Fred Harding has written a good introductory article on 70 volt speakers for CEPro. At this moment there’s a link to it above the thread list here in the Custom Installers Forum. Someone please provide the link here: I’m writing on an iPad mini and don’t 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, it’s 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!

Fred’s article is brief but good and accurate. I’d 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! Stereo’s goal is to provide one “sweet spot” 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 can’t 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, it’s 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.

[Link: capitolsales.com]

Stereo is for smaller spaces unless the event needs stereo for effect, but only briefly. Large venues have areas where the 'other speaker' isn't audible at all, so achieving stereo in a way that doesn't screw it up for others is difficult.

There's also the perception that 70V sounds bad- it's can, but doesn't have to. I did an audio upgrade for a school gym system and used JBL Control 26D in-ceiling speakers, a Control SS2210 sub, Soundcraft EPM-8 mixer, Shure wireless mic and a Crown CDi1000 amp- if I could have replaced the back boxes, I would, because they weren't made for these speakers, or even the old Atlas speakers that I replaced. They were too shallow and the baffle had a gap at each end, but they were installed with conduit and the cables passed through most of them, so I put some strips of thin plywood over the gaps and used the original grills to cover them. Since the low end was cut off and they're about 24' from the floor, it wasn't as much of a problem as it would be if they were lower and used for full-range.

Everyone who I spoke with after it was done was happy with the sound, some were impressed- probably because the old system sounded like a pocket radio.

And I did speak with Fred when I was choosing the mixer- he was OK with the rest of the equipment choices.

My team did the Vail golf course a couple years back with JBL Pentdant speakers and Crown amps. We can get this room pretty rocking, especially when it is empty and we are the only ones there. :)

[Link: vailclubhouse.com]

Always check your local codes before bidding on one of these systems. Some jurisdictions require the speaker wire to be run in conduit which changes everything.

The one I updated had been installed in the '50s and it was up to code. That's the reason I couldn't easily change the boxes (I thought I mentioned that). The cable was actually shielded.

The guy who was there for my walk through said he wanted four big box speakers in the corners and I said that would be the last choice. He was a bit surprised, but I had been told about his idea before I even became involved and when I explained why, he understood. When he heard it for the first time, he raised his eyebrows and said "Wow!". I left some headroom, but limited the maximum output.

Thanks for the kind words. There will be a follow up with an examination of audio matrixes later this week.

Follow up article just landed.

[Link: cepro.com]

I have done a fair bit of 70V in commercial and landscape systems but Fred taught me the basics. I am going to be the a huge number of people got their first 70V education from Fred.