Live Sound University Article Mon, December 01, 2008

“You know, I’ve been doing sound here at my church for about two years now, and there are a couple of things that aren’t quite clear to me. First, where’s the bass and treble control? And, what are these knobs for - the ones on the console labeled high, mid and low?”

Believe it or not, I’ve heard questions like this posed more than once by people who do sound at their churches. It’s these folks, and others afraid to ask about things like the EQ section on the console, to whom this article is devoted.

First let’s take a look at the audio console EQ section (see figure, left, and cut-away insert below). This picture is an example of a rather basic EQ section on a Mackie 3204, a common board in many churches.

As you can see there are four separate knobs, one each for High frequencies, Mid-Range frequencies, and Low frequencies, and one to select the center frequency for the Mid control. To equate that to the stereo at home the High frequencies would be those controlled by your Treble control, which also overlaps into the Mid-Range frequencies.

The Bass control at home would be similar to the Low frequency control on the console. That fourth knob, the one for determining the frequency for the Mid-Range filter is what confuses many people. Let me take a shot at clearing up the confusion.

First let’s review just what happens when we turn any of the control knobs. If we turn the High, Mid, or Low knob to the left we will begin to turn down those frequencies. Most High frequency controls such as this one are centered around 12K hertz. That frequency is, for you musicians, about F# in the ninth octave on the piano. Or in layman’s terms, really high.

What we control up at those frequencies would be mostly to add crispness to an instrument or to take the “S” sounds out of the speaking or singing voice. The control though centered at 12K will effect on most consoles, about 2 octaves of frequencies.

The same is true of the Low frequency control. It is usually centered around 80 hertz and is used to enhance bass vocals, and low frequency instruments.

Also, because low frequencies tend to go everywhere and often cause feedback, we can use this control to cut that frequency back in some inputs. Generally speaking , with mics used for vocalists and pastors, you will want to turn down the low frequency for those channels to reduce the tendency for low end rumble, and also to help speech intelligibility.

The Mid-Range control is not on most home stereos, and therefore creates the most questions. This is compounded when deciding what frequency to set the filter. This filter works the same as High and Low, turns down to the left and turns up to the right. It effects, unless adjustable, (next time) usually about a two-octave range of frequencies. So what that means is in this case we can select at what frequency the center of the adjustment will occur.

The range here can be as low as 100 hertz and go up as high as 3,000 hertz, or 3K. This range of frequencies is where most of what we hear happens. A bass player is playing from about 30 hertz up to about 240 hertz, while a bass singer is in the 55 hertz to 500 hertz.

All vocalists, from the lowest to the highest, will range from about 55 hertz to about 1,700 hertz, all within the area of this particular EQ control. This is where we can either make the speaker or singer sound crisp and clear, or dull and lifeless.

So, how do you get comfortable using these controls? It is not as difficult as it sounds, and it can be fun if you like your calling and have a little time. Just plug in a mic and start to talk into it. Set all the controls straight up to “0”, no cut, no boost.

While talking begin to cut then boost the High control just to see what if any effect it has on your voice. Do this with each control just so you can hear what happens in each frequency range. There is no magic here, and not much to fear unless you like to listen at real high levels. That too I would suggest you do. Turn it up until you get some feedback, best done while others aren’t present, and see which frequency range cuts out the feedback.

Also play some music through the system and do the same cuts and boosts. You will be surprised at what you hear and don’t hear. You will also start to become more comfortable using these controls the next time you are “live” and getting the results you want.

Joe Wisler works with Ashly Audio and we thank him for this excellent contribution.