Now hear this: the high and low volumes of solutions to unwanted noise

When I was in graduate school, I was awakened one night by a phone call from my downstairs neighbour. “Whatever noise you’re making up there, could you please cut it out,” she said. “I can’t sleep.”

“I’m not doing anything,” I replied. “I was asleep.” And I was pretty sure I wasn’t snoring. On the rare occasions that I snore, I tend to wake myself up.

She didn’t buy it. “You’re still doing it,” she said.

“I can’t hear anything,” I said, then hesitated. “Except the train.”

We lived about 1500 metres from a rail line, and I could hear the distant rumble of a passing freight.

There was a pause. “Oh.” She then went on to explain that she’d grown up on a farm in Montana or some such place, where nights were quiet, and nothing interrupted your sleep.

Today, we call the sounds that disturbed her “noise pollution” and tend to think of them as inevitable side effects of living, working, and socialising close to other people. But as scientists suggested a few weeks ago at a meeting of the Acoustical Society of America in Denver, Colorado, maybe that needn’t be the case.

Maybe there are ways to make these unwanted auditory intrusions less intrusive – or, in the words of Bonnie Schnitta, president and owner of the acoustical consulting and engineering company SoundSense, more “bearable”.

Such things are already being done to protect marine mammals from disturbing sounds – including ones from important green-energy projects such as offshore windfarms. “[Underwater] sound is a big [issue] because it travels far,” says Frank Thomsen, of underwater engineering specialists DHI Copenhagen. During windfarm construction, he says, the sounds from pile drivers are so loud that harbour porpoises avoid them by distances of 20 to 25 kilometres.

But such loud, disturbing noises aren’t inevitable. In the case of windfarm construction, it’s possible to mitigate their spread, Thomsen says, by putting “bubble curtains” around pile drivers. They work not by reducing sound at its source, but by blocking its transmission to those who might be disturbed by it. And it turns out that there are ways to do this in human environments as well.

The sounds from pile drivers are so loud that harbour porpoises avoid them by distances of 20 to 25 kilometres.

Consider, for example, the difficulty many of us experience having a conversation in a pub whose management thinks the best way to drown out distracting noise is by blaring loud music over the sound system. Yes, that does give everyone a sense of privacy in their own conversations… except, all too often we can barely hear ourselves think, let alone have a clue what’s being said to us.

It sounds like an intractable problem, but Ryan Corey, an electrical and computer engineer at the University of Illinois, Urbana-Champaign, has come up with a unique solution: why not turn “smart” hearing-aid-style devices into noise-cancelling systems?

Such systems are already in use for the opposite purpose, he says. They come in the form of earbuds or headsets designed to filter out sounds other than the music, allowing you to listen to it better, free of interfering voices or distortion from bad acoustics in the concert venue. They can also be used to help people with hearing loss more clearly hear a teacher or a conference speaker, and are also of value to theater-goers. “If you go to see a play, you can check out a headset,” Corey says. “Their purpose is to improve intelligibility of something that’s far away, or when there’s a lot of noise.”

So, he says, why not do the reverse? Use the same type of devices to remove the music and allow you to hear your friends’ voices, without having to shout at each other.

It works by using WiFi devices to monitor the signal coming out of the speakers, coupled with smart earbuds that can determine how that signal is received by your ear and then cancel out unwanted noises. In the case of devices designed to improve your ability to hear at a concert, conference, or theater, what’s cancelled out are extraneous noises and distortions from suboptimal room acoustics. In the case of devices designed to improve your ability to converse in a bar, what’s removed is the deafening music. “So, you can still hear me talking, but with less background noise,” Corey says.

In tests, he says, “we managed about 10 to 15 decibels of noise reduction”. To put that in context, that’s about the difference between the sound of a vacuum cleaner and a normal conversation at home. Bottom line: 10–15 decibels is a lot.

It’s also possible to work at scales larger than your neighborhood pub. One of Schnitta’s interests, for example, is in protecting neighbours from the whine of revved-up engines and cheering spectators on automobile racetracks.

In one project, her team modeled the sound emanating from a race circuit near South Haven, Michigan, paying particular attention to the sections of the track where vehicles typically accelerate, producing the most noise. Then they looked for ways to mitigate it, especially for motorcycle races which, she says, are typically the loudest.

Most of us might think that the best solution would be a bunch of trees between the racetrack and its neighbors. But there was a large wooded area between my graduate-school apartment and the railroad track that woke my downstairs neighbor. Trees are good for the environment, but inefficient at reducing noise.

What’s needed Schnitta says, is an acoustical fence or berm, high enough to block the sound from reaching the neighbors beyond. “It typically takes a 200-foot [60m] depth of foliage to equal one acoustic fence or berm,” she says. “So, if you plant 100 feet [30m] of dense foliage, it’s going to cost a lot of money and not get you anywhere.”

“It’s also important to talk to the neighbors.”

Based on that, she recommended a number of ways in which the racetrack could reduce the disturbance to the surrounding community. But building berms and other noise-reducing structures, she says, isn’t always the only thing that’s needed. It’s also important to talk to the neighbors and bring them into the process.

That was something I’d known long before my neighbour called to complain about the noise of a distant rail line. My great-grandfather was a high mucky-muck on a railroad line that at its peak spanned 13 US states (his title was “chief engineer,” whatever that means). I knew that railroads were important. And they’re especially so, now that we’re staring down the global-warming future. They are one of the most energy-efficient ways to ship goods to market. So what if they rumble a bit in the distance? Some of us find that soothing. Songwriter Steve Goodman caught it perfectly in his homage to long-gone railroads, his classic song City of New Orleans.

And the sons of pullman porters
And the sons of engineers
Ride their father’s magic carpets made of steel
Mothers with their babes asleep
Are rockin’ to the gentle beat
And the rhythm of the rails is all they feel

Noise isn’t always bad.

Schnitta took a similar approach with the Michigan raceway. The big problem, she discovered, was that there were churches nearby. They were accustomed to the lowing of cattle and the sounds of cars on nearby roads, but not the whine of motorcycles at full acceleration. Putting up a berm helped, but what was also needed, she realised, wasn’t so much science as a bit of compromise.

“So, I had the minister talk to the raceway owner,” she says.

The solution was for the raceway to allow practice runs (with the sound-reducing berm in place) until 11 am, which was when church services began. Race activities would come to a halt, and begin again at noon once church was out. Schnitta also offered to engineer sound-reducing windows for the church, which the raceway owner offered to pay for. She also suggested that the raceway owner take anyone complaining about the noise out for a spin around the track in his fastest car.

All of which worked. “You have to bring both sides together,” Schnitta says. “The minister and the raceway owner are now very good friends.”