How Far a Signalling Drum Carries: Range by Terrain, Size and Tension

How far away can a coded rhythm on a drum or slit gong still be recognised? This paper computes that distance from stated assumptions: geometric spreading, atmospheric absorption at the drum's dominant low frequency, an excess attenuation term for ground and vegetation, and a detection criterion for a known, repeated rhythm. For a reference drum of 0.60 m diameter sounding at 95 Hz and 100.0 dB at 1 m, the computed maximum range is 2.11 km over flat open ground, 0.83 km in forest, and 3.82 km along a valley. A large drum of 1.00 m reaches 3.57 km on flat ground, 1.69 times the reference range, while raising the membrane tension by a factor of two shortens the flat-ground range slightly, to 2.02 km. A sizing rule follows: range is bought with diameter, not with tension. SIMULATED, NOT MEASURED.