The midrange is where the real musical action is invariably found, and a smooth midband is an invaluable loudspeaker quality. Enter Kevlar. It's been B&W's cone material of choice since 1974, and with good reason. The basic woven fabric is first impregnated with a stiffening resin that cures during the cone forming process. The cone is then further treated with a polymer coat, which seals the fibres and adds damping. The result is a semi-flexible cone, which exhibits a peculiar style of break-up behaviour, not found in more conventional materials, that maintains a more constant dispersion pattern at all frequencies in its range and transmits far fewer delayed, time-smearing sounds to the listener. Not only does it deliver a cleaner sound, it can do so to a wider group of listeners.
The parts of a speaker doing the hard, mechanical work, the drivers, act on the signals distributed to them by the electrical processing part: the crossover. The thing to look for is its simplicity. Some speakers demand complex crossovers to compensate for the shortcomings in their drive units. The better the mechanical design, the simpler the electronic design can be.
We are still working to understand fully why and how certain components influence the sound of a speaker. Different manufacturers' versions of nominally the same component significantly alter the character of the sound, the only solution is to put our trust in our ears and to choose what sounds best. We carry out exhaustive listening tests rigorously assessing the performance of each component until we find the optimum component for each position in the circuit. Fine-tuning by ear is only possible if the crossover is simple and the section of the crossover that perhaps benefits most from our policy of listen-and-learn is the part handling the signal for the tweeter. In most B&W speakers, it is carried by a single, ear-chosen component that preserves the very finest detail.
Preventing mechanical vibration from the bass cabinet reaching the tweeter leads to a much cleaner, sweeter high frequency performance. For the 800 Series, we've adopted a new synthetic gel to cushion the tweeter better than ever before. Not only that, we've also isolated the tweeter assembly from the tube and mounting behind, which reduces external interference to virtually nil.
Why use diamond for tweeter domes? It may seem extravagant, but the move is simply an extension of B&W'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, B&W 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.
Bowers & Wilkins' FST™ mid-range drive unit maximises the effects of Kevlar® by improving cone response times and integrity of sound transmission. Surrounds both keep the cone in line and help to absorb bending waves. As the mid-range diaphragm only moves a little, B&W has improved outer edge cone termination by means of "surroundless" suspension. A foamed material ring, with resistive mechanical impedance identical to that at the edge of the cone, is placed under the cone's edge. Bending waves travelling up the cone are almost totally absorbed by the foam ring, which also compresses sufficiently to accommodate cone movement at mid frequencies.
All our careful refinements of the Kevlar® cone would count for nothing if we didn't do all we can to minimise other sources of disturbance. Moving air behind the cone, for example. The chassis of the FST™ driver is designed to minimise any impedance to the flow of air from the rear of the driver. To reduce the clutter immediately behind the cone still further, we've adopted neodymium magnets, which deliver the same magnetic force from a smaller device.
Resonances in the body of an instrument such as a violin are an essential part of defining its character. There, the skill of the designer is engineering the resonances to support each note in the instrument's range evenly. The opposite is true of a loudspeaker. Resonances in its body or cabinet only serve to make the speaker's character superimpose itself on that of the music it is there to portray. Bracing is an essential tool in keeping the 'loud speaking' to the drivers, not the cabinet, so the original character of the instruments can come through cleanly.
Unique to B&W, Matrix's™ interlocking panels take cabinet bracing to the ultimate level. With powerful bass drivers trying to shake the cabinet and high air pressures inside trying to make the panels flex and blur the sound, this three-dimensional honeycomb structure reinforces the cabinet at small intervals and in every direction. Offering a dramatic cut in the level of cabinet coloration, Matrix™ allows you to focus on where the performers are, rather than being aware of where the speakers are.
At a live gig, a truly powerful, clean PA system will deliver bass with a drive and 'punch' that gets the blood pumping and sets the senses on fire. It's hard to get that same excitement from a home hi-fi, but ensuring the mechanical integrity of the bass driver is essential to the pursuit. B&W's bass drivers use a 'mushroom' type diaphragm construction, maximising rigidity by bonding the cone, dust cap and extended voice coil bobbin into a stiffening girder-like unit.
Nautilus tapering tube
The sound of silence. Not all sound generated by speaker drive units is good sound. The kind that emerges from the back of a working driver, into a conventional box cabinet, can bounce around and make a mess of the good sound coming out of the front. B&W's trailblazing Nautilus™ speaker found a way around boxes. Tapering tubes filled with absorbent wadding soaked up the wayward sound energy and reduced resonances to an insignificant minimum.
Nautilus™ Tapering Tubes are fitted to nearly all B&W speakers, even when they're not visible to the eye. Sound is channelled through a hollow pole magnet, away from the diaphragm, and disappears into the tail. So all the sound you hear is good sound.
B&W bass drivers are backed up by an imposing magnet/voice coil system to preserve the speed and 'slam' of the most demanding bass lines. The construction of the cone is critical. What we're aiming for is 'perfect piston' behaviour: the ability to move air with complete freedom while resisting deformation.
The cone must be as light as possible for maximum agility, but absolutely rigid in order to retain its shape as it pumps in and out. Rohacell® is a sophisticated composite construction having a hard foam core, sandwiched between carbon fibre skins. It's the kind of material normally used for aircraft, rockets and performance cars bodies. So high air pressures are definitely not a problem. For speed, stiffness and unshakable bass, it's the bottom line.
Tweeter on top
B&W's tweeter on top technology has two benefits.
It avoids the situation with normal cabinet construction, where sound waves from the tweeter not only radiate towards the listener but also travel along the baffle surface towards the cabinet edges.
When sound waves meet sharp cabinet edges they re-radiate (a process known as diffraction) and, due to the time delay, interfere with and time-smear the sound coming directly from the drive unit.
Having the tweeter separate from the main cabinet also allows it to be set back and time-aligned with the acoustic centre of the bass/midrange cone, which is located behind the plane of the front baffle.
The effects of this improvement in time-coherence are greater clarity and the formation of a more convincing three-dimensional image.
Wide dispersion driver
Traditionally, the driver has had the best seat for sound in cars. Passengers have had to make do with second and even third best. Those days are over. B&W's solution is a distribution of sound that gives everyone a fair hearing.
Passengers in back of the Jaguar C-XF will notice a trio of small speakers above their heads. This array, controlled by digital signal processing, can be set to 'steer' the sound toward the rear occupants, producing extraordinary image clarity and height.
This unique arrangement delivers optimum staging and sound directionality without distracting those in front. Don't let the small size fool you; these speakers are full-range.
To complete the surround sound system, the wide dispersion drivers integrated into the rear deck speaker panel are designed to produce uniform off-axis response, overcoming the problems that are usually part-and-parcel of direct-radiating speakers placed behind listeners' heads.
The delicate brush strokes across the surface of a cymbal can only be recaptured by a tweeter that's truly linear in operation. And that means one that uses a dome that stays
rigid and operates like a piston throughout its operating range. Most B&W speakers feature alloy dome tweeters. Our newest tweeters - as found in the 800 Series- feature a 'crowned' voice-coil bobbin and a silver-plated pole piece, extending the bandwidth well over an octave above the limits of human hearing, and rendering a separate 'supertweeter' quite unnecessary.
Car designers go to a lot of trouble to make sure their vehicles slice efficiently through the air. If they don't, not only does turbulence reduce performance, it also increases wind noise. So it is with the reflex port in a loudspeaker cabinet. If turbulence occurs as the air moves in and out of the port, you'll hear extraneous noise and, as you turn the volume up, the bass won't be as tight and well timed as it should be.
B&W's Flowport™ minimises turbulence in the same way as a golf ball. Dimples on the surface generate tiny eddy currents over which air can flow smoothly and, above all, silently. It's a perfect hole. But don't use it for putting practice.
Unlike tweeters, where the movement is small and the coil stays in the gap, bass driver cones move a long way. Making the coil overhang the gap ensures that, even when the coil is well away from its rest position, the same length of winding overlaps the top plate, so the force remains more or less constant. Nice in theory, but in practice the magnetic energy is not constrained to the gap itself, but extends each side. This fringe field plays an important part in how distortion is created and making it symmetrical through the use of a dual magnet system keeps distortion low.
Quad magnet tweeter motor system
If a tweeter is to fully respond to the dynamics of music, it must run as cool as possible, especially when driven hard. The problem is that a tweeter’s voice coil has to be small and light for it to respond to very high frequencies and so it heats up very quickly. The hotter the coil gets, the higher its electrical resistance becomes and the current through it, which determines for force exerted on the dome, ceases to be proportional to the voltage signal from the amplifier. Compression is the result, with the music losing its true life.
The use of neodymium-iron-boron magnets for their small size can make the problem worse because they make a less effective heat sink. That’s why the Nautilus tubes of 800 Series tweeters are metal. They help carry heat away from the voice coil. Forcing more magnetic energy into the voice coil gap would reduce the current required to reach any given output level, allowing the coil to run cooler. But how, given that the gap is small and the steel parts are already close to saturation?