KEF's forthcoming Muon high-end loudspeakers look certain to attract the design fraternity, but what about the rest of us. What does £70,000 buy you in speaker design these days? Here are some extracts from KEF's Muon white paper giving you the lowdown, from the horse's mouth. You can also see that the white paper's author - senior acoustic engineer Dr Andrew Watson has to say in our Muon mini feature .

System design

The Muon is a four way closed box loudspeaker system utilising four 250mm bass drivers, a single 250mm lower midrange driver, and the latest high end Uni-Q array featuring a 165mm upper midrange driver and a 25mm high frequency driver. In addition, there are two further 250mm bass drivers on the rear of the enclosure to allow switch-able low frequency directivity control.

The system utilizes KEF's Acoustic Compliance Enhancement (ACE) technology: The bass drivers are mounted in closed box enclosures that are filled with activated carbon. This greatly increases the bass extension available from a normal sized enclosure.

The enclosure is a work of Engineering Art - smooth outer curves dictated by the need for low acoustic diffraction, structurally rigid and inert to allow the drivers to be fixed in space, and a blended form that optimizes the radiation pattern over the whole frequency range.

Acoustical Features

Drivers - KEF's new High End Uni-Q, point source, driver array. New 250mm bass driver (four on the front, two on the back) with a vented neodymium magnet system. Existing 250mm lower midrange driver from the current Reference 207

Bass loading - acoustically sealed low frequency enclosures with ACE loading.

Enclosure - optimally shaped enclosure for pure sound radiation, free from stray reflections and focused diffraction anomalies. Rigid construction creates an inert enclosure which does not drain energy away from the drive units or radiate uncontrolled acoustic energy into the room.

Acoustic directivity control - two rear mounted bass drive units allow switchable low frequency directivity control to ensure that the reverberant sound in the listening room is free from unwanted bass colourations.

Crossover network - the internally mounted electrical crossover network receives the output from the amplifier and sends the appropriately filtered signal to each drive unit, so that the different sections of the loudspeaker seamlessly blend together to sound like one perfect transducer. Made from the highest quality components - including polypropylene capacitors and air cored inductors - with all internal connections being made with KEFs own oxygen free copper cable.

Acoustical specifications

  • 4 x 250mm bass drive units with ultra low distortion vented neodimium magnet systems and distortion reducing Faraday loops
  • 2 x 250mm rear mounted bass drivers for low frequency directivity control (switchable)
  • 1 x 250mm lower midrange drive unit - with ultra low distortion neodimium magnet system and a chromed phase plug, shaped to optimize its high frequency acoustic response (where it crosses over to the Uni-Q array) and also acts as a second Faraday loop for distortion reduction.
  • 1 x 165mm Uni-Q driver array incorporating a 165mm midrange unit and a 25mm high frequency unit

Key technical points about the drivers

New high end 'Austin' Uni-Q driver array. The key developments in this new Uni-Q design are wider dispersion, and an advanced tweeter design.

The mid-range section

The design of the mid-range diaphragm is critical as it not only has to function as a high quality mid-range radiator but also acts as a waveguide for the tweeter, and controls the way the tweeters' radiation emanates into the listing room. Its shape is therefore critical.

The shape is very much determined by the dispersion we want from the tweeter - we then optimize its performance as a mid-range radiator by adjusting the cone thickness and material properties.

To obtain wider dispersion the mid-range cone must be shallower. This will normally make the cone less stiff and compromise its acoustic performance. But with the aid of KEFs Finite and Boundary Element Analysis techniques to model its performance, this potential problem is neatly circumvented to produce the finest mid-range design yet.

The wider dispersion allows the sound of both the midrange and tweeter units to radiate much more freely into the listening room, so the sound is more consistent over a wider listening area. This improves the naturalness of the reproduction and makes recordings sound more 'life-like'.

The tweeter section

The tweeter is significantly developed from the previous model. It now incorporates a vented magnet assembly - allowing a much greater volume of air behind the diaphragm than before. This reduces the acoustic pressure behind the dome giving a smoother sound with enhanced dynamics.

Venting the magnet is not easy in Uni-Q systems because of the necessarily compact nature of the Uni-Q tweeter. To create extra air volume we have to drill though the main neodymium magnet - and this reduces the sensitivity of the unit.

To overcome this KEF has two extra neodymium rings - critically placed to maximize the magnetic flux around the tweeters' voice coil. It's sophisticated but the acoustic benefits prove its value.

The tweeter diaphragm have also received significant advances thanks primarily to our ongoing research program in to Uni-Q performance that utilizes the latest Finite and Boundary Element Analysis techniques.

The dome shape has been revised to provide better acoustic performance at very high frequencies, and to maintain its rigidity it is constructed in two parts - the dome itself and a stiffening voice coil former which contacts the dome at two points and braces it - allowing pistonic motion to well above 30kHz.

This titanium compound dome gives a smooth, natural sound in the main audio band, a smooth response through to the ultrasonic range above 20kHz, and has useful energy right up to 60kHz - so the loudspeaker has the feeling of being completely 'open' and 'unrestrained' at the very high frequencies.

Technical specification

  • Sensitivity : 90dB/2.83V/1m
  • Input Impedance : 4 Ohms
  • Frequency Response : 25Hz to 60kHz ( /-3dB), in-room
  • Bass Extension : 20Hz (-6dB), in-room
  • Maximum Output : 118dB
  • Amplifier Requirements: 100 to 400W (typical)
  • Crossover Frequencies: 120Hz, 300Hz, 2.3kHz
  • Dimensions: 600mm wide x 2000mm high (with feet fitted) x 380mm deep
  • Weight: 120kg