Most
PA systems, no matter how large or small, are run in
essentially the same way. Once the basic components
of equalizer, mixer, effects, microphones, amplifiers
and speakers are in place, the basic principles for
running a huge stadium PA are no different than those
used for running a tiny club or pub in-house system.
After
it's all set up and connected, the first thing you
will probably want to do is turn it all on. This is
trickier than you might think. Although turning it on
seems simple enough, doing it improperly can cause
damage to some parts of the system. Specifically, in
addition to scaring the hell out of the people
hanging out in the room, the loud "pop"
that sometimes occurs when you flip the
"on" switch has the potential to tear up
the midrange horns. Although there's no way to avoid
this popping altogether, there are a couple of things
you can do to keep it to a bare minimum.
First,
before you turn any knobs or switches into the
"on" position, you should make sure that
the master levels on the amplifiers and the mixer are
turned all the way down. If you don't make sure you
check those levels, the Law of Sod might take effect
and ensure that one of the levels is set incredibly
high (maybe the slider got bumped in transit) which
will cause horrendous and unexpected feedback
immediately after flipping the "on" switch.
That instant kind of feedback can easily blow a
midrange horn, so it's best to play safe. The levels
you should be most concerned with are the output
levels on the amps (usually knobs), and the main outs
(usually sliders) and monitor outs (sliders or knobs)
on the mixer. Once these levels have been
"pulled down", it's safe to turn the system
on. Other master levels such as those on the
equilizers and effects are safe if left at or near
their usual setting, but if you're in doubt (or
haven't yet determined a "usual setting"),
pull them down to zero as well.
The
components of the system should be switched on in the
following order: Effects, EQ, mixer, crossovers and
amps (lows first, highs last).
This
order keeps the majority of the popping signals
created by that initial power surge when each
component is turned on from ever reaching the
speakers. The main thing to remember is that the amps
should be turned on last. The purpose of the amps is
to increase the weaker line level signal to a high
level signal that drives the speakers. If they aren't
turned on, then there's no signal going out to the
speakers. If the speakers don't get the high power
signal from the amps, they can't "pop".
Turning the amp on last reduces the number of
"pops" from one for each piece of equipment
you turn on to just one when the amp itself is
switched on.
Whenever
turning anything on (or off) that's connected to the
PA system (microphones, keyboards, acoustic
guitars...), make sure the "mono" knob and
the "level" slider for the channel it's
plugged into is pulled all the way down. Switches on
active mics in particular make loud pops when being
turned on or off.
Now
that it's all turned on, the first thing to do is run
the system through a series of tests to make sure
everything's operating properly. There are a lot of
things in a PA system to plug in, and it's very easy
to make a mistake somewhere along the way. Running
these simple tests will make it easier to quickly
find and isolate these mistakes without any
unnecessary aggravation.
Powered
Mixer System:
The powered mixer setup is probably the smallest
system that should be used for gigging. It's very
convenient in that most of the components (Effects,
EQ, reverb, mixer) are already built into one unit.
This combining of components means there are very few
external things to hook up, and therefore there's
very little likelihood of making an error when
putting it all together.
The
least complicated system is of course the easiest
system to test. To test the system, you need only go
through a few simple steps. The steps listed below
are there as a guide to help you locate any problems.
If something in your system doesn't work properly,
and the suggestions listed don't seem to be the
problem, you should first go back to "setting it
up" and make sure you wired it all together
properly. If it turns out that everything is hooked
up correctly, you should then check all your cables
to make sure they're working. After you've determined
that they're in good shape, it's then time to look at
the possibility that something may be wrong with one
of the larger components of your system.
To
begin testing, it's a good idea to set all the knobs
on the board to relatively neutral positions. To do
this, set all of the EQ knobs on the input channels
(Low, Mid, High) to the straight up twelve o'clock
position, Set all the sliders on the main EQ to the
centre position (this is called "flat"),
turn all the effects and auxiliary knobs all the way
down, set all the "pan" (balance) knobs to
twelve o'clock, turn all the gains on the individual
channels all the way down, and make sure the main and
monitor master levels are all the way down. After
these knobs are set, follow the steps below to make
sure the system is connected properly.
Mono
(1 output channel):
1) Gradually turn
the main (volume or level) knob or slider up to near
it's normal setting. On knobs, straight up at twelve
o'clock is good. On sliders, three quarters of the
way up is good. These settings will vary depending on
the mixer, and the personal preferences of the
soundman. It's a flexible setting that's inversely
proportionate (when one is high, the other will be
low and vice versa) to the final settings of the
levels and gains of the individual input channels.
Just make sure you don't turn it all the way up, or
all the way down. Somewhere between one quarter and
three quarters is fine.
2) If your mixer
has one (some don't), turn the gain on the lead
vocalist's microphone channel up to about the nine or
ten o'clock position. If it doesn't have a gain knob,
simply proceed to step 3.
3) While
repeating the word "check" into the lead
vocalist's microphone, gradually turn up the
"level" knob or slider for that input
channel until you can clearly hear your voice coming
out of the speakers. If you don't hear your voice,
recheck your connections and settings.
4)
Now, have someone else check the mic (or
you can do it yourself if the lead's long enough)
while you go out to the speakers and listen to them
to see if each is working. Make sure to place your
head in front of the midrange horns and the
individual speakers in each cabinet to check them
individually. If a whole cabinet is not working,
check your connections to that cabinet. If just a
speaker or horn in a cabinet isn't working, and the
others in that same cabinet are, check to make sure
you plugged the cable into the "full range"
input on the speaker. If it still isn't working, you
probably have a bad internal connection inside the
speaker cabinet or a blown speaker or horn.
5) If
everything's working fine up to this point, check all
the other input channels in the same way as in steps
2 and 3. Some channels may have instruments plugged
directly into them instead of microphones. If so,
instead of checking a mic, simply play the instrument
while you turn that channel's "level" up.
If one of the channels isn't coming out of the
speakers, and all the others are, you either have a
bad connection or cord, or something's wrong at the
instrument end.
If
your mixer's equipped with a powered monitor output
channel, then proceed to steps 6 through to 8. If the
monitor output channel is not powered (ready made to
plug a speaker into), then it'll require you to use
an external amplifier and equalizer.
6) Turn the main
master slider or knob all the way back down. This
will make it easier to hear your monitors
independently of the mains while you make sure they
are working correctly.
7)
Gradually turn the master mono (volume
or level) knob or slider up to near it's normal
setting. On knobs, straight up at twelve o'clock is
good. On sliders, three quarters of the way up is
good. Again, this isn't an exact science. Somewhere
between one quarter and three quarters is fine.
8)
Now, perform the same procedures
described in step 3, step 4, and step 5, only this
time make the adjustments to the "Mono"
knobs or sliders rather than the main
"level" sliders or knobs.
Stereo
(2 output channel):
The only visible difference between the mono powered
mixer and the stereo powered mixer is the addition of
a "pan" knob for each input channel and a
master "pan" knob that controls the panning
of all the channels at once. The "pan" knob
is basically the same thing as the
"balance" knob on your car or home stereo
system. Now having said that, here's the long, drawn
out, semi-technical version of what it does in a
stereo PA system.
A
stereo setup has two separate channels going out of
the system to the speakers. These are usually labeled
either "left" and "right", or
"A" and "B". Each of these
channels has it's own independent amplification. In a
powered mixer, this is all set up internally as part
of one self contained unit. Using the "pan"
knobs allows you to change the volume of channel
"A" (or left channel) in relation to the
volume of channel "B" (or right channel).
In other words, when you adjust the "pan"
knob towards the left, the left output channel will
get louder in relation to the volume of the right
channel, and the opposite will happen if you turn it
to the right.
To
test a stereo PA system, first follow steps 1 through
5 just like in the mono system, then procede to these
next few steps.
5a) While checking
a microphone, gradually turn the main "pan"
knob all the way to the left. You should hear the
sound gradually move entirely to the left main
speaker (from the audience point of view) as you turn
the knob. If not, check your connections to see if
the "left speaker out" is connected to the
left speaker and the "right speaker out" is
connected to the right speaker.
5b) Now, pan the
sound with the main "pan" knob all the way
to the right. The sound should now move all the way
to the speaker on the right side of the stage as it
is viewed from the audience's perspective.
If,
when you turn the "pan" knob to the left,
the sound goes to the right, and when you turn it to
the right, the sound goes to the left, all you need
to do to fix the problem is check your speaker
connections and make sure you plugged the right
"speaker out" into the right speaker, and
the left "speaker out" into the left
speaker.
5c) Finally, set
the main "pan" knob back to twelve o'clock.
Then check the "pan" knobs on the
individual channels using the same technique. If the
main "pan" knobs are working properly, and
an individual channel's "pan" knob isn't,
there may be an internal electronic problem with the
mixer.
Once
you've completed all these steps with your powered
mixer, and everything's working properly, you're
finally ready to begin your soundcheck.
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