Measuring noise with people in mind: Soundscapes

May 23, 2011

There are probably places near where you live or work where it’s pretty noisy. The definition of what’s too loud is highly technical. Now, acoustical engineers have developed a new way of measuring noise that includes how it feels.

This week in Seattle, the Acoustical Society of America is offering training with the new approach for architects and planners. (The training is Tuesday at Seattle City Hall, as the group's annual meeting runs all week.)

Brigitte Schulte-Fortkamp, a professor at Berlin's Technical University, who describes herself as a psycho-acoustician, is leading the session. She took me on a brief "sound-walk" in downtown Seattle. (You can listen by playing the Audio version of the story.) Sound-walks are a key innovation in the field of acoustics. They focus on the way people experience noise.

That's in contrast to the traditional way engineers evaluate noise, by setting up a sound-meter, which measures how loud it is in decibels.

Schulte-Fortkamp says decibels don't capture everything. She became a fan of sound-walks in the late 1990’s. After a meeting of acoustical engineers, she began experimenting with new ways of measuring noise. On one occasion, early on, she had gathered a group of people in a noisy neighborhood in Berlin, and they walked around.

At one point, some residents saw them and asked if they could have some input. She hadn’t included the residents!

"The people living there came out and said, 'This is the most awful thing we have on this road, [a cobblestone street] -- when a bus is passing by, it is coming up in our homes and you cannot measure out here, outside on the street.'"

So, the engineers and urban planners went inside the homes, and immediately felt the deep rumbles -- and even saw chairs vibrating. "This was interesting, because then suddenly we saw these low frequencies and vibrations which came through the wall," says Schulte-Fortkamp.

What’s revolutionary about the soundscapes approach is getting input from people.

The method involves inviting people in the affected area to walk around with the engineers and planners, describing which places are noisy. The residents fill out surveys that rank the noise in different spots. The acoustical engineers also make a stereo recording of the sounds to analyze later, and take traditional decibel measurements. All this data end up in a numerical analysis.

They call this mapping the soundscape.

The National Park Service is trying to preserve quiet soundscapes, so that there are areas with no sounds of machinery – including jets overhead. 

Once you have a map, it can be difficult finding solutions. If the problem area is a public park or plaza, the designers can try "masking" the noise by creating other sounds or distractions. Otherwise, the solution might mean reducing speed limits. In some cities, including Berlin, they’re taking away lanes of traffic, or limiting hours of nightclubs and restaurants.

Noise is defined as unwanted sound ... meaning, what’s noise to you, just might be music to your neighbor’s ears.