Live Sound for dummies

During any live show or presentation, the on stage talent is only one piece of the equation. There are lighting people, sound people, set up people and a host of other folks that put the show together. If you really want an eye opener, try and get on the set of a movie shoot as an extra and just look at how many people it takes to capture 30 seconds to 5 minutes of film.

Live presentation offers similar challenges. One of the most critical people in a live presentation is the mix console operator (MCO). The MCO is a widely misunderstood job, they are no different than the lighting operators, and have a whole lot more to do. A mix console operator is the person that makes electrical adjustments to electrical equipment to change sound. With lights, if you turn the dial up the lights just go to the max. With sound if you turn the dial all the way up you get pops, clicks, bangs, hisses and speakers can be blown. It is pretty hard to damage a lighting system by turning the lights up full bright. Most lighting controllers will auto dim or auto shut off if they get to hot.

The MCO isn’t that lucky, one wrong twist and “BOOM BOOM baby out goes the sound.” Even though a lot of people like to think of mix consoles as electrical devices, I prefer to think of them as plumbing controllers. We all know what happens when we turn on the water full blast with a cheap hose that has a kink right? No flow and leaks every where. This is how electricity works too. At the mix board, think of every little knob as a unique water pressure knob, too much pressure causes leaks and damage.

The key difference between the MCO and lighting operator is the input and output both are variable. Even after the mixing board there is the potential to have a room equalizing computer, then amplifiers and finally speakers. All of those components can change their characteristics based on the input, temperature or room capacity. People absorb a little sound and reflect a little sound. In an auditorium with hard seats, the sound difference is incredible.

So here is the question, How does the console operator know? I am sure you are saying “By watching the LED’s or the gauges”. Sadly those gauges don’t always help. The entire system is working against the console operator. Another variable that mix console have to deal with is the input power. The lighting guy is pretty comfortable knowing that he is getting 12V, 120V or 240V or 440V depending on the way the house system is designed.

A mix console operator never knows what he is getting. A mic change mid stream could suddenly increase your incoming signal pressure. Imagine a hose that someone doubled the water pressure coming in, and didn’t give you a bigger hose, it would burst. If the console was set for a weak mic that was sending 1.13V mean average and suddenly the new one is sending 1.68V mean average, you have increased the input 50% without turning a single knob. Since mic’s send only what gets put in, moving the kick drum mic closer to the kick drum can change all the settings.

Every change on stage changes the input side of the mixing board. A mix console operators job is to make the output, or sound heard by the audience, all sound the same no matter what happens on stage. To make things more difficult, some consoles have to mix the feedback to the stage as well, and they don’t even hear that sound. In ear monitors can do all kinds of funny things to the sound curves and the operator will have no idea until the person on stage speaks up.

Where a console operator gets into trouble is when an input signal exceeds the boards ability to process the signal. This is called exceeding the headroom, or clipping. Just like a computer, garbage in = garbage out. If a mic is set to high or an guitar effects pedal set to max, the incoming signal may be so strong it clips or is cut off. The MCO has no control of this during a live performance.

Next if the signal is near the max the board can handle and the MCO cranks it up, then signal going to the amp can do the same thing. Lets use a 2V limited amp for an example, the Volts don’t really matter but I want to illustrate this effect. If the input signal to the amp is 0V, the amp ideally puts out 0Watts to the speakers. At 2V the amp puts out its max, lets say 150W for this discussion. If the mixing board sends out 2.2V and the red LEDs are solid, the amp is trying to go to 168W or so, but the signal is stopped at 150 and sounds horrible. At least in this case the MCO can dial it down.

An output from the stage becomes an input to the mix board. This is where the MCO may not have enough control. That “hot” mic or guitar effects pedal may be sending an over powered signal adding distortion or clipping to the signal line no matter what the MCO does.

An artist can do this to you by moving the mic closer to their mouth and increasing their voice instead of moving the mic away. A screamer in a heavy metal band can really be trouble here. An MCO that knows their artist or speaker will know they do this and be ready. Being prepared, the input can be toned down just in time so the audience gets the correct effect. Really good artists will move the mic to keep the averages in the right area. This is why the artists have stage monitors and in ear monitors. The stage monitors or in ear monitors will let the artist know they goofed at the same time the house speakers let the audience know. It won’t matter, “The MCO should have caught it” will be the answer.

In the worst case, the amp can go to 168W but the speakers can only handle 125W. All kinds of interesting things happen here. I have seen cones crack open, which is known as blowing the speaker, a cone moving past its limit and getting stuck and internal crossovers melting. None of them led to a good finish of the show.

Starting with the line diagram of the console, an operator should be able to pretty quickly make adjustments to the sound field by watching the meters and using his ears. For really loud environments a set of musicians earplugs that cut out sound evenly might be a good idea.

In simple terms the mix console operator is the master regulator of the show. The MCO must kick up the signals that are weak, tone down the signals that are hot, adjust for frequency variance of the environment and make sure that the show sounds great. Sounds easy right, get mixing.


  1. I noticed your blog on facebook groups. I just added you to my MSN News Reader. Keep up the good work pal! Look forward to reading more from you in the future.

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