Active noise reducing headphones are avoided by professional sound engineers, while passive designs are used. Why is this?
It was 1978, on a return transatlantic flight from Europe to his home near Boston, that Dr. Amar Bose had an “ah-hah” moment that led to the design of the first active noise reducing headphones.
Bose tried a new set of airline-supplied headphones on the flight, finding their performance very disappointing. He couldn’t hear well, as the roar of the airplane engines drowned out the music, making it difficult to listen. Most of us would have simply written the the headphones off. Not, Bose.
The engineer took out a notepad and went to work on the flight, immediately designing and calculating what it would take to make better headphones for use while flying.
When he returned home, Bose, who ran the Bose Corporation in addition to teaching at MIT, established a research group wholly dedicated to the development of noise reduction technology. It would take ten years and $50 million before the first Bose noise-reducing headphones became available for sale.
Those first headphones were not for passengers, but for pilots flying the planes. To this day, Bose continues to sell its popular Aviation Headset X.
The Bose idea, conceived on the flight, was to compare all the sounds a person hears through the headphones – no matter whether it is music or offensive background noise. His patent uses internal microphones to sense when ambient noise is present and to instantly generate a “mirror image” of the unwanted sound.
This unwanted signal is then sent to internal electronics that creates the exact opposite sound waves — negating the original noise. The revised signal is sent to each ear-cup of the headphones, resulting is a signal with the unwanted noise reduced.
Other manufacturers (including some of the makers of active noise reduction models) make headphones with passive noise isolation, which are usually either in-ear monitors or closed-back headphones which tightly clamp over the head.
Over time, passive noise reduction has improved dramatically by using proprietary technologies in the ear cushions and physically blocking further undesirable noise before it enters the ear-cup.
Through the combination of active and passive noise reduction technologies, unwanted noise has been reduced and sound can be reproduced faithfully, especially with higher-end, better quality headphones. Both types of headphones are also now more comfortable to wear. Improvements are a continuously moving target.
Active noise cancelling headphones excel at blocking environmental sounds. They are most effective at lower and some middle frequencies like the humming sound of an airplane engine, which is why they are so popular with air travelers. They are most effective for users wanting to let louder noise into the ear while keeping the more constant and predictable ambient sound out.
This means active noise reduction headphones are more expensive and tend to be larger due to the added electronics. Newer models, like the Bose QuietComfort 35 ($349.95), also add Bluetooth circuitry for wireless use.
So why are headphones with active noise reduction not used by professionals for monitoring audio? There are several reasons. Noise cancelling technology is not 100 percent accurate all the time and can lead to occasional errors. Some units display a slight high-frequency hissing sound when turned on.
But the most important reason is some of the frequencies of the original recording are often cancelled out with the active circuitry. Active headphones, some critical users say, can give the illusion of better sound quality than there actually is.
Though active designs continue to improve, professionals have shied away from their use in professional monitoring situations. Whether that changes in the future is open to question.
Passive designs are generally favored by professionals, especially those who monitor sound in noisy locations. The tight clamping of some over-the-ear designs can make wearers uncomfortable, however, and even get headaches. A disadvantage with passive noise isolating headphones is also a poorer soundstage, meaning users don’t get the illusion of spacious sound that they do with high-end, open-back headphones.
With headphones, as with everything else, buyers get what they pay for. There are no absolute rules anymore for any types of headphones. For example, a model where users can get comparable soundstage even with closed-back design, are Beyerdynamic’s DT 770 PRO, one of the best closed-back headphones available for under $200.
Noise cancellation, whether active or passive, has changed headphone listening for nearly everyone. It makes it possible to listen to music without raising the volume excessively, helps pilots have comfortable conversations with the tower and helps passengers sleep in noisy airliners.
But when it comes to professional audio monitoring, active headphone designs aren’t quite there yet.
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