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Martin Logan Ethos loudspeaker review
Hi-Fi World, January 2011 issue
Being aficionados of the electrostatic loudspeaker at Hi-Fi World, we have tested and used most of the Quads ever produced, plus a good number of Kingsounds and many Martin Logans too – and Martin Logans are as good as electrostatics get. So the announcement of the new Martin Logan Ethos had us scrabbling for the phone to get a pair for review.
There’s not been one Martin Logan I have not enjoyed, so I had high hopes for the Ethos – and they weren’t dashed. It’s expensive, costing £6,498, but we’re looking here at a model quite a way up the Martin Logan range and for a top quality loudspeaker of its great and unusual abilities this is a reasonable price.
If you’re wondering what an electrostatic loudspeaker is all about, just think ‘transparency’. As in transparency of sound and with a Martin Logan panel, physical transparency too. Here’s a loudspeaker that physically communicates its strengths: how many loudspeakers can you see through? Electrostatic loudspeakers produce sound from a sheet of 'Clingfilm' hung in the open air (well, sort of). There’s no cone flapping around and no box to honk – so forget colouration!
Notionally, an electrostatic loudspeaker is perfect – and believe me, they sound divine. What you get with the Ethos is Martin Logan’s top quality XStat electrostatic panel, mated to a powered subwoofer, in a room-friendly package. Although standing almost 5ft tall each unit weighs 19kgs, or 42lbs, so once in place they are not immovable like some top quality monitors. A little under one foot wide, they don’t dominate the domestic landscape either and that’s how Martin Logan play it. Look at rivals and you’ll find they are more visually intrusive, including Quads of course. The main reason is that Martin Logan choose not to produce bass from their electrostatic panel (except in the large CLX), but from the small box that supports it, in which there is a conventional bass unit that works below 375Hz. That makes the Ethos a hybrid electrostatic, unlike Quads and the bigger Kingsounds.
Like all electrostatics each Ethos needs mains power, to charge the panel stators to a high static voltage and to drive the internal Class D 200W bass power amplifier. Mains power connection is through a normal IEC three pin socket and power consumption at idle is just 1 Watt. This model has a bass level control able to apply both boost and cut. It doesn’t simply cut signal level to the woofer, but affects deep bass output below 100Hz, offering substantial amounts of boost or cut when set to maximum.
I should quickly mention that the Spire, sitting above the Ethos in Martin Logan's premium Reserve ESL Series, has more bass control functions, whilst the new and less expensive Theos below it has a passive subwoofer and can be bi-wired or bi-amped, so is more flexible in the bass department. The Ethos is a quality model aimed at those who don’t want to fiddle. It has just enough bass control to allow easy adjustment with a self evident outcome. The bass knob, which has a centre zero detent, is turned one way or t’other to suit both taste and room conditions. It’s zero position will suit bigger rooms and a position far from walls. In our 28ft square listening room -3 to -4 was about right, on a scale of +/-10, so there is plenty of leeway.
The only criticism I would make of a hybrid like this is that small bass cabinets have limitations and putting a 200 Watt amplifier inside doesn’t solve them. Quite the reverse. Martin Logan have taken the opportunity to force the bass unit to produce subsonics it would not otherwise have produced, resulting in very large cone excursions and a huge amount of rear radiated energy that has to go somewhere; back out through the cones, making for a boxy sound. You can’t trap an elephant in a small box and hope it won’t be heard. Our measurements confirm this and if there is one criticism of Martin Logans it is that their bass tends to be not too well matched to the lithe electrostatic panel.
You have to accept that there is a trade-off here. The Ethos is compact and domestically friendly, yet it’s still a fabulous sounding electrostatic loudspeaker. You get a sensible marriage of principles that gives results to die for in many ways, at a sane price too. But small boxes do not produce superb bass and they cannot be forced to do so. Also, electrostatic panels are open backed ‘dipoles’ whilst bass bins are closed box ‘monopoles’ with entirely different radiation patterns and you’ll always detect a difference between them. That’s why Quads are full range panels, as are the bigger Kingsounds and Martin Logan’s top model, the CLX. Such loudspeakers are both big and room sensitive though. The Ethos is a domestically acceptable and adaptable package. To speed bass up they really needed a high pass filter at 40Hz and this would have been a useful option in the onboard DSP. However, turning bass level down helped improve quality all round so some amelioration is available.
The great Martin Logan XStat electrostatic panel is the crucial part that is an almost-invisible wonder. That it is see-through is not a trivial fact. I found out long ago whilst progressively stripping my Quad ESL-63s that every layer degraded the sound. Off came the cosmetic brown cloth sock: it sounded better. Then I removed the perforated metal safety covers and suddenly I felt I could hear a pin drop through these loudspeakers. Finally, off came the dust covers and it just got better again. Martin Logan stripped the panel right back to basics very cleverly, so what looks simple is in truth an ingenious design extremely well engineered. The charged stators, those perforated outer black panels, have a protective coating so the cat will survive contact with them, and Martin Logan say the panels and films can be vacuumed to remove dust. The curve improves lateral dispersion and smooths response by lessening phase cancellations/ additions. A special film from DuPont onto which a conductive coat is applied is used.
Inside the bass enclosure there’s polarising power supply and an audio step-up transformer and a crossover that keeps bass out of the panel, usefully limiting excursion of the film. Any electrostatic is complicated and the technology, especially of film coating and behaviour, is obscure and difficult to implement. Which is why there are so few electrostatic loudspeakers around, why the Ethos XStat panel is particularly clever and why this loudspeaker is also keenly priced for what it is. Measurement revealed a smoother response than the less expensive panel of the Purity and Source models in the ESL range, which we tested in our Sept 08 and Nov 08 issues. It was also very consistent off the main listening axis, so as I walked around the basic tonal balance remained the same. This made the listening sweet spot uncritical and it made the Ethos enjoyable to others in the room, rather than dull except to those in the favoured spot on the settee.
Although a lot of audio religion surrounds electrostatic loudspeakers they are simple enough and fuss free to use, the Ethos especially so. Where my Quad ESL-57s and their doppelgangers, a pair of Brauns I owned for a short time, both sparked viciously if I got too carefree with the volume control, Martin Logans avoid this scenario. They turn on quietly and do not so much as murmur in use. A small LED at the rear lights red or blue indicating no-signal/signal, but nothing is visible from the front. I didn’t push the bass bin too hard but both the bass unit and especially the underside mounted ABR (auxiliary bass radiator), moved large distances and were obviously working very hard but Martin Logan told me the onboard DSP monitors amplifier and drive units to prevent overload.
Where Quad ESL-63s would ‘crowbar’ an amplifier if overloaded, causing it to blow up, the Martin Logans do no such thing. And where Kingsounds are very insensitive and need high drive voltages (i.e. very powerful amplifiers) the Martin Logans managed a very healthy 91dB sound pressure level from just 1W of power in our tests, putting them on par with the best box loudspeakers. So the Ethos can be used with low power amplifiers: 20 Watts will do and 40W should be enough.
Some of you may be wondering, as I did, how Martin Logan have arranged signal processing in the Ethos. From the single pair of input terminals the signal goes via a 375Hz high pass filter into the audio step-up transformer and direct to the electrostatic panel. Our impedance curve confirms this; if there was any buffer device it would not sink to one ohm at 20kHz! So the XStat panel works direct from whatever amplifier is being used to drive the loudspeaker.
Matters are very different below 375Hz. The amplifier’s output is attenuated, converted to digital via a 24bit ADC, processed in a Digital Signal Processor (DSP), then converted back to analogue via an DAC before being fed to a Class D amplifier which drives the bass unit that reaches up into the low midrange in the Ethos, so you are faced with listening to a heavily processed signal below 375Hz, and Class D solid-state amplification. I guessed, when measuring the Ethos, that Martin Logan had equalised it electronically to boost bass for an extended subsonic response, because small boxes don’t reach flat down to 20Hz on their own, and they confirmed this.
I tried both our resident Musical Fidelity AMS50 Class A solid-state amplifier (50 Watts) and the also resident Icon Audio MB845 MkII valve amplifier (100W). Valve amps are known to be a good match to electrostatics, quality wise and because they tolerate a capacitive load that sinks to 1 Ohm or less at 20kHz (this is a freakout for solid-state amps., so most have protective Zobel networks to cope). As expected, the valve amplifier gave best results, with its slight sense of warmth from the Jensen paper-in-oil, copper foil caps perfect for the XStat panel.
I was only listening to the valve amplifier above 375Hz of course; below this frequency I was listening to a signal that had been converted to digital, processed, turned back to analogue then passed through a 200W solid-state amplifier.