IF YOUR neighbours hold all-night raves and play loud music in the dead of night, the way to get a good night鈥檚 sleep may be to use the loudspeakers on your own hi-fi to eliminate the noise.
Researchers at the University of Southampton are investigating the scope for neutralising low-frequency bass notes by generating 鈥渁ntiphase鈥� sound with an ordinary hi-fi system.
鈥淚t鈥檚 well known that the low-frequency bass beat can create very serious disturbances to neighbours,鈥� says Frank Fahy, professor of engineering acoustics at Southampton. 鈥淚t has even led to murder鈥� he adds. 鈥淭here鈥檚 so much sound energy at low frequencies that conventional, passive sound insulation within walls doesn鈥檛 work,鈥� says Fahy.
Advertisement
The idea is that microphones in the bedroom would pick up the bass notes and relay them to the victim鈥檚 own hi-fi. The hi-fi would process the signal, and produce 鈥渁ntiphase鈥� sound waves that would cancel the offending bass note.
Fahy and his colleague Steve Elliott stress that their three-year project is simply a feasibility study to assess whether such technology would be worth developing. 鈥淎t this stage, we don鈥檛 know if it can be done,鈥� says Fahy.
But active noise-damping systems are already used in factories, cars, helicopters and aircraft. The team at Southampton has developed several such systems for industry, but this is its first attempt to apply the technology in homes.
Fahy and Elliott want to blot out bass notes with frequencies of around 50 hertz. 鈥淲e are looking to mop up the 鈥榖oom, boom, boom鈥� sound that drives people mad,鈥� says Elliott. In effect, he says, the wall separating neighbours acts as a giant loudspeaker, resonating at the same low frequencies.
In preliminary experiments, Fahy and Elliott made a mock-up of two rooms separated by a wall. The bass notes that passed through the dividing wall were picked up and fed to an amplifier, which adjusted their amplitude and phase so that the sound waves coming out of the loudspeakers neutralised the sound of the bass notes from next door.
Fahy and Elliott stress that the technology would only cope with bass notes and would be no substitute for good wall insulation, which cuts out higher frequencies.
They hope to fit their system into ordinary hi-fis, so that people could use their existing loudspeakers to blot out noisy neighbours. 鈥淚t鈥檚 relatively long-term stuff,鈥� admits Elliott. 鈥淏ut it鈥檚 such an important problem, and it makes so many people鈥檚 lives a misery.鈥�
