Free · Waves and acoustics calculators 🔊

Point-Source Sound Level at a New Distance

Estimate the sound-pressure-level change between two source distances under ideal spherical spreading.

  • Formula & worked example
  • Private in your browser
  • No signup
Go to tool

Calculator inputs

Loading calculator…

How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A level of 80 dB at 1 m becomes 60 dB at 10 m under ideal spherical spreading: a 20 dB decrease.

Level₂ = level₁ − 20 log₁₀(distance₂ / distance₁)

Worked example

Enter these known values and leave the other values blank.

First distance from the source
1 m
Sound pressure level at first distance
80 dB (20 log₁₀)
Second distance from the source
10 m
Sound pressure level at second distance
60 dB (20 log₁₀)
Level decrease from first point to second
20 dB (20 log₁₀)

Assumptions and limitations

  • Both distances are positive and measured from the same source. Sound levels can be positive, zero or negative relative to the same pressure reference.
  • The model assumes a point source with spherical spreading in a uniform free field. It excludes absorption, reflections, barriers, near-field structure and changes in source output.
  • The standard display uses 20-log sound-pressure-level decibels. The optional 10-log display is half that numerical level and is not a different acoustic power prediction. A linear attenuation ratio compares first-point to second-point pressure magnitude.
  • Negative attenuation means the second point is louder because it is closer. This estimate does not determine hearing-exposure limits or frequency weighting.

Common questions

Do I enter the distance between the two points?

No. Enter each point’s distance from the common sound source.

Why can the attenuation be negative?

Moving closer increases level. Since the displayed decrease is first level minus second level, an increase at the second point produces a negative value.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

Explore waves and acoustics calculators 🔊 or browse all physics calculators.