In response to the Live Sound Considerations: Mics, PAs, Mixes and More article, a reader sent me a super interesting and informative email about using the EQ section of your mixer to “tune the room,” so I thought I’d share it with you…
How to EQ a PA System
GUEST POST BY LONNIE SHURTLEFF
I will venture to add some detail to the discussion of the EQ process, the first point being to understand what the EQ section is and what it does, and consequently, how to take advantage of it.
What Happens When We Sing (or Play) Into a Mic
When a sound strikes a microphone (of whatever type) it generates an electrical signal that (theoretically at least) duplicates the characteristics of the sound.
(We’re talking pitch, amplitude, harmonics, phase, etc. – technical stuff here).
It never works 100% perfectly – that’s why different mics sound differently, and why a sound technician will choose different mics for different applications.
That electrical signal typically travels through some cabling to a channel preamp. From there, that signal (along with others) goes to a power amplifier, which in turn strengthens the signal and ships it out to some transducers (speakers) via cables again.
The speaker’s job is to bounce air molecules around in exactly the same way that they entered the mic but many times BIGGER and LOUDER.
The amplifiers are never 100% perfect. Neither are the speakers. The cables always have issues and affect the signal somewhat.
There is a lot of technical stuff to learn here if you want to be an engineer, but for our purposes, these are things that affect the signal.
These things are part of what the EQ section is supposed to correct.
The PA’s All Set Up – Now What?
Suppose you set your PA up somewhere quiet, outdoors, maybe in the desert, with nothing close by to reflect or otherwise mess with the noise. Everything is set up flat on your mixer.
Crank the master gain up, and what comes out of the speakers is (supposedly) what the sound going into the mic was, only BIG.
(It’s not really the same, but the only way you could sort it out would be by making measurements with expensive audio test gear.)
So, all you have is your ears, and you think it sounds “muddy,” or “shrill,” or “thin,” or “distorted,” etc.
So you “smiley-face” the EQ (boosting low and high end, and dropping some midrange frequencies) and use it like a tone control–and it works!
It sounds much better!
It works largely because the human ear does not work in a linear fashion and it hears soft sounds differently than loud ones.
But this is not really what the EQ section is for!
Most of the time, you are not out in the desert. You’re inside some structure or room that has walls and ceilings and floors and windows and reflective surfaces.
Some of the stuff in the room absorbs some sounds and some reflects some sounds.
Here’s where that EQ section really earns its keep. You set up your gear, and then…you EQ the room! You make that room behave like it was the middle of the wide open desert.
Here’s how I like to do it…
How to EQ The Room
After everything is set up, using only one mic with the channel gain about 3/4 up (that is usually a pretty sweet spot for the preamp), other mics off, monitors off (we are EQing the mains and the room–monitors are a separate deal!), then…
- Put the EQ sliders all about half way up
- Start bringing the master gains up (CAREFULLY!) until something starts to squeal or roar or whistle (feedback).
- Hunt around on the EQ bands and find the slider that affects that sound the most, and back it down a bit.
- Next, push the masters a little higher until you get feedback again in a different place. When we get to the point where we have touched most of the sliders, and any more gain brings random feedback at different pitches, we know we are compensating for all the different stuff that’s reflecting and absorbing sound in that environment. That threshold is the maximum overall amplification that can be applied in that environment. (A more sensitive mic or an omni-directional mic will cause that threshold to be lower, which is why we typically choose cardioid mics like Shure 57s and Shure 58s.)
- Then, simply pull the masters back away from that feedback threshold and the room is EQed!
- A simple trick to spot check this is to cup your hand around the mic. If it starts squealing, you’re too close to that feedback threshold.
Now, bring the other mics up and use the channel controls to make each mic sound good.
That’s what those controls are for!
This leads to a couple of final thoughts…
You probably just EQed a cold room! When the sun goes down, the temperature drops, the humidity goes up, people fill the place up with smoke and sweat, etc., the EQ changes, and you’re going to need to tweak it on the fly.
But at least you know you started in the right place!
Typically, hot humid air soaks up highs, so a little boost in the top end will help.
Also, the human voice likes a “presence peak” around maybe 2kHz or a little higher.
Rolling off some bass down around 400 Hz will often clean up “muddiness” and “rumble” in the bottom end.
Lots more to share, but I’ve already written a book here!
Editor’s Note (from Dave)
I asked Lonnie if there were other practical tips he’d want to share concerning live sound, and here’s what he said:
“There are a bunch of other aspects that I might talk about, for instance…
- how to get that little “ball of sound” around your head that makes it possible for you to perform at your best
- why people grouse that “It’s too loud!” when that isn’t really the problem at all
- why everybody else sounds out of tune when it is really the bass guitar
- (if anybody really cares) what Dbs (decibels) mean and why it matters
- stuff like “low impedance vs. high impedance,” “balanced vs. unbalanced mic cables,” “4 ohm speakers vs. 8 ohms” (rabbit hole stuff)
- or maybe how to set up the pickups on your Strat (kinda problematic)
- or why Leo Fender designed a flat peg head that required those little string-hold-down thingies that make a Strat so tough to tune!
Looks like I’m on a roll again, sorry!”
Lonnie said he’ll be glad to respond to any questions or comments this might provoke, so jump into the “Comments” section below and let’s discuss!
About The Author
Lonnie Shurtleff, aka “Lonnie The Eclectic Cowboy,” is a retired broadcast engineer terminally addicted to guitars and getting people to laugh and clap.
Based in La Grande OR, Lonnie performs wherever he can afford to go. He’s in the Artist-in-Residence program from Arts East serving ten rural counties in Oregon, performs in two duos doing everything from big band swing to Oregon Trail “Americana,” and does cowboy poetry workshops in schools and libraries where he talks about the history and legacy of the west.
About The Blog
The Educate and Entertain blog provides articles, tips, encouragements, and how-to’s for regional performers (in any region) interested in making a great full-time living in the arts.