Audio Note AN-E SPx-Ltd Loudspeaker Review

Once in a while, a product comes along that rewrites the rules, pushes the boundaries and gives you new and exciting insights into music that you thought you knew well. The Audio Note AN-E Ltd 'field coil' loudspeaker is, in my view, just such a product. 

Most speakers use drive units with permanent 'hard' magnets. The cones or domes are attached to a voice coil, and when an electrical signal is applied, this moves to and fro within the magnetic field created by the magnets. Back in 1925, however, when Edward Kellogg and Chester Rice at the General Electric laboratories in the USA developed the first 'moving coil' loudspeaker, there were no permanent magnets large or strong enough for the job, so they used an electromagnet – or field coil – to create that magnetic field.

When more powerful Alnico permanent magnets came along in the nineteen forties, followed by cheaper ferrite magnets and later still ceramic/ferrite magnets like we have today, field coils were consigned to history. The new permanent magnets were cheaper, and no longer needed external mains or battery power supplies.

So what made Audio Note boss Peter Qvortrup resurrect field coil technology for the twenty-first century? He tells me that when he was running his retail shop in Denmark in the seventies, a customer told him he had seen some amplifiers in an old cinema that was being torn down. Qvortrup discovered that these were triode valve amps. He rescued one, got it working, and that started his love affair with the breed. He also rescued some old field coil loudspeaker drive units, and when he hooked those up and compared them with the Alnico drivers of the day, he could not believe how good they were.

He duly vowed to investigate the technology, and although he and Guy Adams looked at it again in the early nineties, other priorities got in the way – such as Audio Note's non-oversampling DACs and in-house transformer manufacturing. And so it wasn't until 2018 that the project was picked up again in earnest.

Up Close

Audio Note chief designer Andy Grove says there are sound technical reasons why field coils outperform permanent magnets. He explains that the magnetic field is stiffer and more robust when using an electromagnet. The hard materials used in permanent magnets, he says, retain a charge after being energised by the signal, whereas the 'soft' magnetic materials used in transformers and electromagnets do not retain any such residual magnetism.

When the voice coil moves, it interacts with the driver's static magnetic field, generating a 'stepping' distortion known as the Barkhausen Effect, and hysteresis distortions occur during the magnetising/demagnetising cycle. These distortions, says Grove, are far more pronounced in permanent magnets, and Peter Qvortrup adds that you can clearly hear the way that noise and distortion affect sound quality.

It took the team some time to find the right materials for the electromagnetic system of these field coil speakers. First prototypes used a mild-steel core, but this was inefficient and led to excessive heat buildup. After working with a foundry in England's Black Country, in the West Midlands, they ended up with a ferritised, heat-treated casting with pure-iron pole-pieces. The new materials solved the overheating problems thanks to an increase in efficiency. The external mains power supply for the speakers is based on an in-house mains transformer and stabiliser circuitry developed from the filament supplies used for Audio Note's M3 to M10 preamplifiers. They tried passive power supplies, but these did not cope well with the back-EMF from the speakers or mains fluctuations.

The AN-E Ltd standmount speaker comes in six iterations, and sits at the top of the Audio Note range – the SPx model I am reviewing here is the least expensive. As you move up the range, prices go up as they start to use different grades of silver internal wiring, Audio Note's own copper or silver mylar capacitors and external crossovers mounted in the stands. Stands will set you back an additional £670 for the internal crossover models and £1,500 for those with the crossover built in.

Both the tweeter, a 25mm SEAS silk dome, and the 200mm SEAS hemp-coned driver with silver voice coil, are field coil units, and Qvortrup tells me this makes the E-Ltd the only speaker on the market where all the drivers are field coils. The cones, baskets and all other parts of the drive units are the same as standard E models, the only difference being the magnet assembly.

This 790x360x270mm [HxWxD], 29kg design uses birch ply cabinets that adhere to Audio Note's cabinet philosophy, where they don't try to kill resonances with loads of acoustic wool or damping panels, and instead tailor the cabinets to put those resonances in bands where they enhance the operation of the drive units. The wide baffles are intended to act as a virtual wall and are said to provide the most even dispersion and undisturbed sound field.

Crossovers are also kept simple and are essentially the same as in the standard Es, apart from a specially developed, hand-made resistor with a phenolic former, which avoids the 'zing' they were getting from resistors with ceramic or alumina substrates. Inductors are air-core, and capacitors are either bipolar or polypropylene. They use first-order roll-offs and are hard-wired.

Unusual as this speaker is in terms of its technology, it still made perfect sense to evaluate it by slotting the review pair into my usual home system of Audio Note Meishu Tonmeister single-ended 300B integrated valve amp fed by Audio Note's TT3/Arm Two/Io1 and S9 transformer vinyl front end. I also used an Audio Note CDT Five transport with DAC 5 Special number cruncher. With a claimed efficiency of 97dB, this 6-ohm speaker is, of course, ideal for low-powered valve amplifiers. Both QED Supremus Zr and Audio Note's own silver speaker cables were used.

The Listening

From the very first few bars of the first track I played, I knew that this speaker was something very different and very special. The AN-E SPx-Ltd manages to combine some extraordinary qualities – it's fast and dynamic, and separates out instruments better than anything else I have had at home. It reveals nuances of play in a way that enhances your appreciation of the music – something that you can't help but notice when a vocalist or saxophonist really pumps up the volume. It keeps the soundstage natural, with practically no artifice.

Cueing up Larry Carlton's excellent cover of The Doobie Brothers' Minute by Minute, I was immediately struck by the sheer abundance of detail. All the musicians spread in front of me were more sharply etched and real than I had ever heard them before. I could listen into the lead guitar playing, the pounding percussion line, and that sinuous, driving bass line really precisely – allowing me to better appreciate their musical contribution to the track. That bass line was deep, super-tight and moved really well, while subtle extra detail in the percussion emerged to delight me. I could also hear the shape and phrasing of Carlton's guitar, the dynamics of each note and precisely how loud it was played.

As a consequence, the texture and timbre of instruments were amazing. George Benson's Being With You juxtaposes Fender Rhodes piano work with mellow Ibanez guitar playing. Via this Audio Note loudspeaker, not only was the string backing more real, alive and detailed, but the Fender Rhodes came in with a solidity, sparkle, dynamics and focus that took me by surprise. And subtle nuances in the phrasing, note shaping and voicing of Benson's guitar had me aghast. The bass had an astonishing tightness, control and note integrity, with notes packing a punch I had not heard before.

It was as if everything was supremely clearly etched, yet highly authentic-sounding. This visceral live feel was masterfully embodied in hearing Fergus McCreadie's Sun Pillars, where, from the first few notes, his piano had more weight, more dynamics, more movement and fluidity, and more power in the lower registers. Drums and cymbals sounded wonderfully open, delicate and fast, while the acoustic bass line was much weightier than I had heard before, yet still agile and nimble. When McCreadie really let his fingers fly, this speaker kept everything focused and tight. Each musician was clearly separated from the others, making them very easy to follow.

The musical fireworks generated by the Audio Note AN-E SPx-Ltd are quite a thing to hear. Ben Sidran's It Didn't All Come True was a festival of the senses. I heard life and dynamics from his piano that I'd never experienced before. Drums were tight, yet had effortless detail and power. It was all laid out in one cohesive, sharply focused, beautifully balanced and nuanced musical tableau. With each subsequent track I played, this speaker continued to delight. Vocals from Astrud Gilberto, Luther Vandross, Anita Baker, John Mellencamp, Randy Crawford, and Joe Cocker were all masterfully conveyed with their subtle nuances of style, voice, and phrasing brilliantly signposted. At the same time, you would never call this speaker harsh – indeed, it tended to minimise the intrusiveness of any surface noise or crackles on LP records. All the above, while still delivering outstanding musical dynamics.

The Verdict

The new Audio Note AN-E SPx-Ltd is an extraordinary loudspeaker, then, as it should be at this price. It took only a few tracks for me to realise that listening to a pair was like putting on new glasses after you'd let your old prescription get out of date. Suddenly, everything was more vivid, visceral and sharply focused. So anyone who has this kind of money to spend on speakers should not overlook this design – audition it if you can, and your ears will thank you.

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