Mellow Acoustics

FrontRo Loudspeakers

£9,500

Conventional loudspeakers are very flawed things. Little has changed about the dynamic drive units they use for the best part of a century; the principle of a coil in a magnetic field pushing a cone backwards and forwards to make sound has remained the same. Various improvements have come along, but you might say they've been about coping with inherent problems rather than radically rethinking the design itself.

Most speaker manufacturers persist with 'moving coil' drive units because they're relatively inexpensive and a known quantity. In other words, there are a lot of people who know how to make the drivers well and reasonably cheaply. But this isn't good enough for everyone, and that's why we've seen several very different solutions appear over the decades – from electrostatic panels and ribbons to Balanced Mode Radiators.

Quad's ESL-57 was the world's first production electrostatic, launched in 1957. A landmark in loudspeaker design, it got around the main downside of moving coil drive units elegantly by using a film diaphragm stretched across a panel which is moved by static electricity. This is dramatically lighter than the cone in conventional drive units – being around one-sixth of the width of a human hair – and thus far faster to move and more controlled in the way it 'breaks up' or distorts.

DESIGN MATTERS

Meet the new £9,500 Mellow Acoustics FrontRo. “The inspiration came from hearing the breathtaking transparency of the Quad ESL-63”, designer Tim Mellow tells me. “With its very light and flexible diaphragm and lack of a box, an electrostatic speaker is the closest thing to moving air directly without any intervening mechanical structure.”

Fascinatingly, his new speaker isn't simply another reworking of Quad's take on electrostatics but an innovative new one that uses Tim's so-called 'oscillating sphere concept' to improve how sound waves propagate from the panel. “It prevents the waves from beaming towards you… Imagine a rigid sphere oscillating back and forth in free space, spreading the sound out in all directions across the entire musical spectrum. This is the perfect dipole sound source and has a smooth response.”

Tim's design divides the FrontRo's electrodes into concentric rings, which are fed from a delay line. Hence the sound radiates from the centre first and then from each successive ring until it leaves the outermost ring, by which time the sound from the centre is some distance from the diaphragm. In other words, the sound travels out into the room like ripples in a pond. To allow the sound out, he has created electrodes with a pattern of holes that resembles the seeds on a sunflower head. If you'd like to know more, further information can be seen on his website.

Tim is a newcomer to the hi-fi industry, but not to loudspeaker design. “It was Leo Beranek's 1954 book Acoustics that sparked my interest in loudspeakers, microphones and headphones,” he tells me, “because it used electrical circuit analogies to describe mechanical and acoustic elements like diaphragms, suspensions, cavities and sound holes, etc., so it was using a language I already understood.” Years later, while working for Nokia, Tim met Leo Kärkkäinen in Helsinki, a physicist who became his mentor in calculating how sound is radiated from various sources. He suggested that Tim update Beranek's book, which he has now done. “My hope is that our new version will save others from the trouble I had of extracting the information I needed from many different books and papers by different authors, using different notations and mathematical methods”, he tells me.

Tim felt that the Quad ESL-63 – the archetype of a great electrostatic speaker, to many people's ears – was, “a little too directional at higher frequencies… the sound spread out over an arc angle of about +/- 40 degrees either side of the main axis. Over the years, I noticed that only very small speakers give spacious, room-filling sound that immerses you like most live acoustic instruments and voices do. This is due to the virtually omnidirectional pattern such small speakers have in the midrange.” He thought, “what if we could design an electrostatic speaker to create this effect together with the inherent transparency of an electrostatic design?” His other issue with Quads was their lack of domestic acceptability, in other words, their blocky looks.

The FrontRo has been around since 2013 in various stages of development. “My challenge”, he says, “was to find a manufacturer to take it on, and teach them how to tension the diaphragm and assemble the electrostatic driver. The first five pairs came off the production line of a manufacturer in Hungerford, England, in 2018. Unfortunately, they got rid of their production to focus on design, so we had to start again with a specialist in Reading, close to where the joinery is done. The first speakers were delivered in 2020, but have been subject to a number of improvements…”

Tim says the FrontRo is the intellectually correct way to make an electrostatic loudspeaker. “One day, it occurred to me that the ideal dipole source would be a sphere oscillating back and forth in space because there is no edge discontinuity. If we could arrange the delay line to imitate such a source using a flat diaphragm, there would be no need to attenuate the delay, and so we would have greater efficiency, which in turn would enable a more compact design.”

The striking-looking industrial design was done by Josh Ford. I think it's fair to say that some will love it, and others not; it's a bold look that's more likely to fit in bijou riverside apartments than the dungeon-like basement listening rooms that some audiophiles have. “Josh knew how much I admire twentieth-century classics such as the cantilever chair by Mart Stam, or the Paimio chair by Alvar Aalto with its curved plywood frame. I like to think this is reflected in his design for the FrontRo”, Tim told me.

UP CLOSE

To my eyes, the shape won't appeal to everyone, but it should be applauded for its aesthetic purity and sense of form following function. The electrostatic driver is, in effect, suspended in free space away from reflecting surfaces; the woofer box is pyramid-shaped to minimise standing waves, and it's well separated from the mid/treble unit.

Tim says that the bass driver is a 6.5-inch Tang Band unit with a very long coil that overhangs the magnetic gap by a large amount, giving it a linear excursion of plus or minus half an inch. “The long coil adds extra mass, which enables it to work down to low frequencies in a small box but having so much of the coil outside the magnetic gap with no force acting on it reduces efficiency. However, this is compensated for by the large, powerful rare earth magnet.”

The frame is beautifully made – in the UK – and the rear panel treatment is very tidy. Being part electrostatic, it is, of course, necessary to plug each speaker into the mains, whereupon a small green power LED illuminates on the rear of the woofer box, next to the speaker binding posts. Measuring 762x494x291mm (HxWxD), the FrontRo is surprisingly small and room-friendly. It sports a single oscillating sphere electrostatic panel mounted above a dynamic bass unit that takes over at 600Hz and below – so it is effectively a hybrid design.

It has a quoted power handling of 25 to 100W RMS and a frequency response of 40Hz to 20kHz. It is more sensitive than the original Quads, with a figure of 84dB (@ 1m for 2.83 VRMS) and a nominal impedance of 8 ohms. Tim says its maximum output level is 98dB SPL (for 14 VRMS, input protected). I found it relatively easy to drive with a variety of power amplifiers; I used everything from a World Audio Design K5881 tube amp to a Sony TA-N86B Class A solid-state design. A modern mid-price integrated like an Exposure 3510 should work a treat. Placement was surprisingly easy, the FrontRo being able to work unexpectedly close to a boundary wall if need be. It's certainly more room-friendly than most electrostatics, in my experience. Notably, it required relatively little toe-in in my room.

THE LISTENING

This is one of the most interesting loudspeakers that I have heard in a long time. Despite its somewhat whimsical appearance, the FrontRo produces a very middle-of-the-road sound – but I mean that in a good way. First, you get an unexpectedly even response, despite this being a hybrid. There's no sense of listening to 'two speakers in one', where the bass arrives with you half a second after the midband and treble. Instead, it's impressively seamless, and wide range too.

Second, it possesses all the desirable traits of a great electrostatic – a superb, near translucent midband, super quick transients and no nasty boomy box sounds. Nor do you hear any moving coil drivers quacking or harrumphing along to the music. Third, you get an excellent sense of spatiality; it's a truly expansive sound and not one that beams out at you – like, for example, some dual concentric or horn-loaded designs.

The overall effect is a very self-effacing speaker. Whilst the styling might draw attention to itself, the sound doesn't. It's almost as if the FrontRo is not there – or there in the room with you in body only, not in spirit. The music just comes out at you from two places in space, and you don't think anything of this process; you just focus on the music. For example, a slice of classic techno in the shape of Leftfield's Not Forgotten was beautifully revealed. It's a great dance song with a pile-driving bassline that can have lesser speakers tripping over their own shoelaces, but this one just dived in and had fun.

My attention was immediately drawn to the lead electric piano riff, which along with the drum programming, sounds quite infectious. The FrontRo took it completely in its stride, sashaying along without breaking into a sweat – even at the highest volumes. The purity of tone on the piano sound was lovely to behold, as was the way that this speaker seemed to deconstruct all elements in the mix but also put them back again intact, so everything played in a very natural way.

This superb coherence stayed with me when I moved to more complex pop music. Slave to the Rhythm by Grace Jones is a hard song to reproduce convincingly, as it can sound flat with the wrong loudspeakers. With the right ones, however, it comes over like the musical equivalent of a coiled spring that releases its energy when Grace's vocals come to a peak. The FrontRo handled it very deftly, giving a spacious recorded acoustic with a fine sense of scale; inside this, the rhythm section thumped away, overlaid by the vocal line and keyboards. Everything was kept in its correct proportion, and stayed locked in place regardless of the soaring vocal track and the chewy bass line. The music was clean, crisp and tight, with all aspects of it beautifully syncopated – a fantastic achievement for such a (relatively) small speaker.

This little loudspeaker has tremendous precision and poise – and is sufficiently transparent to really make the most of well-recorded classical. My favourite Karajan-conducted rendition of Beethoven's Pastoral Symphony (Berlin Philharmonic) was great fun. There's less bass content here than most pop music, but the woofer integrated beautifully with the electrostatic driver and never appeared out of control, or behind the times. There was a fine sense of body to the cellos, with up in the midband violins had a gorgeous, sinewy, wiry sound that never grated. Best of all, the music flowed along, with a strong sense of where it wanted to go.

The FrontRo's only weakness that I can hear is simply that it lacks the physical scale of some of its price rivals. That's an inevitable function of its size because those smallish drivers can only move a certain amount of air. Yet while not having a huge, visceral sound within its own self-imposed confines, it's very good at sound staging and depth perspective, with great imaging precision too. The result is that this is a far better all-rounder than many electrostatic loudspeakers or other hybrids.

THE VERDICT

There's simply nothing not to like about this speaker if you're the sort of music fan who wants accuracy and musicality in a relatively compact package. It's not cheap, of course, but it is still nevertheless excellent value for money compared to its rivals at the price. It sounds great, but not in an analytical way. It has practically all the benefits of conventional electrostatics and almost none of the drawbacks. In short, Mellow Acoustics' new FrontRo is an excellent high-end loudspeaker that deserves an audition if you're in the market for something different.

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