Though you might not think it, subwoofers are actually shy, retiring types: affordable examples are often hidden behind sofas, while pricier designs are commonly disguised in coffee-table-esque wood and glass. You aren't supposed to notice your subwoofer at all, in fact: both sonically and visually, the best designs are intended to be as ‘invisible' as possible.
But B&W thinks differently. This compact silver sphere is as visually arresting as you'd imagine a subwoofer could ever be. And the styling isn't simply for show: it's a great example of form following function. The declared design aim was “the Holy Grail of subwoofer design: deep and clean bass from a near-invisible box”. So, while you might not believe it, the spherical cabinet was actually created for technical, not marketing reasons.
Here's the science bit: the smaller you make a subwoofer cabinet, the smaller the drive unit has to be. If you want to preserve bass output, you have to compensate with increased power and fancier drive unit technology – but this only increases the already considerable pressures exerted on your small cabinet. The upshot is resonance, caused by distortions of the cabinet's structure under the air-pressure load generated by the driver's movement, and that's bad for sound quality.
B&W's PV1 is light and stiff
The solutions? A port can help increase bass, and it's a relatively cheap solution to engineer, but sonically, it can often create more problems than it solves. The alternative approach, a sealed-box enclosure, tends to deliver quick, agile bass – but using a wooden cabinet design, it's also harder to keep free of resonance. The simplest solution is to construct a heavy design that's jam-packed with cross-braces – but though the end-product can be comparatively inert, it also tends to be big, which is counter-productive.
Hence B&W's Pressure Vessel concept of a spherical enclosure. The company draws analogies with diving vessels and soap bubbles: the PV1's curved shell, formed of thin aluminium, is a light, immensely stiff structure that both supports and reinforces itself, much as an egg does. The approach virtually eliminates cabinet resonance and so sounds ‘cleaner' than a conventional subwoofer, because the drive units devote their energy to driving air, not the cabinet.
Note, we said drive units, by the way: the PV1 uses two 20cm drivers in an opposed, in-phase array powered by a prodigious 500w Class-D amplifier using the sub's aluminium enclosure as its heat sink. This has the obvious benefit of increased drive unit area, but the opposed-driver arrangement also inherently ‘balances' the sub, especially in terms of the kinetic reaction forces generated by each driver's forward and backward movements. This only serves to reduce resonance still further, and also limits floor-borne vibration.
The PV1 sounds stunning
The results are sensational. The PV1's triumph is that it's virtually ‘dead' – even operating at full power, you'll struggle to feel any resonance being transmitted through the cabinet – yet it'll fit through a basketball hoop.
And it sounds stunning: there's no other way to put it. Often, style kit suffers when compared to conventional designs: it might look better, but it seldom sounds it. With the PV1, that theory is turned on its head: this bold design can easily challenge more expensive ‘normal' subs for extension and speed.
It's this latter facet of the PV1's appeal that is perhaps most remarkable of all. The B&W generates clean, uncoloured, amazingly deep bass: push the limits with some of Dr Dre's sillier low-end-licks, and you're left in no doubt about the sonic authority on show. Even the extreme outputs of Saving Private Ryan's soundtrack pose no problems: each explosive impact has glorious weight.
We're hugely impressed. In fact, we reckon the only thing B&W failed to notice was the PV1's remarkable resemblence to Barnes Wallis' Highball bouncing bomb. The Highball was developed to destroy battleships: we reckon the PV1 will have a similarly powerful impact on conventional subwoofer thinking.
Click here to watch our video review of the B&W PV1.