The first and most important decision when it came to designing the Colibri, was to recognize that achieving both bass extension and sensitivity within the size and price constraints envisaged meant dumping the bass: not literally, but making it someone else’s problem. The combination of home theatre and affordable, configurable Class d plate amps has meant that not only are there plenty of decent, compact sub-woofers on the market, choose carefully and they can be both capable and surprisingly affordable.
The second realisation was that the necessary sensitivity was incompatible with traditional notions of bandwidth and speaker topology. The massive Avantgarde Trio uses three spherical horns, the largest almost 1m in diameter, to reproduce the musical range from 100Hz to beyond 20kHz. Producing a considerably more compact yet still high-sensitivity system was going to take a very different approach. At which point the company started to ask, “How much bandwidth is enough?” Or, “What happens if you don’t need to go all the way to 20kHz?” After all, the highest fundamental frequencies generally produced by the violin and piano are 3520Hz and 4186Hz respectively. Those notes have upper harmonics, but there’s no escaping that most of the musical action actually occurs below 10kHz.
Once you discard the 20kHz imperative, a whole world of opportunity presents itself. Suddenly the old rules and assumptions no longer apply. The Colibri C2 is built around a single, 1.5”/37.5mm mid/high-frequency driver, loaded with a spherical horn 14”/350mm in diameter. It delivers useable output from 700Hz to a -3dB point at 19kHz. Let’s not minimise the challenges here. That performance is the result of an incredibly light driver diaphragm, coupled to an incredibly powerful motor – and as any athlete will tell you, performance is all about the power to weight ratio. It’s no accident that Avantgarde chose Colibri (Humming Bird) as the name for this project.
The implications of using a single horn-loaded driver to cover such a wide range are profound. By reaching down as far as 700Hz, not only does it move the crossover point away from the super-sensitive 3kHz point, but it allows a very different approach to generating bass – especially as you’ve already decided to farm out deep bass to an external sub-woofer. In the Colibri C2, a pair of 165mm bass-drivers use horn reinforcement to extend the speaker’s range down to 70Hz. That might not seem that deep, but it’s still deeper than that perennial audiophile favourite, the LS3/5a, covers enough of the bottom end to keep it honest, just about allows the C2 to work as a standalone speaker and makes the job of any matching sub-woofer considerably easier. All that while maintaining a system sensitivity of 98dB! To put that in context, compared to more traditional designs, a 6dB increase in sensitivity represents a doubling of amplitude for a given input, a 10dB increase will actually sound twice as loud. The Colibri C2, with a roughly two cubic foot volume, might be a little larger than the likes of B&W’s 805, but with its integral stand it takes up no more room and is considerably more potent.
