Nearly every time a highway or airport expansion is proposed, transportation planners face opposition from residents who fear the increased noise levels in their homes and businesses. Traffic noise is often mitigated with physical noise barriers, but the large, thick walls often draw opposition as well.

A new technology developed by University
 of Minnesota mechanical engineering professor 
Rajesh Rajamani as part of 
a research project funded
 by the National Science
 Foundation could soon
 provide a nearly invisible
 solution for transportation 
noise cancellation—and 
give transportation planners another tool for overcoming project opposition.

Noise enters homes close to airports and highways primarily through windows, and windows can transmit ten times the sound energy as walls can, says Rajamani. With this in mind, researchers set out to reduce the amount of transportation noise transmitted through windows.

To accomplish this goal, researchers created a method of active noise control for windows. Active noise control works by using speakers to generate a sound wave that is a mirror image of the undesirable sound wave. Superimposing an “anti-noise” wave of the same amplitude as the undesirable noise wave results in a reduced decibel level of noise in the environment.

The research team began by designing thin, transparent speaker panels to fit in the empty space between the two panes of a double-pane window. Then, the researchers tested the effectiveness of the new speakers, using them to cancel out undesirable transportation noise from outside the home while preserving the desirable noise from inside the home.

In addition to mitigating traffic noise, this new technology offers other surprising benefits. Researchers have found that the “smart window” speakers can actually be used as home audio speakers without losing any of their noise-control benefits.

Read the full article in the February issue of Catalyst.