7
Operating Manual - PROTEA SYSTEM II 3.24CL 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 vari-
able, not fixed, and that the bandwidth, or how
"wide" the filter affects the frequency spec-
trum at the center frequency, is completely
variable. The smaller the bandwidth, the less
the audio signal on either side of the fre-
quency 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 situations. It is well worth the time getting proficient with parametric EQ filters, as
they offer the best solution to many EQ problems.
Protea 3.24CL 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 frequencies (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 three inputs and six 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.
4.6c Delay
The 3.24CL-d is the same as
the 3.34CL in every respect except for
the delay structure.
On the 3.24CL-d,
the input delay is adjustable up to
85ms, and the output delay adjustable
up to 256ms.
In large installations or outdoor 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 20°C), multiple loudspeaker locations can
create a situation where the original audio signal, simultaneously leaving all loudspeakers, 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 unintelligible in the farther reaches of the venue with direct line-of-sound to multiple
loudspeakers. The solution is to delay the audio signal to the loudspeakers located beyond the main stage area, so that
sound comes out of the distant loudspeakers at the exact time that sound from the main stage loudspeakers arrives.
Within the Protea 3.24CL, up to 682 milliseconds of time delay are available on each input channel, allowing secondary
loudspeaker clusters to be time aligned with the primary speakers up to 771 feet (235m) away from the main stage area.
200Hz
2KHz
20KHz
20Hz
0dB
-10dB
-20dB
+10dB
+20dB
-30dB
3.24CL Parametric Filters
Wide (High) Bandwidth
Narrow (Low) Bandwidth
