Ashly Electronic Amplifier none - Manual (Page 28)

two fixed-response filters to form a crossover. Instead, a single state-
variable filter provides both low-pass and high-pass outputs, and a single
control adjusts the crossover frequency. Because the state-variable filter
allows complete control over all filter parameters, it is possible to tune the
response shape of the filter for the best possible summed response. As you'll
recall,
response shape is determined by filter damping, and so all Ashly
crossovers feature a damping control, labeled dB, at each crossover point.
Figure 29
This state-variable filter,
representative of the filters
used in Ashly SC-series
crossovers, is an analog
computer realization of a
second-order (two pole or two
integrator) filter system.
HP OUT IP OUT
From the standpoint .of the ..sound system operator,. the Ashly filter approach
combines the one-knob frequency control convenience of the first crossover
example (fig. 27) with the summed response flexibility of the second crossover
example (fig. 28). In contrast to the bumpy response of fig. 28, Ashly cross­
overs exhibit the smooth and predictable summed response curves shown below.
(a) Figure 30. (b)
This graph plots the high-pass and
low-pass
outputs of the Ashly
12dB/octave filter for 4 different
settings of the dB control. The line
marked "3" shows Butterworth
response, and is obtained by setting
the control to 3. The other curves
show the response shapes obtained by
over and underdamping the filter.
This graph shows
curves of (a)
electronically
Butterworth curves
how the response
combine when
summed. The
sum with a gentle
3dB peak, but other responses are
easily obtained; for a flat summed
response, set the dB control to 6.
(12dB per octave models only)
27