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14 15
Being within the human audio range, the break-
up has to be tamed, rather than putting it out of
hearing range. This is done by introducing a exible,
decoupling material between the cone neck and the
voice coil former.
The high-Q resonances are tamed to the extent that
they may be properly attenuated by the crossover
and not break through the tweeter output. Figure
37 illustrates the improvement in the unit’s response
as a result of using the lossy interface. Mechanical
correction is far better than equalising the peaks with
the crossover. The latter does not subdue peaks in the
THD at sub-multiples of the fundamental.
Z-Flex Surround
The midrange cone and outer surround form a
waveguide for the tweeter and the normal roll
surround is not ideal in this respect, especially close to
the driver’s axis, where symmetry has a large effect.
The Z-Flex surround has been specially designed to
allow the necessary movement of the bass/midrange
cone, but provide a low prole to allow the cone and
surround to act together more accurately as a tweeter
waveguide.
It will be seen that the outer vertical wall of the
surround is another possible source of discontinuity,
so the outer trim ring is part of the whole design,
giving a smooth transition all the way from the tweeter
diaphragm to the front bafe.
The optimum dome shape for waveguide loading
is a spherical cross-section, but the optimal shape
for stiffness is an elliptical cross-section. Both were
combined into the patented KEF Stiffened Dome. A
one-piece elliptical dome and voice coil former is deep
drawn and the centre removed. This is capped by a
spherical dome and a very stiff triangular section is
formed where the two parts join.
Tangerine Waveguide
The interface between the radiating dome of the
tweeter and the waveguide formed by the midrange
dome is extremely critical. Ideally, the diaphragm
should be a pulsating dome, which would involve
the radius of curvature changing. This is not possible
and the motion is in the same direction all over the
surface of the dome. To compensate for this non-
ideal situation and taking a leaf out of the design of
compression drivers, the Tangerine Waveguide was
developed to restore correct coupling between the
dome and the whole waveguide.
The improved coupling at high frequencies above
5kHz brings with it a useful increase in sensitivity and
a reduction in the height of the rst resonance peak,
illustrated by gure 34.
Figure 35 shows the tangerine waveguide in place in
the Uni-Q array. Note that this is the basic operation
of the tangerine waveguide that is carried over from
previous models. It is enhanced by the extra stiffening
described in the new features section (gure 12).
Bass/Midrange driver
Diaphragm
The cone is formed from a magnesium/aluminium
alloy. Like the tweeter dome, it serves to provide the
necessary stiffness to give pure pistonic motion over
the driver’s working range. The stiffness is increased by
the radial embossing in the cone prole. Nevertheless
the cone is still prone to high-Q break-up, but this time
in the frequency range covered by the tweeter.
Figure 33
3D CAD sectional views of the tweeter dome and extended
former that meet to form a triangular stiffening member
at the dome edge
Figure 34
FEA Simulation of tweeter output
without tangerine waveguide (red)
with tangerine waveguide (blue)
Figure 35
Tangerine waveguide in position on top of tweeter dome
Figure 36
Cone Neck Control interface between voice coil former and driver cone.
Figure 37
Effect of lossy interface on response of LF/MF driver
Figure 38
Z-Flex surround - line drawing
Figure 39
Cross section of complete Uni-Q driver and trim ring
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