I used DRA Labs’ MLSSA system and a calibrated DPA 4006 microphone with an Earthworks microphone preamplifier to measure the Mission 770’s farfield frequency behavior and dispersion. I used an Earthworks QTC-40 mike for the nearfield and in-room responses and Dayton Audio’s DATS V2 system to measure the impedance magnitude and electrical phase angle.
Mission specifies the 770’s anechoic sensitivity as 88dB/2.83V/m. My B-weighted estimate was lower, at 85.5dB/2.83V/m, which is the same as that measured by Paul Miller for our sister magazine, . The 770’s impedance, specified as 8 ohms, remains higher than 8 ohms for most of the audioband (fig.1, solid trace) but drops to just below 6 ohms in the mid-treble region. The electrical phase angle (dashed trace) is is generally benign, though it drops below 4 ohms between 85Hz and 116Hz and between 2.3kHz and 4.9kHz. The minimum EPDR is 3.7 ohms at 96Hz and 3 ohms between 3.35kHz and 3.9kHz. The 770 shouldn’t be a difficult load for amplifiers, though tubed designs will best be used from their 4 ohm taps.
