Understanding How a Basic PA System Works

1. Understanding How a Basic PA System Works www.channelaudiogroup.com AV Equipment

2. www.channelaudiogroup.com What is a PA System? • PA system stands for “Public Address System.” • Origins date back to around 1910 • Automatic Electric Company of Chicago, Illinois developed the first loudspeaker • By 1913, multiple units were installed throughout the Comiskey Park baseball stadium in Chicago • Any system of one or more speakers designed to replicate audio or speech to a group of people qualifies as a PA system

3. Main Components

4. www.channelaudiogroup.com Speakers • PA speakers come in countless different shapes and sizes. • Each type of speaker serves a different function within the system, but each depends on the other. Main Speakers (often referred to as tops) • Create the bulk of the PA’s sound • Mains are either placed on speaker stands or mounted on top of the subwoofers • Normally sized between 10"-15" with a smaller tweeter speaker above the woofer Subwoofers (often referred to as bottoms) • Larger than the main speakers and produce lower frequencies than the mains • Has the effect of “filling out” the sound that the ear will hear • Typically 15"-20" speakers Stage Monitors • Usually positioned near the performer or speaker to help them hear themselves • They are on a separate mix than the mains and subs • Many main speakers are purpose-designed to also act as stage monitors if needed

5. www.channelaudiogroup.com Amplifiers • PA speakers can either be passive or active • Active speakers have an internal amplifier of their own while passive speakers have no internal amplifier and require an external amplifier • Amplifiers convert the line-level signal of the mixer to a level where it can drive the speaker to the necessary volume • In a passive PA system, you are trusting the entirety of the system’s sound to one component

6. www.channelaudiogroup.com Mixing Consoles • One of the most important parts of a PA system • Mixing boards have a set number of channels/inputs • Inputs on a mixer are commonly XLR and TRS (¼") • Responsible for combining sounds, routing, and changing the volume level, timbre (tone color), or dynamics of many different audio signals • Can provide phantom power, pan control on each channel, and monitoring mixes, for the stage monitors

7. www.channelaudiogroup.com Cabling • To connect the components of a PA system and transmit an audio signal, various cabling is required • PA speakers most commonly take one of three forms of cable: XLR, TRS, or Speakon • Mixers and amplifiers usually have main outputs and inputs of both XLR and TRS • Some amplifiers can have a form of RCA outputs called banana cabling • Using the correct cabling when setting up a PA is vitally important XLR TRS SPEAKON

8. www.channelaudiogroup.com Effects • An optional, yet common component of a typical PA system • Many modern mixers will have onboard effects • Effects paired with a PA system are usually outboard, meaning stand-alone units. Common effects paired with a PA system are: • Reverb • Compression • Delay • Gates • Equalizers

9. www.channelaudiogroup.com Sound Sources There are a variety of common sound sources for PA Systems depending on the application • The most common source is the sound from a microphone • Microphones also have a variety of uses and placements, ranging from vocal mics, instruments mics, and room mics • PA systems are also great at reproducing already recorded music • Music can be played through a PA system by feeding the sound through one or more channels on the mixer

10. www.channelaudiogroup.com Operation Operating even a simple PA system can be frustrating, although rewarding. • For small-scale events such as speeches, require little to no tweaking of the settings after soundcheck • For large-scale productions such as concerts, it is imperative that an engineer is present to mix the sound for the duration of the event • Due to the complex nature of music, vital changes to the PA systems sound are often required constantly • Those renting a PA system can often regret opting to forego hiring an engineer, as they find out quickly that their event’s sound required much more attention to detail