Drawing No. EH–ES–003 // Environmental & Safety Engineering
Reviewed August 2026
Estimate free-field sound-pressure level at a receiver from point or idealized line sources, with optional atmospheric absorption and logarithmic addition of multiple independent sources.
Propagates a known sound-pressure level from a reference distance to a receiver using geometric spreading and an optional effective atmospheric-absorption term. In multiple-source mode, each contribution is propagated separately and then combined on an acoustic-energy basis.
Receiver level, attenuation and source-dominance summary.
A site has two noise sources near a shared property-line receiver: a set of cooling tower fans and a pump house. Both source levels are specified at the source (1 m), the standard convention this calculator now uses, atmospheric absorption ignored for clarity.
EngineerHub.orgMultiple sources.98 dB at the source, receiver at 50 m.90 dB at the source, receiver at 30 m.64.0 dB60.5 dB65.6 dBThis calculator estimates how a given source level arrives at a receiver. Reducing that arriving level means acting on one of three things: the source itself, the path between source and receiver, or the receiver — in that order of usual effectiveness.
Source control — the most effective lever, because it reduces the level everywhere at once,
not just for one receiver.
Every dB removed at the source is a dB removed in every direction, for every receiver, permanently
— which is why it is almost always the first thing worth pursuing, even though it is often the
hardest to retrofit onto equipment already installed.
Path control — what this calculator actually models.
Every input on this page other than the source level itself is a path-control lever:
Two further path measures are genuinely effective on real sites but are not modelled by this calculator, since they need more than a distance-and-absorption estimate:
Receiver control — the last resort, not a substitute for the above.
Hearing protection or sound-rated building facades protect a specific receiver but do nothing for
anyone else nearby, and do nothing to the source itself. This is standard practice for occupational
noise exposure inside a plant, but it is not usually an acceptable answer for a community noise
complaint or an environmental permit condition — regulators and neighbours generally expect the
source or path to be addressed first.
Engineering basis, assumptions, interpretation and practical limitations.
Point source: ΔL = 20 log₁₀(d₂/d₁), equivalent to approximately 6 dB reduction for each doubling of distance in an ideal free field.
Ideal line source: ΔL = 10 log₁₀(d₂/d₁), approximately 3 dB per distance doubling while line-source behavior remains a reasonable approximation.
Real industrial sources can transition between these behaviors as distance becomes large relative to the physical source dimensions.
The calculator applies a simple linear term α(d₂ − d₁). The entered coefficient is an effective broadband screening value. Real atmospheric absorption varies strongly with frequency, temperature, relative humidity and atmospheric pressure.
For environmental-noise assessment, octave- or one-third-octave-band propagation methods are generally more appropriate than a single broadband coefficient.
Independent sound-pressure levels are combined by acoustic energy:
Ltotal = 10 log₁₀(Σ 10^(Li/10))
Two equal sources increase the level by about 3 dB. A source much quieter than the dominant contribution adds little to the combined result.
These effects can change a real receiver level by several decibels or more.
Use a dedicated environmental-noise method or acoustic model when the result supports permitting, compliance, community-noise assessment, barrier design, complex site layouts or long-distance propagation. Occupational noise exposure also requires time-weighted exposure assessment rather than this distance-only propagation screen.
Practical questions about source geometry, decibels and model limitations.
Enter sound pressure level measured or specified at a known reference distance. Sound power level cannot be inserted directly without a radiation and propagation conversion.
In an ideal free field the acoustic energy spreads over an area proportional to distance squared. Sound-pressure level therefore decreases by about 20 log10(2), or 6 dB, for each doubling.
Use it only when the source is long enough relative to the receiver distance that cylindrical spreading is a reasonable approximation, such as a sufficiently long traffic corridor or distributed linear source. Many industrial sources behave as point sources at larger distances.
No. Independent source levels must be converted to acoustic-energy ratios, summed, and converted back to decibels. Two 60 dB sources combine to about 63 dB, not 120 dB.
No. Atmospheric absorption is frequency- and weather-dependent. A single broadband coefficient is a screening approximation.
Not by itself. Compliance studies typically require frequency-dependent propagation, source directivity, terrain, ground effect, barriers, meteorology and the applicable local or international assessment method.
Include the inputs and assumptions used.