2
Cabinet:
One of the design goals of this system was to make the enclosure as small as possible. Since the
target group is the DIY enthusiasts the design also required reasonable simplicity.
The subwoofer needs a 12L closed box as a minimum to have a nice response. However, the used
enclosure is 15.6L. This is a slight reduction in volume compared to the MK II, a compromise to
retain the same outer dimensions while providing a larger housing for the FA503 (or FA253). This
compromise is fine as the reduction in box volume is rather small and we are using a more powerful
amplifier which compensates for the increased air stiffness of a lower volume enclosure.
The coaxial uses a closed box of 10.4L, which was the smallest possible enclosure on top of the
subwoofer and still have an easy build. That gives the midrange excellent working conditions and a
nice response.
Crossover:
The crossover for this system is all handled by the Hypex plate amplifier- the design is fairly similar to
the MK II version however the midrange & tweeter having a channel of equalisation each has
allowed for a slightly finer tuned and more consistent frequency response and the increased power
of the amplifier has allowed for extended bass response of the L26RO4Y.
Sub/Midrange:
The sub and midrange are crossed at 215Hz, the sub rolls off with a 3
rd
order Butterworth slope and
the midrange rolls on with a 4
th
order Linkwitz-Riley resulting with a -6dB point for each driver at
215Hz which can be observed in the measurements section. The sub has a second order 0.7Q high-
pass filter set to 17Hz, this is a protect for the driver, so it does not reach excursion limits for sub-
sonic frequencies in some recordings. There is a fair amount of EQ on the sub, since the cabinet is
very small for the size of driver. The most prominent EQ points are a low shelf at 53Hz and a low
peak at 27Hz, these serve to maximise the frequency response in the low end, extending the low end
comfortably beyond what would usually be expected for a cabinet of this size. The low Qts of the
L26RO4Y and high-power amplifier are what allow for this. The rest of the EQ on the L26RO4Y is
mostly to tidy up resonances.
The EQ on the midrange uses BoostCut points (points which raise or lower gain within a certain
bandwidth and slope according to their Q value) to keep the frequency response as even as possible
within the crossover bandwidth.
Midrange/Tweeter:
The crossover configuration between the midrange and tweeter follows the same pattern as the sub
to midrange so the midrange rolls of with a 3
rd
order Butterworth slope and the tweeter rolls on with
a 4
th
order Linkwitz-Riley. The filters are set to 1880Hz however this translates closer to a -6dB point
of around 1600Hz in the measurements, this is because of the EQ applied to both drivers. As can be
seen in the measurements, the phase coherence through the crossover region (represented by the
null when the midrange is inverted) is strong between the drivers, if a little less smooth than the
subwoofer/midrange cross.
Like the subwoofer the EQ on the tweeter uses shelving points to balance the frequency response
and resonances are controlled with BoostCut, effort has been made to minimise the Q and gain on
boosts to avoid amplifying distortion.
