Sound Attenuation Over Distance Calculator

Model sound decay from any reference point. Choose spherical, cylindrical, or custom absorption settings here. Get clear dB predictions for outdoor and indoor projects.

All values are in decibels (dB) and distance units you choose.
Internally computed in meters, then displayed back.
Choose the geometry that best matches the source and environment.
Typical: n=2 (point) or n=1 (line). Use 0 for no spreading.
Often SPL measured at the reference distance.
Common choice: 1 m (or 3.28 ft).
Distance where you want a prediction or requirement.
Used for “required level” and “maximum distance” modes.
Presets are rough ranges; verify with your context.
Applied over (target − reference) distance.
Optional: directional boost toward the receiver.
Wind, temperature gradients, reflections, or measurement offset.
Extra attenuation due to ground interaction (simplified).
Insertion loss of a wall, berm, or screen.

Formula used

This calculator combines geometric spreading, air absorption, and simple extra losses:

  • Adjusted reference level: L₁ = Lref + DI + C
  • Spreading loss: Lspread = k · log₁₀(d₂/d₁), where k=20 (spherical), k=10 (cylindrical), or k=10·n (custom).
  • Air absorption loss: Lair = α · (d₂ − d₁)
  • Extra losses: Lextra = Lground + Lbarrier
  • Predicted level: L₂ = L₁ − Lspread − Lair − Lextra

Notes: This is a practical estimator. Complex environments may need frequency-band models or standards-based methods.

How to use

  1. Pick a calculation mode (predict, required level, or maximum distance).
  2. Enter the reference level and reference distance from measurement or spec data.
  3. Choose a spreading model that matches the source geometry.
  4. Set air absorption α (or pick a preset range), then add optional losses and corrections.
  5. Click Calculate and export results using CSV or PDF.

Tip: Keep distances consistent, and treat extra losses as conservative if unsure.

Example data table

Reference level Reference distance Model Air absorption Target distance Predicted level
90 dB 1 m Spherical 0.6 dB/km 10 m ≈ 70.0 dB
90 dB 1 m Spherical 0.6 dB/km 50 m ≈ 56.0 dB
90 dB 1 m Spherical 0.6 dB/km 100 m ≈ 49.9 dB
90 dB 1 m Spherical 0.6 dB/km 200 m ≈ 43.9 dB
90 dB 1 m Spherical 0.6 dB/km 500 m ≈ 35.7 dB

These examples assume no barrier/ground losses and no corrections.

Sound attenuation over distance guide

1) What this calculator estimates

This tool estimates how sound level (in dB) changes as the receiver moves away from a reference point. It combines geometric spreading, optional air absorption, and simple losses like barriers and ground effects. Use it for planning, comparison, and “what-if” checks when you have a known reference level.

2) Typical decay rates you can sanity-check

For a point source in free field, spherical spreading predicts about 6 dB drop for each distance doubling (20·log10). A line-like source trends closer to 3 dB per doubling (10·log10). These rules help you confirm whether your inputs and results are in a realistic range.

3) Reference level and reference distance data

A common starting point is a measured level at 1 m or 3.28 ft. If you only have a datasheet level at a different distance, enter that distance as the reference. The calculator then scales to any target distance using the chosen spreading model and losses.

4) Air absorption values and distance impact

Air absorption is entered as α in dB/km or dB/m and is applied over (target − reference) distance. For short runs like 10–100 m, air loss is often small; for hundreds of meters it can become noticeable. Use the presets as rough ranges, then replace with your own verified values.

5) Directivity index and correction factors

Directivity index (DI) adds a directional boost when the source aims toward the receiver. A positive DI increases predicted level at distance, while a negative correction can represent unfavorable wind, shielding by geometry, or conservative safety margins. Keep corrections small unless you have strong evidence.

6) Barrier and ground losses as practical inputs

Barrier loss models the insertion loss from a wall, berm, or screen, commonly ranging from a few dB to tens of dB, depending on height and placement. Ground loss is highly site-dependent; treat it as a simplified adjustment that helps compare scenarios rather than an exact acoustics simulation.

7) Three advanced modes for real projects

Besides predicting level at a distance, you can compute the required source level to meet a target at a receiver location, or solve the maximum distance where a target level is still achieved. These modes help with compliance checks, venue planning, and selecting quieter equipment.

8) Example data walkthrough

Suppose 90 dB at 1 m with spherical spreading and α=0.6 dB/km. At 50 m, spreading is 20·log10(50/1)=33.98 dB and air loss is 0.6·(49/1000)=0.029 dB, so the estimate is about 56.0 dB before extras. Add a 10 dB barrier and you would expect about 46.0 dB.

FAQs

1) Is this a replacement for standards-based noise modeling?

No. It is a practical estimator for planning and comparison. For compliance work, use standards-based methods, banded frequency models, and site measurements where required.

2) Which spreading model should I choose?

Use spherical for point-like sources in open space. Use cylindrical for long, line-like sources. Use custom n when you want to match observed decay between these cases.

3) Why does air absorption feel too small at short distances?

Because α is often expressed per kilometer and the tool applies it only over the extra distance beyond the reference. Over 10–100 meters, the air-loss term can be a fraction of a dB.

4) What does DI do in the results?

DI adds a directional gain at the reference level before attenuation. If the source is aimed toward the receiver, DI can increase predicted level; if not, use DI=0 or a conservative correction.

5) Can I use it for indoor rooms?

You can approximate near-field decay, but reflections and reverberation can dominate indoors. For rooms, combine distance spreading with room acoustics measures or dedicated reverberation models.

6) How should I pick barrier and ground losses?

Use measured insertion loss if available. Otherwise, run multiple scenarios (for example 0, 5, 10, 15 dB) to bracket outcomes and choose conservative values for planning.

7) What is a good reference distance to use?

Use the distance at which your reference level was measured or specified. Many sources use 1 m, but any positive distance works as long as the reference level matches it.