Most everyone has heard of the concept of 70.7 volt distributed audio systems at some point. They are one of the most potentially confusing, easiest to screw up and yet most versatile wiring methods commonly used. This is the first of a multi part blog about how and when to implement a distributed audio system. The parts will be as follows.

• Part #1 - General overview
• Part #2 - Wire size, and how to know what size you need. Useful info even for impedance based systems.
• Part #3 - All things amplifiers. How to avoid overloads and potentially hazardous conditions, and how to decide how big of an amplifier you need. Also, other voltages other than 70.7 that are common.
• Part #4- Speak up! The ins and outs of loudspeakers, and some interfacing tricks that I think are cool. Also some helpful information regarding size, type, quality and location of speakers.  A look at how the transformers themselves can affect audio quality.
• Part #5 - Practical uses. When this can be especially helpful, including "mixed" systems using a hierarchy of impedance, line level and distributed topologies.
• Part #6 - Other interesting information about this concept.   

So, here goes with part #1:

Basically, you have an amplifier that outputs a higher voltage. Each loudspeaker has a transformer mounted to it that reduces the voltage to a level that matches the requirements of the speakers. The benefits are that smaller cable can be used, and a higher number of loudspeakers can be connected to a single amplifier or amplifier channel. The smaller wire is easier to work with, and costs less than the larger wire that would be required for impedance based systems.

It's the same concept that the "power company" uses to get AC power into buildings. Chances are the nearest power plant really isn't near at all. A very, very high (usually a measure of thousands of volts) voltage leaves the power plant and is distributed to various sub-stations along the way. As you get farther away from the power plant and closer to customers, the wire gets bigger, voltage is decreased, and current flow increases. This is a very broad overview - and there are many steps involved with this process. I'll run a blog series later detailing all things electrical. Furthermore, a grid system is employed to ensure that even if one power station or other component malfunctions, power will still end up where it needs to be.

It's a known fact that high current causes loss in wiring. As voltage is increased, current is decreased. In order for your home or business to receive line voltage directly from its point of generation, conductors large enough to deliver the required current would be of prohibitive size and cost. It just simply wouldn't be an option. The solution is to step up voltage, reduce current, and transmit electricity across smaller wires without inefficient losses. It is necessary, then, for each customer to have a step down transformer. In neighborhoods, these are usually, if not always, shared among multiple houses. In commercial applications, businesses commonly have their own step-down transformer. These reduce the voltage to levels that are commonly found in these applications. 120/240 volts for residential, 120/208volts for commercial, and in different phase configurations. This will be the subject of another post at a later time in a different series.

Wiring a distributed sound system is the same concept. You have a higher voltage leaving your amplifier, and speakers are equipped with a transformer to reduce the voltage to that which is required. Typical PA system transformers have "wattage taps" These taps are used to set how much electricity from the amplifier is reduced in voltage and delivered to the loudspeaker.  A higher wattage tap means that more electricity flows, and the speaker will be louder. This is especially useful when one amplifier is to power many areas. For example, a hotel lobby with two bathrooms. The lobby will need to be louder than the bathrooms, so, the lobby speakers would have their taps set higher. The end result is a very economical way of achieving different levels within the same system. I'll continue to use this hotel example throughout upcoming posts. Check back for Myths and Legends, part 2. Distributed audio systems simplified: wire size. Thanks for reading!