Enter the distances and heights of the source, the receiver and the top of the barrier, and this page works out how much longer the path over the wall is than the straight path, then turns that path difference into the shadow zone insertion loss. The wall top has to rise above the line of sight for the calculation to hold.
The path difference is divided by half the wavelength to give the Fresnel number, which then goes into the insertion loss expression reported in acoustic analysis documentation and academic papers. Distances and heights are entered in feet and converted to meters internally (1 ft = 0.3048 m); the wavelength comes from a speed of sound of about 1,125 ft/s (343 m/s) divided by the frequency, and the straight distance, path difference, wavelength and speed used are printed in feet with meters in parentheses. These figures come from secondary sources, so check the originals before relying on them for anything important. Figures current as of October 2026.
The reported valid range is a Fresnel number above 0.2 and below 12.5, and inputs outside it stop the calculation with a notice. The upper limit on insertion loss differs between sources at 24 dB and 25 dB, and which one is correct is not confirmed by an authoritative source, so no single value is asserted and the result only reports whether either would bite; inside the valid range the computed value stays below both. Transmission loss through the wall itself, the illuminated zone, multiple source summation and regulatory limit checks are not covered. This calculator is for reference and does not replace design. Review by a qualified engineer is required.
Frequently Asked Questions
The formula used here is reported as valid for Fresnel numbers above 0.2 and below 12.5, so outside that the calculation stops with a notice. A low wall or a low frequency falls below, while a very tall wall at high frequency goes above.
Sources cut it at either 24 dB or 25 dB and which one is correct cannot be settled here, so the computed value is reported as is and the result only notes whether either limit would bite. Inside the valid range the computed value stays below both.
If the barrier top is not above the straight line from source to receiver, the receiver is not in the shadow zone and the calculation stops. This formula covers the shadow zone only; the illuminated zone follows a different curve.