Loudspeakers

For both the aspen FR30 and FR20, PS Audio has engineered its crossover to achieve a 'flat impedance curve', specifying a nominal 4ohm load with a 3.5ohm minimum. In practice, the FR20's impedance hits an 'easier' minimum of 4.1ohm at the frequency extremes of 26Hz and 20kHz [black trace, inset Graph] just as its modest –37°/+17° swings in phase angle [blue trace] occur at 22Hz and 4.9kHz, respectively. However, while the impedance is kept to tight 4.2-8.4ohm limits through the audio range, there are larger swings up to 10.2ohm/16.8Hz and down to just 3.1ohm at an ultrasonic 25.7kHz. Higher still, a +56° phase angle delivers a tough 0.98ohm EPDR at 29.8kHz [red trace] where, fortunately, musical energy will likely be much reduced.

The FR20's EPDR (equivalent peak dissipation resistance) swings between 1.9ohm/23Hz to 8.1ohm/12kHz with a mean of 4.1ohm from 20Hz-20kHz, so while the load is indeed quite 'flat' it is not especially 'easy'. Incidentally, the slight 'roughness' in the traces at 40Hz-200Hz correlates with the resonant modes detected in the nearfield measurement of the flat and 'hard-surfaced' 255mm ABRs. PM