Loudspeakers

Such is the difference in acoustic centres/path lengths of the drivers – between the treble and mid/bass horns in particular – that the wavefront from the former arrives significantly ahead of the latter, complicating the time-windowed response measurement. The step function at the 4.5kHz crossover is clear enough on both the forward response [grey trace, Graph 1] and CSD waterfall [see Graph 2], a feature ameliorated at greater listening distances. Note that the huge mid/treble grille panel adds its own ripples through the midrange [blue trace, Graph 1] but that any HF horn resonances [Graph 2] are generally more subdued than we've seen with other horn-loaded designs. THD – entirely 2nd harmonic – is <0.7% (20Hz-20kHz, 90dB SPL).

Normalising each path length to 1m and plotting separately, including a diffraction-corrected nearfield below 400Hz, realises a far flatter, more even 'real world' output [bass/mid, black; treble, red] with errors of just ±2.8dB and ±3.0dB, respectively, from 400Hz-18kHz (the HF response rolls away thereafter to –6dB/~19kHz). The 3.1dB pair matching is also a function of variations in HF output but this has no practical impact on the 104.2dB/1kHz sensitivity, a figure lifted to 105dB with IEC/perceptual-weighting (200Hz-20kHz). Bass is not as 'big as the box' and drops sharply below 50Hz while its output is dominated by three modes at 105Hz, 190Hz and 300Hz [green shaded area, Graph 1]. Otherwise, while the AK6 will raise high sound levels with very low-powered amps, it is not quite the '8ohm' load specified – the 2.8ohm/110Hz minimum and ±50° phase angles yielding a harsher 1.3ohm/120Hz EPDR. PM