Nautilus™ was born out of asking a few simple questions. What if we don’t follow market driven speaker design conventions? How good a speaker could we make if we took everything we know and invested it in one design? What if we didn’t have to worry about the price and launch date?
Questions like these are perhaps asked only once in a speaker design generation and represent not only an opportunity for designers single-mindedly to express their craft, but also for a technology and design driven organisation like Bowers & Wilkins fully to express its corporate philosophy and ethos.
In a world where those who design the complex consumer products that inhabit our homes have had to become niche specialists, loudspeaker designers still have something of the Victorian polymath about them.
Ask an, ’embedded software user-interface engineer’ for example to design, say, an injection moulded plastic component and he or she would probably stand about as much chance as the rest of us. Ask one of Bowers & Wilkins’ speaker engineers to design an injection moulded plastic component, however, and they would probably make a pretty good stab at it (they’d also probably have a go at some embedded software user-interface design too). The reason for this, and the reason why speaker design attracts engineers with polymath tendencies, is that speaker design, like few other fields, is multi-disciplinary. A speaker designer needs to know acoustics, electronics, electro-acoustics, mechanical engineering and production engineering intimately for a start; and on top of that he or she needs a good knowledge of furniture design and an enthusiastic knowledge of recorded music. It helps quite a bit if a speaker designer plays an instrument too, and many do (strangely, there seems to be a preponderance of bass players). Speakers, you see, operate across multiple physical domains. They take musical information encoded in electrical signals and convert that information, via the electro-mechanical domain, into musical signals encoded in the acoustic domain. Multiple domains unavoidably implies multi-disciplinary design.
But to get back to our polymath speaker engineers for a moment, the multi-disciplinary nature of speaker design means they are ‘jacks of all trades’ and masters of, well, compromise actually. Compromise may seem a negative term, but in this context it describes the art of finding solutions to the numerous conflicting requirements that inevitably occur when designing multi-disciplinary products that have to hit a target price and a launch date, and that range across multiple domains. Very occasionally, however, engineers get the opportunity to put compromise aside for once and, on those rare occasions, extraordinary products like the Bowers & Wilkins Nautilus™ are created.
Nautilus™ is unlike any other that went before and, perhaps, unlike anything that might appear in the future. In some respects Nautilus™ defines a ‘pinch-point’ in speaker technology; a summation of everything learned in the past that lead to an expansion of new technologies in the years after. The story of Bowers & Wilkins’ engineering and technology could justifiably be documented in terms of Before Nautilus™ (BN), and After Nautilus™ (AN).
Of course the aspect of Nautilus™ that stands out as most unconventional is its physical form. It is completely unlike any other speaker. Its spiral curvature and lance like projections seem to speak more in the language of science fiction than consumer electronics. They are forms driven purely by function, however, and ironically, given the propensity of science fiction imagery to borrow from naturally occurring forms, Nautilus™ borrows from nature too. There’s another irony inherent in the extraordinary physical form of Nautilus™; in audio performance terms it is far more about what you don’t hear than what you do hear. Speaker drivers radiate as much sound energy backwards as they do forwards and the role of speaker enclosures is to stop the sound radiated backwards from interfering with, distorting and cancelling-out the sound radiated forwards. Sound energy is, however, not easily constrained or dissipated and in conventional speakers, despite all the traditional techniques available to “manage” the unwanted energy, some will always leak out through the enclosure walls or reflect back through the driver diaphragms. It was this fundamental issue of speaker engineering that the Nautilus™ designers faced right from the outset – how do you make the rear radiated energy from a speaker driver magically disappear?
The key to understanding how the rear radiation of the Nautilus™ drivers disappears is to imagine a driver mounted at the ends of an infinitely long tube. If the tube goes on for ever, the rear radiation has, to all intents and purposes, been dealt with. It can’t reflect back through the driver diaphragms because there’s no end to the tube from which it can bounce. Obviously, even in the context of a no compromise project like Nautilus™, infinitely long tubes are a little impractical. However, by using tubes that reduce in diameter at a carefully calculated rate, and that are lined with graded quantities of absorbent materials, it is possible to configure an arrangement in which the driver is ‘tricked’ into ‘seeing’ an infinitely long tube. The acoustic energy dissipates before it reaches the end of the tube.
The length of tube necessary is a function of the bandwidth over which the driver operates. At high frequencies, where the wavelength of sound waves is measured in a few centimetres, only a relatively short tube is necessary, and at mid frequencies the length of tube required grows towards a metre. At low frequencies, however, the tube length required grows to many metres and the only feasible way of integrating such a tube is to curl it up into a spiral. It’s the spiral that not only defines the Nautilus™ aesthetic, but also gave the speaker its name. In the natural world, a nautilus is a marine cephalopod and, remarkably, the logarithmic spiral reduction in cross-sectional area of a cephalopod’s shell mirrors exactly the necessary rate of spiral reduction in the Nautilus™ low-frequency tube. Nautilus™ tube technology has, of course, gone on to feature in numerous Bowers & Wilkins speaker products, from the most modest right up to the high-end 800 Series Diamond.
Having developed a technology that could, at a stroke, resolve a significant weakness of traditional moving coil speaker engineering, the Nautilus™ designers then went on to develop a series of drivers that could do it justice. The act of combining the twin factors of driver size and bandwidth with the practicalities of Nautilus™ tube lengths pushed the speaker system design solution towards a four-way configuration. Four new drivers were developed, each one not only designed to express the highest possible level of performance in terms of traditional time and frequency domain measurements, but also to offer the least impediment to rear radiation. This meant developing some highly innovative neodymium-iron-boron based magnet systems. Sitting directly behind the speaker diaphragms, where traditional bulky ceramic magnets create potential reflective barriers, these miniaturised designs enable each driver’s rear radiation to propagate freely down the Nautilus™ tubes.
In detail, and from bottom to top, the Nautilus™ drivers are a 300mm diameter one-piece aluminium diaphragm bass unit, a 100mm flat aluminium diaphragm low-mid unit, a 50mm aluminium dome upper midrange unit, and a 25mm aluminium dome high-frequency unit. Crossover frequencies are 220Hz, 880Hz, and 3.5kHz, and no driver operates outside its perfectly pistonic bandwidth. Rather than potentially inhibit the performance of the system by employing a conventional passive crossover network, Nautilus™ employs sophisticated active filters and separate power amplifiers for each driver. Active filters and separate power amplifiers, while impractical for most domestic audio applications through cost and the shear bulk of necessary electronics, are the true no-compromise solution to dividing the audio bandwidth between drivers. As a ‘no compromise’ project, Nautilus™ could really follow no other path.
The true value of the Nautilus™ project is not just its extraordinary sound and striking aesthetic appeal, for only a lucky few can ever hope to experience those more than very occasionally. The true value is in its legacy. Not only do Nautilus™ tubes now feature in numerous Bowers & Wilkins speakers, there is probably not a single Bowers & Wilkins product in which an element of Nautilus™ thinking has not been infused. In any creative manufacturing organisation like Bowers & Wilkins, no-compromise projects such as Nautilus™ act as a lever on the entire creative culture – teaching lessons, adding to the knowledge, demonstrating what can be achieved and undoubtedly raising the bar. Without Nautilus™, it wouldn’t be simply a case of technologies going un-developed, without Nautilus™ Bowers & Wilkins would today be a less creative organisation.