Overhead Paging
Why do some paging systems work fantastically, some are sporadic and others…well, let’s just say they are at the other end of the spectrum. It’s all in the design and execution.
The early days of overhead office paging were like the Wild West. Most project managers new nothing, or very little about the science of paging. You have speakers, an amplifier and hook everything together with telephone wire. Presto, you have a paging system…that typically took longer to balance than it did to install. But that’s the way it was done.
The equipment manufacturers like Bogen, Valcom, Viking and TOA didn’t pay electrical engineers to design something that worked on telephone wire. If it’s designed properly, then it goes in easy, correctly and can be balanced in short order. How do we do this? There are generally 2 voltages that re used. There is a 70v system and a 25v system. Today we will focus on the 70v system with non-powered speakers. It all starts with a floor plan. You first need to see where you need the coverage. You need to take into account ceiling height, wall construction ,environment, floor covering and noise level, just to name a few. Just because you ceiling is higher doesn’t mean you need more speakers. It can actually be just the opposite. You can get a larger coverage area from a higher speaker than with a lower one, depending on the environment.
OK. You have a design layout on the floor plan. The next step is, are you going to have multiple zones, like the warehouse only, separated by departments or by floor? Now you can design how to connect everything. All your zones need to be wired separately. We call these legs. A rule of thumb is to have no more than 14 devices per leg. You can have as many legs as you need per zone, and as many zones as the project dictates. All devices on each leg are wired in parallel. The best way to connect each device is to have a single lead connecting from the leg to the device, so should there be a problem; the only device affected is the trouble one.
Now that your layout is complete, you need to figure out what you need for electronics to drive them. A rule of thumb is to allow 4 watts per speaker and 8 watts per single horn. Add all these up and that will be the approximate wattage that will be used on every page. You want to get an amplifier that will cover this plus an additional 30%. If you have to add anything, you don’t want a maxed out amplifier. If you need to, you can have multiple amplifiers and link them together.
If you are going to have a single zone, then all you need to do is to connect the speaker legs to the output of the amplifier. If you have multiple legs it is easier and cleaner to terminate all the legs on a screw terminal strip and have a single connection going to the amplifier. It is also easier to put spade tips on the wires. A single zone system is also the only system we recommend using a microphone as opposed to telephone access. You then connect either your microphone cable, which should be a 4 conductor 16AWG stranded shielded cable, to the microphone input of the amplifier, or connect your PBX analog paging port to the input of the amplifier.
For multiple zone systems, you can use separate amplifiers for each zone with a distinct trunk or paging port from the PBX for each zone. Then all the amplifiers would be linked together with an all-call port. Another option would be to use a paging zone controller. This allows you to access multiple zones through a single amplifier using telephone access. Each zone’s PBX port would be connected to the zone controller, with the all call connecting also. Each zone would be terminated separately on a terminal strip, and then a connection to the amplifier. The larger your system is, the more you need to take into account, like power, cable size for distance, just to name a couple. For this scenario, we will keep it a simple, one closet system without any additional power requirements.
You now have your design separated by zones and legs. If you number your legs and the devices on the legs, your documentation is easy to manage. To wire them you need the right wire. You want to get an 18AWG stranded 4 conductor wire at a minimum. You only need 2 conductors for each device. This will allow you 2 spare conductors in the cable should anything happen to one being used. When you run the legs, leave a coil at each speaker location and tie the speaker in with a jumper.
You have to “balance” the system after is up and running. This can either go easy, or be the most difficult part of the project. By balancing the system, we mean that the volume of each speaker is not overpowering and the output is clear and audible. There are 2 devices you can incorporate into the design that will make this portion much easier. The first is installing volume controlled speakers. This will allow each individual speaker to be controlled. But beware. Install the speakers with recessed controls as opposed to easily accessible control knobs. The people in the area are less likely to play with the volume if you do. The other device is a volume control that can be hooked up to an entire leg. This way the volume can be adjusted on all devices attached to it together, especially if they are in a high noise area. We suggest these devices because once you have the main controls on the amplifier set, you really don’t want to mess with them because at that point you are adjusting the entire system and can through everything out of whack. If you are in a facility with multiple shifts, we’ve found that if you get a sign off from the customer on volume levels and people are complaining, the call back won’t affect the original labor estimate.
Now that you’re up and running and everyone is happy, the last thing you need is your close out documentation. This includes pictures, decibel readings (if requested) and as built drawings. If you have distinctly labeled your legs, Leg 1, Leg 2, etc and you know your speaker sequence, 01, 02, etc, your as built drawings should be clean with the speaker numbers, 1-01, 1-02, 2-09, 2-12, etc. Post this drawing in the wiring closet and email it to your customer. Your speakers should also be labeled.
Installing an overhead paging system isn’t difficult. Planning, customer involvement and product knowledge will get the job done every time.
Until next time…
