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Find the dB SPL at any target distance with point, line, and plane models, plus loss, pressure and intensity ratios and a 6-tier reference chart.

📘 How to Use

  1. Enter the source dB SPL and the reference distance it was measured at
  2. Set the target distance with the slider
  3. Pick the point, line, or plane propagation model

Sound Pressure Level Distance Attenuation Calculator

dB SPL
m

Distance where the source dB SPL was measured (typically 1 m)

10 m
0.1 m 10 m 100 m 500 m

6 dB drop per distance doubling (free field, outdoor speaker)

dB SPL at target distance
80.0 dB SPL
Loss -20.0 dB
Pressure ratio
0.10x
Intensity ratio
0.01x
130 dB
Jet takeoff (30 m from runway)
100 dB
Concert front row, subway pass
85 dB
Heavy traffic / large machinery
60 dB
Normal conversation, AC running
40 dB
Quiet library, residential night
20 dB
Whisper, leaves rustling

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※ L₂ = L₁ − N × log₁₀(d₂/d₁). Point N=20, line N=10, plane N=0

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Article

Sound Pressure Level Distance Attenuation Calculator | How dB SPL Drops With Distance

Enter a source dB SPL, its reference distance, and a target distance to work out the attenuated level. Switch between point-source, line-source, and plane-wave propagation models to compare how an outdoor speaker, a line array, and a near-field source lose level over distance.

💡 About this tool

A speaker spec sheet might say "100 dB SPL at 1 m," but what you actually get 20 m back in the crowd is a different number. Sound spreads over a larger area as it travels, and for a point source it drops 6 dB every time you double the distance. That 6 dB figure comes straight from the inverse-square law: the sound energy spreads spherically, the sphere's surface area grows with the square of the distance, so intensity quarters and the level falls 6.02 dB (rounded to 6) per doubling in a free field.

The tool uses L₂ = L₁ − N × log₁₀(d₂/d₁) and swaps the coefficient N per model: 20 for a point source, 10 for a line source, 0 for an ideal plane wave. Alongside the attenuated dB SPL it reports the loss, the pressure ratio, and the intensity ratio, plus a six-tier reference chart (whisper 20 dB, conversation 60 dB, heavy machinery 85 dB, concert front row 100 dB) so you can sanity-check what the calculated number actually sounds like.

🧐 Frequently Asked Questions

Q. Why do point and line sources attenuate differently? A point source radiates spherically, so its surface area grows with the square of the distance and the level drops 6 dB per doubling. A line source (a line array or a long noise source) radiates cylindrically, so the area grows linearly and the level drops only 3 dB per doubling. That is why line arrays carry to the back of a room more evenly.

Q. Does a line array always lose 3 dB per doubling? No. The 3 dB/doubling figure is a near-field (cylindrical) approximation. Past a transition distance the wavefront reverts to spherical spreading and the array behaves like a point source again at 6 dB/doubling. The plane-wave case (N=0) is an even more idealized model; a perfect plane wave does not exist in practice.

Q. How much do I lose at 10× the distance? For a point source, 20 × log₁₀(10) = 20 dB. A 100 dB source reads 100 dB at 1 m, 80 dB at 10 m, and 60 dB at 100 m.

Q. Will the real world match this number? It is a free-field figure with no reflections or obstacles. Real venues add wall reflections, ground absorption, air absorption of high frequencies, and wind or temperature gradients, so treat the result as a planning estimate rather than a measurement.

📚 Why the model matters in live sound

The point-versus-line difference is one of the first things a live-sound engineer internalizes. Cover a long room with a single point-source box and the front rows get blasted while the back still strains to hear, because every doubling of distance costs 6 dB. Hang a line array and the cylindrical 3 dB/doubling behavior flattens that front-to-back gradient, so the back is louder without cranking the front. The catch the pros stress: that flat behavior only holds within the array's coupling window, and once you pass it the rig slides back toward inverse-square spreading. Knowing where that transition sits is the difference between a rig that covers a venue and one that just fatigues the front rows.