Bowers & Wilkins’ team of acoustic engineers are constantly pushing the limits of their understanding of audio technology. The result of this dedicated pursuit of perfection is an almost constant flow of technological advances that continue to keep the company’s products (at least) one step ahead of the competition. Here we look at one of our most famous innovations – the use of Kevlar as a midrange cone material.
Kevlar ® is the material-technology most people associate with Bowers & Wilkins. The reason is two-fold: it has been used as the mid-range material of choice in Bowers & Wilkins speakers since 1976; plus, it is an incredibly distinctive yellow colour, and has therefore been a visual as well as acoustic signature of many great-sounding products.
Kevlar is a synthetic aramid fibre, manufactured by DuPont, and probably best known for its use in bulletproof vests. Indeed, those same mechanical properties of strength and the ability to dissipate the energy of a bullet have benefits for speaker cones.
Bowers & Wilkins first started using Kevlar as a cone material in 1976, with the introduction of the DM6 speaker. At that time, the science of speaker development was rather less well developed than it is today, and it was a case of trying out promising materials, measuring the response of the driver and listening to the result. So although it was understood that Kevlar could give better results than other materials around at the time, especially in the critical midrange, it wasn’t understood in any real detail how the cones were actually behaving – in effect, why they sounded better.
Bowers & Wilkins’ Dr Peter Fryer, a pioneer in the field of laser interferometry applied to speakers, used this technique to look at how driver diaphragms move in response to different signals. Looking at the behaviour of a single frequency with a sine wave readily shows standing waves or resonances in the diaphragm at that frequency. It also gives an indication of the way the sound disperses as it leaves the cone. It was by using this and other techniques that the secrets of Kevlar were revealed over time, and new and improved Kevlar cones were developed over the next 40 years – each iteration sounding better than the last.
Today, we still use Kevlar in the drive units of the CM Series and 600 Series, but another major research project has led to the new Continuum cone in the latest 800 Series Diamond range.