Accuton BD51-6-585 Diamond Tweeter

The Accuton BD51-6-585 is a large-format diamond dome driver, and its size sets it apart from the compact tweeters in the same family. A dome of this diameter displaces considerably more air than a 20 or 25 mm unit, which allows it to operate lower in frequency and with far less excursion for a given output.

That combination is what makes a large dome attractive in a three-way design. It can take over from the bass driver well below the frequency at which a conventional tweeter could be used, which in turn allows the bass-midrange unit to be crossed out before cone break-up and narrowing directivity begin to colour the vocal range. Handing over low is one of the most effective structural decisions available to a loudspeaker designer, and it requires a driver capable of accepting the band.

The trade is directivity at the top. A larger radiating surface beams sooner, so the very highest frequencies are progressively confined to the on-axis direction. In a three-way system this is normally addressed by pairing the large dome with a smaller high frequency unit above it, or by accepting a narrower listening window in exchange for the cleaner midrange.

As with every driver in this range, the dome material is chosen so that its first break-up mode sits above the working band, and the crossover must be designed from measurements taken in the finished baffle. Respect the manufacturer's minimum crossover frequency, use a slope steep enough to enforce it, and protect the driver with a correctly rated series capacitor.