Sunshine’s n00b Guide To PA Systems
Seeing an influx of questions related to PA gear and how to build a system, in addition to many requests about how to plug in X gear to Y gear, I feel it might be helpful to consolidate all this information into one spot. Mods feel free to sticky this if you feel it’s good enough, but hopefully it will simply help lessen the number of “How do I hook up my Mixtrack in a club” questions and the like. As a DJ, it is important to know at least something about PA sound systems. Doing so can be the difference between showing up for a gig and rocking it or packing up and going home because your controller lost sound somewhere and you don’t knows how to fix it. This is information that I have gathered mainly from personal experience working with various aspects of sound equipment over the years, and I’m not really going to be going incredibly in-depth into the nitty-gritty technological aspects of each topic. This is simply aimed at helping someone with little to no PA/sound reinforcement experience get started and to keep them from doing anything that would be catastrophic to their beloved equipment. This deals with Junior-grade sound systems, not the big concert-level sound reinforcement. If you’re looking to build a festival sound system with hundreds of thousands of watts of power, I’d look at getting some help or further researching each of these aspects in much more detail. If you are curious about any particular topic further, I’ve found that the pro audio threads at Sweetwater.com and the Amp/Speaker thread on DJForums have been very helpful, and the guys really know their stuff. There is a plethora of other information available on the web as well, I’m mainly consolidating it and putting this here for convenience. If I make an error somewhere or you feel I have left out something critical, PM me with the details rather than flaming the living bejesus outta me! I'm sure I haven't covered every base, so if people would like to add to this or help me clarify what I'm trying to say, please feel free. Now here we go:
Disclaimer: This guide is simply that: a guide. It is not the be-all end-all rules of running live sound; it is simply a basic walkthrough of the core individual pieces of equipment an average PA system utilizes. If unsure about something involving your system, always consult your owner’s manual(s).
Before we even begin looking at amps/speakers/mixers/etc., we need to understand a bit about the cables that hook everything together and the proper functions that each fulfills. We will look at the main types of audio cables that you are most likely to run into AS A DJ. Optical audio, HDMI, etc. will not be covered. So until the DJM-5000 comes out rocking full optical and HDMI, you probably do not have to worry about encountering either of these. I am including a Wikipedia link to each in case more information is needed. So let’s start at the beginning:
RCA
This is the standard red and white jack you see on just about every DJ mixer and the outputs on most controllers. This cable sends a stereo signal from one component to another. Red is for the right channel, white or black is for the left channel.
http://en.wikipedia.org/wiki/RCA_jack
XLR
The cables you see connecting to microphones, these cables carry a balanced audio signal between audio components. They are also used to control various aspects of lighting equipment (called DMX). They vary between 3 and 7 pins, however you will most likely only encounter the 3-pin version, as it tends to be the most common.
http://en.wikipedia.org/wiki/XLR_connector#Three_pin
TS/TRS Cable
The more common name of this is the 1/4in. cable, however this can be misleading, as there are two types. The first, a TS 1/4in. cable, sends one side of an audio signal or a summed mono signal between audio components. If you have a background with electric guitars, you might be aware that this is the same cable you would use to plug a guitar into your amplifier. The second type is the TRS 1/4in. cable. This is a stereo cable of the same size and dimensions, however you will notice that there is an extra ring around the male end of the plug. There is a smaller version of the TRS cable that is found on your average headphone earbuds/cans. This is the 3.5mm 1/8in. jack.
http://en.wikipedia.org/wiki/TRS_connector#Audio
SPEAKON
Speakon cables are relatively new and very similar to XLR cables. However, the main benefit of speakon cables is their locking mechanism that prevents them from being yanked out of a power amplifier/speaker by accident. Speakon cables are designed to handle voltage-level (speaker-level) signals.
http://en.wikipedia.org/wiki/Speakon_connector
MIDI
Not considered an audio cable, but digital DJs will most likely encounter these at some point along the line, so they’re worth mentioning. MIDI cables send data values to allow two pieces of equipment to communicate with each other. Things such as digital controllers, drum samplers, and other digital gear typically communicate via USB over MIDI. This is but one of a few different ways these work. MIDI is complicated and this was an incredibly brief summary of MIDI functionality, and so further reading is advised.
http://en.wikipedia.org/wiki/MIDI
Now that we know a bit about our connectors, let us look at the equipment they will be used in. PA systems at their core consist of three main parts: The signal, the power, and finally the speakers.
MIXERS
Mixers are defined as any device that is capable of taking one or more audio signals and having the ability to combine them, change the timbre (color) of the signals, or add effects to them and combine the output into a single combined output. The 2-channel DJ mixer is one such style of mixer, however these are modified specifically for DJ use. The general components remain more or less the same, however.
POWER AMPLIFIERS
A power amplifier takes a line-level signal (such as an instrument, microphone input, iPod, etc.) and converts it to a voltage-level signal and sends it to the speakers. Technical jargon aside; it is what makes your system loud. If building a PA system, you will need at least one of these. Power amplifiers can be bought standalone or built into speakers and mixers (more on this below). Standalone power amplifiers have power ratings based on the resistance the amp is presented. In general though, the higher the numbers are, the more powerful/loud the amp will be. When powering up a system, turn the power amp on last. When powering the system down, bring the knobs all the way down then turn it off first. This will prevent your speakers from doing a nasty “thump” sound that could possibly damage them.
SPEAKERS/SUBWOOFERS
We have sent our signal through the mixer, into the power amplifier, and now it has reached the speakers. The forcing of air back and forth by the speakers inside their cabinet is what projects the sound out into the audience’s ears. Speakers come in two different types: Active and Passive. Remember reading above about how power amplifiers could be built into speakers? Such a design is called an active speaker, and features a built-in power amplifier that drives the speakers. This allows the engineer to simply plug the main outputs of their mixer straight into the individual speakers and to generate sound. Passive speakers are simply speakers with input connection terminals, but no amplifier. They require an amplifier or mixer with a built-in power amplifier to output sound.
Slightly different from your average speaker is the subwoofer. Subwoofers are designed to handle the low and sub-bass frequencies put out by the signal, such as kick drums. Subwoofers are the reason you feel your chest vibrate at a loud concert. Like regular speakers, subwoofers also come in both active and passive models.
Speakers typically are categorized by the wattage they are able to handle (called Peak Power rating) and how much is ideal to run them (called RMS rating). When selecting a power amplifier and speakers, you ideally want an amp that puts out double the RMS rating of the speakers (i.e. if my 8-ohm speakers handle 400W RMS, I want an amp that would put out 800W of power at 8 ohms). Overpowering a speaker is much better than underpowering it.
CROSSOVERS
The crossover is specifically designed to take a full audio spectrum sound input (such as a song) and split it, designating which frequencies will go to the speakers and which will go to the subwoofers. The crossover is convenient for many reasons, one being that it will prevent your main speakers from attempting to push heavy bass frequencies once you have subwoofers connected.
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