Single source
With the Concept Blade prototype and the production Blade,
the point-source idea of Uni-Q was cleverly extended to the complete system.
Four bass units were placed on the cabinet sides in positions such that their
combined acoustic centre exactly coincided with the acoustic centre of the
Uni-Q driver on the front. So KEF was able to describe the Blade as the world's
‘first Single Apparent Source loudspeaker'.
This approach isn't followed in the Reference 5, but the 6.5
inch bass units are placed as close as possible to the Uni-Q midrange/treble
unit to minimise lobeing and interference dips at the crossover point. With
bass units above and below the Uni-Q, this resembles a D'Appolito array, but
not with the usual arrangement of two bass/mid units crossing over to a single
tweeter. In this case, because the relevant (bass to mid) crossover frequency
is much lower, the wavelength at crossover is very much longer than the spacing
of the drivers, so any interference dips in the response will be well off any
possible listening axis.
With bass units
above and below the Uni-Q, the KEF Reference 5 resembles a D'Appolito array
Also, KEF points out, the apparent acoustic source does not
shift away from the position of the Uni-Q driver at any point in the frequency
range. Rather than a conventional cone, the bass diaphragm is a shallow
aluminium disc, which gives the driver a lower profile and ensures a minimal
effect on the frequency response of the midrange and tweeter. Connecting the
back of this diaphragm to the very large-diameter voice coil is a vented
coupler, an innovation first developed for the Blade. Air can move very freely
away from the back of the diaphragm, between the ‘spokes' of the coupler and right
out to the back of the magnet assembly through the large venting hole.
As you'd expect, the Reference 5 speakers are massively
constructed, and they come with heavy steel platforms which provide outrigger
mountings for the spiked feet. Internally, the cabinet is comprehensively
braced but makes use of a technology that originated from the development of
the small, EISA Award- winning LS50 - KEF's Uni-Q-based answer to the BBC
LS3/5A.
EISA Award-winning
KEF LS50’s technology is the original of the cabinet in KEF Reference 5
For the Reference 5, the drivers are braced by the internal
structure but connected to it via a lossy damping material. Similarly, the
front baffle is in aluminium laminated with resin, connected resiliently to the
high-density wood cabinet using high-loss pads.
Both the Reference 3 and 5 are bass-reflex loaded by two
rear ports, but KEF provides a choice between two different bass tunings. Two
sets of foam port liners are provided, one long and one short. While the long
ports give a smooth and gentle bass roll-off, the short port gives a more
extended bass response, albeit at the expense of some loss of accuracy in
transient response.
This big and tall
speaker has really been made as slim as possible, with its array of four 165mm
aluminium-coned bass drive units flanking a new 125mm version of KEF’s famous
Uni-Q combined midrange and treble unit
It's suggested that the long ports are likely to be
preferred with the speaker near walls, and the short one when it is further out
in the room.
Finally, while the array of rear-panel connectors might look
like something you'd find in an upmarket bathroom centre, it does make the
loudspeaker very easy to wire up. Four heavy-duty chromed terminals provide for
bi-wiring, while the two smaller ‘taps' in between are turned to make or break
the internal links that allow for single wiring.
