Understanding The PA System
We’ve all been there. You’ve finally booked a gig at the venue in town that you’ve been working on for weeks, and upon loading in you talk to the manager about where to setup. The manager points to a corner and says, “The PA System’s over there.” At first glance, you notice a tangled pile of cables, and what seems to be a mixer that looks like it has served as a coffee (beer) table for the musicians’ green room.
So what do we make of this mess? It’s important as musicians to educate ourselves on the equipment we may encounter and the practices of operating it, so that not if but when you’re presented with this situation, you can spring into action! No longer will you look at this pile of cables and see a scene that makes your blood boil. Instead you’ll see a window of opportunity!
But where to start?
Elements of a PA System
To further explore the phenomenon of PA systems, we must first have a basic understanding of Signal Flow. Signal Flow is the term used to describe the path at which an audio signal travels. Think of it as a “Road Map” for the Audio signal, where the signal travels along a guided route to reach its final destination: the listener.
The image below describes the typical signal path that we typically encounter in PA systems. The microphone is routed to a mixer where you’ll have the option of adjusting EQ, effects such as reverb, and the overall vocal level. The outputs of the mixer go to an amplifier (which in some cases is built into a speaker), at which point the signal is amplified. Finally, the amplifier connects to a speaker and, voila! We have sound!
Connecting your Mixer Properly
XLR Microphone inputs: This step is pretty self explanatory – you’ll want to connect your microphone cable to the XLR inputs on the mixer to ensure that your mic is connected properly.
Master/Main outputs: Also self explanatory – these ¼” outputs are used to connect the Master Output of the mixer to the amplifier (which, in many cases, is built into the speaker).
Getting a Clean Signal
“Gain” or “Trim” knob: This knob is very important in getting the amount of signal that the mixer allows into itself. It is the foundation of the mixing board and without being set properly, can ruin a vocal sound. You’ll want to be conservative in where you set the Gain knob (usually safe around 12, and perhaps a little further) to ensure that you don’t cause feedback in the speakers.
EQ Section: The EQ section is where you can adjust the High, Mid, and Low level frequencies of an audio signal. This section can be used to lessen harsh frequencies, to avoid feedback, or to sonically shape a sound to your liking. For a more in-depth discussion of EQ for vocals, check out the article on the Shed Light Events blog.
Aux Sends: The Auxiliary sends on a mixer can be used for a number of purposes. Typically the auxiliary sends will be labeled “Effects,” or used for this purpose. We can control the amount of reverb, delay, or other effects through the aux sends to find a sound to your liking. Additionally, some mixers may label this feature as a “Monitor” level, in which case you’re using an aux send as a level adjustment for amount of signal you’ll hear in the stage monitors.
Fader/Output Knob: Mixers will always feature a fader or knob to control the output level of the individual channel to the Master Fader, which feeds the main/master output connections on the mixer. This level adjustment works closely with the Gain/Trim knob, and you may need to adjust the two accordingly to attain your desired output level.
Powered vs. Unpowered – Mixers
You are likely to encounter both powered and unpowered mixers in venues that require you to do your own sound, so it’s important to have a general understanding of both. Powered mixers have built-in power amplifiers, and can output a signal that can feed a set of unpowered speakers. Conversely, unpowered mixers require an external amplifier to amplify the audio signal to an audible level.
An example of a powered mixer is the Mackie 808m, which has been a staple amongst mixers of its kind for a number of years
Similar units to the Mackie 808m are the Yamaha EMX series and the Behringer Europower series.
As a general rule of thumb, powered mixers will be accompanied by unpowered speakers, and vice versa. The one exception being a case where an unpowered mixer feeds an external amplifier, which feeds a set of unpowered speakers. It is very important to remember not to send a signal from a powered mixer to a powered speaker, as your amplifiers will overload the circuit, or you will blow your speakers.
Unpowered mixers will require an amplifier to supply additional signal to the speakers so that an audio signal can be heard. While these exist both in standalone units and built into speakers, both work interchangeably. Examples of unpowered mixers are the Allen & Heath Mixwizard series, and the Behringer Xenyx series.
Powered vs. Unpowered Speakers
Powered speakers feature a built-in amplifier, which amplifies the audio signal to an audible output level. These speakers typically have an output adjustment level, and sometimes a High and Low EQ. Common powered speakers are the Behringer Eurolive series and the JBL EON series.
Unpowered speakers will require an additional power amplifier in order to amplify the signal properly. These external amplifiers exist in rackmount format, and can be purchased in a number of different wattage levels. It is important to ensure that you’re never in a situation where you’ll overload your speakers, so it’s always safe to say that you should use a power amplifier that outputs less wattage than your speakers can handle.
Unpowered speakers that you may typically encounter are the Yamaha Club Series and the JBL JRX series.
Both of the above speakers require a power amplifier, which is available in different wattage and power levels.
Some venues may wish to provide a more modular, custo built sound system, and will opt for the route of an unpowered speaker system with external power amplifiers. Some notable brands include Crown, QSC, and Peavey.
As you’ve probably discovered, you can never know quite what to expect when entering a venue with an in-house system. You may be graced with an organised system (or better, a sound engineer to operate the system), or you may end up digging through a pile of beer soaked cables only to then dive head first into a heavily used system. Either way, having a basic understanding of how to do your own sound and operate the mixing board will put you one step in front of the rest. So go out, make some noise, and try to get a feel for what it’s like to do live sound!
Michael Harmon is a Berklee College of Music graduate. While drumming remains one of his first passions, Michael performs with several bands around the Northeast U.S. He educates young musicians in audio production and supports the art of independent record making. www.wachusettrecording.com
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