EMI is normal and present in everyday life. EMI is caused naturally or from man-made sources, metal inherent in buildings (flooring, ceiling, structure), problems with electrical wiring, nearby electrical transformers, etc. – and has NOTHING to do with an assistive listening system.
Why is EMI important? Hearing loops and neckloops can pick up EMI and create a buzz or hum. Low and medium levels can be managed. However, higher EMI levels usually indicate a problem that cannot be corrected by the facility owner quickly. Sometimes an electrician or other expert consultant needs to be called by the building owner.
If the magnetic noise is between -22dB and -32dB, further investigation into the nature of the noise is required before an ALS can be installed. The background noise may sit outside of the frequency response of the hearing aid and therefore presents no problem. Or possibly, the background noise is due to an electrical fault, which, in any event, must be rectified. Univox (website)
« Back to Glossary Index“In most cases, EMI is caused by neutral-to-earth faults, defective water heaters or air-conditioning equipment, or electrical wiring that is not in compliance with the National Electrical Code (NEC). These issues are more common in older buildings and can typically be rectified by an experienced electrician with relative ease. If the guidelines of the NEC are observed—which is the case for basically every new building—and/or if ground fault interrupters (GFIs) are installed, EMI is almost never present to the extent that it compromises hearing loop performance.
Furthermore, an important consideration is that EMI is not only an issue for room (hearing) loops, but for any assistive listening system that utilizes the telecoil in a user’s hearing device. EMI affects telecoil performance on the user’s end and not hearing loop performance per se. Thus, neck loops used with IR or FM systems are equally affected by EMI. Therefore, it is important to ensure that a venue’s EMI levels are adequate prior to installing any of the three ALS options.”
Hearing Loops, The Preferred Assistive Listening Technology 2015.