Live Sound Can Be Dangerous
May 9, 2013
Deathcore metal band Emmure got a dose of live sound danger at their Moscow show Tuesday night. During their set, singer Frankie Palmeri got a strong electric shock which was delivered through the microphone, that took him straight to the ground. He is OK now, but the ended up having to cancel the rest of that show. You can check out the video of this here –
So what went wrong? There isn’t any official word on what caused the shock, but we can consider a few things.
First off, in America, the active voltage on most electrical outlets is 120V. In Russia, where this show happened, the devices run off 220V circuits, so that is a bit more of a substantial shock. Most music equipment runs on electricity, even dynamic mics, such as the SM58 seen in the video, will use a small amount of electricity to transfer the audio information from the mic capsule to the preamp.
Looking at a standard XLR cable, used for most microphones, you will notice three pins. This is similar to the electrical plug in the wall, where there is a hot, neutral and ground connection. Most of the electricity resides on the hot and neutral connections, and the ground is a safety design to balance any excess power and prevent shocks from happening.
In some cases, you may experience a “ground loop”. This occurs when there are too many grounds, or the grounds are incorrectly connected, and can result in a steady hum. In the US, that would be a 60Hz hum, since we us AC voltage that runs at that frequency. Russia runs at 50Hz, and also uses AC. This hum can become a bit of a problem, especially in a large PA setting, adding unwanted noise and load to the sound system. Most electronic and electrical devices have the possibility of a ground lift, which will disconnect the ground in order to prevent a ground loop from occurring.
There is a good chance that improper usage of a ground lift is what caused this to happen. There may have also been incorrect wiring in either the mic, the mic cable, or the preamp/distro box it was connected to. In some cases, I have seen people buy 3-prong to 2-prong adapters to work as a ground lift, or simply just pull out the ground pin from the connector itself. This is incredibly dangerous, and as we can see in the video above, accidents can certainly happen.
There is also speculation that perhaps there was phantom power applied to the mic. Phantom power is a 48V DC feed that is used to power most condenser microphones. While it is possible this was the culprit, it is highly unlikely. Even if that is the case, there must be some bad wiring in either the mic and/or the mic cable to cause this. While most dynamic mics don’t require phantom power, they do have built in transformers to prevent damage from occurring if phantom power is accidentally applied.
With all this in mind, this is why we have dedicated classes here at the Conservatory just for electronics and electrical troubleshooting. Today is in fact Troubleshooting day, with teachers Jim Bender and Terry Bussoletti going over information like AC versus DC, impedance, voltages and how circuits work, so that you as an audio engineer can run the safest shows possible!