Sound level
SPL vs. Distance Calculator
Estimate free-field sound-pressure level at a new distance from a point source using the inverse-square relationship.
Calculate level change with distance
Enter a measured or specified SPL at one distance and the distance where you want to estimate the new level.
Because only the distance ratio matters, the two distance entries may be feet, metres or any other identical unit.
When the inverse-square estimate works
The relationship is a useful first estimate for a compact source radiating into a free field. It assumes the source remains acoustically similar between positions and that reflected sound is not dominating the measurement.
Where real systems differ
Rooms, ground planes, walls, arrays, horns and other directional sources can produce substantially different distance loss. Near a source, individual drivers and cabinet geometry can also prevent point-source behavior. Use the calculator as a planning estimate, then verify with measurement where accuracy matters.
Interpreting the result
A negative change means the new point is quieter; a positive change means it is closer and therefore louder under the model. The familiar 6 dB-per-distance-doubling rule is simply one special case of the full logarithmic relationship.