Ashly Protea 4.8SP Panduan Pengoperasian - Halaman 7
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down and eliminate problem feedback fre-
quencies, add or remove a characteristic "hot
spot" from microphones, or clean up room reso-
nance situations. It is well worth the time
getting proficient with parametric EQ filters,
as they offer the best solution to many EQ
problems.
Protea SP 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 dra-
matically cut, or "notch out", very narrow fre-
quencies (low bandwidth) in order to elimi-
nate 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 4.8SP
or 3.6SP EQ section of Protea NE 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 SP 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), multiple loud-
speaker 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 SP, up to 682 milliseconds of time delay are available, allowing secondary
loudspeaker clusters to be time aligned with the primary speakers up to 771 feet (235m) away from the main stage area.
Operating Manual - PROTEA 4.8SP and 3.6SP System Processors
+20dB
+10dB
0dB
-10dB
-20dB
-30dB
20Hz
Narrow (Low) Bandwidth
Wide (High) Bandwidth
200Hz
4.8SP and 3.6SP Parametric Filters
DELAY 1
0.00m
2KHz
0.00ms
0.00ft
20KHz
7