Plane & Pilot
Tuesday, August 11, 2009

Headset Guide: Technology Still Rules

New developments in sound technology

Beyerdynamic HS 300
When I came back to aviation after a 20-year absence, one of the biggest changes was headsets. Back when I was training, it was considered a big deal if you had even one of those boom microphones with the little Velcro push-to-talk switch that you would carry from airplane to airplane. Most pilots still shouted over the engine noise and used the airplane’s cheapo speaker to hear ATC. Hearing damage was just starting to get headlines, but few people thought about it within the context of aviation. Fast-forward to today, and as little as $100 will buy you a headset that will protect your hearing pretty decently.

While it’s no secret that doctors warn about cockpit noise seriously damaging your hearing, few pilots understand the mechanics of why it happens. Understanding how your hearing is affected by flying can help you choose the best headset for your particular environment. Also, it’s not enough to focus only on the noise attenuation ratings given by headset manufacturers, because that’s only one small factor in a headset’s ability to protect your hearing. There’s more to the headset than meets the ear.

Peltor 9500 Digital
Hearing Damage 101
The sound in a cockpit (or anywhere else) is a mechanical form of energy. Sound waves are variations in air pressure that can be measured by three distinct variables: frequency, intensity and duration. Frequency is measured in wave cycles per second, or hertz (Hz). Sound that’s audible to the human ear falls in the frequency range of 20 to 20,000 Hz, with human speech in the range of 500 to 3,000 Hz.

Sound intensity is measured in decibels (dB), with the average human ear having greatest sensitivity between -10 dB and +25 dB. Duration is a measurement of how long a sound lasts. Coupled with intensity and frequency, the hearing damage caused by exposure to an intense short-duration sound can be as bad as exposure to a less intense sound for a long period. Finally, noise refers to any unpleasant or unwanted sound. In aviation, there are many sources of noise, with the two main culprits being engine noise and slipstream noise—the sound of air going over the airplane’s fuselage.

Great strides are being made in headset technology, with many developments being driven by the music industry—a longtime pioneer of sound.

Doctors warn that steady exposure to sounds around the 90 to 110 dB intensity range will cause permanent hearing loss. Unfortunately, the average small airplane cockpit noise level is right at that range. Sound duration is also a critical factor. While exposure to 90 dB for eight hours can cause permanent hearing damage, exposure to 110 dB for as little as 30 minutes can do the same harm. It’s interesting to note that many busy city streets and public address systems fall right into the 100 dB range. Rock concerts are typically around 120 dB, and most airliner cabins are between 60 and 90 dB.


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