Plant noise mapping calculator
Noise contours show where hearing protection is required and whether a new package pushes a working area over its limit. This module propagates the sound power of each item of equipment across the plot-plan using free-field inverse-square spreading and sums the contributions logarithmically at every grid point.
Open the Noise Mapping moduleWhat this calculator returns
- Sound pressure level at any receptor point
- Noise contour map across the plot-plan
- Dominant contributing source at a selected location
- Areas exceeding a nominated exposure limit
Required inputs
- Equipment coordinates and sound power levels
- Receptor height and grid resolution
- Limit level for contour shading
Calculation method
Each source is treated as a point radiator; the sound pressure level falls with the logarithm of distance under hemispherical free-field spreading.
Contributions from all sources are combined on an energy basis rather than arithmetically.
The resulting field is gridded and contoured over the plot-plan extents.
Governing equations
Lp = Lw - 20 log10( r ) - 8Free-field sound pressure level from a point source at distance r.
Lp_total = 10 log10( sum( 10 ^ ( Lp_i / 10 ) ) )Logarithmic summation of multiple sources at a receptor.
Nomenclature
- Lw
- sound power level of the source, dB re 1 pW
- Lp
- sound pressure level at the receptor, dB(A)
- r
- distance from source to receptor, m
Assumptions and limitations
- Free-field propagation with no barriers, reflections or ground absorption.
- Omnidirectional sources at their nominal sound power.
- Atmospheric absorption is neglected at typical plot-plan distances.
Reference practice
- Free-field propagation consistent with the point-source treatment of ISO 9613 for open plant areas.
Worked example
A compressor with a sound power level of 105 dB(A) assessed at 30 m in a free field.
| Step | Value | Basis |
|---|---|---|
| Source level Lw | 105 dB(A) | Sound power from the vendor datasheet |
| Distance term | 20 log10 (30) = 29.5 dB | Spherical divergence |
| Constant | -8 dB | Free-field point-source relation Lp = Lw - 20 log10 r - 8 |
| Result | about 67 dB(A) | Below the 85 dB(A) hearing-protection threshold |
Each doubling of distance removes 6 dB, so distance alone rarely solves a noise problem near a high-power source; acoustic enclosures or silencers are needed close in.
Illustrative numbers only — rerun the module with the project basis of design before using any result.
Common questions
Why does the map use sound power and not sound pressure?
Sound power is a property of the equipment, independent of where it is measured. Sound pressure at a receptor is derived from it plus geometry.
How are multiple sources combined?
Logarithmically on an energy basis, so two equal sources add 3 dB rather than doubling the level.
What limits usually apply?
85 dB(A) for hearing protection zones in plant areas and much lower values, often 55 to 70 dB(A), at the site boundary.
Related calculators
- Gas Detection Mapping — Gas detection coverage mapping