Accuton BD20-5-048 Diamond Tweeter

The Accuton BD20-5-048 is the smallest diamond dome tweeter in this group, and dome size is the most consequential variable in a high frequency driver once the material has been chosen.

A smaller dome has two advantages and one cost. Because it is smaller relative to the wavelengths it radiates, it holds its dispersion further up the band, so the top octave remains audible off axis instead of collapsing into a narrow beam directly in front of the speaker. That matters in a real room, where a large share of what the listener hears has reflected off a wall or ceiling first, and it also means the tonal balance changes less when the listener moves out of the ideal seat. The second advantage is a lighter moving assembly, which needs less force to accelerate.

The cost is at the other end of its range. A small dome displaces less air, so it reaches a given sound pressure level with more excursion, and it therefore needs to be crossed over higher than a larger unit would. Attempting to run it low, or filtering it with a shallow slope, is the reliable way to damage one.

In practice this makes the BD20-5-048 a natural fit for designs with a genuine midrange driver, where the tweeter can be handed a comparatively narrow band starting well above two kilohertz. Use a steep filter, respect the manufacturer's minimum crossover frequency, and mount the driver on a baffle with rounded edges so that diffraction does not undo the dispersion advantage the small dome was chosen for.