Thursday, March 8, 2012

70 Volt Systems

It's not every day you run into a constant voltage distributed system but in case you do I thought I'd write a quick post about it.  Here's a link to another article if you want to read more about the particulars, I'm just going to do a basic outline.


If you have a large building that you want to get audio circulating throughout, you're going to run into a problem almost right away.  Most amps are built to run just a couple of boxes per channel before they start to get stressed out.  So you can buy a huge rack of amps, or you can set up a distributed, constant voltage system.

In its simplest form you have a line coming from the back of your amp which is transformed up to a higher voltage (either internally or with an add-on box) and then you snake that line continuously out to all the places you want sound.  Everywhere you want a speaker you splice in a transformer, which allows the transmission line to maintain electrical properties that keep the amp happy, and let's the speaker take what it needs.  Most transformers will have multiple taps, for 70.7 volt or 50 or 25 on the input side, and then taps for different impedance speakers, as well as different wattages for the output.

All you have to do is keep track of how many watts you're tapping and as long as you don't exceed the spec of the amp you're in good shape.  Just don't expect it to be spectacular audio.  One of the downfalls of this type of system is that the audio pass band is usually pretty narrow, think telephone sounding, no lows, no super highs.  That saves some power and for the most part, these types of system are usually just feeding a live feed to dressing rooms, or background music to a waiting area, or announcements to a number of places.  If you need high quality sound in a lot of far flung places, the system can be designed to accomplish that, but it may be prohibitively expensive and there are other options. 

So I'll leave you with just one further thought.  If you ever wind up working on a system like this, make sure you don't just splice an 8 ohm speaker into the line.  You may not blow the system up immediately but you'll definitely be putting more stress on it than was intended and you're going to wear things out faster than need be.  In fact, do some serious studying before you attempt anything, it may sound simple on paper but it gets hectic pretty quick when you're on the top rung of a ladder with your head in the ceiling and your flashlight in your teeth, trying to figure out if it's the blue wire or the green wire that's a 5 watt feed.

Till next time...

No comments:

Post a Comment

You're the Scotty to our Kirk