The Torus has been around in one form or another for a while. We first saw a prototype the Spring before last at the High End show in Frankfurt.

It is a subwoofer (Wilson Benesch calls it something more grandiose, and we'll get back to that point soon) like no other you have seen before - or since. Among many superlatives, it is surely the most eye-turning subwoofer ever, inhabiting a reasonably compact, but clearly potent heavyweight enclosure.

It is passively driven, and typically comes with a matching 200W monaural amplifier/low pass filter unit/ interface box, about the size of a conventional integrated amplifier. The two are available separately, and in principal, at least, if you find an alternative suitably specified electronics package, you could use that instead.

As a combination, the Torus 'infrasonic generator' (Wilson Benesch's terminology) and amplifier are functionally the same as a standard subwoofer, though it could hardly be described as conventional, as there is no formal drive unit involved.

Instead, there is a large-area diaphragm, made from immensely strong but light carbon fibre, driven by two 82mm voice coils, working in push-pull to create an intrinsic restoring force.

Normally, a driver's suspension would do the same job, but with a time delay, due to the mechanical hysteresis involved. The push-pull voice coil also results in a cancellation of third order distortion products.

Instead of a combination of driver basket and enclosure, the reaction force from the diaphragm travels through a massive component called 'The Core'; a two-part 16kg central rod which is rigidly coupled to a steel baseplate and then to ground, which acts as a mechanical, essentially compliance-free earth.

This major component is also used to conduct heat away, assisted by a Boron Nitride coating. The outer structure of the Torus is there simply to provide air sealing around the diaphragm.

How the Torus components have been arrived at is not easy to nail down, because Wilson Benesch's claims are couched in generalities.

Moreover, in the instruction manual, it attributes the role of 'architect of subwoofers' to REL's Richard Lord, where in fact much of the early pioneering work was attributable to Karl-Erik Stahl back in the late 1970s. His ACE-Bass technology - applied to the Audio Pro subwoofer range - specifically addressed key problems facing subwoofer designers, long before REL was formed.

Wilson Benesch also ignores the recent trend to decoupling subwoofer enclosures from their drive units, and the use of multiple opposed drivers (which is part of the solution to the problem identified by Wilson Benesch), for example by Mordaunt-Short and Eclipse.

However, Wilson Benesch does point out that although a large-area drive unit is needed to move enough air for serious bass, a large drive unit cannot accelerate and decelerate the diaphragm efficiently enough to be successfully integrated with satellite speakers.

An early solution to this problem, the Isobaric Tactic, was developed with SMART (government) funding about eight years ago. The new Torus driver is a more practical clean-sheet design, which is claimed to be a more efficient and readily built solution, than was available before.

The matching Torus amplifier has two inputs, one at 'high' level, for use with preamp outputs in a stereo system, or via a REL-like Neutrik Speakon balanced connector, with bare wire to connect to the speaker outputs of a power amp, or integrated in parallel with the main stereo pair.

This takes care of low frequency programme content. Alternatively, it can be driven at low level from a preamp output or the LFE output of a multichannel AV amplifier, primarily for special effects.

Both inputs can be wired simultaneously, and the system adjusted to provide a combination of low frequency support for stereo and LFE output - similar to the generic pattern from REL (and some other) subwoofers, in fact.

Each input has its own independently adjustable low pass filter and gain control. A DIL switch fitted to the base, sets the overall high pass or bypass settings: a one-time adjustment. The front panel controls (and display) provide everyday low pass fine adjustment.

It took some time to get a measure of the performance of the Torus, which was eventually tackled by using it with a range of speakers of different size and intrinsic bandwidth.

At the two extremes, we used the ALR Jordan Classic 1, which is almost small enough to stand in the palm of your hand and the Triangle Magellan Concerto SW2, that would crush the same hand paper-thin given half a chance (both speakers are reviewed elsewhere in this issue).