Uni-Q Co-incident Source Array

The Uni-Q is KEF’s unique audiophile technology [5]: it is not a driver, but two drivers - an array. The Uni-Q array has undergone a dramatic design review for the Reference 207.

The MF and HF units have been symbiotically designed, leading to much improved ‘single-source’ performance. By relieving the cone driver of any low-frequency obligations, the reduced excursion requirement allows the use of a flat surround (patent pending), thus diffraction effects are completely removed. This continuous cone and surround acts as an optimised waveguide for radiation from the tweeter dome.

The Uni-Q tweeter has been through a radical metamorphosis. At the outset it was decided to employ a metal dome for improved mechanical performance. It is well documented in the literature that well-designed metal diaphragms retain mechanical integrity to beyond 20kHz, whereas fabric or plastic devices typically enter ‘breakup’ (resonance) around 10kHz. The starting point for the new tweeter was an existing high-performance titanium dome device. This dome, in common with other 25mm metal dome devices, goes into mechanical 'break-up' resonance at or around 25kHz, causing some sub-20kHz artefacts. The design team believed that it was possible to raise this resonance to beyond 30kHz, resulting in unblemished performance up to 20kHz. Extensive virtual prototyping was carried out using Finite Element Analysis [7]. This work resulted in a 32kHz main dome resonance and a patent application for the pure ellipse dome profile. The requirement for a deep-drawn titanium dome raised new challenges for the KEF production team.

The next step was to optimise the cone profile. The MF diaphragm acts as an acoustic waveguide for the radiation from the tweeter. Again Finite Element Analysis was employed to gain an understanding of the propagation of wavefronts along the waveguide [7].

The midrange performance of the cone is then controlled by careful choice of the material properties and a varying thickness along its radius. This variation, in combination with the geometry of the diaphragm, provides an optimized ‘stiffness profile’ leading to mechanical integrity in the operating bandwidth.

The Injection-Moulded copolymer polypropylene cone and surround are produced as one entity by a (patented) co-moulding process, improving manufacturing consistency. The surround is made of a thermoplastic rubber and has high damping to terminate travelling waves propagated through the cone from the voice coil.

The two magnetic circuits required for the MF and HF units are provided by a Compound neodymium magnet assembly (patent pending) which ensures optimum flux profiles for both MF and HF coils. The small magnet size and open chassis design ensure minimal acoustic reflections behind the midrange cone. The significant reduction in mass of the Uni-Q afforded by the use of neodymium motors allows for effective decoupling from the cabinet, preventing excitation of panels in a frequency band where cabinet resonance could otherwise occur.

The audible results of this extensive re-design are greatly improved imaging and integration and lower colouration.

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