Its impressive deep bass ensures that even the lowest frequencies are presented cleanly, while the mid-range section handles challenging passages with freedom and total naturalness, and the treble range is transparent and as smooth as silk. We resolved to adopt an advanced three-way system incorporating two long-throw bass drivers, one wide-range mid-range unit and a High-End dome treble unit. This arrangement ensures that on the one hand the ST 21 can deliver accurate, intense bass, and on the other a natural, uncoloured mid-range which is conveyed by the mid-range unit only, as the low crossover frequency avoids phase shifts and gaps in the frequency response. All the cones are manufactured from different thicknesses of aluminium using specially calculated embossing tools, resulting in lightweight cones which are very strong and stiff. Extremely powerful magnets are employed, while the magnet and coil systems are of very refined design, and made using premium materials. The result is that these High-End drivers are capable of generating enormously high levels combined with extraordinary dynamism and speed. An accurately computed crossover unit based on low-loss components ensures perfect control of all drive units in their optimum working range, and outstandingly good radiation characteristics. The crossovers have separate earth systems for the bass and mid-range, and this makes them perfectly suited to bi-wiring arrangements.