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Cancelling Out CPU Fan Noise
Percy_Blakeney writes "After realizing how noisy his computer was, a professor at BYU has created a new CPU fan that uses small microphones and speakers to cancel out its own noise. It isn't perfected yet -- it only nixes the whine, not the whoosh -- but it looks like it could be promising, especially given the professor's background: making jet engines quieter."
Installing a Zalman HSF is exactly what I did. Highly recommended. Or (and), you can just buy a fan controller for the money (or both) to really quiet down your system.
Where this would be really useful is for the whine of hard drives. It would be far better than the current system of enclosing it in some casing thus making it run even hotter.
In most offices, they don't use noise generators (ie Gossip Support Group) to cancel out talking noises, instead they put in a lot of plants, cubicles, which act to absorb most of the noises.
If the noise is pointing at your directly, then you probably need a cancelling method. If it is a general-direction noise, it should be absorbed rather than trying to cancel it (where you need to find it in the first place).
Rock that crushes, Paper & Scissors that don't matter.
Most car noise these days is not from the engine running. Technology these days allows new cars to run incredibly quiet. Probably 99% of the noise you hear while traveling down the highway is road noise. Noise produced from your rubber tires against pavement. I saw a news flash a couple years ago about a new type of pavement that dramatically reduces that noise, but it's too expensive to be widely used.
For instance, you can buy noise-cancelling headphones, but the cancellation only works for your own ears, which gets the sound in just right right phase; to the people around you, there will be a perceptible noise coming from your headphones! Conservation of energy says you can't just destroy the energy of those sound waves. Most likely you're just sending extra-strength sounds waves somewhere else.
I own a set of noise cancelling headphones and there is no perceptible noise being emmitted from them to the outside world. The noise cancellation circuitry takes the incoming signal and inverts it to cancel out the original incoming sound wave. Conservation of energy doesn't really apply. You aren't really destroying the energy of the sound waves, just cancelling it. Energy is spent on both the positive and negative signal. Although I just minored in acoustics so I'm probably missing something. Any professional opinion is appreciated.
Well, I do have a PhD in physics, but I should bow to your actual experience with the device
My guess is that the sound coming into your ears is only a tiny amount of power, so reradiating that power in all directions doesn't make any amount of sound that would be perceptible to someone a significant distance away. Your eardrums only have a surface area of a few square mm, the the amount of energy impinging on them is normally only a gazillionth of a watt. Your ears are amazingly sensitive devices.
Conservation of energy doesn't really apply.
I was obviously wrong in my prediction about an audible noise for people not wearing the headphones, but I'll bet both my testicles that it's not because conservation of energy is violated. You'd get the Nobel Prize if you found a violation of conservation of energy.
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