MEASURED PERFORMANCE
The big XStat panel of the Summit X measured almost flat over its working range from 270Hz to 20kHz, our analysis shows. There’s some summation from the bass unit and panel above 300Hz, irrespective of bass control settings, although they were set to zero for this analysis. The peak lowered slightly off axis, however, as dipole panel output lowered, so this is unlikely to be of great subjective importance in use, although if anything it will add to lower midband (voice) warmth and body, which electrostatics are often accused of lacking, so it might be beneficial.
    XStat panel output is very smooth all the way to 20kHz, suggesting even tonal balance and low coloration, as well as strong detailing from sustained output in the usual loudspeaker crossover region of 3kHz where there’s often a dip (as well as phase anomalies).
    Martin Logan have this big electrostatic panel working beautifully, with even output over a wide range of measuring-microphone positions in front of the panel, where in the past there was variation (as is common from panels due to phase cancellation), which meant seating position affected sound quality.
    The Summit X will sound consistent over a wide forward angle and shouldn’t change too much even when standing; traditionally big panels have sweet spots but the XStat largely eliminates this problem.
    The bass unit runs strongly right down to 30Hz, so subsonics will be quite obvious. The 25Hz and 50Hz level controls provided substantial lift and cut below 100Hz, and did not affect upper bass.
    From the side, output from the monopole bass bin rose smoothly above that from the panel, the transition between them being smooth.
    However, the bass bin is a monopole, not a dipole like Celestion’s SL-6000 that I once used with Quad ESL-63s, so it does not have to be steered.
    Sensitivity measured a reasonable 87dB sound pressure level at one metre from one nominal Watt of input (2.8V). Our impedance plot shows the panel is connected direct to an external amplifier, not via an internal amp, and being a capacitor its impedance falls steadily toward high frequencies to become the input transformer’s DCR value of 1 Ohm or so at 20kHz – quite a challenge for transistor amplifiers (or their protection circuits should I say). Because the bass unit is powered little current is drawn below 100Hz. Amplifiers of around 40 Watts upward are needed to go reasonably loud, and 100 Watts or so is sensible for high volume, bearing in mind the amplifier is not driving the bass unit, only the XStat panel. Valve amps with a 4 Ohm output tap are a good choice; transistor amps need to be able to deliver current at 20kHz without protection circuits interfering (or, worse, failing).
    The Summit X measures well in all respects. Its XStat panel looks superb and the bass unit a tight match.  NK


FREQUENCY RESPONSE (what it means)



IMPEDANCE (what it means)