Constant-voltage audio systems, aka 70 volt systems

💬 Lounge
1

In case anyone is interested...

I was looking at ways to set up the speakers/sirens for an Elk M1 Gold (M1G) security panel in the house we are building. Drywall is going up really soon, so I had to make some decisions. In my previous house, the M1G drove a couple of speakers "strategically" located in the house. Note that the speakers are used for voice announcements and siren sounds. Since there were only two, they were at a pretty high volume so they could be heard throughout the house.

For this house, I wanted to have multiple speakers (at least eight) so they could be heard without being so loud. I have an M1G add-on board that is a three zone amplifier. Each zone puts out 1/2 watt and each zone has a volume control on the board. So that's what I'm working with on the M1G panel.

I decided that if I was having a speaker in every room, I should look at using the speakers for background music in addition to supporting the M1G voice announcements and siren. That led me to constant-voltage audio distribution systems, i.e., 70V systems...

https://en.wikipedia.org/wiki/Constant-voltage_speaker_system

These are the systems that are commonly used in restaurants, etc. to provide background music and voice announcements (via microphone). Most have a "priority" setting on one or more microphone inputs that cause the background music from other input sources to be lowered or muted when a signal is detected on the priority microphone. In my case, I wanted the background music, if playing, to be muted when the M1G was sending a voice announcement or siren signal.

To bench test it, I bought a 70V amplifier and a couple of 70V speakers. I hooked up a CD player and verified that the basic background music function worked, i.e., the CD played. The amp can also receive signals from a bluetooth device (e.g., iPhone), an SD card, or a USB drive. I tested bluetooth with an iPhone and that worked.

The final task was getting the amp to input a signal from the M1G via the MIC 1 input (the priority microphone input). The M1G signal I had to work with was the unbalanced speaker level signal from the three zone amplifier. Fortunately, the amp company sells a "converter" that can take an unbalanced monaural speaker level signal and turn it into an XLR microphone signal.

To test all of this, I connected the CD player to a small stereo amp I had in the miscellaneous drawer to get an unbalanced speaker level output. I connected one of the stereo amp's speaker output wires to a 1/4" TRS plug to get that signal into the converter and ran an XLR microphone cable from the converter to the MIC 1 input on the amp. Essentially, the CD player and small stereo amp were emulating the M1G. I started some background music from the iPhone. As soon as the CD player played music, the iPhone/bluetooth music was muted and only the CD player music came thru. When I stopped the CD player, the iPhone/bluetooth music was unmuted.

I still have some bench testing to do, but it looks like this setup will work. The 70V amp doesn't have any communications capabilities (no wifi, serial, etc.), so it won't be very "controllable" from HE. It does have a limited function IR remote that can probably be automated a little.

2 Likes
2

It's been a while since I've messed with 70 volt audio distribution. My experience is in schools. They work for their intended purpose. I'm not sure that reasonable audio quality is easily achievable. Here is an interesting and detailed read on 70 volt systems. High Voltage (70/100V) Audio

3

I agree that the audio quality won't be great, especially compared to a decent "regular" home stereo system, but so far it seems okay. I connected an 8-ohm bookshelf speaker to it (the amp allows 8-ohm speakers or 70V speakers on a given output, but not both), and it sounded pretty good. No distortion and wasn't "muddled". My plan is to have one 6" ceiling speaker in each room/area. The amp sums the stereo input on a channel and presents it as monaural audio, so no stereo imaging. I think the audio quality will be fine as long as it's background music and nobody is listening to it as they would if they were listening to a high quality stereo or home theater system.

Second round of bench testing went well. This time, I brought in the M1G audio (voice announcements). While background music was playing, I triggered some M1G announcements, and it worked as hoped. When the amp sensed the M1G signal, it immediately muted the background music until the voice announcement completed, then it came back on. The muting was fast enough that the background music stopped before the first word of the M1G announcement. I can have the background music playing at a low volume and the M1G announcements playing at a high volume when they occur.

There's a lot of fine tuning to be done. Each input has gain, volume, high tone, and low tone controls. Each output has volume, high tone, mid tone, and low tone controls. The speaker level to mic level converter (seller calls it a "passive DI box") has a 3-position input attenuation switch. The M1G amplifier has a volume control. Speaker quality will certainly be a consideration. All that will have to wait until the house is ready for move in.

Looks like this solution is a keeper. Time to box it up until move in.

1 Like