WHEN Scott Summerfeldt turned off his computer one night after work, he was amazed at just how quiet his office suddenly became. He hadn’t realised how noisy the fan in his PC was, so he decided to do something about it. And this week he announced the results of his efforts to a meeting of the Acoustical Society of America in New York.
Summerfeldt, a physicist at Brigham Young University in Provo, Utah, said he and his team have developed an anti-noise system suitable for any PC’s fan mechanism. It reduces noise in the same way that noise-cancelling headphones block out external sounds. The system is likely to catch on, as microprocessors grow more powerful and demand bigger, faster fans to keep them from frying.
A whirring fan generates frequencies that depend on the speed of the rotating blades. The faster they spin, the louder and more high-pitched the noise. To counter the hum, Summerfeldt’s team used the technique known as active noise control. The idea is to measure the unwanted noise signal and reproduce it precisely out of phase with the original sound wave. When the signals merge, the troughs of the generated wave cancel the peaks of the noise, and vice versa.
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People have previously tried using anti-noise to quell computer din, but their systems were unwieldy and expensive because they involved equipping rooms with networks of microphones. Summerfeldt opted instead to keep costs down by developing a silent fan that could simply take the place of a standard one. That way, each computer minimises its own noise level.
After testing various speaker combinations, the team got the best results – a drop of 20 decibels over a standard PC fan – by placing four 20-millimetre speakers on the corners of an 80-millimetre fan unit. Four microphones placed around the edges of the fan detect the din and a circuit inverts the signal so the speakers generate the appropriate anti-noise.
Summerfeldt has filed for a patent and estimates that if his noise-killing fans are mass-produced, they should only cost about $20 more than a standard PC fan. And PC users won’t be the only customers: Summerfeldt believes owners of home cinema systems will want to muffle the loud cooling fans inside their costly projector televisions. Even Dutch air traffic control, which uses such projectors to display aircraft positions, are interested in adopting his idea.
