Automation, Smart Home, complex lighting networks and on top of that PA systems - considering all the different technologies, which are integrated into buildings nowadays, it is understandable and logical that not all electricians are familiar with every niche. At MONACOR our experts are able to support installers and also planners in any project imaginable. Therefore, we compiled here useful knowledge for PA projects.
This article will show you:
- How easy it is to enter the field of PA applications for electricians and installers, thanks to the 100 V line technique
- A sensible approach to PA projects: requirement analysis, defining zones, determining required amplifier output power
- How the distance of speakers to people influences the volume: each doubling of the distance to the sound source reduces the sound pressure by 6 dB
Are you an electrician, a radio and television technician, career changer or stage mechanic? It is not hard to understand the concept of Public Address. Basically, you have 2 components, special 100 V speakers and respective amplifiers. You simply add up the power ratings (watts) of all connected speakers and select an amplifier which provides at least that amount of power in watts. You can use thin cables and connect speakers over large distances with the same connection without risk of line loss and performance loss. Inhibitions to delve into a new field of technology are often high, yet with PA technology they are unwarranted.
The first thing to do when working on a PA project is analysing what the user of the system wants. What do they want to realise now and how much potential for later expansion of the system is required? Discuss with the system's user if the PA system has to grow with the object or if it is louder in summer than in winter, e.g. when the beer garden in front of the house is packed. An open conversation with the user about day to day operation is absolutely necessary. Only owners or tenants know how loud guests, surroundings and other conditions are.
Ground rule: The sound from the PA system reaching the ear should be 10 dB louder than the environment volume. Thus, the PA signal clearly stands out from the ambient noise.
Though zones in PA applications are not always the same as rooms, they often are: dining room A, dining room B, function room, restroom area, outdoor area A. There is no rule as to how many square metres a zone should have. As installer and planner you should walk through the rooms methodically and write down individual zones. This only works with the future user. You get the most accurate impression while the room is used under real conditions. If that is not possible, it is worth asking more detailed questions:
- Is the room always used in the same way or does it have to be versatile?
- Are announcements, i.e. speech transmissions, planned?
- Which audio sources are planned? CD, MP3, USB; SD/MMC cards, Internet radio, DAB+ or FM radio?
Zones vary basically due to their requirements. Reasons for using several smaller zones instead of one big zone could be:
- The basic volume in operation without PA application varies: are some areas louder than others?
- The type of PA application: is music supposed to be noticeable or unobtrusive?
- Different audio signals in different areas or selective announcements in different areas
- Acoustics within a zone
Everything in a room causes a sound reduction and 'swallows' energy, including customers. Therefore, you have to decide how much power is required on a case-by-case basis.
Given volume conditions are relevant to determine the amplifier's power rating. Here are some basics on this topic: the sound pressure of a loudspeaker in decibels is measured at 1 Watt at a distance of 1 metre. To be more precise, the speaker gets 1 watt power via the amplifier and at a distance of 1 metre a sound level meter measures the sound pressure.
For example, if the speaker gets 1 watt of the amplifier, it will produce a sound pressure of 90 dB at a distance of 1 metre. It is supposed to be louder?
Raising the volume by 3 dB doubles the power requirement.
That means in this case you need 2 watts for 93 dB and for 96 dB 4 watts per speaker are required. We recommend planning amplifiers with power reserves in case you or the users wish to expand the PA system sometime in the future.
By the way, you do not have to measure the sound pressure of our speakers. We already did that for you.
Attention: sound pressure drops at bigger distances to the speaker
Each time the distance to the speaker is doubled, volume decreases by 6 dB. For example, at a distance of 1 metre the speaker provides 96 dB. At a distance of precisely 2 metres you can hear a sound pressure of 90 dB, at 4 metres 84 dB. That way you can estimate the volume which is required for guests who are farther from the sound source. To determine how close to the speakers guests are in different parts of the property can give guidance when you distribute speakers.
Even though requirements are individual, in some fields you can still rely on similar basic conditions. Typical fields are retail as well as educational establishments and workplaces.
Planning a PA system in retail
Whether it is a supermarket, DIY store, boutique, shop or gas station, planners and installers have to take especially the size of each store into account. However, there are some overall requirements all kinds of retail have in common:
Pleasant, usually rather calm background music; ceiling speakers are particularly adequate for this purpose. Stereo sound would be unsuitable as people move around inside the building and stereo sound from different directions would be pointless.
The option to make announcements via microphone anytime, in one or several places and with easy-to-use hardware
Ball speakers which direct the sound downwards are suitable for very large rooms with high ceilings
Different speaker zones, which can be controlled independently
The option for automated, timed and recurrent advertising announcements and informative announcements; for users, you can integrate this feature comfortably via a message and timer insertion
Planning a PA system for educational establishments and workplaces
In this area music is irrelevant, speech intelligibility has priority.
- High speech quality and clearly understandable announcements can be achieved with full range speakers
- Is the room very big, e.g. a lecture hall or a conference hall? Then column speakers are the right choice, as they provide very dynamic and detailed sound for speech and music.
- Do you need more bass? Use an additional subwoofer.
Certainly, there are even more things to consider regarding PA systems. However, we hope this practical knowledge inspires some ideas on how you can implement future projects even better and more efficient.
You do not specialise in PA projects but would like to enter this field? Your Project is Our Project. Therefore we compiled basic knowledge on 100 V line technique and on planning ceiling speakers for you.
Image source headergrafic: svetavo – stock.adobe.com