This post assumes you have read our previous post on the difference between an 8 Ohm system and a 70.7V system. This post will give you the basics on how to design a simple, basic 70.7V system for paging and/or background music. Larger, more sophisticated systems require more expertise, and we will, of course, be happy to help you design systems of any size. Just give our experts a call at any time!
The first thing to understand is how a 70.7V speaker is comprised. The speaker itself is an 8 Ohm speaker, but on its side or inside the cabinet, if it is so built, there is a transformer. The transformer will take the signal from the amplifier – which is 70.7V and not 8 Ohm – and “transform” it to the 8 Ohm the speaker wants. This is also what is called a step-down transformer. You will note that the speaker has different possible settings or simply loose wires you are expected to connect to. In the case of loose wires, there will always be a negative, usually black, wire which will go back to the terminal on the amplifier marked common or simply “c.” Each one of the other wires corresponds to a specific setting measured in Watts, and the one you choose will go back to the positive or + terminal. (As you already know, all the speakers are wired on a loop). For example, a 10 Watt speaker would have a wire (let’s say blue) for 10W speaker output, another wire (let’s say green) for 5 Watt speaker output, and a third for 2.5 watts. This allows the installer to make slight changes to the speaker output of individual speakers while still allowing a certain volume output to be adjusted from the amplifier itself. Some 70.7V speakers are placed in a pre-existing enclosure, and all you have to do is connect to the two terminals available. The speaker output, also called the “tap-setting,” is then adjusted via a switch located somewhere on the speaker.
In selecting the right amplifier, it is important to calculate how many watts each speaker will demand from the amplifier and then calculate the total watts. For example, if we have 10 speakers each demanding (also called “drawing”) 10 Watts each, the total draw is 100W, and you would need at least a 100W amplifier. A good rule of thumb is to never go above 80% of the amplifier capabilities.
The right amplifier would, of course, also need to have the inputs you need for your different sources. In a background music system, you would need a player of some kind. Be aware that a commercial environment has to pay royalties to the musicians whose music they play. This is, of course, a complicated system of fees best handled by professionals, and many companies provide players where the business owner can choose a genre and pay for it monthly. The songs are also updated on a regular basis to avoid repetition. If you need advice, call us, we work with many such background music providers. A second input for a microphone is also desired if you plan on using the system for paging. Please note that microphones and audio players of any kind require different types of inputs, and you cannot simply connect a microphone to a music input.
Lastly, a note on Watts. You may note that 8 Ohm systems often mention a capability of hundreds of watts per speaker, and in our above example we used as little as 2.5 watts per speaker. Commercial speakers for background music and paging tend to be structured a little differently and do not require massive watts to be loud and clear, but this is a separate discussion for a future blog post.