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Sound Pressure Level & Distance Attenuation Calculator

Acoustic energy radiates outward spherically from a point sound source, spreading across increasingly large surface areas.

Sound pressure level at the reference distance in dB SPL (90 dB = power lawnmower).

Distance at which the initial sound level was measured (typically 1 meter).

Distance to the listener or receiver position in meters.

Reflective boundary condition around the acoustic source.

Calculated Result
70.0 dB

Sound Level at Distance (dB SPL)

Attenuation Drop

20.0 dB

Perceived Loudness

25.0%

Distance Ratio

10.0×

Radiation Field

free spherical

Calculation Breakdown

  1. Distance Geometric Divergence Ratio10 m / 1 m = 10.00× distancer2r1\frac{r_2}{r_1}
  2. Inverse Square Law SPL AttenuationDrop of 20.0 dB (6.02 dB per distance doubling)L2=L1−20log⁡10(r2r1)L_2 = L_1 - 20 \log_{10}\left(\frac{r_2}{r_1}\right)
  3. Target Sound Pressure Level70.0 dB SPL @ 10 mL2L_2
  4. Perceived Psychoacoustic Loudness25.0% of reference volume at 1 m2ΔL/102^{\Delta L / 10}

Sound Level Decay vs Distance (90 dB at 1 m)

Interactive visualization based on your current inputs

Sound Level (dB)
0.0234568901 m2 m4 m8 m16 mDistance (m)Sound Level (dB)

What Is the Sound Pressure Level & Distance Attenuation Calculator?

Sound distance attenuation describes the reduction in sound pressure level as acoustic wave fronts diverge geometrically from an emitter.

It is a fundamental tool in architectural acoustics, environmental noise impact assessments, and concert audio PA system design.

How Does the Sound Pressure Level & Distance Attenuation Calculator Work?

Sound radiates outward on expanding spherical wave fronts with surface area A = 4πr².

Because total acoustic power is conserved, acoustic intensity (Watts/m²) decays with the inverse square of distance.

Sound Pressure Level & Distance Attenuation Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

L2=L1−20log⁡10(r2r1)L_2 = L_1 - 20 \log_{10}\left(\frac{r_2}{r_1}\right)

Sound intensity drops with 1/r² (inverse square law), which translates on the logarithmic decibel scale to a 6.02 dB drop per doubling of distance.

How to Use the Sound Pressure Level & Distance Attenuation Calculator

  1. Enter the sound measurement in dB SPL and the measurement distance in meters.
  2. Provide the target listener distance.
  3. Select whether sound radiates spherically in open air or hemispherically over flat ground.

Step-by-Step Example Calculation

Lawnmower Noise at 10 Meters

Input Values:

initialDb:90
initialDistance:1
targetDistance:10
environment:free_spherical
Worked Steps: A 90 dB lawnmower at 1 meter attenuates by 20 dB at 10 meters, producing 70.0 dB SPL (a 75% drop in psychoacoustic perceived loudness).

Understanding Your Result

Target Sound Level (dB SPL): Decibel reading at listener position.

Perceived Loudness (%): Psychoacoustic percentage relative to reference level.

Safety Assessment: Evaluates whether level exceeds workplace hearing protection criteria.

Factors That Affect the Result

  • Distance Ratio: Geometric divergence is the primary driver of sound attenuation.
  • Reflections: Enclosures and walls reflect sound, preventing true free-field decay.

When Should You Use This Calculator?

  • Evaluating generator, HVAC chiller, or industrial machinery noise at property boundaries.
  • Concert sound reinforcement speaker throw distance modeling.

Assumptions & Limitations

  • Assumes a point acoustic source (line sources like highways decay at 3 dB per doubling instead of 6 dB).
  • Neglects air molecular relaxation absorption over very long distances.

Frequently Asked Questions

Calculation Accuracy & Reference Note

Standard ISO 9613-2 geometric divergence formulation with 100% mathematical precision.

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