70V System Cabling Notes
Any of the regular speaker cable (PVC) types can be used for 70-Volt systems, but there are some exceptions:
- Since it is recommended that 70-Volt speaker cable be installed (pulled) inside conduit, you can use regular speaker cable most of the time.
- If the conduit is going underground, it is recommended to use a gel-filled / waterproof type of speaker cable. Keep in mind that there are some “Direct Bury” types of speaker cable that can be used “underground” without the need for conduit. You simply dig a small trench, run the cable in the trench and bury the cable.
- In 70-Volt systems smaller gauge speaker cables can be used, and cable runs can be longer.
- Plenum cable – Very Important: When running 70-Volt speaker cabling inside a building you should use a plenum type speaker cable because regular PVC type speaker cable will burn and is toxic. This is very important! You need to check your local building codes regarding 70-Volt Systems being installed inside a building. Inside a building means office areas, close quarters, classrooms – not large open spaces / buildings.
Use Non-Shielded, Twisted Pair Cable for 70-Volt System installations.
Speaker Cabling Installation Note:
In my experiences, I found that most mistakes were made when I tried to hurry things up. I wanted to install the system and get out of there. Time is money right! The worst feeling is when you’ve finished the installation and you start the initial testing, and you find issues. You have to now spend hours and hours troubleshooting something that could have been avoided. Take your time, verify connections as you go. Get it right the first time!
Cable Size / Length vs Power and dB Loss
When deciding on which speaker cables to use for your application you will need to consider the cables “gauge” and the “length” requirements. The chart below shows Cable sizes vs. Power and dB loss in the cable.
Let’s look at an example using the chart below:
- At 4-ohms / 18-gauge cable can be run 120 feet and will realize a 50% / 3dB loss on the line.
- At 8-ohms / 18-gauge cable can be run 235 feet and will realize a 50% / 3dB loss on the line.
- 70 Volt Systems have very high impedances, so at 70-Volts an 18-gauge cable can be run 5600 feet in order to realize a 50% / 3dB loss on the line. This is one of the main advantages of using a 70V system – being able to run a cable a couple hundred feet away and not realizing any significant loss on the speaker line.
- Reminder: The calculations in the chart below are not exact (only approximated for demonstration).
Looking at the chart above you can see that 70 Volt speaker lines have very little Power / dB loss over longer distances than those of 4-ohm or 8-ohm speaker line distances. This is one of the advantages of Constant Voltage Systems.
In my experience, we mainly used 70V systems since our installations were mostly on Rides / Large outdoor spaces. Ex: We would install 70V speakers every 8-10 feet all the way up a 200-foot lift, and it worked great every time.
