Telecoil and EMI Noise - Any Other Telecoil Users Experience EMI Noise Like This?

Hearing Aids
#1

I found a surprising source of EMI (electromagnetic interference) with my ReSound Omnia telecoils: an Energizer LED headlamp.

I normally don’t use telecoil at all. But in going to see the movie Oppenheimer, in part as just a spectacle of sound and sight in IMAX 70 mm film format, I wanted to have some assistive listening available. So I set up the telecoil program for my Omnias.

Lots of times, because a summer day in Texas is a blazing inferno with scorching UV, I’m checking out my sprinkler system in the cooler dark of night by running around with an LED headlamp on.

From fooling around with my program settings, I happened to be in the telecoil program for my ReSound Omnias when I turned on the white beam of my Energizer headlamp. I was greeted with a tremendous amount of “electrostatic” noise. Curiously, the night vision saver options for a red or a green beam did not cause EMI (they have a much lower LED power output). I haven’t looked yet to see if Energizer has any FCC compliance info for the model headlamp I was using. But I was surprised at both the amount of EMI the device is apparently allowed to put out and the susceptibility of the telecoil to EMI. I have a bunch of electronic devices inside my house that produce sound (Amazon Echo and Google Home devices, computers, smartphones, etc.), and I’ve worn my headlamp for various reasons inside my house, e.g., to see into very dark recesses, and never experienced the headlamp EMI with anything else.

I wonder if anyone with any other brand of HA or with other EMI sources has ever experienced such annoying EMI? Made me think that telecoil really belongs in the dustbin of history. Bring on Bluetooth Low-Energy Audio! (I don’t experience BT interference with the same headlamp and the telecoil program NOT running)…

#3

Jim,

I don’t have telecoil in my Oticon aids so I can’t test with my LED headlamp and flashlights so the following is an educated guess.

Typical LED drivers use pulse width modulation (PWM) to adjust the brightness level. So the LED is pulsed on/off at some frequency where the duty cycle is varied to adjust the brightness. I expect your headlamp is plastic so probably not shielded so your aids in telecoil mode are picking up either the fundamental driver frequency and possibly harmonics for the white LED driver. Better LED drivers (new cellphones, high quality LED lamps, etc) operate at frequencies above what we can hear and are better shielded but who knows with a headlamp or flashlight. If you take the headlamp off and set it down and walk away from it, does the interference in your aids in telecoil mode decrease with distance? The much lower power red and green LEDs are possibly run at full power so not using PWM hence no interference.

Good luck with your new science experiment - reminds me of many weeks of chasing down interference sources in an optics lab :wink:

1 Like
#4

News flash! There is likely a simpler explanation than LED pulse width modulation directly from the LEDs themselves.

When I put on the headlamp to try it again, I noticed all the EMI noise was in the right ear. The headlamp in question is an Energizer Hardcase Professional Headlamp bought in 2014. It has a battery pack mounted at the back of the headband that takes three AA batteries, and a WIRE runs around the right side of the headband to the LED lenses in the headlamp in the front. The EMI appears to be EM leakage from the current in the wire. If I rotate the headlamp band 180 degrees on my head so the battery pack is now in the front and the LED lamps are in the back and the wire runs right by my left ear, I hear the EMI in my left ear and not my right. The wire, when it comes out of the battery pack, is coiled in a pigtail, too, going through eight 360 degrees loops to provide tensioned slack in the wire to allow for adjustment in the headband for different head sizes.

Perhaps if PWM is involved, it’s showing up most significantly in the current flowing to the wire, and the wire pigtail forms an EM coil that helps amplify the PWM signal (my physics knowledge is half a century in the past!). As soon as I take off the headlamp, the EMI stops. An Energizer headlamp that I bought in 2022 that has the whole works in the front headlamp, including the 3 AAA batteries, does not generate telecoil EMI interference.