Generator Decibel Distance Calculator

What this calculator measures

Estimate point-source sound level in an ideal free field from a measured reference level and two distances. Any site adjustment must come from documented evidence; fence and environment labels do not imply fixed attenuation.

Inputs and units

Use readings and ratings that describe the same equipment, operating interval, and measurement boundary. The sample entries are editable examples; they do not establish the specifications of your generator.

Calculation method

L2 = L1 − 20 log10(r2/r1) + documented site adjustment. L1 is the sound-pressure level at reference distance r1. Both distances must use the same unit. The output retains the weighting and measurement basis of the reference, for example dBA when the reference is dBA.

The numerical implementation agrees with that logarithmic equation to better than 0.00001 dB across the supported distance ratios. This numerical precision does not describe the uncertainty of a real site prediction.

Worked example

With 70 dBA measured at 7 m and a target distance of 14 m, enter a zero site adjustment for the ideal comparison. The level decreases by approximately 6.02 dB to 63.98 dBA. At 28 m, the ideal reduction is about 12.04 dB, giving 57.96 dBA. At the same distance, the unadjusted result equals the reference level.

Limitations and checks

This relationship assumes point-source geometric spreading in a free field. Near-field effects, buildings, terrain, ground absorption, weather, source directivity, and other noise sources can change a measured result. It does not establish a property-line noise limit, legal compliance, or an acceptable generator location.

Leave the site adjustment at zero unless you have a suitable measured or engineered value. A positive value makes the prediction louder and a negative value makes it quieter. Do not assume that a generic fence or enclosure provides a particular reduction.

For a practical decision, keep the original readings, the generator model, the relevant manual or specification, and the assumptions alongside the result. A different load, site condition, rating basis, or unit convention can answer a different question even when the arithmetic is correct.

Sources and methodology

• OSHA Technical Manual: noise and distance

Publisher: CSP Digital Media Ltd. To report a formula, unit, or example error, contact us with the tool name, inputs, displayed result, and expected calculation.