by Neil Bauman, Ph.D.
When she set her hearing aids to t-coil mode, a lady had trouble with interference when using her phone around florescent lights. She wrote:
The florescent light is in my kitchen is an old fixture, but I also tried the new florescent bulbs that screw into a regular light socket in the ceiling fan I have in the kitchen, and I would have to leave the kitchen to talk at all on the phone. As soon as I switched the light bulbs back to the regular ones, the noise quit (except when I stand near the sink where the old fixture is located above the sink.) The old kitchen fixture still causes a buzzing noise in my hearing aids.
What you have discovered is one of the few problems when using t- coils—they are subject to interference from stray magnetic fields. This stray magnetic field is typically caused by the alternating current in your house wiring. You hear this 60 cycle A/C as a loud humming or buzzing sound.
Certain electrical fixtures and appliances cause a lot of interference. Florescent lights, particularly older fixtures, are one of the culprits. Sometimes just changing the old ballast for a new one largely eliminates the problem. Other than that, just moving a few feet away often reduces the interference to a low level.
Another source of interference are TVs and computer monitors that use CRT tubes. Again, just moving back 3 feet or so generally reduces the interference to a very low level. (Note: flat screen LCD TVs and computer monitors do not cause this kind of interference.)