If you go downtown you're likely to hear a variety of announcements broadcast from shops and other facilities. The sound systems that broadcast the information you're hearing have been carefully designed and installed to suit the needs of each individual facility... or at least, they should have been.

You've probably heard the term "PA system" used to describe a sound system that is used to deliver speech, music, or other content to an audience. "PA" stands for "public address," which is really just another way of saying "public announcements," which is precisely the type of application we're going to discuss in this section. Sound systems that are used primarily for music or other content that is not announcements are more appropriately referred to as "sound reinforcement systems."

Of course it's possible to make announcements without using a PA system, but if the announcements need to cover a large area or multiple rooms, and/or if your audience is large, simply speaking in a loud voice becomes impractical. The basic rule is that a PA system is required if any part of the audience is more than seven meters away from the source (i.e. the person making the announcement).

If you're in a large store or mall you might hear announcements that bring store events or lost children to your attention. At the train station announcements might provide schedule or track number information, or warnings when a train is approaching. A significant amount of the information we receive when out and about is received in the form of audible announcements. Some of those announcements, such as those for bargain sales, for example, might only be of interest to a small number of people, but announcements that involve safety or public order are important to everyone. People who are struggling with a visual impairment are particularly dependent on audible information. In such cases it is important to design a sound system that is optimally suited to broadcasting announcements in order to contribute to a safe, secure environment.

What are the most important points to consider when designing a sound system that will be used for announcements? The first thing to consider is sound quality. Distorted sound or sound that breaks up will only make announcements difficult to understand. Older people or people who have suffered some hearing loss will have a particularly difficult time understanding what is being said. Sound quality is largely dependent on the quality and performance of the system, so it makes sense to purchase high-quality equipment. But in most cases just acquiring the best equipment is not enough. The acoustic environment must be taken into consideration as well. A room that is prone to sounding boomy, for example, will sound boomy regardless of the quality of the sound system used unless the sound system is designed to compensate accordingly. Controllability is another important issue. For example, in a store in which the customer traffic varies greatly throughout the day, the amount of background noise caused by people talking and walking will vary accordingly. If the volume of the announcements can't be adjusted to match the background noise level, the announcements can become inaudible during peak periods. Conversely, the sound system might be too loud during quiet periods. At facilities where background music is played through the sound system, it is necessary to be able to lower the volume of the background when an announcement is to be made. Recent advances in sound equipment design have made many of these operations easy or even automatic, and such features should be kept in mind when choosing equipment.

(Figure: Unless the system is properly designed and set up for the application and environment, even the highest-quality equipment will not deliver intelligible sound.)

We've learned that high-quality sound equipment alone is not a guarantee of high-quality sound in every environment and application. This does not apply only to announcements, but to every other sound system application as well. The sound system must be specifically designed for the application if optimum performance is to be achieved. In the next section we'll take a look at systems designed for background music.