Ask Rob: PA Design 101

In this edition of “Ask Rob” we are going to explore some of the key questions we need to answer when beginning the process of designing a PA (Public Address) System. During our last round of Ideal Connected training last year we focused on this area. During the training, we established that with a few simple questions we can choose the correct products suited to our customer requirements.

Like other categories in a commercial project, for example lighting and electrical, there can be many ways to interpret our client’s needs. If the right information is not gathered right from the start, we can
run into issues at the critical stages of a project. If we quickly establish our client’s true requirements right from the start, we can ensure that we provide a suitable and satisfactory outcome. When we answer the questions below, we can narrow down to which PA product is going to be fit for purpose.

1: Speech Only? BGM (Background Music)? Foreground Music?

The reason we ask this question early on is to establish what the customer expectations are for the performance of the system and what their main use is going to be. If the system is purely for paging and voice announcement only, we can explore using traditional horn speakers. Perfect for public transport, schools, sports grounds, warehouses, factories etc. Generally, this type of system will be 100v line.

If the customer requires BGM (Background Music) they are looking for something that they can playback music through with possible requirement of paging as well. The music playback is to create atmosphere and ambience but not a real focus point in a venue. In this situation we need to look at a speaker system that has a wider frequency response than the horn speakers to ensure we produce a more “musical” experience. BGM systems are typically found in cafes, restaurants, supermarkets, shopping centres etc. The BGM system can be 100v line system but sometimes low impedance depending on the size and budget.

When we mention a foreground system, we are talking about PA systems that are typically used in school halls, theatres, clubs/bars, churches etc. This type of system requires higher SPL (Sound Pressure Level) performance. In a BGM system the audio source is not the main focus, whereas in a foreground system the focal point is what is being produced by the PA. In a church the pastor or singers and musicians, on a dance floor in a bar the DJ or band, in a theatre the performers or a lecturer are all the focal points. We need to be able to produce a clear, musical sounding system that can provide power and volume to cover a venue. In most foreground system designs, we would use low impedance.

2: Types and numbers of inputs?

In our day to day audio systems there are two types of inputs – mic level (balanced) and line level (unbalanced). The key difference here is a mic output has a lower signal level output than a line level. On a mixer or mixer amplifier we have both mic or line level inputs. A microphone output is typically low output and the microphone input on the mixer is higher to bring the lower level of the mic input up to provide a good level of audio through to your speakers. The opposite applies for a line level signal which has a higher output and the line level input which is typically lower. Combining the two balances out to provide a clean, non-distorted signal. If you accidentally plugged a higher output line level signal into the higher-level mic input on a mixer you will overload the input and the result is a distorted outcome. Also, if you connect the microphone to a line level input you will get a very low output signal to your speakers. Therefore, it is important to always connect a mic signal to the mic input and the line level signal to the line level input only.

It is very important we know what type (mic or line) of input and how many are going into the system. This will help workout the requirements of the mixer amp.

3: Do we require Multizone or Single Zone Paging?

We ask this question to work out whether the client wants the ability to page into different zones independently. For example, if we had a supermarket that had four zones (main store, deli, backroom, offices) they may want to be able to page only into the backroom but not the other three zones. Or they may want to page into two zones simultaneously without disturbing the other two zones. This is what we call multizone paging.

A single zone paging system means that the page announcement would be broadcast to all areas simultaneously without the ability to segregate the announcement into different zones.

4: What is the size of the venue?

A simple question but a highly important one. We need to know the width, length and height of a space to start working out speaker placement. Also, speaker type will help ensure we achieve the best coverage and performance result. We need to also establish what is happening in the area. Is there very low background noise in the space or is the facility running heavy machinery that produces high levels of noise that the sound system will need to compete with. This helps with making sure we provide enough speakers, in the right place to provide the best result.

Now we have covered some of the key questions in Public Address System designs we can start piecing together the correct combination of audio sources, mixers or mixer amplifiers, amplifiers and speakers. Like all areas of our business, the more information we have the better equipped we are to provide a suitable solution! If you have any PA system design enquiries or questions, Ask Rob.