Loudspeaker kills noise from fans

Researchers working for ABB in Sweden have developed an active noise cancellation system for ventilation systems that could be used to kill irritating low-frequency sounds from other sources, including industrial fans.

Although active noise cancellation is not a new technology, the ABB researchers claim that their digital system is more efficient and easier to apply than previous systems. They say that the system, called SiFlex, can cut noise levels below 300Hz by 10dB without the loss in energy that affects passive attenuation systems using sound-muffling materials.

A microphone between the source of the sound - typically a fan - and a silencer, picks up the low-frequency sounds and sends them to a digital processor which feeds an out-of-phase version of the sounds to a loudspeaker to "kill" the noise. No manual adjustments are needed. A second microphone, downstream from the silencer checks that the noise level has been reduced.

A fibrous material called Dacron helps to mop up higher frequency sounds.

The SiFlex system, which is aimed both at new and retrofit ventilation applications, is due to go on sale in Scandinavia later this year and is expected to reach the UK next year. The technology could be adapted to tackle other sources of low-frequency noise, including industrial fans.