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Martin Logan's new CLX
From Hi-Fi World - July 2009 issue


Film Star


Martin Logan's new CLX Linear electrostatic loudspeaker is a flight of fancy for the few. Noel Keywood joins the jet set..


"We solemnly agreed to change into black and meet in due course in the workhouse" said Gilbert Briggs, founder of Wharfedale, after hearing the first demonstration of a full range electrostatic loudspeaker in 1955. Quad's first electrostatic sounded so good it seemed to spell the end of the conventional box loudspeakers, which Wharfedale were making in large quantities at the time. It didn't turn out like that of course, for reasons that Gilbert later lists, but since then a small group of dedicated manufacturers around the world have continued doggedly onward developing this esoteric way of producing sound. Premiere among them is Martin Logan, who launched a new top model one year ago, the £25,000 CLX Anniversary.



But I'm not reviewing it here. Instead I am looking at the newly launched standard production model, the CLX Linear, which you'll be pleased to know is much less expensive - just £15,990! It has all the same working parts and sounds identical to the Anniversary, I am told, only the price and level of finish are different.


If £16k, less 10p, seems like a lot of money to spend on something that uses Clingfilm instead of loudspeaker cones to move air - it is! The CLX's best known rival is Quad's 2905, priced at a slightly more accessible £7,990 and the little known Kingsound Prince II from Hong Kong, fit for paupers at a devastatingly low price of £2,995 and reviewed by me in our April 09 issue. The Prince II and the Quads give amazing sound so the big CLXs should, in a sane world, give proportionately more. But as I ruefully watch open Bentleys drive this way and that directly the sun comes out I realise that for some, £16k is a mere bagatelle and proportionality doesn't come into it. For some, only the best is good enough and they can afford it, in which case the CLX Linear nicely partners the Bentley. The rest of us can at least dream - or perhaps sneak a visit into a showroom to hear what an ultimate electrostatic sounds like, or hope that their importers, Absolute Sounds, will have them on demo at the Audio 09 Show in September (see If so, it could even be me that demonstrates them to you, because I'm slated to run demos at that Show and need a pair of electrostatics! I am adept at hustling manufacturers for a good cause, so we'll see...


Having just returned from an after-6pm session in our listening room rounded off by the stridently forceful yet insinuating voice of Ariel Ramirez singing 'Missa Criolla', backed by a heavenly choir stretched slightly above me in a wide arc across the room, with a power and delicacy that was both awesome and beautiful at the same time, I'm reminded that big electrostatics border on a religious experience. If you want a choir of angels singing with heavenly purity from wall to wall across the end of your lounge then there's no better way to achieve it than this. Vocalists sing slightly from above - I preferred to sit just below centre - and are perhaps slightly larger than life image wise, making their presence imposing. The CLXs look big and the sound stage they throw is every bit in keeping with their physical size.




The base houses a power

supply. It has single-wire

inputs that accept 4mm plugs,

and it has two light switches



But you will need a big room, because the CLXs stand 176 cms high and are 66 cms wide so they have a looming presence. They fire as much sound backwards as forwards - there is no cabinet - and the rear sound needs to be 'lost' to some reasonable degree if midrange and high frequency muddle is not to set in. We ran them 6ft forward of a rear wall and had 22ft to play with down our 28ft room. Behind them, against the wall, were placed absorptive panels to soak up higher frequency rear radiation. This turned out to be fine tuning however. The CLXs drive a room over a large area and are reasonably uncritical about their environment, I found. Like the Prince IIs they dominate it acoustically and sound balance did not change dramatically down the length of the room - there were no low frequency pressure nodes. Even off-axis the sound balance held up, although being a directional dipole treble does fall away. However, so much musical energy is being pumped into the room and bouncing off the walls that the diffuse field is strong and I could walk around and still appreciate music. Because of their sheer size though a room at least 20ft long is needed and 30ft or more would be ideal. Being relatively wide they don't blend in visually and need to be 8ft or so apart. At 56kgs apiece they are weighty too, and can be tilted forward or backward by adjustable spikes.

The CLXs have a tall, narrow treble panel for smooth lateral dispersion, flanked by large, flat bass panels. Total area is increased by a single side baffle, to smooth and deepen bass. This is an issue with any open panel loudspeaker - the bigger the panel area the deeper the bass.


The CLX comes in handed pairs, the treble panel on the inside edge as usual, for a smooth response untainted by reflections off the bass panels. They need mains power, to generate a static charge on the moving film, which carries a special resistive coating.


So why is the CLX so costly? One significant benefit of Martin Logan panels is their transparency to sound produced by the Mylar film diaphragm, that must disperse through the perforated stator panels. The company also use a curved cross section and strengthening ribs for mechanical strength, and a special coating to prevent high voltage arcing and make them safe. As a result the treble panel is acoustically very transparent, as well as visually transparent of course. This is a lot different from Quads, that have an array of protective covers that obstruct the flow of sound from their film diaphragm. I removed both the outer sock and protective metal grilles of Quad ESL-63s I once used and this improved resolution of fine detail significantly, so it is an issue with electrostatics. The bit you need to hear is buried deep inside, like the filling of a sandwich, and if its properties of low mass and minimal colouration are to be appreciated then the acoustically transparent perforated panels of Martin Logans are likely the best way of doing so.


The vertical high frequency panels work from 350Hz all the way up to 20kHz. Below 350Hz Martin Logan use double layer bass panels to develop sufficient bass drive, comprising two driven films sandwiched by three stators. They are split into sections of differing sizes to avoid a single main resonance, Martin Logan tell me.




Treble panel is curved to smooth frequency response

and improve dispersion.


Electrostatics are known for bass that 'drifts' from the loudspeaker, bass that lacks slam. With the CLX Martin Logan have eliminated this by increasing motor power, to overcome air load damping (which is considerable), and they have extended front-to-rear path length by the use of that single side baffle. So the CLX has been designed to deliver bass slam, yet it draws almost no bass current (or power) from an amplifier to do this, due to high impedance below 100Hz. This is especially complementary to valve amps, minimising bass distortion.


In their handbook, which you can download (go to, Martin Logan suggest the CLX is kept away from side walls, but Peter Walker of Quad liked to use side walls to increase panel area and, therefore bass, pushing Quads up against them. It strikes me this positioning will suit a long narrow room - then the wide walls are best damped using curtains or such like, Martin Logan suggest. Our measurements show the CLXs go very low, down to 40Hz (-6dB), which is lower than most box loudspeakers, and their dipole radiation pattern little excited our listening room's main mode at 24Hz, something I also noticed in use. Wherever I listened in the room, even against a wall (which is a high pressure point) there was no bass boom, or 'room boom'. So the CLX has strong bass that runs deep, but it does not excite room boom and this helps keep things lean and clean. This is a positive feature of dipole radiation and contributes to bass quality, but you won't find it discussed anywhere because how a dipole works in a room is little understood - and probably not understandable either without the aid of computer modelling.


One of the many drawbacks of electrostatics that Gilbert Briggs went on to list was limited power handling. This is another area where Martin Logan's electrostatic panels excel. Quoted power handling is a massive 225 Watts, but this is peak power. The suggestion here is that amplifiers up to 200 Watts or so per channel be used. However, our measurements showed the CLX has a reasonably normal sensitivity of 84dB Sound Pressure Level from one Watt (2.8V) input so they will work from low powers, unlike the Prince IIs, and in use our Icon Audio MB845 valve power amplifiers never swung more than 20V peak (50 Watts peak) across them - playing Darkness at shattering volume! So the big CLXs don't demand big power, giving plenty of leeway in amplifier choice. As always I recommend a valve amplifier; the transparency of an electrostatic like the CLX does transistor amplifiers no favours at all (I tried one and it sounded like a cat being strangled).


Worse, anyone aware of an electrostatic foible that Gilbert never did mention may have spotted in our tests that the CLX falls to 1.5 Ohms load at 20kHz and some transistors may blow if faced with delivering a strong signal into this, whilst valves are unaffected.



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