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Operating Manual - PROTEA SYSTEM II 4.24C Crossover / System Processor
Parametric EQ (PEQ) uses peak fil-
ters with the ability to control boost or cut,
frequency center, and bandwidth. Think of
one band of parametric EQ as a single graphic
equalizer fader except that the frequency is
variable, not fixed, and that the bandwidth,
or how "wide" the filter affects the frequency
spectrum at the center frequency, is com-
pletely variable. The smaller the bandwidth,
the less the audio signal on either side of the
frequency center is boost or cut, whereas a
larger "wider" bandwidth produces an audible
change to the overall tone of a signal. Para-
metric filters are best used to hunt down and
eliminate problem feedback frequencies, add
or remove a characteristic "hot spot" from mi-
crophones, or clean up room resonance situ-
ations. It is well worth the time getting pro-
ficient with parametric EQ filters, as they
offer the best solution to many EQ problems.
Protea 4.24C parametric filters have a boost/cut range of +15dB to -30dB. There is more cut than boost
because one of the more common uses for parametric filters is to dramatically cut, or "notch out", very narrow fre-
quencies (low bandwidth) in order to eliminate system feedback problems.
Every instance of a parametric EQ filter has a center frequency selected. The factory default is 1kHz, but each
filter's center frequency is adjustable from 19.7Hz to 21.9kHz in 1/24 octave steps. Carefully sweeping a narrow
bandwidth filter through a problem feedback area, with just a slight boost, is a quick way to find the exact frequency
causing trouble. Once the offensive frequency has been found, cut the filters level, and then the bandwidth is adjusted
as narrow as possible while still eliminating the feedback problem. Bandwidth is adjustable from about 1/64 octave to
four octaves, and the lower the bandwidth, the less audible the filter action will be. Finding the problem frequency is
relatively easy, but finding the best combination of cut and bandwidth takes a little practice. Again, it is well worth the
time becoming comfortable with the notching procedure, so that problems can be quickly addressed with a sufficient
but minimal amount of correction.
The EQ functions on all four inputs and eight outputs are switched in or out on an individual channel basis. In
other words, each input or output has one "switch" for all of its EQ filters. If certain filters are not going to be used
within a channel, simply leave the gain for that filter at 0.0dB, and the filter will have no effect.
For an excellent interactive display of the way parametric and shelving filters work, experiment with the
4.24C EQ section of Protea System Software. The software works whether a unit is connected or not, so it is an
invaluable teaching tool as well as an audio setup tool for Protea products. The program is shipped with 4.24C units,
but is also available on the Ashly web site.
4.6c Delay
In large installations or out-
door venues there are often many
speaker clusters in various locations
to get the best coverage possible.
Since sound travels relatively slow
through air (1130 ft/s at 20ºC), mul-
tiple loudspeaker locations can create a situation where the original audio signal, simultaneously leaving all loud-
speakers, arrives at a single point in the venue at several different times. Needless to say this causes problems, and
what may be crystal clear sound directly in front of any one loudspeaker can be a jumbled mess in the farther reaches
200Hz 2KHz 20KHz20Hz
0dB
-10dB
-20dB
+10dB
+20dB
-30dB
4.24C Parametric Filters
Wide
(
Hi
g
h
)
Bandwidth
Narrow
(
Low
)
Bandwidth
Ch. A-D Delay
Ch. 1-8 Delay
Distance
In Meters
Dela
y
LCD Displa
y
Time (ms)
Distance
In Feet
Delay
DELAY 1
0.00m
0.00ms
0.00ft