NOTE: Much of my writing published here has taken a broad look at the industry and with a fairly philosophical tone. Other posts have been super geeky and designed for industry technical peers. This one is a very basic intro to an AV topic. If you have much experience in the technical side of production, you probably already know this, but if you’re less confident in your understanding of audio technology, or are just getting started in the events industry, you might check it out. I break down the very basic building blocks of a Public Address system. If it’s not your jam, feel free to gloss over. Even if this isn’t your cup of tea, I hope you’ll come back to see my future writings - I’ll be jumping between tech-heavy and more general postings.
The Basics of a Public Address System
I recently received a message from a long-time client asking for help understanding how to amplify voices at a socially-distanced, outdoor event. They knew they because their very small audience was all separated from each other and from the presenters that they needed microphones for their event, but were unsure how all the pieces worked together. This article came out of offering one client some basic help understanding how the pieces of an event sound system (often called a “Public Address” or “PA” system) fit together.
In general the basic components of a public address system are the microphone(s), the mixer, the amplifier, and the speakers. Sometimes one or more of these components are combined in all-in-one units.
Microphones
In terms of microphones, a very common live sound microphone (in fact probably the most popular / famous mic in the world) is the Shure SM58. A microphone is a transducer that takes the physical sounds of your voice (or a musical instrument) and turns it into electrical energy, which is carried over a wire to the rest of the system.
Wireless microphones have two more parts - the transmitter, and the receiver. The transmitter has the microphone element attached to it, and that picks up the sound from the person speaking, and the transmitter converts the electrical energy from the mic element into radio waves. The receiver turns those radio waves back into an electrical signal that connects to your mixer. You can think of a wireless microphone transmitter as a tiny radio station, to which the receiver is “listening.”
Wireless microphone transmitters typically come in either a Hand-Held form factor, which can be held or placed into a stand, or a “Body Pack” form factor that is designed to be clipped to the belt and used with a lapel microphone or a headset microphone.
Because wireless microphones use radio frequency to transmit sound, they offer different "channels" which adjust the frequency each mic is using. The transmitter and the receiver need to be on the same channel to work, just like you have to have your car radio on the correct frequency to hear your favorite FM station. If another microphone, or a local TV station, or a walkie talkie, or any other device uses an overlapping frequency, the mic will get radio interference, causing dropouts or unpleasant noises. There is a whole science to frequency coordination, but a great start is to use the “scan frequencies” function on your microphone system to find available channels in your area.
Many new wireless microphones use digital encoding to provide high-quality audio over minimal radio bandwidth, but the basic principles above still apply.
Mixers
The next component of the sound system is the mixer. Mixers take multiple audio signals and “mix” them together, allowing the operator to change the relative volumes of the inputs and adjust aspects of the sound from each one.
Mixers can come with as few as 2 up to 70+ inputs, and come in various feature sets. To use 4 microphones with one PA you would need a mixer with 4 microphone inputs, and to mix an arena rock concert, you probably need a much bigger mixer.
Small, low channel-count mixers are usually analog devices that manipulate the sound with physical electronic components. Larger, higher-channel count mixers are often digital, encoding the audio into a digital signal and using digital signal processing to manipulate and mix the signals. This approach gives a great deal of control over the audio when working with complex systems.
Amplifier and Speakers
The mixer connects to the amplifier, which raises the amplitude of the audio signal high enough to physically move the speaker drivers, and then to the speakers, which are transducers that physically reproduce the electrical signals as sound waves.
Some mixers have built in amps (amplified or “powered” mixers) and some speakers have built in amplifiers (“active” or “powered” speakers). Depending on the configuration, you may be able to connect your mixer directly to your speakers, because the amplifier is built into one or the other.
NOTE: You should not cannot connect the output of an amplifier or amplified mixer to the input of a powered or active speaker - make sure you are connecting the appropriate kind of equipment.
There are also many all-in-one PA systems, some with batteries, that have built in wireless mics, mixers, and amplifiers. These are super useful for small events and events in unique or challenging locations that may not have available electrical power. Note that most will only work with a limited number of inputs and may have somewhat limited output power due to the limitations of the battery.
Connecting it All Together
Once you have all the components, you can connect them together. You will use several different kinds of cables to connect your system together. Make sure components are all connected while they are powered off, and then when you power them on, turn them on in the direction of signal flow. That is, Sources, then Mixer, then Amps. When powering down, turn off the power in the opposite order - Amps, then Mixer, then Sources. This helps avoid unwanted pops and noises that can occur during power up and down.
For most events, your AV provider will be using a fairly complex sound and video system, with multiple types of speakers, electronic mixing and routing controls and several trained operators, but even the biggest audio rigs for arena rock tours are combinations of these basic parts.
So now you have the basics of a PA system.
Tim Kerbavaz (he/him) is the founder and Technical Director of Talon Entertainment Audio Visual as well as a freelance Technical Producer with over a decade in corporate event production after an early career in live music production management. As both a live event technology professional and a creative geek, Tim serves as an event technology sherpa, guiding clients through production and technology decision making and delivering events to production bliss.