Reducing noise pollution

Reducing noise pollution

How one engineer is making the world a little quieter
October 11, 2012

Constant exposure to industrial noises can cause myriad health problems — trouble concentrating, headaches, hypertension and hearing loss have all been linked to noise pollution.

But Alain Berry’s research is reducing the auditory overload of our industrial society, especially when it comes to air- and car-traffic noise.

“Transportation is the main source of noise globally and tends to continuously increase year after year — a one-decibel-a-year increase according to some authors,” says the Université de Sherbrooke mechanical engineer. Berry’s research delves into where and how noise is generated and how to lower it using sound waves that oppose and cancel out the offending sound.

In a mock-up of a Bombardier jet, 80 microphones designed by Université de Sherbrooke record the sounds from a vibrating fuselage.

Called “active control,” the technique is a relatively new strategy for creating silence.

“Imagine noise as waves on water’s surface,” says Berry. “If you want to reduce the waves, you generate the exact opposite wave and combine them. You create a very quiet surface.”

In the case of airplanes, a main source of interior noise is the vibrations from the fuselage that travel into the cabin and cockpit. By using a series of strategically placed “shakers” — small, vibrating loudspeakers — Berry can create opposing sound waves that stop the noise.

Montréal-based Bombardier Inc. became interested in Berry’s work after visiting McGill University’s Centre for Interdisciplinary Research in Music Media and Technology (CIRMMT), where he conducts some of his studies. Funded in part by the Canada Foundation for Innovation, CIRMMT’s system of highly sensitive microphones and sophisticated hardware and software allows Berry to simulate industrial noises, analyze sound waves and test active control systems.

For the past four years, Berry and his team have been working with Bombardier to simulate the true acoustic experience of being a passenger in a private jet designed to generate as little noise as possible.

To do this, Berry’s team first recorded the sounds generated in a real Bombardier CRJ plane cabin while it was taxiing, taking off, cruising and landing. They then replicated the exact sounds in a CRJ cabin mock-up in CIRMMT and used a number of small shakers to cancel out the sounds.

Bombardier now plans to use the acoustic simulation as part of its sales strategy.

“In this market, comfort is really important,” explains Berry. “People are ready to spend a lot of money to buy comfort. More and more, that includes a quiet cabin.”