I've become an electrical conductor for my headphones... but how?

Question

So I have a pair of Bose noise-cancellation headphones that I plug into my keyboard every night to charge them (via my keyboard's USB port). My keyboard happens to be a metallic Apple keyboard. You will see why this may be important to note later.

Over time, I noticed a certain dull, electrical buzzing sound in my right earbud which occurred when I turned the noise-cancellation on. This buzzing sound was not constantly there. It would randomly appear for arbitrary periods of time and then vanish. It wasn't loud either, but it was loud enough to be noticeable and annoying.

For the longest time, I had no clue why this would happen. Sometimes the earbud would be perfectly silent (as it's supposed to be)... and then a buzzing noise would come out of nowhere. This was incredibly annoying and my only remedy was to listen to loud electronic music which blended in with the buzz and made it relatively unnoticeable. Of course, listening to almost any other kind of music proved annoying since my earbud would randomly, intermittently buzz at me.

Finally, one day, I noticed that when I touched my Android phone, the buzzing sound would increase in volume. I thought at first that this was due to my bodily position somehow stretching the wire, but with further testing I confirmed that my Android phone was the culprit. I slowly discovered that touching different objects, even when the headphones were not plugged into the speakers, would result in volume changes of this buzz.

One thing I noticed was that touching the headphone jack, whilst touching the Android phone that increased volume, would silence the buzz. With further testing, I noticed that touching my metallic keyboard would also silence the buzz, even whilst touching the Android phone or under any other circumstance in which there was a buzz.

I finally realized that my body is somehow conducting electricity when touching objects such as my Apple keyboard, headphone jack, or Android phone and that these are all related to the annoying buzz and nullification thereof. I found this bizarre and fascinating.

Ever since this discovery, I've found that I can silence this annoying buzz by pressing any of my fingertips on my metallic keyboard. This is also annoying, since it can make typing awkward to continually have one finger pressing against the metallic part. Nonetheless, I have no idea why this works at all; I suspect it might have something to do with my usage of the keyboard to charge the headphones via its USB port every night, but I have no substantiation of this hypothesis.

So my question is twofold:

1. How does this bizarre phenomenon work wherein my body is apparently conducting electricity from objects which somehow control some anomalous buzz in my headphones?
2. And how can I make this buzzing sound stop without keeping my body in contact with those objects? Obviously, I can't hold the headphone jack and listen to anything at the same time, and this habit of touching the metallic part of my keyboard is not great for typing nor my wrists which already suffer from CTS.

Any insight is appreciated.

Answer 1

The "buzz" is almost certainly RF pickup. This can be the mains (low frequency, 50/60/100/120Hz, unlikely in this scenario given a phone is involved) or rectification of the carrier frequency of the phone - remember how old tape players would make a "duh duh, duh duh" sound whenever a text message is received.

Human bodies are conductive. When your skin is dry you are about 100kOhm to 1MOhm. When your skin is wet, that goes down to about 10kOhm to 100kOhm. So there is nothing unusual about becoming a conductor.

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As to why touching a metal keyboard kills the hum, or even touching the headphones jack. Basically as you are a nice large conductive area. When connected either to earth (e.g. via the keyboard shell and PC) or to the ground of the phone (e.g. headphones jack), you are basically changing how your body is interacting with the electric fields around you.

EMI is a dark art - it's hard to say exactly what current path you are interrupting, or how you are interacting with the fields. But generally if you ground yourself it stops you acting as an antenna - sort of like shorting yourself out.

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One simple option you could try is to buy an anti-static wristband. That would allow yourself to be connected to earth (or to your keyboard) without having to touch the keyboard. Alternatively you could try simply charging your phone from something other than your keyboard to see if that stops noise injection.

Answer 2

The main fact, in my opinion, is that noise is heard only in right channel.

First thing comes to mind is issue with grounding. But then both channels would receive the noise.

Second - the source of this noise. You must try another headphones to see if noise is caused by headphones or is emitted by the source device.

Third, reposition your phone to the left (if it is on the right) to see if the noise moves into left bud.

Generally I think you will come to the conclusion that something is wrong with right channel of the headphones and headphones are faulty (as the right wire "picks up the RF" as Tom said in his answer, and then amplifies this signal when you turn noise cancellation on, but left does not).

Answer 3

My guess is that there is a break in the insulation of the right earbud and that electrical hum from your body is flowing into the noise cancellation amplifier.

Try wrapping the bud in cling film and see if that stops the buzz.

Answer 4

If you have a multimeter available, you can put it into AC voltage measurement mode and try to measure between the different metallic objects. Note that you should only touch the objects with the probe, not with your skin when measuring. For example, touch one probe to the keyboard and other probe to some metal part on the phone.

If you find a ~60 volt (for 120VAC countries) or ~120 volt (for 240VAC countries) voltage between the objects, it is most likely due to ground potential in the devices. Many mains-powered devices nowadays are designed without a ground wire, and RF filtering capacitors inside the device will leak a small amount of electricity. This becomes apparent when you are between a grounded and an ungrounded object.

These issues can usually be solved by placing a galvanic isolator between the headphones and the computer. You can search for "3.5mm audio isolator" to find suitable devices.

Answer 5

This is a really lame workaround to the buzzing noise, but if you're desperate...

Skin Contact via USB Charge cord

Comments on Tom's answer re: grounding straps not working, led me to this (one weird trick that all buzzing noise Bose owners should know :P).

With the USB charge cord attached on the Bose end (the USB micro-b end), take the USB-A end of the cord and keep it in contact with your skin.

How you do that is up to your imagination.

(Stick it in your waistband, trapped under your armpit, taped to your forehead, chained to your ankle like a 20kg metal ball, etc.)