemispherical, Point source, spherical, Line source (road or rail): Point source, hemispherical
Target Noise Levelminimum 0 dB: 45 dB

Results

Sound Pressure Level At Distance: 56.500
Level Before Air Absorption: 57.000
Decay Per Doubling Of Distance: 6.0
Distance To Reach Target Level: 375.8

Step by step

1Values used
2Point source
3Line source
4Sound Pressure Level At Distance= 56.500
5Level Before Air Absorption= 57.000
6Decay Per Doubling Of Distance= 6.0
7Distance To Reach Target Level= 375.8

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Noise limits and assessment methods are set by planning conditions, permits or occupational regulation. Use the prescribed method rather than a simplified estimate.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Noise limits and assessment methods are set by planning conditions, permits or occupational regulation. Use the prescribed method rather than a simplified estimate.

Frequently Asked Questions

Why do roads carry so much further than point sources?

Cylindrical spreading loses only 3 dB per doubling instead of 6. A road audible at 100 m is still audible at 400 m where a single machine would have faded.

What else affects propagation?

Ground absorption, meteorological conditions — downwind and temperature inversions increase levels substantially — screening by terrain and buildings, and reflections. Simple spreading models can be several decibels out.