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All Video Conference Meeting Tables Should Be Metal January 18, 2008

Posted by gordonwatts in physics life.

IMG_0211Have you ever noticed that buzzing sound that comes from your computer speakers? Sounds like some sort of very evil bug? Happens when your cell phone is near your speakers?

I think it is caused by a GSM phone communicating data over the packet network (do Verizon phones do this as well??). The iPhone is a heavy user of the packet data network and so is a particularly bad offender.

Now, think about a video conference room. This is a room with a large table in the middle that everyone sits around, and there are numerous microphones distributed around its top. The microphones are, of course, hooked into the electronics via cables — which are perfect pick-up antennas for this GSM noise. Every self respecting physicist has a cell phone and many of them are smart phones – heavy users of the GSM packet network. This can be hell for those on the other end of a video conference. The buzzing is very loud and can drown out everybody’s conversation, prompting remote participants to yell “move your cell phones away!”

My Dad’s iPhone will cause the buzzing in computer speakers from 4 feet away. He has a very simple solution — just put it on a bit of tin foil. This effectively kills the induced sound. A metal table will do the same thing. Now, I’m sure not every single phone is designed the same way, but if this could eliminate those noisy video conference calls…



1. Buzz, Buzz…. | VC Rox - January 19, 2008

[…] Anyway…look what popped up in my Google alert. It is from a physicist, Gordon Watts, University of Washington. He has a trick to keep the GSM phones from interfering with speakers. Yes, we will have to test this. […]

2. Kevin - January 19, 2008

OK, but I’ve also read that the shielding caused by the Al makes the transmitter send out its strongest signal to contact the cell tower. This decreases battery life. Maybe better shielding on the speaker wires is in order. Mu metal? Braided wire thingies? I’m sure you HEP folks can figure out how to shield a wire πŸ˜‰

3. gordonwatts - January 19, 2008

Kevin — my Dad and I had a long debate on this. We couldn’t figure it out. First of all, the cell phone works just fine after it is on the tin foil — you can’t tell. Second, the level of sound transmitted to the speaker was tiny.

We figured if it was a Faraday cage (sheilding), then the cell phone would have to up its power in order to contact the cell phone tower. And that means that the speakers should have picked up the same amount.

An alternative is the tin foil becomes a better antenna. So the signal from the cell phone tower is stronger. This means the cell phone will use less power to transmit (I think). We’d need some program that looked at the internal workings of the cell phone to tell that.

The last thing we could think of was the tin foil acts as an attenna, and makes the signal more diffuse or a gives it a different propagation pattern — in a way that doesn’t matter for the cell phone and the cell phone tower but does for the speaker. We tried rotating the cell phone and moving it around a bit, but that didn’t seem to have an effect, which I would have expected in this case.

BTW, we only tested with the iPhone – it has a metal back. My 3G phone has its data connection turned off so it doesn’t cost me $1000’s of bucks in Europe. So this is a test of one. πŸ™‚

I do not have too much time on my hands. 😐

4. Pat - January 21, 2008

That is a great tip! I use ooVoo for all of my video conferencing needs, but of course sometimes I still get someone putting their phone too close to the speakers. I’ve embarassingly done it a couple times myself with my smartphone. If any of you are paying for your video conferencing service i highly recommend http://www.oovoo.com.

Maybe we should design a tin foil lined iphone holder to sell to video conferencers?

5. nimesh - April 9, 2008

is there a version for n/95 8gb cellular phone to download?

6. gordonwatts - April 9, 2008

I’m afraid I have no idea!

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