1.
How to ring out a room
I am often asked as a sound technician about why certain
sound systems seem to ring a lot. There are several reasons for this. If you have
an understanding of all of these problems it might save you some time and money
when you are having problems with your sound system.
Problem 1 – Not understanding the Gain and the Volume
Controls
Gain
and Volume are not the same thing. Gain (sometimes labeled Trim) is the amount
of sound that you are allowing into the microphone that is on the stage. Let’s
consider this scenario. You are running sound for a recording session, and the
artist wants a particularly open and far away sound. You could just add a lot
of reverb, but that would sound like you’ve added a lot of reverb. Another way
to get this sound is to place a mic in a far corner of the room, and crank up
the gain, and have the artist stand all the way across the room, or even in the
next room and yell at the mic. By cranking up the gain, the mic now has a wide
pattern, and is picking up sound from all over the place. Remember mics have
patterns to their pickup ability. Cardioid mics have a bit of a heart shaped
pattern. This “heart” can grow and contrast as you turn the gain up or down. A
shotgun mic has a pretty straight pattern, and picks up signal along a
lengthwise pattern. Some mics are “omni-directional” where they pick up sound
from all directions. Some are “uni-directional” where they only pick up sound
from one direction. The thing to remember is that adjusting the gain changes
the size of this pattern, no matter what the pattern is.
Now
consider this, if you are on a stage, and there are lots of instruments blaring
away, and you crank up the gain all the way on a singers mic, you’ve adjusted
the amount of sound that the mic can pick up. If you adjust the “cardioid”
pattern wider than the singers head, then now you have whatever is behind the
singer coming into the mic as well. So gain is something that you want to probably
keep low, and often times is the first thing that causes ringing in a room.
Since
we are talking about gain, we need to also go over volume. Volume is controlled
by two or more controls on a mixer. The first volume control is the main
channel fader, usually these are numbered 1 through however many channels you
have on your board. Another volume knob is usually located above the main
volume fader and is usually labeled 1, 2, 3, or 4, or Aux 1, 2, 3, 4. These are
the volume knobs for the different Auxiliary monitor signals. You may have only
1 or you might have 2 Aux sends on your board, or you might have four depending
on how advanced your board is. These knobs are the monitor signals. Now
something that might cause ringing is if you have the gain up on the mic, and
it starts to pick up the signal from the monitor. This will cause a feedback
loop, and will cause the earsplitting ringing that inexperienced soundmen are
known to cause. It’s wonderful when this happens in a church full of old
people. (No, I’m just kidding.) Anyway, this is another reason why you want to
be careful about cranking the gain wide open.
Problem 2 - Not Understanding the Volume Faders
The
main volume fader is labeled in a strange way, it has a line for zero, and then
it counts up in decibels, and down in decibels. Many people think that they
have to have the volume fader set at zero. A really common thing for soundmen
to do, is to ignore all those markings, and pretend that when you are pulled
all the way down, that is zero. And then blend in the volume from there. Sometimes
no matter what you do you will experience a little bit of ringing. A trick my
mentor taught me was to take a piece of gaff tape, or labeling tape, and find
where the channel rings, and then put a piece of tape so the fader cannot reach
that point. That way when you are in the middle of a show, you won’t
accidentally turn up that fader too much.
A lot
of boards have bus faders. These are volume knobs that can control a whole
bunch of channels at once. You can assign which faders you want to control by
pressing the right buttons. The trick with these is to set all your volume
knobs first, and then use the bus to bring the whole section up or down.
The
final group of faders are the mains. These are the left and right channel.
Typically, at most shows, unless there is a specific need for stereo, I run
these in mono in the left channel, and sometimes have even used the right
channel as a monitor send if I didn’t have enough monitor sends. This gives me
one monitor that has the full mix (somebody always wants that mix anyway) and
then I can use the aux sends for the other mixes. On a two aux send board, this
gives me three monitor mixes, and for a small band that is perfect usually.
Anyway, just like the other volume faders, you want to make sure you find out
where everything starts to ring and tape them so you don’t bump up your volume
too much.
Problem 3 - Not Adjusting your Powered amps and speakers volume knobs properly
All
your powered amps and speakers will have volume knobs too, if they are too
close to microphones or each other they will cause ringing. So make sure they
are not feeding into any live mics.
Problem 4 - Not ringing out the room ahead of time
Ringing
out the room – this is an important topic that I want to end with. Every mixer
has at least two EQ settings, a high setting and a low setting. Some mixers
will have a mid setting, and some will have two mid settings. Then some mixers
have built in graphic eqs, with several settings. But I find that having a
separate eq for each of the mains channels, and each of the monitor sends is
important. Here is the problem, certain frequencies are just tricky and will
cause ringing when you try to bump the volume. If you use a spectral analyzer
(frequensee is a good app for your phone) you can see exactly which frequencies
are ringing. Once you get the room to ring (by playing white noise through the
system) you find where the first ringing is, and turn down that frequency on
the eq for that speaker. Then you turn it up some more until it rings again,
and then you locate that frequency and turn it down. Then you do this until you
can crank the volume all the way up. (Like I mentioned before some rooms are
just tricky, or you might not have enough eq faders to mess with to do a
perfect job. This is a good reason to go ahead and splurge on the EQ with a ton
of faders instead of buying the cheap one. Anyway do your best, and then mark
the board if you can’t get all the ringing out.) Just repeat this process for
each one of the speaker systems you set up. If you run your mains in mono, then
EQ them first. Then turn off the mains, and EQ each of the monitor lines you
set up. Then turn everything on and double check it all to make sure everything
is going to work.
Once
you’ve rung out the room, and set up all the sound, then bring in the band to
do a sound check. If there is anything ringing after that, it’s probably
something that can be adjusted with the eqs that are built into the board
itself.
Hope
this helps.
