You probably know how to connect a speaker: Simply connect one two-wire cable from the amplifier to the speaker – done.
This is similar with industrial PA/GA systems, however, the approach is quite different here when considering the premise Safety and Reliability.
Cable break – What next?
What happens if the cable from the amplifier cabinet to the speaker lines breaks? The cable could probably be more than 1000 meters long for 100-V speaker systems. If speakers are only connected to just one cable, they may completely fail in the worst case, depending on the location of the failure. The main reasons for cable breaks are wear effects, cable works, or simply carelessness.
If speaker monitoring is available, the failure can be detected and a message is displayed. The failure can be indicated as break, short circuit, ground fault or as general impedance failure.
If cables are laid underground (burried cables), troubleshooting can sometimes be difficult and expensive. During this time, speaker zones may not be addressed and also warnings, alarms, and other information cannot be broadcasted via the PA/GA system, for example.
People are in danger – time is running out!
Here comes the solution!
You can improve the reliability of speaker wiring using the so-called loop wiring of speakers which is required for almost all offshore PA/GA systems today and will probably become the accepted standard in the near future.
Speaker loop wiring provides a second cable which is connected from the amplifier outputs to the speaker lines.
This way, several disadvantages of a single cable can be eliminated:
- The second cable route is laid separately from the first one to prevent that both cables will be damaged by a single incident.
- Feeding the speakers from both sides due to the parallel connection has the effect that the cable cross-section doubles and thus also the possible cable length.
- An interruption of the speaker line, no matter where, will not cause a failure.
Keep in mind that the speaker loop wiring cannot prevent the following: A short circuit will still lead to a failure of the corresponding speaker line.