Fred Harding has written a good introductory article on 70 volt speakers for CEPro. At this moment thereís a link to it above the thread list here in the Custom Installers Forum. Someone please provide the link here: Iím writing on an iPad mini and donít know how to get it.
Most of us, at some point, consider using or have to use a 70 volt setup to make things work. Even if you only do two channel high end audio, itís worth your while to understand the totally different approach to multiple speakers and large rooms that is 70 volt. It ALWAYS pays to know more about your general subject than just what is required for your day to day work!
Fredís article is brief but good and accurate. Iíd like to add an answer to the first question that people ask when talking about 70 volt systems: why are they usually mono?
70 volt systems are excellent for evenly filling large or oddly shaped spaces. Restaurants come to mind, but some stadiums use it, too! Stereoís goal is to provide one ďsweet spotĒ in a space with a three dimensional sound image. (Successful surround does that, too.)
You can use the different 70 volt power taps to put a little more sound, or a little less, here or there. Unlike in a stereo space, there are no seats where you canít hear the other channel. Stereo amps are based on 8 ohm or 4 ohm loads, so the number of speakers you can have is limited and must be deployed in matched numbers. With 70 volt, if you have 12 speakers and must add a 13th, itís no big deal, especially if your initial design was properly conservative!
Look up how to connect balanced and unbalanced sources to balanced inputs. Learn the correct way to mix the two channels of a stereo source into one. You have a powerful tool at your disposal when you understand 70 volt systems.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. ďBernieĒ Shaw