PureLow LO Subwoofer

Purelow Acoustic LO
PureLow LO Subwoofer

It’s not often that you come across something genuinely new in audio. From contra-rotating turntable platters to tangentially correcting headshells it’s all been done (or at least attempted) before. In one sense, the same is true of PureLow’s LO sub-woofer. It is based on the Orthophase driver design, a topology that dates back as far as 1959 – or 1929 if you count its genesis in the wonderfully named Blatthaller PA system. But there’s never been an Orthophase driver quite like this! The originals were 10cm square quasi-ribbon designs. The PureLow LO subwoofer uses just one driver – but it’s a metre square!

Perhaps I should start at the beginning…

The Orthophase drive system is perhaps most easily understood with reference to planar magnetics like the Magneplanars. Except that, rather than having a flat ‘voice-coil’ placed in front of a magnetic array (a situation that means that the larger the excursion, the further the voice-coil – and diaphragm – moves from the magnetic field) the Orthophase design places the wires of the voice coil on stand-offs, behind the diaphragm and contained in deep, U-shaped magnetic channels, so that they remain firmly within the field’s grip. Scaled up to a metre square, the result is a diaphragm with a swept area equivalent to eleven 15” drivers, with a maximum excursion that’s greater than ±9mm and that’s driven across it’s entire area! Throw in a remarkably benign impedance that sits around 4 Ohms, an efficiency of 90dB, a fundamental resonance at 9Hz and phase-linear output to well beyond its pass-band and you’ve got an absolute monster on your hands – and that’s before you physically examine the beast! Anyway you look at it, the PureLow LO sub is as imposing as it is impressive, as potentially potent as it undeniably pricey. At €36,000 a pop, this is a serious sub-bass solution for serious listeners with seriously deep pockets. It is also a revelation!

The LO’s cabinet stands 125cm tall and wide, but it’s only 12cm thick. Unlike most planar speakers, it is not a di-pole, the tightly packed magnetic channels behind the diaphragm effectively creating an enclosed but vented rear chamber. Of course, the ‘voice-coil’ sits in free air, an arrangement that, combined with being more than 50m in length, effectively eliminates thermal compression. The diaphragm itself is formed from a light, rigid, fibre mat, with the bracing struts and stand-offs hand-constructed from more than 1000 of the 2700 discrete parts that a single LO speaker contains. In fact, the entire speaker is hand assembled and exactingly tuned in France by Patrick Marchandot and his team, a process that takes more than 200 hours for each unit. Like all right-thinking subwoofers, the LO contains neither a crossover nor a driving amplifier, which isolates the electronics from mechanical battering and crucially, allows you to match your low-frequency amplification to the amps driving the rest of the range. It also means that you need to source your own crossover from those available. I used both the Wilson WATCH Controller and the Wilson Benesch Torus crossover/amplifier with excellent results, although there was no escaping the clearly audible superiority of the (much) more expensive Wilson/CH Precision A1.5 pairing. And therein lies a tale… 

When it comes to injecting scale and presence into recordings, the sense of real people and real instruments, there’s no substitute for bandwidth – at either extreme. If you’ve spent any sort of time with subwoofers you’ll know that when it comes to bass, that bandwidth is best supplied naturally aspirated. That means devoid of heavy equalization or DSP ‘correction’ – and that makes sub-bass solutions necessarily big. You’ll also know that the bigger the woofer and the wider its bandwidth, the more critical its adjustment and positioning. Most subwoofer fans reckon to take several weeks really zeroing in serious subs. That is where the PureLow LO breaks all the rules. Okay, so a frontal aspect that’s all of four-foot square definitely qualifies as big, but then it’s only four inches deep and you can use it a matter of six inches from the wall. More importantly, this is by far the easiest subwoofer I’ve ever had to position and adjust. You should be able to achieve excellent results in as little as 15 minutes, a direct result of the unit’s astonishing clarity and transparency.

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