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What is a PA System? – You Have To Know!

Do you understand the difference between different sound systems? Ever wondered what makes them suitable for various applications? Whether you are a consumer or a professional audio engineer, it always helps to know the distinction between various amplification systems. Hence, today we will be asking another important question – What is a PA System?

Sound amplification systems are often seen as having the same purpose, in the eyes of most people. Thus, in this article, you will learn what sets the PA system apart from other entertainment or sound systems. Understand its basic functioning principle, and how it applies to various venues and situations. Now, let us not waste precious time, and start learning!

Horn Speaker

Photo by ŠJů / CC BY-SA 3.0

Introduction – Its Function

The public address system (simply referred to as PA System), is fundamentally an electronic sound distribution and amplification system which consists of transducers (microphones), amplifiers and loudspeakers. It is typically used by the operator to address large crowds in public, for instance, announcements of train arrival times at large rail terminals.

PA systems, at times, may also include an additional mixing console, together with power amplifiers and loudspeakers that are designed to be ideal for both music and speech. It can be utilized to amplify a sound source, such as music players or a person giving a speech, and then distributing the audio throughout a building or venue.

You can find PA systems installed in smaller sized venues such as campus auditoriums, small pubs and churches. The ones with multiple speakers are often used to make announcements at outdoor spaces and commercial establishments.

School PA

School PA system / Photo by Wikidenizen / CC BY 2.5

There are also “Intercom systems” (installed in certain buildings), that allows occupants of a room to respond to announcements via built-in microphones.

PA systems are often compared to sound reinforcement systems as both of them do share some similar components. However, it is generally understood among audio professionals that the two systems have different applications, although their distinction is not clear-cut. Sound reinforcement systems are for live concerts (often large-scale), and PA systems are typically for speech reproductions.

Let us look at the various topics we will be covering:

  • Small systems
  • Large systems
  • Live entertainment
  • Acoustic feedback

Small Systems

The most basic PA systems will include at least one microphone, an amplifier, and one or two loudspeakers. Simple and low powered systems are capable of providing 50 to 200 watts of power, and typically used in smaller venues such as pubs and school auditoriums. Sound sources such as Compact Disc players or radios can be patched to a PA system, for music playback purposes.

PA System Setup

Photo by TOPCHOICEDJSELECT / CC BY 3.0

Microphones are the primary source of sound input in PA systems, and are used for any sort of sound recording. There may also be a system in place, which allows the user, or an automated electronic equipment, to choose from a list of pre-recorded messages (or other audio recordings). These audio sources are transmitted to pre-amplifiers and signal routers that feeds the audio signal to the assigned zones.

Control Equipment

PA control equipment / Photo by Misternomer / CC BY 3.0

Ultimately, the pre-amplified signals are fed into the power amplifiers, which in turn, powers the loudspeakers. Depending on situational requirements, these amplifiers typically amplify the audio signals to 50V, 70V or 100V speaker line level. Amplifiers and speaker lines are monitored by control equipment for faults, before the audio signal reaches the loudspeakers.

This same control equipment is also engineered to be used for separating zones within a PA system. Take note that the equipment at the end of every PA system’s signal chain, will be a loudspeaker. This device is used to convert electrical audio signals into sound waves, which is then heard by the target audience.

Large Systems

Larger systems fundamentally follow the same operating principles of smaller PA systems. The most noticeable difference is that, larger systems have many loudspeakers that can provide audio coverage over an entire campus of an institution or industrial site, or even an entire outdoor facility (like a swimming complex). A large PA system is also often integrated into emergency systems (like fire alarm systems).

Live Entertainment

For smaller clubs, a very basic set-up is used, with large speakers and subwoofers positioned at the front of the stage (Front-of-House speakers), facing the audience. Smaller speakers (monitors) are then placed on stage, aimed towards the performers, to let them hear their vocals and instruments.

Large system

Photo by Joe Mabel / CC BY-SA 3.0

Often times, the Front of House speakers will be mounted on poles (tripods) or by “flying” them using anchors that are attached to the ceiling. The subwoofers will always stay on the ground level.  You may notice that in smaller pubs, the audio mixer is sometimes placed on stage for the performers to adjust their levels.

In larger pubs, the mixing console is usually positioned behind the audience seating area. This allows the sound engineer to have a better listening perspective on the overall sound. The levels for the monitor speakers may be controlled by the same sound engineer that is using the main mixing console, or they could be handled by another sound engineer using a separate mixing board.

Acoustic Feedback

Feedback Loop

Feedback Loop / Photo by Hyacinth / CC BY-SA 3.0

The problem of audio feedback can happen to any PA system. This occurs when sound produced by the speakers is captured by the microphone, goes through re-amplification, and then sent to the speakers again. It typically sounds like a loud high-pitched squeal or screech, and is often caused by an overall gain level (for the PA system) that is too high.

Audio feedback is never desirable in any live entertainment situation, as it causes an annoyance to audience and affects the overall “live show” experience negatively. Sound engineers often use tools such as graphic equalizers, parametric equalizers and notch filters in order to prevent feedback from occurring.

That is all I have for you today. I hope you can now make the distinction between various PA systems, and know when to use them appropriately!

Do leave a comment or question below, and share if you like!

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Farhan

When I'm not rocking out to great music, I'd prefer to be sleeping on a field on a windy day =)

7 Comments

  1. What an interesting article! I was involved for many years at school in music, rock music and guitars never knowing what are these sound toola that they put on the floor any time we are going live. It was a large entertainment system 🙂
    So cool, I had a goo d read and learned aot from you, thanks.
    I will know from now on what do to regarding music and live show – Id I will want to run a live one.

    • Hey there Alexey!

      Its good to know that you have found this article to be educational. Well, this is what the website is all about anyway. Feel free to drop by again any time!

      Thanks a lot!

  2. Hey, very nice overview of the PA systems. As a musician myself and an electronics engineer, this topic feels very relevant to me. There are a lot of feedback problems in the past and modern PA systems and this is an ongoing challenge that I believe will always exist, but we would only be able to tune it down and “filter” it, the more expensive the system the better it filters. It’s a good introduction to what PA is and the many different types available, well written and I wish you good luck!

    • Hi Elias!

      Every sound engineer dreams of a world without feedback. But unfortunately, this problem stresses out even the most experienced engineers out there. I am happy that an industry practitioner such as yourself, with electronics background, have found this article valuable.

      Thanks for your comments, and do visit again sometime!

  3. Hi Farhan
    Its so awesome to learn that there is actually a term for that “squealing” noise that is heard over the PA system at public functions, namely ‘audio feedback.’

    I learnt something new and thank you for that.

    I am sure at live concerts of big named musicians that they use more sophisticated equalizers to prevent this feedback,

    Do sound engineers also have to take into account whether the environment is closed or open when choosing the correct PA system, or can the same setup be used in both cases?

    Thanks for the lovely article.
    Regards
    Roopesh

    • Hello Roopesh!

      Fundamentally, every Graphic Equalizer does the same thing. There will be more expensive equalizers, but it all boils down to components and build quality.

      PA systems are generally chosen based on its power capacity. The larger the venue and the audience is, the more power is needed in order to amplify sound. In theory, yes, the same PA system can be used for both outdoors and indoor venues. However, the effectiveness of the system, will be dependent on the factors that I have mentioned.

      Thanks for dropping by. Do come back if you have any more questions!

  4. Thanks for explaining the different types of PA systems and their parts as well as how the levels of the monitor speakers can be controlled with the same sound engineer that is using the main mixing console. Knowing how the equipment works and who controls it would probably be important to make sure you can have everything set up properly and use the different parts whenever you need them. When choosing a PA system, you’d probably want to consider what it’s for and then look into the different brands and stores in order to get the right product for your event so that you get the best sound.

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