XTA DC1048 - Manual (Page 55)

Operator’s Manual DC1048 Integrated Audio Management Page 55
Elliptical filters
The elliptical filter has adjustable
frequency only. This sets the 3dB
point of the filter which features a
steep roll-off of approximately
36dB/Octave down to one Octave
above (or below in the case of a
HPF) the turnover frequency.
However, the gain does increase
again above this frequency to
settle at 12dB down from 0dBr.
This filter can be used in
conjunction with the standard
crossover filters to produce
sharper roll-offs than would be
otherwise achievable. The use of this filter is explained in the following example.
The graph shows three different
low pass filter shapes.
Number 1 is a standard
24dB/Octave Linkwitz-Riley
curve.
Number 2 is a 48dB/Octave
Linkwitz-Riley.
As can be seen, number 2 is
significantly steeper in roll-off
than number 1, as would be
expected.
However, number 3 is a 12dB/Octave Butterworth filter with an Elliptical Low Pass
filter following it. This produces a combined roll-off very close to that of the
48dB/Octave (with the side effect of the response rising again after the initial
drop from the pass band).To produce a crossover filter of this shape it is simply a
case of setting the low (or high) pass filter for that output to the desired
crossover frequency, and selecting a 12dB Butterworth response:
Then select a parametric section on the same output, and modify its behaviour to
select an HPF Elliptical filter. Set the turnover frequency of this filter to be the
same as that of the crossover filter. Make sure you choose a high pass elliptical
to work with a high pass crossover, and low pass elliptical to work with a low pass
crossover.
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2
3