Ashly Electronic Amplifier none - Manual (Page 6)

This infinitely-variable control allows you to select an appropriate crossover
point for your speakers. Turning the knob clockwise moves the crossover point
to a higher frequency, while turning it counterclockwise moves it to a lower
frequency.
Crossover frequencies are marked on standard ISO 1/3 octave center frequencies
with
every octave calibrated. Calibration accuracy is very good, typically
within 1/3 octave or better. If greater accuracy than this is necessary,
measurement of the actual crossover frequency with an accurate oscillator
and/or frequency counter is suggested.
The choice of crossover frequencies depends on the type of speakers being
used, personal taste, room acoustics, and many other factors. Experiment to
see what works best for you.
CAUTION: High frequency compression drivers may be destroyed by the use of
too low a crossover frequency. Follow the driver manufacturer's
recommendations carefully.
ROLLOFF (dB) CONTROL
This control, found adjacent to the crossover frequency control, adjusts the
damping of the filter at the crossover point, affecting the response shape of
the filters. The dial calibrations (1.5, 3, 6, 10, 12) refer to the amount of
attenuation
effected by the filters at the crossover frequency, i.e., a
setting of 3 means that the filter's response is "rolled off 3dB at the
crossover point", which describes Butterworth filter response.
In actual use, the rolloff control acts much like an equalizer tuned exactly
to the crossover frequency. For example, with our 12dB per octave models, a
setting of 6 on the control will give you flat response through the crossover
region. Turning the control counterclockwise will cause a dip in the response
at
the crossover frequency, while turning it clockwise will cause a gentle
peak in the response. On our I8dB per octave models, a setting of 3 will
yield flat summed response.
The purpose of the control is to help offset the inaccuracies inherent in
typical
loudspeaker response, thereby helping you to achieve a flat system
response. If you use a spectrum analyzer to set up your system, adjust the
rolloff
control to obtain the flattest response through the crossover region
before any equalization is applied to the system. If adjusting by ear, we
recommend an initial setting of 6 for our 12dB per octave models, and a
setting of 3 for our 18dB per octave models. Then adjust from this point if
the system appears to have an excess or deficiency of response at the
crossover point.
CROSSOVER FREQUENCY CONTROL
NOTE: The rolloff control is not a "slope" control. A 12dB/octave crossover
will always have a slope of 12dB/octave regardless of the setting of
this
control. Likewise, an 18dB/octave crossover will always have a
slope of 18dB/octave. The dB control only affects filter response
shape in the immediate vicinity of the crossover frequency; the
ultimate slope of the crossover is a fixed parameter.