Sounds of Silence

Sounds of Silence
With noise-canceling headphones, it can get almost as quiet as when you ask your stockbroker to explain what happened in November 2008.
Thursday, December 1, 2011 (All day)

Manufacturers invest considerable time and effort to try to lower decibel levels in business jet cabins, many of which are marvels of acoustic ingenuity. Still, there's no complete escape from the fact that a jet is pushing air out of its way at close to the speed of sound, propelled by a pair of turbines with blades spinning at many thousands of rpms and generating thousands of pounds of fiery thrust. You just can't make all that noise go mute.

But electronic noise-canceling headsets can help. These devices–often called active noise reduction (ANR) or active noise control or cancellation (ANC) headsets–were introduced during the 1986 around-the-world flight of Burt Rutan's Voyager. The Voyager was a tiny sarcophagus tube of an airplane, constructed of carbon fiber with piston/propeller engines in the nose and tail. With no insulation, it was incredibly loud, and with the crew facing nine days to circumnavigate the globe, fatigue was a huge issue.

MIT graduate electrical engineer Dr. Amar Bose, founder of the Bose Corporation, was already famous in hi-fi circles as creator of the direct-reflecting loudspeaker in 1968, which also used electronic phase manipulation to optimize sound reproduction. Dr. Bose began work on a noise-canceling headset in the late 1970s, and donated a pair of his prototypes for use on the Voyager flight.

The headsets work by combining passive and active noise-control strategies. "Passive" means simply isolating the ears from the outside world as much as possible. This is done by maximizing the cushioning seal around where the headset contacts the head and by applying as much pressure as possible to create that seal without causing a headache. It's a delicate balance.

"Active" noise canceling takes the technology a step further: Tiny microphones within the ear cup of the headset pick up the frequency of ongoing noise–from engines, wind around the fuselage, any noise that is constant; then tiny speakers inside the ear cups generate a matching frequency that is 180 degrees out of phase with the ambient noise. The result is almost total cancellation of the offending sound. Every ANR demonstration involves switching the electronics on and off to dramatize the drop-off in noise level. With the system on, it can get almost as quiet as when you ask your stockbroker to explain what happened in November 2008.

Some marketing campaigns have seemed to imply that ANR headsets can also block out unwanted conversation, but that's not true. The passive element might dull the sound of a fellow passenger droning on, but the electronic element acts only on a continuous frequency, such as engine noise. So unless the offending neighbor has an extremely monotone voice, the electronics won't cancel it. (Come to think of it, ANR might work if you're sitting next to economist Ben Stein).

There have been attempts to bring ANR technology to an entire aircraft cabin, and some have been successful in generating significantly lower decibel levels–but usually focused on a single cabin seat (the one where the boss is most likely to sit). And that brings us to some of the more subtle arguments for and against using ANR headsets in business aircraft.

It's true that ANR technology has the capability to reduce your fatigue level, particularly following a long day of flying–even in a jet that is significantly quieter than an airliner's first-class section. The down side is that one of the reasons people fly privately is because they can interact with colleagues along the way. And nothing says "leave me alone" like slipping on a headset.

If you're traveling with your boss, that might not be a savvy career move.

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