Gadget to block local cellphone transmissions?

I've heard this theory and based on what I've read about the math I don't believe that is the case.

For a handwaving argument why this doesn't seem to make sense, imagine you were trying to beat me at a game where I either have a less random "more modulated" strategy versus where I have just randomly toss a coin heads or tails. If there is more structure it would seem to be easier for any sort of computation to be able to decide what to do to counter my strategy and beat me. The more random it is the less you can do to cancel anything. But that is just handwaving and not a boardful of mathematics.

When I spent a week studying that text on active cancellation it was describing the process of measuring the amplitude and phase of each frequency, introducing a suitable phase and amplitude shift to make up for the distance between microphone and earphone and ear and then generating approximately the needed signal to sum to zero at the destination.

Now as the frequencies go up the sampling rates need to go up, the precision of the sampling needs to go up, the number of the calculations needs to go up, etc, etc, etc. But I still haven't heard a really convincing argument whether it would be possible to have tens of dB better cancellation over octaves more frequency range if I were just willing to carry around three pounds of batteries for a couple hours of cancellation calculations, instead of a couple of silly little double-A batteries for dozens of hours of operation.

Good points. Just after posting I realized that "random" was not going to cut it.

If more sampling is needed, and more calculations per sample to really cut down the noise AND spoken word, one can conjecture that a laptop PC configured with a mic, earphones, and appropriate software might do better than the QuietComfort(r) and others, albeit at the expense of lugging along your PC. Perhaps real work could also get done on other threads or processors... Does anyone know of any investigations into this possibility?

-georgeK

A 12 volt gel cell, and an old fashioned "OOGHA" horn from a couple feet away. Tell them that you are talking to your invisible friend from Alpha Centuri with it, while yo fake messages in Morse Code.