Mellow Acoustics  FrontRo II is the second incarnation of this interesting electrostatic-hybrid loudspeaker. The loudspeakers cost £9500, are manufactured in England and have some interesting design features. Janine Elliot takes a listen.

Front view of the Mellow Acoustics FrontRo II Loudspeakers

I wrote about the original Mellow acoustics FrontRo hybrid loudspeaker a few years ago. I was impressed with the technology and precision of performance but found there were a few shortcomings; the lower bass needed more oomph and mid frequencies were slightly too obtrusive. I am pleased to hear that Tim Mellow wasn’t put off with my criticisms and worked hard to get the FrontRo to the next level, and boy has he just!

Just as Skoda, Kia and Seat improved their cars profoundly in their second generations, so this has happened with a number of now-famous HiFi brands I could mention, Mellow Acoustics included. Made in Berkshire, UK, the FrontRo II is a beautiful art deco looking feature to any living room with a triangular diaphragm bass unit with circular electrostatic unit atop, the whole standing only 80cm from the floor. Tim has had an enviable career in acoustic technology, initially working as an electronics design engineer, as an acoustical engineer and then at Nokia in Farnborough until its closure in the UK.  Around the time, he left Nokia in 2011 he started up Mellow Acoustics. After about two and a half years the first prototype was made, and now the FrontRo is as mentioned, in its second edition.

One of my all-time heroes is Peter Walker, founder of the Acoustical Manufacturing Co. Ltd, later known as Quad, synonymous with electrostatic speakers. He is also a hero of Tim’s, and whilst Tim never actually met him, he worked with his other acoustical hero Leo Beranek, co-authoring an updated version of Leo’s classic 1954 book ‘Acoustics’, including 43 pages allotted to electrostatics.  Tim’s knowledge on speaker design is to be revered, having also published 11 papers in the Journal of the Acoustical Society of America.

CONSTRUCTION

The FrontRo is a hybrid electrostatic loudspeaker weighing in at £9500 and employing an LP-sized lollypop shaped electrostatic unit to handle the mid and treble frequencies (600 to 20,000kHz) above a tetrahedron shaped box employing a conventional 5.25” dynamic woofer to handle the lower midrange and bass, taking it down to 40Hz. The company have improved the bass end considerably from the earlier model. For a start, it is a completely new woofer with a smaller but more powerful neodymium magnet that is less obstructive to rear waves. It has a more linear suspension, a longer throw coil, and an air-core crossover inductor (low-pass filter) to replace the less linear ferrite one. As Tim also told me “The higher winding resistance of the air-core inductor is compensated for by the slightly greater sensitivity of the new woofer”. This woofer is considerably better than the original driver and having it in sealed box helps get the frequencies down to numbers not to be sneered at.

The top half of the unit supplies 600Hz and higher. A single electrostatic unit covering the essential mid frequencies and above. Like Mr Mellow, I am a big fan of the principle of electrostatics. Not only does it mean doing away with both a cabinet and ‘slower’ conventional drivers that are both prone to adding their own signature to the music, but also the dipoles are incredibly light and therefore much more responsive to the signal. I found the original FrontRo wasn’t quite as fast at initial transients as I wanted to hear and hoped that the new model would feed my ears with clarity as well as low colouration and low distortion. The only drawback with electrostatics is that they are generally not quite so efficient as conventional drivers, and indeed the FrontRo is low at 84dB/m at 2.83VRMS. However, trying to get a realistic portrayal of the music from an electrostatic loudspeaker is far from easy. If it isn’t designed well, an electrostatic unit can be quite forceful and only sound good at a single sweet spot on the settee.  Martin Logan created their distinctive curve-shaped electrostatic hybrid to enable a far larger dispersal of mid/high frequencies. Mr Mellow considered curving the diaphragm, but this would add distortion to an otherwise distortion-free loudspeaker and curtail the lower notes due to increased diaphragm stiffness. What he did do, however, is create a spherical waveform – to mimic the natural sounds we hear – by employing six rings fed from a tapping on a delay line that progressively increase from the centre towards the outer edge, so that by the time the audio comes from the edge, the sound from the centre has already had a head start, and since it is a distance from the diaphragm it creates a curved wave-front. Incidentally, Peter Walker was to do this a different way in what became known as ‘Peter’s Balls’; a pre-production spherical creation built just before his untimely death that had three diaphragms and four plates in front of each other with time delays going forward in order to create a spherical waveform. This rear-ported cardioid design was shelved as they believed the revolutionary shape would put people off. A spherical wave is ideal because it has constant directivity and a perfectly smooth frequency response. Where I felt the original speaker was too pronounced in the vocal frequencies meaning it lost some of that detail in the top end, for this model he has tweaked the delay line slightly to lift the output at around 10 kHz where it was previously sagging. As an aside, the pattern of holes on the diaphragms are apparently the same as the seeds on a sunflower head, showing that a link to nature is perhaps possible. Sweet. And because the membrane is flexible, each part can move more-or-less independently from the rest according to the signal on the nearest ring.

The triangular woofer box is made of half-inch thick birch plywood that is heavily damped with a special lining material, just as was used in BBC LS3/5a’s. On the rear are two sets of speaker terminals to allow it the ability to be bi-wired or bi-amped. A figure-of-eight power connection is provided with a green LED to let you know the electrostatic diaphragm is powered up. As it consumes less than 1W, some owners may well leave it plugged in permanently. The unit is also provided with 4 adjustable conical feet, plus cups to be placed underneath if you don’t want to scratch your floor. I needed to angle up the unit in order to have the speaker aimed correctly for my armchair. Speaker placement was not a problem for me in my listening room, not least because the electrostatic loudspeaker is usually less sensitive to room placement than a conventional loudspeaker box. However, as the electrostatic diaphragm has a figure-of-eight output, sounds will be heard equally behind as in front, so placement near to a reflective surface is not suggested. The bass unit being an infinite baffle design also meant that I could place the speaker easily, though at least a foot away from the nearest object was found to be the best starting point. Generally electrostatic speakers need to be placed in big rooms well away from walls, but the FrontRo’s were ideal for small rooms and I could place it closer to the room boundaries. The unit is finished in light oak veneer (though you can choose your own preference such as American walnut), with a choice of non-removable grille cloths in gunmetal, navy or burgundy. Underneath the cloth of the electrostatic unit is a special screen that keeps out dust and moisture.

Around the back of the loudspeakers

THE MUSIC

My first listening, via Synthesis KT88 valve amplification, was to Bach’s Toccata and Fugue, BWV454 (Chasing the Dragon 2), in order to test out those lowest frequencies from the Organ. This was a totally new speaker! I played this same track in my first outing with the FrontRo and noted that it missed the lowest octave. This new speaker went all the way down to 40Hz with no problem at all. Similarly, the top end was tight and clear. Only the fact that I needed to turn up the wick a few stops to get the same volume of sound. Toed in as requested, the speakers produced a full and detailed sound. Turning to Saint Saens ‘Carnival of the Animals’ (Orchestre Philharmonique de Mexica), this has very spacious orchestration ably shown off by the FrontRo, the two pianos performing side by side centre stage (I preferred the left-hand piano!) This work has 14 movements, including the famous movement “The Aquarium”. Instrumentation includes glass harmonica and xylophone, all clearly reproduced in a forward space in my music room. Similarly, the double bass in ‘The Elephant’ was extended, making the FrontRo an all-round hybrid serving both bottom and tops in a pint-sized package.

My only criticism of the speaker was a little lack of speed and gumption, that could sound a little “mellow”, to use Tim’s surname. In order to dispel this comment, I zapped up the music with Russell Watson singing “Nella Fantasia”. This lovely classical vocal number gave me a chance to add some excitement into the foray, with excellent vocals and punchy orchestration. The speakers really gave as much as they could muster, and ably so; this was actually one of the best performances of this song I have heard.  The improved bass and more focussed mids and highs from the electrostatics made for much enjoyment. Turning to ‘De Profundis’ and “Stabat Mater” (Russian National Orchestra and Moscow Synodal Choir) the repeated melodic and harmonic phrases sounded powerful and emotional. The speakers could live above their size, though not quite as powerful a performance as from my resident gear.

The FronRo II are small in stature

To test the speed and focus of the electrostatic membranes I turned to Sven Vath ‘The Harlequin, the Robot and the Ballet Dancer’. This is an electro-acoustic album with both real and electronic sources, put together to make a highly 3D performance with pin-sharp top end and extended bass. The Mellow Acoustics FrontRo was simply excellent in portraying the composer’s thoughts, working well at low level as well as loud. Birds and sea waves were equally real that my cat even pricked its ears to go hunting for game.

I wanted to test the issues I had with the earlier FrontRo speaker in terms of mid frequencies. Genesis ‘Selling England by the Pound’ is often confused in the mid frequencies with the vocals, synth and piano all fighting for supremacy. The FrontRo allowed a very clear performance, helped by the very low cross-over frequency, and definitely an improvement on the earlier incarnation. Carol King’s “I Feel the Love” didn’t quite do it for me; the piano and vocals were still too present for my liking, though detail from the percussion and guitars was very focussed with excellent transients. The piano in “You’ve Got a Friend” was so focussed it showed off the inefficiencies of the recording; sounding like an upright that badly needing tuning. Vocals were clearly and realistically delivered, due in part to the 1st order crossover point being at 600Hz, two octaves below a typical loudspeaker.  This generally allowed vocals to be exceptionally good in my listening tests, and certainly better than the first FrontRo. All that seemed lacking was oomph in that bass when playing at loud volume, though this would be better in smaller rooms; this speaker being so small making them ideal where space was limited. Where this speaker shone, dare I say better than a Quad ESL63, was in the detail of positioning of sounds. Playing Kitaro ‘Live in America’ was a case in point. This is a very aesthetic album performed in Atlanta, April 1990. The synths and instruments, particularly the percussion, were clearly and keenly delivered and positioned precisely in what is a very large arena. The dipoles were able to give pin-sharp transients with solid and stable imaging, and the bass – being an infinite baffle – was also precise, making for a good pairing. Finally, to Sky and ‘Sky II’, an album that should be in every audio reviewer’s portfolio, including as it does harpsichords, tubas, synthesisers, guitars and drum kits. The “Tuba Smarties” was a sweet tune testing out the bass end, proving that even 5¼” was sufficient, and the harpsichords and synthesisers showed the top end was equally compelling. This is a very energetic album, and I did feel the small overall size did mean some of that drive and punch was lost. In terms of accuracy, though, this new speaker was a stepping-stone towards excellence.

The Mellow Acoustics FrontRo II speakers in situ

CONCLUSION

They might be small in size, but the FrontRo II is large in personality and features. Now that my initial findings have been addressed, I can honestly say that these speakers are ideal for those wanting electrostatic accuracy yet with enough bass to fill your room, creating a great listening environment whatever type of music you play, especially vocals.

These speakers can also be placed closer to walls than most electrostatic designs and work well with all types of music. The improvements in bass end and clarity at the top make this a much better proposition that well deserves to be put in the front row.

AT A GLANCE

Build Quality: Well-built design that also looks great as furniture

Sound Quality:  Excellent detail in mids and highs with much improved bass. Works well at lower levels

Value for Money £9500 may be more than the original Frontro, but the price gain more than pays for the improvements in sound 

Pros:

An involving presentation

Excellent soundstage retrieval

Very low distortion

Works particularly good at lower levels

Cons:

Can lack in excitement unless matched with appropriate amplification

Price: £9500

Janine Elliot

Review Equipment:

Synthesis Roma 98DC and Leak Stereo20 (amplification), Music First Audio Baby Reference (pre-amp), Pre-Audio (turntable)/AT33sa (cartridge)/Manley Steelhead (Phono-stage), Krell KPS20i (CD), Ferrograph Logic7 15ips/½ track (Reel to reel), Tellurium Q and Townshend (cables).

Technical specifications

Overall dimensions (without feet): 762 mm (H) x 494 mm (W) x 291 mm (D)
Recommended amplifier power rating: 25 to 100 W
Frequency response: 40 Hz to 20 kHz
Input impedance: nominal 8 ohms.
Sensitivity: 84 dB @ 1m for 2.83 VRMS.
Maximum output: 98dB SPL from electrostatic unit for 14 VRMS (input protected).
Crossover frequency: 600 Hz, 1st-order, time-correct
Mains connection: 240 V, 4 mA