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Conventional or 70V Commercial Speaker Systems: Which is the right choice?

Many small venues such as bars, restaurants, schools, and churches use a commercial speaker wiring format known as 70V. This wiring format has a higher signal voltage that allows for many advantages. Let's take a look at the differences, how it works, and how to decide which format is best for your application.

A conventional speaker system has one or more speakers that typically have an impedance of 8 Ohms, but 4, and 16 Ohm speakers are common as well. The impedance is similar to resistance, and can be used to determine how much load a speaker will put on an amplifier. A quality amplifier will list what the allowed range of load impedance is and what the maximum output will be at various loads. For example, an amplifier may list that it can handle speaker configurations between 4 and 16 Ohms. Hooking up any speaker configuration that places a load that is outside this range can cause damage to the amplifier.

The amplifier in our example states that its maximum output will be 200 Watts at an 8-Ohm load and 600 Watts at a 4-Ohm load. As you can see, by increasing the load from 8 Ohms to 4 Ohms (a smaller Ohms value equates to a higher load, as it indicates less resistance) the amplifier max output went from 200W to 600W. This illustrates how a load even just slightly higher than the specified range can work the amplifier much harder then intended.

Speakers can be wired in series, parallel, or mixtures of both to allow for many different combinations that will result in the desired load impedance. The more speakers that you want to incorporate into your system, the more complex you wiring configuration may become. Also, if a speaker were to become disconnected or shorted accidently, the amplifier may become overloaded and damaged.

A 70V speaker configuration simplifies this problem significantly. The 70V system works by using a transformer after the amplifier to step up the signal voltage. Another transformer is used at each speaker to step the voltage back down to conventional speaker levels. The higher voltage system is much less sensitive to small changes in impedance. The transformers at each speaker typically have multiple lugs that are labeled at the wattage they will draw from the amplifier. Any number and combination of speakers can be added to the circuit, so long as the total wattage draw from the amplifier does not exceed the stated max 70V wattage load. If a speaker is connected or disconnected, it will not throw of the impedance balance of the reset of the network, like can happen with conventional speaker voltages.

Another great advantage to the 70V speaker system is that it allows for longer wiring runs and the use of smaller gauge speaker wire. This is because the higher voltage from the step-up transformer also translates to less current and as a result less power loss over longer lengths of wire. This is similar to why the electric power utilities use step-up transformers and run the power long distances over high tension power lines and then uses step-down transformers at the power poles right before they enter a consumer's home.

One more advantage to a 70V system is in cases where you want to have separate volume controls at each speaker, in a multi-room setup for example. You can purchase 70V volume controls that are placed directly before a speaker's step-down transformer. These volumes controls are much more reliable and safer for your amplifier then their conventional speaker level counterparts.

So how do you decide which setup is best for you? The more speakers you want to use on a single amplifier channel, the stronger the argument for a 70V system. Other factors, such as very long runs of speaker wire also will support the case for a 70V system. Generally any single channel that needs 5 or more speakers, or has speaker runs over 75 feet may be better served with a 70V system. System's with only one or two speakers per channel, such as in a typical home theater setup, a 70V system offers few advantages and would add cost and complexity.

Posted by Mark at 21:02
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