Moved in part by my experiences with the REL 'cube' and the Ruark subwoofer, I now find myself less resistant to boom boxes than I did before. No, I'm not enamoured of subwoofers and I could quite easily remove them from my system without suddenly feeling as if the bottom had dropped out of the sound. But I still think that subwoofers are no substitute for whacking great main speakers in which the entire sound is integrated into a cohesive whole.

Unlike the similarly-priced but decidedly grisly Q200E, REL's Strata III seems like a piece of furniture worth displaying. A hundred years from now, I expect whoever is working on the will try to find its lid, for it looks like a Victorian wine cooler or some other arcane box with an obscure purpose. But turn it around, and you see that it is a sophisticated subwoofer with enough knobs to twirl in the quest for making it blend in with your existing speakers.

Among its facilties are an enhanced version of REL's ABC filtering circuit, for setting the upper response limit in 24 'musically correct' semi-tone increments, between 22Hz and 96Hz. Separate volume controls are provided for both high and low level inputs, along with a 'straight through' facility which bypasses the filter when it's fed the LFE component of discrete multi-channel formats such as Dolby Digital and dts. It differs from its predecessor, the Strata II, in that it's a closed-box design for greater phase accuracy. It contains new custom-engineered 100W DC-coupled MOSFET amplifier and high quality 250mm long-throw, downward firing woofer with a cast chassis. Also fitted is REL's 'audibly transparent' Set-Safe protection circuitry.

REL describes the topology as an 'Active zeroQ Acoustic Suspension System with ABC semi-tone variable bass filter'. Its frequency range is 20-120Hz, which will allow it to merge with all but the tiniest speakers. On the back are rotaries for 'Mode', Lo Level Gain' and 'Hi Level Gain' with an 80dB range, 'Coarse' and 'Fine' roll-off, 10k ohm low and 100k ohm high level phono inputs and the same again in balanced mode, an IEC mains input and a green illuminated on-off rocker. A pity it's not on the front: those who choose NOT to leave it on at all times would appreciate not having to look around the back for confirmation. So, Richard, how about a tiny tell-tale on the front of the Mk IV?

As with the Q200E and the other RELs, the surfeit of adjustments doesn't make set-up any easier, and you will eventually learn that what it finally gets down to are your own ears and preferences. Life is made simpler if you happen to be using it in a multi-channel system controlled by a surround processor with comprehensive facilities for setting up a subwoofer; blessedly, the Lexicon MC-1 is such a beast, so I was able to do some of the fine-tuning, especially output level and some of the crossover setting, from the listening position. Conversely, if you love knob twiddling and tweaking, the REL will prove to be as much fun as a DreamCast. In addition to overall gain setting and crossover points, you can play with polarity and slope to your heart's content.

In my installation, the REL was used to augment the Martin-Logan Script/Scenario array, even though I was perfectly happy with the bass they produce in my 14x22ft room. The Strata III was driven by the subwoofer output of the Lexicon, its connection made with Transparent Ultra, while sources included Region 1 and 2 Pioneer DVD players; the assorted Martin-Logans were driven by the Theta Dreadnaught and the Acurus 200X3.

Armed with an array of bass-oriented discs - both Dolby and dts versions of , the Region 2 version of and the Region 1 edition of - I homed in on portions of the material where sonic 'mass' could make a worthwhile difference. And it wasn't all explosions and or thunderclaps. Indeed, the most effective justification proved to be 'atmospherics', such as the ambient sound inside the U-boat in and the under-water sequences at the beginning of . These were omnipresent even with the REL switched off, but adding the Strata III to the system increased the sensation quite audibly, to create a far more convincing, all-pervading environment.

But the bangs have it, and there's simply no escaping the usefulness of a sub if you want maximum impact. I repeat: a film can be just as enjoyable without one if you've chosen the correct speakers for your room and tastes, but the Strata III did add more kick wa-a-ay down. It struck me as fuller than the Q200E, if less tight and dry, but at these frequencies and with film soundtracks, it's almost academic. Whatever, I found the Strata more satisfying, certainly more convincing and clearly more to my taste than the slightly smart-arse Q200E; the price you pay is that it's much bigger than its cubist sibling.

On music-only material, though, especially with high bass content - the soundtrack, Prince's latest, (believe it or not) the Vonda Shepard's second volume of Ally McBealisms, Barry White's recent 'best of' - the Strata increases the weight but you must match it with care: all too easily it can add too much richness, particularly on acoustic bass. But then, that's why it has an on/off switch. And all of those other controls, which will amuse you for weeks.

I said that the Strata III is prettier than the Q200E. However, you can, if you so desire and wish to acquire the REL for an all-in basic price of £600, approximate the small cube's hideousness by opting to enclose the 17kg, 416x518x310mm (WHD) box in the basic Grittex Black. Spend an extra c-note, though, and you can select from five real wood veneers including Black Ash, Cherry, Light Oak, Rosenut (?) and Walnut. Trust me: it's worth foregoing, say seven CDs or five DVDs in spending the £100. Why? Because the Strata III is so damned classy that it seems cruel to clothe it in rags.