Technologies

Tri-amplified (250W Rms / Bass, 150W Rms/Medium, 100W Rms/Treble), the SM11 uses class "D" power stages for low and mid-frequencies channels to allow high power together with the purest sound quality.

Class D output stages

Though primarily intended for near field monitoring situations, the SM11 has an outstanding output capability and low frequency extension that could rival or exceed the performance of so called "mid field" or even "main" monitoring systems, despite its compact size. By this Focal have acknowledged the need for ever more demanding headroom dictated by the dynamics of modern recordings.

In order to reach this goal, the SM11 amplification stages have been dimensioned to produce 500W of overall electrical power (250W for the woofer, 150W for the midrange driver, and 100W for the Beryllium tweeter respectively). Achieving such an amazing power in such a compact system would not have been possible with conventional amplifier technology: the SM11 utilises two class-D power stages, one for the woofer amplification and one for the midrange. But only two years ago, this would not have been compatible with the performance level demanded by a high-end monitoring system such as the SM11.

Class-D amplifiers achieve very high efficiency (typically over 90%, compared to -at most- 65% fot conventional amplification stages) by using a high frequency switching scheme of the output transistors, with those operating only in two extreme states: "full speed" or "zero speed".

The benefit being that in either of these two states the losses in the transistors (generating heat) is minimal. Since the theory has been introduced, the penalty has for long been a high level of distortion, making it unsuitable for high quality audio.
The breakthrough only occurred a couple of years ago, and the class-D modules used in the SM11 (under patent by a third party) can match or exceed the performance, both sonically and on objective tests, of the best conventional designs. Having said that, the best class-D stages still suffer from some bandwidth limitation inherent to the switching frequency: to put it simply they can cope well up to 20kHz, but no so well beyond.
Hence the choice, on the SM11, of a conventional, high quality, class AB power stage for the high frequency channel, allowing extended bandwitdh at the expense of lower efficiency: but this was a rational choice knowing that the effective r.m.s. power dissipated on this channel is relatively small when compared to those of the woofer and midrange.