As a sound designer or musician you will often have to design or set up sound rigs for a venue that has no built in equipment. This can initially be daunting particularly with the amount of cables and tape you get through, but the theory behind any rig is actually quite straightforward.
The basic theory
Basically, there are three parts to any sound system: input, control, and output.
Input: These are elements like microphones, musical instruments, and audio players such as computers or CD players
Control: This is everything which the sound engineer has infront of them. At its simplest it can just be a small mixing desk, at the other a graphic equalizer and full digital mixing desk and effects processor.
Output: These are what actually make the sound that the audience can here. Basically speakers, headphones, or a recording device (CD, computer, solid state recorder, video camera).
There are a few items which don’t exactly fit into these categories, and bridge the boundaries between them:
Radio microphones: These are input devices, but the receiver (where the radio signals are converted to electrical signals) acts as a control surface, allowing you to adjust the levels of individual channels and output the results as audio signals, like a one channel mixing desk. In function though, these are inputs – sound comes into the microphone near the performer, and comes in like any other microphone signal into the mixing desk.
Amplifiers: As these can be built into the speakers, a mixing desk, or stand alone, it can often be confusing where these lie in the scheme. Basically they are the line between control and output: they take an output signal and give you one last level of control before the speaker does it’s work. These usually look after themselves, particularly with the popularity of powered speakers nowadays, but it is always good to remember where your output signal is being amplified.
An Example Setup
Okay, lets put this into practice with a sample sound setup. Again, this is for a room that has nothing built in, so expect to run a lot of cables. This is what is needed for this particular rig:
- Ten Radio Headset Microphones
- Two overhead microphones
- A laptop injection
- One orchestra overhead condenser microphone (presuming the orchestra can largely be heard acoustically in the venue, this can be used to pick up quieter woodwind or strings)
- One mixing desk with at least 13 microphone (preamp) inputs and a two-track (RCA) input (see notes below)
- Two powered speakers with internal amplifiers.
- Options also to chain these to additional speakers or sub-woofers using the “thru” outputs on speakers like this
I like to start with the control section, as everything needs to come into and out of this. Set up the mixing desk where you want it, and power it up to test that it works. You can do this by plugging a simple mic or laptop into the input and some headphones into the headphone/monitor port and checking for sound. Or just look for flashing lights.
Always test every stage as you put it together. That way, if nothing happens when you fire everything up, you know already which element isn’t working properly.
Then set up the output. Place the speakers on their stands (presumably on either side of the stage) and run power to each of them. Then run a pair of XLR (or 1/4″ jacks depending on the speaker) cables from them to the board, making sure you check the direction you run them. Male always plugs into female, and if you don’t check there’s a 50% chance you’ll have to lay everything again. Plug the cables into the master outputs of the board and test them, first that you have sound coming out (again with a single mic), and then that you have the Left and Right the right way around (which can be easily done by panning your sound source from one side to the other, and checking it corresponds with what you hear). If need be swap the outputs.
Once you have the rig working, it is time to get sound going into the board. You have probably already plugged your laptop/CD input into the board, but if not you will use a 1/8″ jack to stereo RCA cable, or perhaps a Direct Injection box to give you a bit more control. The overhead microphones need to be hung above the performance area, and the orchestra mic placed on a stand where you want it, and then both plugged into the board, which usually means a lot of XLR cable and Gaffer Tape. If they need phantom power (as most microphones of this type do) make sure it is switched on in the mixing desk. Check that they work with a pair of headphones. Even if nothing noisy is happening you should hear a hollowness which means they are working. You can fine tune later. Finally, get the radio microphones. The receivers usually come in a road-case, if you have hired them so place this somewhere close to your desk where the antennas have clear line of sight to the performance area. If you have planned right you should be in range, otherwise you’ll need to move the whole desk closer. Antennas should be angled 90° apart to get the best coverage. Each receiver then needs a line running from its output to the mixing desk, so you’ll either need a lot of short XLR cables or a multicore/snake. Plug everything in, make sure the receivers have power, then switch them all on. Then make sure the transmitters are ready: the microphones are securely plugged in, the batteries are in and power turned on, and that they are on the same channel/frequency of the reciever. The reciever should give you an indicator of signal strength, and you should be able to test that you have sound in the usual way (headphones is best).
Make sure that you keep cables as short as they can be without pulling on connections, as longer cables give more room for interference and noise. If you have to have longer cables never leave them coiled up on the floor, as the coils will act as an induction loop and make everything noisy and buzzy
With everything set up all you need to do is fine tune everything (easier said than done, but involves less gaffer and cable). This is usually a matter of setting levels so that you don’t get feedback noises, and making sure you have a clean signal all the way through. When you do a soundcheck with the performers you can work on the tone of the radio microphones with EQ and placement, but for the other inputs make sure they are placed correctly and that you set the gain as loud as you can without generating squeals so that you don’t have to worry about remembering levels on your faders.
I find it helps to set everything on the board to a neutral position before you plug everything in. EQ to centre, pan to centre, auxiliaries and effects to zero, and gain to a moderate but small amount (you don’t want to blow the speakers just yet).
This should give you a rough-and-ready rig that you can work with for most purposes. I’ve used similar rigs for plays and musicals, and while it can seem complicated knowing the separate input and output cicuits makes everything simpler and more logical when hunting for problems.
Suggestions for improvements, corrections, comments, or questions? Leave something in the comments below. I’ll read everything, and reply to most things, so be polite.