Klipsch THX Ultra2 Measurements

Figures 10 - 13 are impedance curves for the various systems making up the Klipsch Ultra2 THX home theater system. In Figures 10 & 13 we see the typical saddle-shaped curve at the left, with the impedance minimum (5.3 Ω @ ~ 56 Hz for the KL-650 and 6.7 Ω @ ~ 25 Hz for the KW-120) in each case indicating the vented box tuning frequency. In Figures 11 & 12, the closed box tuning frequency is indicated by the impedance peak (32.6 Ω @ ~ 83 Hz for the KL-525 and 41.6 Ω @ ~ 107 Hz for the KS-525). The second peaks, seen towards the right in Figures 10 - 12 typically arise as a result the interaction of the crossover network 舗 s high- and lowpass sections, setting up a parallel resonance.

The global impedance minimum for the KL-650, KL-525, KS-525, and KW-120 are (respectively): 3.2 Ω (averaged), 4.2 Ω , 3.6 Ω , and 6.7 Ω . The respective system nominal impedance (per IEC standards) are therefore 4 Ω , 6 Ω , 4.5 Ω , and 8 Ω . Obvious from the measurements, no system ever went below 3.2 Ω , as per THX requirements.

The impedance phase swings between +40° and -60° (KL-650), +41° and -64° (KL-525), +60° and -65° (KS-525), and -46° and climbing towards 90° (KW-120). The impedance minima might give cause for concern, but keeping in mind the phase angle at the minima and the high sensitivity of the KL-650, KL-525, and KS-525 the systems shouldn't prove to be a difficult load for most AV receivers, especially THX Ultra2 certified ones.