Full article The constant drone of a computer cooling fan can be annoying. But a professor at Brigham Young University has taken an unusual step to mute this noise: more noise, produced in just the right quantities from tiny loudspeakers that surround the fan. "We make anti-noise," said Scott D. Sommerfeldt, a physicist who created a noise suppression system with his students. It is the latest example of a technology called active noise reduction, or noise cancellation, well known from its use in headphones designed to block out the low rumble of jet engines. The sound waves engineered by Dr. Sommerfeldt are out of phase with sound waves from the fan and thus they cancel each other out, substantially reducing fan noise. Dr. Sommerfeldt's system has four miniature speakers and four even tinier microphones set in a ring around the computer fan. The microphones and other sensors detect the noise of the fan blades and, with the help of digital signal processing and algorithms, radiate opposing tones from the speakers. The whole system can be tucked into the same space that a conventional computer cooling fan would occupy.