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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.
I have a question about active cancellation, as I've heard of it being used in other places. Does the cancellation of a noise of a given frequency have any potentially harmful effects that become less obvious through cancellation? For example, does a high-pitch tone that could cause hearing loss over time become more dangerous now that there are two high-pitch tones (albeit directly off-phase) now sounding, or is the cancellation that complete?
You can never go home again... but I guess you can shop there.
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).
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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.
Well yes and no. Noise cancelling headsets are particularly effective because the ANC speaker and microphone are right next to your ears. This helps insure that the signal that arrives at your year can be sampled and inverted so that the sum cancels at the ear. It would be much harder to accomplish this with speakers and/or mics located away from the ear.
However, remote mics/speakers may work if the noise source is highly directional, like a waveguide (I suspect that's happening here). If you can effectively cancel the sound at the orifice, you'll probably achieve a significant reduction in transmitted sound, no matter the location of the receiver.
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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Heh, I hope I wasn't implying that conservation of energy was being violated. I just though that destruction of energy and cancellation of the signal were different in this case. I think I worded it wrong. No testicles need to be wagered :-)
The experience I've had with the equipment in class showed that the noise cancellation circuitry recorded the original sound wave, inverted it and fed it back into the speaker. The combination of positive and negative voltage basically told the speaker to output zero signal for that particular frequency. Nothing is destroyed, it's more like an electronic tug-of-war. It makes listening to music a lot more enjoyable, however it works.
Thanks for the reply.
My acoustics book said that if you put a person with normal hearing into a sound isolated anechoic chamber, and give them awhile to adjust, they will actually hear the blood flowing in their ear.
Point being is that it would be completely pointless for them to be any more sensitive. Quite amazing really.
Why do I have this? I don't smoke.
My acoustics book said that if you put a person with normal hearing into a sound isolated anechoic chamber, and give them awhile to adjust, they will actually hear the blood flowing in their ear.
An even cheaper demonstration is to simply plug your ears. It works better in an area that's already quiet, but if you simply plug your ears with your fingers, you'll hear the blood flowing in your veins and arteries. That's what that low, rumbling noise is that you'll hear.
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