- Written by Jim Clements
- Published on 04 August 2011
The KEF Q300's feature KEF's latest version of their popular Uni-Q drivers. KEF originally introduced the Uni-Q speakers back in 1988. They have continuously improved upon the original design through a diligent R&D effort. The culmination of this effort has led to the "All New Q Series" of speakers. The Q300 is the larger of two bookshelf speakers in the line.
"Uni-Q" is what KEF's calls their coincident midrange/tweeter array. In this arrangement, the tweeter is mounted at the acoustic center of the midrange cone. KEF's claim about the Uni-Q drivers is that they mimic a point source and so the sound waves retain greater coherency as they propagate through your room. Coincident drivers also have improved off-axis response characteristics because lobing effects between the two drivers are negligible. Take a look at the exploded illustration immediately below and the close-up of the finished product just below that image and you'll get the idea of how it all goes together.
The aluminum drivers in the new Uni-Q speakers embody numerous technical advances that have trickled down from KEF's Concept Blade project. Let's start with the tweeter. Using FFT analysis, KEF has determined that there are two different optimum geometric shapes for each of two important properties of an ideal metal dome tweeter. An elliptical profile is best to optimize the driver's mechanical properties while a spherical shape is best for the dome's acoustic properties. So they found a way to meld these ideas when they layered a spherical cap onto an elliptical substrate to form the tweeter dome.
The KEF Q300 tweeters have tangerine wave guides. The guides protect the tweeter and are said to improve "the coupling between the tweeter dome and the air". The waveguide on the Q300's is more aggressively designed than in past KEF Uni-Q models. They look really neat too!
Another design innovation of the tweeter is a larger sealed duct behind the tweeter. This chamber is filled with a damping material to reduce resonances in the column. The air behind the driver acts as a spring mechanism that dampens the driver and reduces distortion.
The mid/bass driver has a few innovative features of its own. For example, KEF implemented "Cone Breakup Control" in the Q300's. In this system, a "decoupling moulding" is situated between the driver's aluminum cone and the rest of the motor structure. This reduces mid range resonances. Speaking of the motor, the KEF Q300's have a larger, longer-throw motor than in past designs. Consequently, the overhung voice coil is rather large. So KEF wound this coil with aluminum to reduce the weight. It seems like there is a lot of aluminum in the Q300's . . . I finally realize what happens to all those empty soda and beer cans when we recycle!
The last word on the driver design is the choice of surround for the mid driver. KEF calls this ribbed design the "Z-Flex" surround. It ostensibly has two inherent advantages over a common design: it flexes more readily in the bass than in the mid range while the ribs create a waveguide to reduce diffraction in the tweeter's response characteristics.
The All New Q Series speakers come in a variety of finishes that are made from recycled wood fiber. The finish choices are Black Oak, English Cherry and European Walnut. My review samples were European Walnut. I must say that the KEF Q300's are built to a remarkably high standard. And with the brushed aluminum drivers, the tangerine waveguides and KEF logos on the front baffle, these are some very nice looking speakers particularly with the grilles removed.