Cockpit noise is far more than just a nuisance.
I live and work at a small airport. That makes me an expert on noise. I’ve heard it all, from the thop-thop of helicopter blades beating against thick morning air to the supersonic roar of propeller blades on a Cessna pulling it skyward; from the hum of GE turbofans on takeoff to the gentle chirps of rubber on asphalt, followed by a deep roar as the pilot hits the thrust reversers.
And that’s just what I hear standing outside my office. External airport noise, real as it is, generally pales in comparison to the hearing-damaging decibels most of us encounter when our ears are unprotected in the cockpit of a small piston- or turbine-powered propeller airplane or helicopter. I’ve been subjecting myself to these kinds of noises, both on the ramp and in the air for neigh on 45 years, first as a passenger, then as a professional pilot and I can tell you, hearing loss in our profession is real. And the fatigue that comes from being subjected to such loud and constant sound all day or night long is real, too.
Let me quantify this for you. How loud is too loud? Permanent hearing damage can occur from sounds louder than 85 dB, and physical pain occurs at around 125 dB. You can burst an eardrum at 140 dB—a level reached by a jet engine revving up on the ramp as its pilot throttles up to taxi out for takeoff. The graphic at right shows how much a human ear can stand before damage. OSHA requires workers exposed to noise levels higher than 85 dB to use hearing protection equipment.
OSHA is not being overprotective. I fly one of the noiser airplanes out there, an RV-10 with a two-blade propeller. Two-blade propellers are longer than three blade varieties, and have been documented as making more noise. I’ve also got fixed gear, and no sound insulation (we never even got around to putting in a headliner). Measured decibels on takeoff from inside the cabin are—yeah I’m not going to tell you. It’s bad.
Our solution to the noise problem is pretty modern and probably as lightweight as you can get: we opted for high quality active noise canceling headsets. To cancel the lower-frequency portions of the in-flight noise, noise-cancelling headphones incorporate a microphone that measures ambient sound, then generate a waveform that is the exact negative of the ambient sound, and finally, they mix it with any audio signal. Most noise-cancelling headsets in the consumer market generate the noise-cancelling waveform with analogue technology.
Digital processing is the next frontier, and the realm of the high-end headsets. The most sophisticated ANR headsets use digital sound mapping to customize their noise cancellation. Bose A20, Lightspeed Zulu PFX, Sennheiser S1, AKG—these headsets demand a premium, but put them on and fly with them in a noisy cockpit such as mine, and you’ll understand why.
To prevent higher-frequency noise from reaching the ear, most noise-cancelling headphones depend on soundproofing and an excellent fit around the ear. Higher-frequency sound has a shorter wavelength, and is tougher to cancel out. In-the-ear headsets such as Clarity Aloft can claim to efficiently dull the higher-frequency sounds of wind over the fuselage (its louder than you’d think), and generally can do so without the need for active noise cancellation. On long trips it is nice not to have an over-the-ear headset squeezing the stuffing out of my brain. That said, a lot of people don’t like the feel of earplug-type headsets in the ear canal. And if the fit isn’t perfect the noise seeps in. For a price some of these headsets can be fitted with custom shaped ear plugs, but that requires an audiologist to fit them, and a lab to make them.
There are some people who insist that headsets are not the only answer. They spend a lot of time and money insulating their light aircraft cockpits from sound. Today’s lighter weight materials can, if properly applied beneath the floor panels, side panels, bulkheads and headliner, soften external low and high frequency sounds to bring the level at cruise down below 80 dB, but not much lower.
I’m not a fan of the extra weight and complexity that such sound deadening material can add to an aircraft (complexity comes in if you have a certified aircraft: think field approvals and STCs here). I’d rather spend that money on lightweight, high-end digital ANR headsets to connect everyone in my cockpit. I put that money into a decent audio selector panel and intercom, with the ability to isolate the pilot from the conversation in the cabin, when necessary. While I’m isolated and able to communicate clearly with ATC, my companions can talk amongst themselves or even listen to music during the flight. Everyone is happy, and their hearing stays intact.