Electrical interference from railway - solutions?

[Thebaz]

Bit of an off-beat question this, but I'm trying to get a sound system set up in one of the Bermondsey arches (just a simple amp and mic thing is the order of the day) but the sound set up we currently have suffers from random bursts of electrostatic noise from the railway above. Would anyone be able to suggest a way of immunising the kit we have or know what sort of frequencies we should avoid if we go down the route of selecting new gear?

 

[HSTEd]

Your best bet is to probably make sure you are using only balanced connections (XLR et al), try to use only shielded twisted pair cable wherever possible and keep your analogue connections (especially at line level) as short as possible.

If possible in future adopt digital audio distribution for as much of your signal path as you can.
But stay away from phono or similar if at all possible, balanced or digital to the max.

 

[Thebaz]

Great, thanks

 

[edwin_m]

If random bursts are less than about a second then they could be from arcing on the third rail, which is broad spectrum so likely to affect anything that doesn't have sufficient protection. Longer periods could be due to harmonics from electric traction return currents, but these will be at a single frequency that depends on train type and speed. Networker units will produce harmonics at audio frequencies (about 100-500Hz) and the more modern units with IGBT drives should be above 1kHz.

 

[Thebaz]

Interesting. The arch is on the northern side , so could be to do with Networkers. The bursts usually last between 1 and 3 seconds I'd say.

 

[dgl]

Use of star quad cable and Neutrik EMC XLR's can also help.

 

[HSTEd]

Great, thanks

To add to this, if you are doing live music or similar and have microphone connections, these are even more vulnerable than line-level audio systems.
If possible, move microphone preamps as close to the microphones as possible, then follow @dgl 's suggestions with regards cables.

Microphone cables are most susceptible, then line level connections, then speaker connections.

 

[dgl]

Also try to keep power cables away from audio cables, if the noise is being induced in the power cabling then keeping power and audio separate naturally keeps some of the noise away from where signals can be more vulnerable.

 

[RichardAsh1981]

To state the obvious, try hard not to use any radio links (radio mics, in ear monitors) as they are another route to being interfered with by arcing (which produces wide-band RF). If you have to have wireless, consider the Line6 2.4GHz digital kit or similar - higher frequencies don't go through masonry very well, and they have a lot of digital redundancy built in to them (but not cheap).