I used DRA Labs’ MLSSA system with a calibrated DPA 4006 microphone to measure the Harbeth Super HL5plus XD’s behavior in the farfield and an Earthworks QTC-40 mike for the nearfield responses. I measured the speaker without the aluminum-frame grille and performed the primary response measurements on the super-tweeter axis. I measured the speaker’s impedance magnitude and phase with Dayton Audio’s DATS V2 system, but for consistency with Stereophile’s presentation of impedance graphs, I plotted the impedance measurement with the Audio Precision System One software.
My B-weighted estimate of the Super HL5plus’s sensitivity lies below 4 ohms in three regions: between 73Hz and 147Hz; between 320Hz and 660Hz; and above 6kHz. The minimum values are 3.02 ohms at 93Hz and 2.54 ohms at 456Hz. If used with tube amplifiers, the Super HL5plus will work best with their 4 ohm output transformer taps.
