Why use diamond for tweeter domes? It may seem extravagant, but the move is simply an extension of Bowers & Wilkins’s pursuit of the perfect loudspeaker. One element of our quest for the best is the development of drive units that neither add nor subtract from the signal. In a tweeter, that means creating a dome that remains rigid, exhibiting perfectly piston-like behaviour, as far up the frequency scale as possible. Best for this are materials with a high stiffness to density ratio - which is where diamond comes in.
Over the years, Bowers & Wilkins has optimised the design of its aluminium tweeter dome to raise its break-up frequency and bring about a cleaner sound. But the material that gets closest to the behaviour of a hypothetical perfect tweeter – one with infinite stiffness and zero mass that can only exist in a computer - is diamond. Working with the world’s foremost industrial diamond producer, we’ve created the ultimate tweeter dome and the sweetest-sounding tweeter you’ve ever heard.
The core engineering challenge in accurately reproducing audio above and beyond the limits of human hearing is as easy to describe as it is difficult to meet. The challenge is to find a material that is infinitely stiff and can be accurately formed into a wafer-thin, lightweight tweeter dome. That’s all there is to it. It’s that easy.
Infinite stiffness is clearly impossible, but there is one material that, because it is so much stiffer than the materials traditionally used for tweeter domes, potentially offers a genuinely significant advance in performance - pure diamond. There are few materials stiffer than diamond, and there are few materials that present a stiffer challenge to fashion into a tweeter dome. A degree of difficulty however has never stopped us trying to do the right thing, and the engineering case for a diamond tweeter dome is overwhelming.
The basic measurement of how well a material works as a tweeter dome, assuming it is light enough to do the job in the first place, is the dome’s break-up frequency. This is the frequency at which, thanks to the accelerations and forces involved, the dome stops moving as a coherent whole and, potentially, begins to distort the audio signal. Before the advent of practical metal domes in the 1980s, a typical plastic or fabric dome would break-up at below 10kHz - well within the audible band, and easily audible too. Metal domes, sometimes of copper but more usually of aluminium or titanium, raised the bar to around 20kHz - at which point tweeters became significantly more accurate. Advances in manufacturing since, many developed at Bowers & Wilkins, have seen the highest break-up frequency raised to around 30kHz for the best metal dome tweeter - our 26mm Nautilus™ aluminium dome.
Diamond in limited size and shape has been made artificially since the 1950s and we realised some time ago that if a diamond dome could be made it would potentially raise the break-up frequency to around 70kHz. All we could do however was wait for diamond manufacturing techniques to catch-up with our aspirations. That happened recently in the guise of Chemical Vapour Deposition. CVD is a technologically sophisticated technique that enables pure diamond to be “grown” in complex shapes. The CVD principle is analogous to ice-crystals forming on a window. In CVD however the temperatures involved are equivalent to those on the surface of the Sun, and the role of water is taken by carbon. Intensive development with the World’s foremost industrial diamond producer finally bore fruit and we created a tweeter that literally approaches perfection. In two decades we have advanced the dome tweeter from something little more than a simple mechanism capable only of reproducing an approximation of the acoustic signal, to a sophisticated precision engineered device that is almost perfectly accurate.
But what does a diamond tweeter do for the sound? Like the diamond technology, it’s easy to ask and difficult to answer - far better you hear it for yourself. The smart response is that the near perfection of a Nautilus™ diamond dome tweeter means simply that music sounds like it ought to. Nothing added, nothing taken away. In practice it means clarity, detail and a lack of distortion or coloration well beyond anything heard before.
Find out what Bowers & Wilkins customers and audio enthusiasts are talking about on our blogs, and read in-depth articles in the Sound Lab.
An island in a sea of sound – Chris Watson’s Nature DiscoDecember 08,2014