The Eclipse speaker company has been around for a few years now – we reviewed the £4,000 TD712z in 2005 – while the TD510/D6 would seem to be an attempt to retain many of the TD712z's best qualities in a much less costly package.

Certainly the TD510 looks very similar to its senior brother and, with its small solitary full-range driver and 'dinosaur egg' type enclosure, entirely different from everything else on the market.

Somewhat ironically, just as we get to review this TD510 'floor' variation, Eclipse has announced a new £5,000 per pair TD712z MK2 replacement for the original TD712z, with extra driver refinements and a rather larger 'egg'. However, the TD510, first introduced late in 2005 primarily as a desktop monitor with a small integrated platform stand, continues much as before, but now comes complete with the much taller D6 stand, effectively becoming a floorstander at a combined price of £1,800 per pair.

Time Domain design

The initials TD stand for Time Domain and provide the clue that the prime purpose of this design is to create a speaker that accurately reproduces the timing information that many would argue is the very essence of musical performance. To this end it uses a solitary 'full-range' drive unit (the term is used advisedly), covering the whole audio band with just a single voice coil and no intervening network components.

It pretty much stands to reason that if the whole of the audio signal is fed to a single, solitary voice-coil, most of the timing, at least, will necessarily be spot on. (The extra bass output via the port will undergo a modest phase shift.) Regular speakers with more than one drive unit and phase-shifting crossover networks rarely achieve such tight timing.

To operate high into the treble, the solitary drive unit must necessarily have a small, light diaphragm – it's actually woven glass-fibre, just 70mm in diameter and has undergone a process of steady development and refinement. However, even with the help of the rearward-firing port, the small driver means that the bass output is bound to be rather limited.

At the same time, physics dictates that the top end will tend to 'beam' quite strongly once the wavelength being reproduced is less than the cone diameter, so best results are likely to be found when listening fairly close to the main forward axis.

Egg head

One thing's pretty certain: the enclosure is unlikely to make any significant contribution to the overall sound, which has got to be a major plus. Reminding us of the midrange 'head' used by Bower & Wilkins in its 800-series, the eclipse enclosure is an egg-shaped two-piece casting, high pressure injection moulded in a mineral loaded, fibre-reinforced resin, akin to 'artificial marble'.

The internal shape disperses reflections and avoids standing waves. The outside shape somewhat resembles a human head, which should assist speech reproduction.

Furthermore, the 'egg' is effectively decoupled mechanically from the vibrations generated by the drive unit and the drive unit itself is mass and, ultimately, stiffness-loaded, via a bracket down through the stand.

Heavy hitter

The D6 itself is a pretty substantial affair, combining steel and aluminium and weighing nearly 13kg. It has a solitary streamlined central pillar and a flat, but thick and heavy base with a large footprint founded on five rather blunt spikes.

The foolproof way of achieving even floor contact is a tripod, so levelling five spikes accurately and evenly was potentially daunting, but in practice proved surprisingly easy, though the lock-nut arrangement might have been improved. Although the height of the stand (70cm) and head is about the right height to direct the driver axis towards normally seated listeners, the vertical angle at the head can be adjusted via a large bolt.

Anticipating – not without reason – that the TD510 was likely to have limited bass output, we suggested that Eclipse might like to lend us its highly regarded TD725sw subwoofer, to try alongside the TD510s. The TD725sw is a very impressive example of a high-performance, if costly subwoofer.

It might be about as ugly as the 'eggs' are attractive, but it's also one of the best subwoofers around, combining twin reaction-force-cancelling, mechanically decoupled 250mm drivers, with a 500-watt digital amplifier, to deliver plenty of fast, deep bass. However, as it turned out it didn't match up to the TD510s very well in practice for a couple of reasons, more of which later.

Sound quality

It's no great surprise to find considerable similarities between this TD510 and the TD712z that we tried rather more than three years ago. Comparing the far-field in-room averaged responses, this less costly variation on the Eclipse theme shows significantly more relative treble output than the earlier model above 7khz, but is rather less well balanced at the low frequency end of the spectrum and less smooth through the upper midband too.

In fact, it's possible to describe the overall in-room power response as 40Hz-16kHz +/-6dB, which sounds impressive enough and suggests a degree of neutrality. However, this basic statistic does tend to supply a rather optimistic view, whereas the variations within those limits are bound to introduce some character and coloration.

The real problem with the TD510 is that there's too much output at 1-2kHz, a zone where human hearing is at its most sensitive. The peak here is something like 4dB proud of its immediate surroundings, and more like 6dB above the overall average.

Another obvious (+7dB) peak is seen at 52Hz, this time associated with the port, which is tuned to that frequency and further exaggerated by its coincidence with a major room mode. It was this peak that caused problems achieving good integration with the Eclipse subwoofer.

The uneven frequency balance inevitably distorts the tonal balance, so that neutrality is not one of its accomplishments. Happily there's much more to this speaker than basic neutrality and, in several other respects, it turns out to be quite a star.

The combination of magnificent time coherence and the effective elimination of enclosure distortions results in its own impressive believability and realism. Voice band coherence is unequalled, with real and seductive tangibility, though there is a touch of cupped-hands-type 'quack' and also some loss of airiness.

There's no trace of boxiness here, so the stereo imaging is particularly impressive – quite stunning in fact, in the way the tightly focused soundstage simply hangs in the air. Holographic is a term that tends to crop up much too often in the hi-fi press, but on this occasion it seems totally appropriate to the 3-D imaging this speaker pair can supply.

Clean audio

The sound as a whole is quite clean, tidy and sweet and the amount of bass thump available, even with the speakers well out from the wall, came as something of a surprise and a very pleasant one at that. However, although that upper mid exaggeration did project vocal detail very effectively, ensuring superior intelligibility even at very low levels, it also meant that the sound could become rather unforgiving and fierce if the volume is turned up high.

Close-to-wall siting did help provide some extra mid-bass 'fill' and introducing the subwoofer certainly added as much extra weight and scale as you could desire. However, neither of these strategies proved wholly satisfactory.

Wall reinforcement only served to dilute the very special imaging qualities and overall coherence of these speakers, while boosting the bottom end by either means tended to make the lack of top end airiness that much more obvious. Frankly, in this case it seemed best to mount the TD510 well clear of walls and simply put up with their tonal balance anomalies.