Theory of Megaphones and Receiving Horns
G. W. Stewart, G. R. Butz · UNI ScholarWorks (University of Northern Iowa) · 1924
In 1919, A. G. Webster published a theory of the action of horns used as receivers. Recent development has given an increased interest in the megaphone. Webster's theory may be modified to cover the case of the megaphone, assuming the constancy of the acoustic point impedance of the horn at the source. The result obtained is that the emitted energies at different frequencies are related as are the values of [(ad-bc)/(a-cz2)]2 wherein a, b, c and d, have the values specified in Webster's theory and z2=δa2k2 (ki/2π-1/c0), k being 2π divided by wave length, ρ the density, a the velocity of sound and c0 the conductivity of the opening.