Free-Field Sound Distance Loss Calculator

Method, formula and assumptions

Spherical spreading loss = 20 log10(target distance/reference distance). Subtract it from reference level. Solving the same equation yields the distance at the chosen comparison level.

Input definitions and supported units

• Reference level (dB): Measured or assumed numerical value, from 0 to 180; zero is supported where the stated method permits it.
• Reference distance (m): Measured or assumed numerical value, from 0.01 to 10000; must be positive.
• Target distance (m): Measured or assumed numerical value, from 0.01 to 10000; must be positive.
• Comparison level (dB): Measured or assumed numerical value, from 0 to 180; zero is supported where the stated method permits it.

Worked example with answer

90 dB at 1 m predicts 77.9588 dB at 4 m: a 12.0412 dB loss. It is 7.9588 dB above 70 dB, with an ideal 70 dB distance of 10 m.

How to use the results

The comparison level is your own target, not a safety limit. Moving closer than the reference produces a negative loss, subject to the model's near-field limitations.

Results retain full precision internally and display up to four decimal places. Very small nonzero results use scientific notation rather than appearing as zero. Check the labels before comparing values across units.

Limitations and references

Assumes a point source in free field. Reflections, arrays, directivity, atmospheric absorption and near-field behavior can dominate real measurements.

The method is a self-contained arithmetic, geometric or explicitly stated mathematical model. There are no imported tariffs, empirical presets or equipment specifications; measured values and allowances must come from your own process.

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