Tranquillity bass

The trend towards inner-city living in New Zealand cities has brought life to our urban areas, but those who reside in the central city can be in conflict with those who enjoy the nightlife.

Apartment dwellers complain about the noise, and the people who run the cafes, restaurants, bars and nightclubs resent having their businesses curtailed.

IRL, in collaboration with the building research organisation BRANZ and Fletcher Building, is applying novel technology that could help reduce the problem. Wayne Sharman, strategic business development manager for BRANZ, says it is an issue that will only increase in importance.

"Urban intensification, where more people opt for apartment-style living, is inevitable in New Zealand. Conventional low-frequency sound insulation is heavy, bulky and expensive, so BRANZ is looking for a breakthrough solution to this problem."

IRL's Dr Emilio Calius, science leader for the project, says the issue is with frequencies below 1kHz.

"Anyone who’s had to put up with a party going on next door probably knows how annoying this can be. It’s the thump, thump produced by the bass beat from certain music systems and it is an irritatingly penetrating noise," he says.

"It is also the sound spectrum that is most difficult and expensive to exclude with conventional construction."

Currently, good low-frequency sound  isolation means very thick walls and ceilings.  While structurally strong, it eats into living  space in apartment-style dwellings and is too costly for single-unit detached and semi-detached housing. So the IRL researchers are working to produce isolation systems that are thin and affordable.

This research is based on new discoveries  about the physics of wave propagation in meta- materials—complex composite materials that can be engineered to have special characteristics such as cloaking acoustic or electromagnetic waves.

Dr Calius says the aim is to use this knowledge to develop high-performance construction materials that are lightweight and thin, yet can prevent the low-frequency noise getting through.

"We can do this by creating acoustic band gaps using internal structures that resonate at a certain frequency and work to block wave propagation from the unwanted noise source," he says.

Dr KL Chan, who is managing the programme for IRL, says there could be other applications for the technology.

"While we are concentrating at the moment on low-frequency noise insulation in buildings, we can see other applications in this approach to noise reduction in household appliances, aircraft and boats."