Loudspeakers

An effective bass horn is a very large device, so manufacturers of horn speakers often combine direct-radiating bass drivers with midrange and treble horns which, because of the shorter wavelengths involved, are much smaller. This creates a problem, though: how to match the high sensitivity of the horn sections in the bass? Avantgarde's answer with the UNO XD is to use twin bass units and drive them using two 500W internal amplifiers, whose gain can be adjusted to offset the sensitivity shortfall. And Avantgarde goes further: by inserting A/D conversion and DSP ahead of the amplifiers it's able to add powerful bass equalisation capabilities, under the management of its control software.

Set against this modern technology, the UNO XD's midrange and treble horns are from another era, following a German tradition begun by Klangfilm in the early 1950s by using a Kugelwellentrichter (spherical wave horn) profile which assumes that the radius of the wavefront propagating through the horn remains constant along its length. The resulting horn provides good gain – our measurements indicated around +17dB – and narrows directivity but, like all classic horn profiles, it makes assumptions about wave behaviour which are not borne out in practice. Reflections from the horn mouth and cross-modes within the horn cause resonances, some of which can be seen in the cumulative spectral decay waterfall. KH