Calculate sound pressure level attenuation over distance for point and line sources with air absorption and atmospheric effects.
The distance attenuation calculator determines how sound pressure levels decrease as a function of distance from the source. Sound intensity follows the inverse square law for point sources (−6 dB per doubling of distance) and an inverse distance relationship for line sources such as highways (−3 dB per doubling).
Understanding distance attenuation is essential for environmental noise assessment, architectural acoustics, outdoor event planning, and industrial noise control. Engineers and acousticians rely on these calculations to predict noise levels at receptors, design buffer zones, and ensure compliance with noise ordinances. The calculator accounts for both geometric spreading and atmospheric absorption, which becomes significant at higher frequencies and longer distances.
Atmospheric absorption depends on temperature, humidity, and frequency. At standard conditions (20°C, 50% RH), absorption at 1 kHz is approximately 1.5 dB/km, rising to over 100 dB/km at 10 kHz. This calculator provides a simplified absorption input while considering both point and line source geometries for flexible noise modeling.
Distance attenuation calculations are fundamental to noise impact assessments, urban planning, and audio system design. Whether you're sizing a buffer zone for a construction site, predicting concert sound levels at neighboring properties, or estimating jet engine noise at airport boundaries, this calculator provides quick answers. It supports both point and line source models and includes atmospheric absorption for more realistic long-distance estimates.
Point source geometric attenuation: L₂ = L₁ − 20·log₁₀(d₂/d₁), Line source geometric attenuation: L₂ = L₁ − 10·log₁₀(d₂/d₁), Air absorption loss: Lₐ = α·Δd/1000 where α is in dB/km. Total attenuation = geometric + air absorption.
Result: 69.9 dB SPL at 100 m
A 110 dB point source at 1 m drops by 20·log₁₀(100) = 40 dB geometrically, plus 1.5 × 99/1000 ≈ 0.15 dB air absorption, giving ~69.9 dB at 100 m.
Use consistent units, verify assumptions, and document conversion standards for repeatable outcomes.
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For a point source in free field, sound intensity drops with the square of distance, resulting in a −6 dB loss each time the distance doubles. Use this as a practical reminder before finalizing the result.
A line source (like a highway or railway) radiates sound cylindrically rather than spherically, producing only −3 dB per doubling of distance. Keep this note short and outcome-focused for reuse.
Air molecules absorb sound energy, especially at high frequencies. Over hundreds of meters, this absorption significantly reduces high-frequency content.
Yes. Downwind propagation refracts sound toward the ground (less attenuation), while upwind conditions create shadow zones with more loss.
Prolonged exposure above 85 dB can cause hearing damage. Most noise ordinances limit residential exposure to 55–65 dB during daytime.
No. This calculator models free-field propagation. Barriers, ground reflection, and terrain effects require more advanced modeling.