Loudspeakers

There’s a lot of innovation in the design of this loudspeaker but, especially when it comes to the quoted 90dB sensitivity, also some wishful thinking. The ‘db/W/m’ qualification is not worthy of Piega’s engineers (who are clearly a very bright bunch) as this implies the speaker gets louder the further away you get... In practice, the Coax 411’s sensitivity is some 6dB lower than this at 83.9dB/1kHz and 83.5dB/500Hz-8kHz (all 2.83V/1m) so don’t expect rock stadium levels even with a max. rated 200W amplifier. Fortunately, though it has a 3.7ohm/120Hz minimum impedance – and an average of just 6ohm from 20Hz-20kHz – its reduced ±31° phase angles limit the minimum EPDR to just 2.35ohm/166Hz and 2.17ohm/11ohm, so the Coax 411 is not a beast to drive. Good bass extension is another pay-off here with the 55Hz-400Hz (–6dB) bandpass of the 160mm coated alloy cone woofer successfully augmented by the (very clean) 29Hz tuning of its long, narrow port to deliver 37Hz (–6dB re. 200Hz).

Of course, it’s the coaxial planar mid/treble that defines its ‘sound’, beyond the low sensitivity. The response is essentially flat [Graph 1], with errors a mere ~±2dB (200Hz-20kHz) largely caused by a 3-4dB step at the 3.5kHz mid/treble crossover. The poorer 1.6dB pair matching is caused by a shimmer of low-level resonances across the surface of the mid driver, in particular, and revealed here in both the response and CSD waterfall [see Graph 2 and boxout]. The tweeter also has low-level modes and while its response extends out to an impressive 60kHz+, without the vigorous breakup of a hard dome tweeter, note that this falls away more quickly when auditioned off-axis [grey trace]. PM