By Alex Massaad
THE rumbling bass from the party animals next door need no longer keep you awake at night. Cheap and effective soundproofing can be yours in the shape of novel tiles made from latex and a few plastic buttons.
Low-frequency sounds, especially, seem to seep through most domestic walls. That's because of their long wavelength, says Zhiyu Yang at the Hong Kong University of Science and Technology in Kowloon. Bass sounds at 100 hertz have a wavelength of over 3 metres in air, "and several times longer in solids", he says.
To block out all sound, buildings would need walls several metres thick. Now Yang and his team have developed soundproof panels made of latex and plastic buttons, that will do the job (Applied Physics Letters, DOI: 10.1063/1.3299007).
These noise-cancelling panels consist of a latex rubber membrane stretched over a 3-millimetre-thick rigid plastic grid of 1-centimetre-wide squares. In the middle of each square is a small, weighted, plastic button.
When sound waves hit the panel, the membrane and weighted buttons resonate at difference frequencies. "The inner part of the membrane vibrates in opposite phase to the outer region," says Yang. That means the sound waves cancel each other out and no sound gets through.
Each weighted membrane only cancels out sound waves within a small band of frequencies. But changing the weight of the buttons alters the operational frequency, says Yang. By stacking five membranes together, each tuned to a specific band, you can create a soundproof panel that works in the range from 70 to 550 hertz.
With these panels you can soundproof homes, says Yang. And the panel's weight is equivalent to ceramic bathroom tiles, "although it's slightly thicker at 15 millimetres", he adds.
The panels could be used "in noisy environments such as airports", says Xuanlai Fang at the University of Illinois in Urbana-Champaign. "If these metamaterials can be manufactured economically, the impact can be very significant."