Loudspeakers

Most loudspeaker designers are content to use dome tweeters of 25mm diameter or thereabouts for reproducing treble frequencies. They offer good directivity and, when well-designed, low distortion coupled with no breakup resonances within the audible frequency range. Genuine ribbon drivers – in which the diaphragm is also the electrical conductor – are rarely used because they are fragile and require a matching transformer due to the ribbon's low electrical impedance. More popular as an alternative to dome tweeters are pseudo-ribbon drivers like the Raidho tweeter. These have a thin planar polymer diaphragm which, usually on one side only, carries a flat 'voice coil' etched from a conductive surface coating which is bathed in the field of permanent magnets arrayed around it. In the Raidho tweeter, unusually, the conductor tracks are wiggly rather than straight – you can see more photos of one being assembled at http://raidho.dk/downloads1. Because the thin, flat diaphragm is prone to resonance – despite the distributed drive force – mechanical damping has to be carefully applied to ensure a flat frequency response and clean CSD waterfall [see Lab Report]. KH