A public address or PA system is a combination of a set of audio equipment that allows broadcasts over a designated area. Often found in schools and office buildings, PA systems can be used for announcements or emergency information and provide a simple way to get information out quickly. PA systems can be basic or advanced, and can be adapted to fit a variety of needs.

Basic PA systems are comprised of loudspeakers placed in convenient locations around the broadcasting area, an amplifier to increase the sound, and a mixer, which allows variation in sound levels. The user speaks into a microphone, and the sound is transmitted through connected cables to the area surrounding the speakers. Some systems also include microphones or intercoms near the speaker locations, allowing the listener to reply to the central location, although not to the entire system.

In school settings, the PA system is often used to broadcast daily announcements about school activities. It is frequently used in America to lead students in reciting the Pledge of Allegiance, and may be handed over to students to give reports or announce special events. The device can also be used as an emergency warning system. In case of fires, earthquakes or other natural disasters, the PA system may be the best way to instruct students and teachers on how to proceed. With the rise in school shootings since the 1990s, many schools have installed special emergency warnings through PA systems in the event of a violent attack on the school.

Large-scale PA systems are used to amplify sound for concerts or theater productions. Often called sound reinforcement or SR systems, these versions are much more complex than the simple ones found in schools and offices. SR systems frequently use a dual broadcast system, projecting the sound from the stage into the audience, and also into backstage monitors that keep any off-stage personnel informed of what is happening on stage. These systems may have dozens of microphones feeding into them, and may need several technicians to operate correctly.

A simple and portable PA system is still far from inexpensive, typically beginning at around $500 US dollars (USD.) This type of public announcement system will provide you with extremely limited broadcasting range, often only a single speaker. More advanced versions increase in price considerably, with $1000-$5000 USD easily within the normal range for a basic system, especially when considering the necessary cords and adaptors. Clearly, purchasing a PA system is a serious investment, and you should consider doing a lot of comparison shopping before deciding what to purchase.