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!
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.
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
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.
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.
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.
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).
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.
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.
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!
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