Sound Distance Falloff Calculator

How it is calculated

You give a known sound pressure level L1 in dB measured at distance d1, and a new distance d2, both distances in the same unit. The tool computes ratio = d2 ÷ d1, drop = 20 × log10(ratio) and L2 = L1 − drop. Each doubling of distance subtracts about 6.02 dB. It models a single point source in open space (free field): reflections from walls, ground effects, air absorption, wind and a directional speaker are not included, so real levels indoors or over long distances can differ. Both distances must be above zero. If d2 is smaller than d1 the drop is negative, meaning the level rises. Results are rounded to one decimal, and the ratio to two.

Common mistakes

• Using the intensity formula with 10 × log instead of 20 × log. For sound pressure level the factor is 20, which gives 6 dB per doubling, not 3 dB.
• Mixing units for the two distances, such as 1 m and 80 cm. Both must be in the same unit or the ratio is wrong.
• Applying the result indoors. In a room, reflections keep the level higher than the free-field figure at larger distances.
• Treating the reference level as a rating taken at an unspecified distance. L1 must be measured or specified at exactly d1.
• Entering the closer distance as d2 and expecting a drop. Moving closer gives a negative drop and a higher level, for example 94 dB at 4 m becomes 106.0 dB at 1 m.