The PSB Synchrony One is a very interesting and cleverly designed loudspeaker, though not, it must be said, a particularly attractive one. It can be argued that it adheres closely to the form-follows function dictum and also looks commendably discreet, but some may dismiss its appearance as just plain boring, especially in the all-black finish of our review samples.

The dark cherry veneered option pictured on the website does look rather less funereal. And, while we suspect that PSB might derive some commercial benefit from employing an industrial design consultant, there's no denying the technical creativity at work inside this speaker, especially in the way the bass delivery is organised.

This is essentially a three-way speaker, though it actually uses five drive units, as the bass is delivered from three apparently identical 165mm drivers, widely spaced along the front panel – one at the top, one near the middle and one close to the base. Each of the bass drivers is loaded by its own partitioned section of the enclosure, while each sub-enclosure is loaded by a rearward-facing port.

Tuning the sound

By tuning each enclosure/port combination differently and also rolling off each driver at a slightly different frequency, the various individual resonances won't coincide and a smoother bass delivery will be achieved. Likewise, by generating the low bass from up to twelve separate locations (for a stereo pair), individual room standing wave modes and floor-first reflections will also be more evenly spread.

PVC bungs are supplied to block any or all of the ports according to individual taste and room characteristics. Both the midrange driver and the tweeter are mounted below normal seated ear level, but because the tweeter is positioned below the midrange with its deeper set voice-coil, the main axis between the two in the crossover region is directed upwards.

The four cone drivers all have diaphragms made from a sandwich of fine-weave fibreglass and natural fibres, to provide good rigidity with low mass and optimised self-damping. Around a solid aluminium 'bullet' phase plug, the bass diaphragms are 120mm in diameter, the midrange 75mm. The tweeter has a 25mm titanium dome diaphragm.

The enclosure is a very elaborate and exceptionally rigid affair, with gently curved aluminium extrusions for the front and back panels that lock rigidly to veneered, curved seven-layer MDF sides, enhancing overall rigidity and avoiding parallel reflecting surfaces.

Twin terminal pairs are fitted and a black, acoustically transparent perforated aluminium grille, as well as 6mm floor coupling spikes are also supplied. Perhaps, regrettably, there's no additional plinth to enhance physical stability and given its tall and slender design, we doubt it would pass a 'knock over' test, which might prove to be a problem in a home with boisterous children.

Intelligent sound

This is a very clever speaker indeed and the effectiveness of its unusual bass driver layout is reflected in an unusually smooth and even in-room far-field averaged power response through most of the audio band. Indeed, with the speakers well clear of walls and all the ports blocked, this frequency response held within +/-5dB right across the band and within an extremely creditable +/-3dB above 70hz.

The broad midband is much smoother and flatter than is usually the case, the mid-to-treble crossover is virtally seamless and the far-field treble roll-off looks very well judged, with just a little peak at around 18khz confirming the use of a metal dome tweeter.

Opening the ports progressively adds extra bass output around 40-50hz, but this proved progressively excessive under our room conditions, so best results were obtained with the ports blocked.

The driving system consisted of a Naim CDS3/555PS CD player, a Linn Sondek LP12 (modified) turntable with Rega RB1000 tonearm and Soundsmith Strain Gauge cartridge, a Magnum Dynalab MD 106T tuner, a Naim NAC552/NAP500 pre/power amplifier and Vertex AQ cables.

The most immediately obvious factor one notices when the Synchrony One is connected up, is its superb overall neutrality and beautifully judged frequency balance. No part of the audio band seems out of place (provided the ports are all plugged) and the voicing is delightfully open without ever becoming unpleasantly aggressive.

No less obvious is the excellent stereo image focus, particularly through the voice band. This may well explain the lack of aggression and, probably, indicates good control over phase. But the fine enclosure engineering and rigid alloy baffle also plays an important part, by ensuring a substantial freedom from boxy effects and hence a reluctance for the image to hang around the speakers themselves, rather than filling the space around and between.

The bass and lower mid is generally free from box colorations, though its attractive warmth and harmonic richness is achieved at some cost in crispness and drive. We might have anticipated that the image would lack height, since the tweeter is set well below seated ear level, but that didn't seem to be the case at all with the Synchrony One. in fact, the imaging as a whole is very high class.

Minor flaws

So far the news has been exceptionally good, but there are a couple of reservations that should be mentioned. The first was encountered when playing Massive Attack's Protection, with its repetitive bass figures. These sound appropriately smooth and even, when properly seated, but the bass line thickens up and becomes much more obviously coloured when changing the listening position. There's no definite explanation for this observation and it wasn't repeated with any regularity on other material.

It's just possible then, that it might be related to the vertical path differences between listener and bass drivers. The other criticism concerns the dynamic performance. The dynamic range itself is very wide, thanks to the very substantial and intelligent enclosure engineering. But dynamic tension seems a little muted and expression lacks some vigour and drama. The latter observation is actually widespread among general commercial speakers, although some listeners seem not to notice it at all.

But, as far as we're concerned, it distinguishes 'real' from 'reproduced' sound and is one of the reasons some enthusiasts opt for large, costly and ungainly horn speakers and the like. The Synchrony one might not scale the heights of the extreme high end, but it is an exceptionally safe pair of hands that the overwhelming majority will find immensely satisfying.

The fact that it's also a very intelligent and creative design that successfully adopts radical solutions to enclosure construction and in-room bass drive is further icing on the cake.