These headphones keep the noise down

It can be hard to concentrate at Kel & Partners in Westborough, where there are no cubicles or offices. So, copy writer Bill Kelly and public relations director Liz Bradley use noise-canceling headphones to help them filter out the noise at the marketing service agency.

"Before I started working here, I had my own office, so I got used to working in quiet," Bradley said. "It's slightly addicting. It's like listening to a noise machine to help you get to sleep."

Since their invention more than a decade ago, noise-canceling headphones have been an air traveler's best companion, drowning out the drone of plane engines, crying infants, and annoying seatmates. These headphones also have found a home in industry, the military, at sporting events - anywhere listeners want to reduce ambient sound, protect hearing, or listen to music.

Raymond de Callafon, a researcher at the University of California at San Diego, says noise-canceling technologies are used to quiet a variety of sounds, including airplane cabins and commercial air-conditioning systems.

Noise-canceling headphones, which range in price from $40 to more than $400, work through active or passive technology, or a combination of both. Active noise-reduction headphones use sophisticated circuitry, including tiny microphones that pick up incoming background din, then electronically duplicate those frequencies, sending out an opposite sound wave that essentially "cancels" the initial annoying background racket. Passive headphones work like an ear plug, using foam or other material to block noise.

"The active noise-canceling headphones work best at mid to low frequencies," said Rob Enderle, a technology analyst based in San Jose, Calif. "The headphones don't completely block out all noise."

Audiologists say constant background noise can be tiring. And, indeed, many frequent travelers like David Chatham, an account director with Capstrat, a strategic communications firm based in Raleigh, N.C., find traveling more enjoyable using noise-canceling headphones.

"I don't know the reason for the reduced fatigue, but I do notice that I don't feel as tired and seem to have fewer headaches related to my travel," said Chatham, who uses the headphones with his video iPod during long flights.

Of course, no matter what type of headphones you use or where you use them, these devices are not hearing protection by design and can still cause damage to hearing if used carelessly, said Craig A. Kasper, a New York audiologist.

And sound quality may vary widely. That's why when testing noise-canceling headphones, a consumer should listen to the type of music that he or she typically will be tuning into while wearing the headsets, said Paul Ryder, vice president of consumer electronics for Amazon.com.