Hearing Aid Interference

[Steve Thornton]

I have a user who uses a T-coil hearing aid, which works with a special phone. But she's getting a terrible buzzing interference from her CPU. I haven't tested it with anything -- I don't have an EMF meter -- but it's not coming from her monitor (it's still there when the monitor is powered off), and it goes away when she steps about six feet away from the unit.

Her office is really, really cramped, though (it's a poverty-stricken food bank), so options for moving it further away are limited.

I know the metal of the case forms a Faraday Cage, but it's not enough. What are my other options? Wrapping the case in another layer? Meshed metal? Wrapping the cables?

I appreciate your help. Most of what I've found on the web is either "yup, this is a problem that should be addressed" or kooky conspiracy folks with tinfoil hats.

 

[Harvey]

It could be a bad ground in the hearing aid or faulty shielding in the cable from it, or it could be that the device is not well designed to reject magnetic interference. You coult test this possibility by trying another model hearing aid or another copy of the same model to see if the problem persists.

 

[Steve Thornton]

I'm not sure what you mean by "faulty shielding in the cable coming from it" -- it's a tiny device in her ear, no cable.

Could it be the various KVM cables? Ethernet cable from computer to phone?

 

[Sheep221]

Computers are generating strong magnetic interference.

What could work actually is to downclock components, the higher freqs they operate under, the higher is the electromagnetic field around your computer.

And yes while case is faraday cage, the field is still strong, several feet in radius around the unit.

 

[Harvey]

I'm not sure what you mean by "faulty shielding in the cable coming from it" -- it's a tiny device in her ear, no cable.

Sorry, that wan't clear from your first post. The interference could be due to something wrong in the particular phone instrument or it may be a faulty design that is sensitive to some interference fields.

Does the problem happen on any other phone of the same or a different model?

Could it be the various KVM cables? Ethernet cable from computer to phone?

Yes, but it sounds like you have too many variables. Try to simplify the system to get as many extraneous cables and extra peripherals out of the equation. If the problem goes away, add them back one at a time to see if you can determine which of them may be causing the problem.

If some of the peripherals are connected through a USB hub, is it powered or passive?

A USB port is spec'd to deliver 500 mA (0.5 A) of current. If passive, and some device requires a lot of current (such as an external hard drive without its own power brick), and you have other devices plugged into the hub, you could be trying to draw more current than the one USB port it feeds can provide.

Along that same line, you could have problems if a USB hub is powered, but the power supply is faulty or too weak to supply all the devices connected to it.

Good luck.

 

[Steve Thornton]

Yes, but it sounds like you have too many variables.

Yeah, you're telling me! I've gone ahead and sprung for an EMF meter; when it gets here hopefully I can narrow it down. The office is a minefield of stuff plugged in every whichaway, and they've got four people in an office meant for one.

There's no USB, but there is a powered ethernet mini-hub to handle the computer, regular phone, and special assisted-hearing phone attachment thingie.

One thing I've confirmed is that she hears the buzzing when she approaches any computer, not just hers, so I know it's not a defective ground in her PC (unless the whole place is improperly grounded). Back in the CRT days we used to have all sorts of problems with the flourescents interfering with the monitors, but her LCD monitor isn't the problem, and I doubt it's the flourescents since it gets stronger when she sits down. It's definitely coming from the CPU box, or the mini-hub, or the UPS power brick, or the giant tangle of cables, or the wall....

 

[Harvey]

Yeah, you're telling me! I've gone ahead and sprung for an EMF meter; when it gets here hopefully I can narrow it down. The office is a minefield of stuff plugged in every whichaway, and they've got four people in an office meant for one.

Have you checked that the ground lug on the AC outlets are really grounded? If the outlets are connected to extenion devices with multiple outlets, are they all grounded?

There's no USB, but there is a powered ethernet mini-hub to handle the computer, regular phone, and special assisted-hearing phone attachment thingie.

Where does the wireless signal to the in ear piece originate? Are that unit and any other cables/devices connected to it well grounded, and could the power supply be faulty?

One thing I've confirmed is that she hears the buzzing when she approaches any computer, not just hers, so I know it's not a defective ground in her PC (unless the whole place is improperly grounded).

That suggests the easiest test would be to try another of the same or make/model of hearing aid device and, if possible, another make and model, as well, to see if the problem persists.

 

[aigomorla]

the last statement tells me, something might be wrong with the hearing aid.

Im +1 to Harvey's recommendation.

 

[MrK6]

If her hearing aid is that sensitive to EMI, try some makeshift shielding with aluminum foil-wrapped cardboard. Multiple layers compounds the effect.

 

[Steve Thornton]

My EMF meter came, and the results were very interesting. It's not the computer, not the USB hub, not faulty grounding, not any of that stuff. It's the building.

Specifically, it's the fact that her desk is located directly over the main electrical room, with the huge transformer(s) that convert City Light power to 120V power for the building. My meter goes up to 150 milligauss, and the entire area she sits in pins the needle so hard you can hear it smack the peg. I have no idea what the actual level it is, but 150 is already extremely high. Not just her, either, but the office on the other side of the wall, and possibly the corner wall as well. The electrical risers for the entire building run up inside that wall, and they're a huge source too.

It's been that way since the building was built. We never noticed because no one with a hearing aid ever sat there before.

Taking care of her problem is easy; swap desks with the non-hearing-impaired person in the other corner of the room. Even though it's only a few feet away, the reading is almost zero there. But the larger issue of high EMF exposure remains, for the person she switches with, the person who sits on the other side of the wall, and several others throughout the building (near electrical panels).

The science on health effects from high EMF doses is inconclusive, but there are some indications of increased cancer risk, especially leukemia, and many institutions have adopted a policy of "prudent avoidance" which requires mitigation efforts in areas where exposure is between 20 and 1000 milligauss (one gauss). Mitigation can include moving people away from the source, or shielding when that's not possible. I have a consultant coming out next week to look at our situation and make recommendations.

Playing with my meter has given me some surprising results. Things with electrical motors emit tons of EMF, I knew, but also any kind of transformer, including power bricks, for phone chargers, computer speakers, and all sorts of other small electronics. They all pour out EMF; fortunately, it drops off so quickly that even though I have a dozen of them behind my desk the reading where I sit is essentially zero. A desk fan emits almost nothing out the front, but quite a lot out the back, where the motor is.