Loudspeakers

The spherical wavefront horn (Kugelwellentrichter in German), introduced by Klangfilm in Germany around 1950 and revived by Avantgarde, is often mistaken for being the same as Paul Voigt's tractrix horn because the radius of the wavefront is assumed, as in the tractrix, to remain constant as it travels through the horn. But unlike Voigt's horn, the flare of which is a tractrix (mathematically, the involute of the catenary function), the Kugelwellentrichter's flare shape is exponential and so the wavefronts do not consistently meet the horn wall at right angles. The exponential expansion harks back to Webster's original horn profile, described in 1914 and widely used since, but Webster assumed the wavefront in the horn to be flat (planar) rather than spherical. Like all classic horn profiles, the Kugelwellentrichter makes assumptions about wavefront expansion that are not borne out in reality. More typically, the profile of modern horn designs are calculated by numerical methods (BEM or FEA) or using Earl Geddes' elaborated theoretical analysis. KH