I used DRA Labs’ MLSSA system with a calibrated DPA 4006 microphone to measure the MoFi SourcePoint 8’s behavior in the farfield and an Earthworks QTC-40 mike for the nearfield responses. I left the grille off for the acoustic measurements.
The SourcePoint 8’s specified sensitivity is 87dB/2.83V/m; my B-weighted estimate was the same. The SourcePoint 8’s nominal impedance is specified as 8 ohms, with a minimum value of 6.4 ohms.’s presentation of impedance graphs for the past 33 years, I created fig.1 with the Audio Precision System One software. The speaker’s impedance magnitude (solid trace) is greater than 8 ohms for almost all the audioband, dropping to 7.47 ohms at 120Hz. If this speaker is used with tube amplifiers, the significantly higher impedance in the treble compared with that in the midrange will tilt up the high frequencies. With the high average impedance, the equivalent peak dissipation resistance, or EPDR, is generally greater than 4 ohms, though it does drop below that magnitude between 197Hz and 341Hz, with a minimum value of 3.83 ohms at 242Hz. Even so, the Source-Point 8 is an easy load for an amplifier.
