Article Index
Martin Logan Summit X
page 2
page 3
page 4, Sound quality
page 5, Conclusion
page 6, Measured Performance
All Pages

Apart from these unusual practical issues that surround electrostatics – which also influence performance in the tropics as we’ve been told by Hi-Fi World readers – our measurements clearly show the XStat panel smoothly covers the audio band, like no other loudspeaker.Having no crossover at 3kHz it also lacks phase anomalies and character changes between bass/midrange unit and tweeter that afflict conventional box loudspeakers. This consistency contributes much to their exceptional imaging and, for example, gives violin in particular a sense of being a one-piece physical instrument rather than a mellifluous representation.
    But I must not keep talking about the XStat panel, or even electrostatics.For the Summit X also has a compact bass cabinet and progressive phase cancellation toward higher frequencies that, Martin Logan say, makes the bass transition from monopole to dipole radiation at the crossover frequency.
    Put more simply, this means the panel which fires sound forward and backward (dipole), out of phase, better matches the bass bin (monopole) where no such forward/backward cancellation occurs.
    I did once use a true bass dipole, the Celestion SL-6000, to match an electrostatic dipole, Quad ESL-63s, but it was a horribly complicated arrangement and viciously demanding of bass amplifier drive power. I did get ultra-low, near-perfect bass – but what a hassle! Which is why Martin Logan’s less complex blending approach on the Summit X struck a chord with me.

There is just one set of loudspeaker terminals, so bi-wiring is out. The terminals fitted accept 4mm banana plugs or bare wires. Above them are three control knobs, controlling very low bass at 25Hz – subsonics really – and deep bass at 50Hz. These interact with room modes, controlling room boom in effect. The idea is to avoid boomy bass, but alternatively bass power can be increased to add extra oomph, according to taste.Alongside the two bass level controls, that provide both lift and cut, is another rotary switch that controls three lights, to give seven settings for them, including a down light, no less. Response shaping is digital: the signal passes through an ADC, is processed, and is then converted back to analogue for the bass power amplifiers.
    One bass unit moves slowly out of phase with the other as frequency increases to smooth the transition from monopole to dipole and our response graph does show a shallow dip in output above 100Hz due to this effect.
    At the other end of the frequency scale, because the big panel runs flat to 20kHz, our measurements show, it puts out a lot of acoustic power at high frequencies and tilting back using the adjustable feet will lessen this a little. I also used an Audiolab M-DAC with optimised time-domain filtering for CD, to roll down treble smoothly.
    I used acoustic absorption panels against the rear wall, a few feet behind each Summit X, to absorb rear radiation. An obvious partnering amplifier is the solid-state Quad QMP Elite monoblocks I used, or Quad II-eighty valve power amplifiers. Generally, a good valve amplifier with 4 Ohm tap is a fine match for an electrostatic and I used my own WAD 300B amplifiers. Beware of powerful transistor amps having bright treble: the big XStat panel reveals their limitations and this isn’t a match made in heaven.



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