It is often thought that you need to purchase a shielded room in order to record EEG and ERP data. Shielded rooms or "Faraday cages" provide insulation from electromagnetic signals. However, much electrical noise can be eliminated using proper recording practices.
Setting up the room to minimize electrical noise
With the EGI system you can record from 0.01Hz to 400Hz. This includes the mains power frequencies of 60 or 50 Hz. Minimize mains power noise on your EEG signal by following these steps:
- Make sure that the electrode is in contact with the scalp.
- Keep your power cables neat. They should not form loops nor should they run next to your subject.
- Connect EEG equipment and any other equipment in the subject area into outlets with an earth ground.
- Microphones, speakers, floor lamps etc. can be sources of unnecessary noise. Make sure than any extra equipment you add into the subject room is electrically quiet. If you are unsure about any piece of equipment, you can purchase a probe to test for EM signals.
If, after following the above steps, you have any 60/50Hz noise that you would like to remove, you can use our Net Station Digital 60/50Hz Notch Filter.
Why we recommend that you do not purchase a shielded room
All too often the benefits of this expensive facility are nullified by placing electrical equipment directly into the shielded room. Placing the amplifier, monitor, video monitoring system, etc. into the room introduces 60/50Hz noise back into your clean environment.
When a shielded room is necessary
- If your lab is near a broad spectrum emitter (i.e equipment that transmits multiple frequencies under 400Hz), radio tower, mobile phone transmitter or other large field generators, then you should consider a shielded room.
- If your research is in the gamma band and you do not want to use a 60/50Hz notch filter to remove mains power noise, you might consider a shielded room. We recommend taking the steps above to first minimize the mains power noise. If that is not sufficient for your needs, then a shielded room may help.
Sound proofing the room
A sound booth helps isolate your subject from background noise distractions. Alternatively, you can take steps to reduce ambient noise by using in ear headphones with good sound attenuation.
We hope the above information helps your group to evaluate your new facility plans. If you have any questions contact your EGI sales or support representative.
