Loudspeakers

With two horns on show there's a hope of high sensitivity and while Klipsch's 99dB spec. is a trifle optimistic, a mean figure of 95.4dB/1m/2.83V (500Hz-8kHz) is still very generous. The figure at 1kHz is higher still at 96.7dB but this coincides with a peak in output [Graph 1, below] and a resonance detected at 1.2kHz in the nearfield analysis of the 305mm fibre-coned woofer. THD also increases from a low 0.3% through the bass to a higher ~1.8% through this region of the midband (all re. 90dB SPL). This mode is also prominent in the CSD waterfall, along with resonances associated with the mid and treble horns at 4kHz and 14kHz-20kHz [see Graph 2]. The 25mm titanium compression tweeter breaks up at an ultrasonic 36kHz [pink shaded area, Graph 1].

The multiple resonances are reflected in the untidy response from 1kHz-20kHz and the moderate ±4.5dB response error but the overall trend is reasonably flat. One speaker [red trace, Graph 1] had a higher ±5.4dB response error and a deviation between 600-900Hz responsible for the poor 2.3dB pair matching, but this improves to 0.8dB between 1kHz-18kHz. The snugly-fitting grille has no significant impact on response [blue trace, Graph 1]. High sensitivity usually means limited bass extension but the Heresy IV's 30Hz-tuned reflex loading has brought this down to a respectable 47Hz (–6dB re. 200Hz) – a 20Hz improvement over the 'III [HFN Mar '10], albeit with a 'peaky' alignment [green area, Graph 1]. Nominal impedance is given as 8ohm but 4ohm would be more accurate given the min. 4.2ohm/118Hz. The highest +42o/–52o phase angles are also through the bass, but with such low power required, this should not prove troublesome. PM