Headsets and hearing loss

It makes sense that pilots would be testy about headsets. While we’re in the air, they let us communicate with air traffic control, talk to our passengers, or even listen to music on those long cross-country trips. They also serve to protect our ears from the noisy environment of the airplane. But how do I know for sure that my headset is doing what the marketing spiel says it’s doing? How can I quantify if it is or is not protecting my hearing, and more importantly, how does that compare to the headset the other pilot in the FBO is passionately defending?

One of the primary issues we as pilots face is that risk of noise-induced hearing loss is not only dependent on the level of the sounds around us, but also the amount of time we spend subjected to those sounds. The noisy environment of an airplane may not be damaging for a few minutes at a time, but rarely are we only in the airplane for only a few minutes. The more time we spend in a noisy cockpit, the more susceptible we are to permanent, irreversible hearing damage. Organizations such as the National Institute for Occupational Safety and Health (NIOSH) and Occupational Safety and Health Administration (OSHA) both publish standards for “how loud is too loud” in the workplace, but since we don’t pack calibrated noise level measurement rigs to take flying with us, the numbers are difficult to apply. Fortunately, we can still take data from the ground that can be useful in quantifying the effectiveness of headsets.

One of the primary issues we as pilots face is that risk of noise-induced hearing loss is not only dependent on the level of the sounds around us, but also the amount of time we spend subjected to those sounds.So, let’s talk about where noise comes from while we’re in an airplane. In 2002, a pair of NASA scientists rigged up a bunch of microphones in a Cessna 182 to see if they could reduce cabin-level noise using a variety of nontraditional soundproofing measures, including (my personal favorite) an unairworthy twelve-foot exhaust pipe. The results were interesting but could basically be summarized as “airplanes are loud, and there’s no great way to make them substantially quieter without making them extremely heavy and covering up all the windows,” an idea many VFR pilots oppose. This is a concept you probably already understand if you’ve ever flown in a general aviation aircraft: Airplanes are loud, and without proper protection we risk permanently damaging our hearing. Have you ever tried whispering something to an old pilot?

Because our hearing is more susceptible to damage at some frequencies more than others, it’s important to consider not only the volume of noise, but also its frequency. It’s generally stated that humans hear sounds from around 20 Hz to about 20,000 Hz, with our ears being most sensitive in a range of upper mid frequencies (around 1,000 Hz to 5,000 Hz), which happens to line up with where the bulk of speech intelligibility lies. Accordingly most headset designers aim for “peak” protection in this range. It’s important to note, however, that “most susceptible” does not mean “only susceptible.”

The final thing we need to consider is that hearing perception is totally subjective and can vary widely from person to person. My ears are different than your ears, and there’s no way for me to experience sound in the exact same way that you do. Fortunately, the characteristics of headsets are measurable, and so with some applied science, we can provide fuel for your FBO debate. Headsets are designed to attenuate (reduce or “turn down”) noise differently in different ranges of the frequency spectrum, so after some experimentation, we can draw some conclusions about their ability to protect our hearing. I performed an experiment in my attic comparing a couple of popular aviation headset styles and their respective abilities to protect hearing across the frequency spectrum.

Airplanes are loud, and there’s no great way to make them substantially quieter without making them extremely heavy and covering up all the windows—an idea many VFR pilots oppose.If you’ve ever been to an audiologist and had your hearing tested, odds are you’re familiar with an audiogram. In an audiogram, the subject is given calibrated headphones to wear and is presented with tones at various levels to measure where the “floor” of their hearing is across the frequency spectrum. For this experiment, I gave myself a modified audiogram, using a speaker in place of headphones, and an oscillator to generate pure tones at octave centers (beginning at 63 Hz), turning the level up until audible, and then made note of that level for each octave tone. I then repeated the experiment with different headsets, and charted the comparison between the base hearing response and the attenuation of the headset below. (For the testing purists, the noise floor of my experiment area was measured at 39 dB LAeq10, and the experiment was replicated five times and averaged to eliminate error).

Presented here are two aviation headsets: a commonly used passive headset, and a commonly used active headset, tested with ANR activated and deactivated. For comparison, I also tested a pair of disposable foam in-ear plugs (often called foamies) you may have encountered before. For those unfamiliar, a passive headset has no electronic noise cancellation built in. Instead it relies on physical isolation via a robust design, tight fitting ear cups, solid surfaces, and absorptive earcup material which reflect and block sound from entering the ear cups. Active headsets, by comparison, rely on a microphone outside of the headset and a bit of audio magic and math to actively cancel sounds in the ear cup. An active headset with the ANR turned off works like a (very expensive) passive headset.

The chart shows the relative attenuation of the headsets at eight different points across the frequency spectrum. On the y-axis is the relative level of the oscillator compared to my base hearing, so the further down (lower) the value on the graph, the more effective at eliminating noise the headset is at that frequency.

The data indicates that a passive headset behaves a lot like foamies do, with a minor amount of discrepancy in the higher frequencies. Sound waves, just like radio waves, microwaves, or even visible light all have a wavelength, which is the distance it takes a sound wave to complete one full cycle. The wavelengths of higher frequencies are often magnitudes shorter than lower frequencies, which means we can construct a physical barrier (either a wall of tight foam or a rigid, tight sealing shell) that will prevent the weak sound waves from penetrating. Lower frequencies, however, have much longer wavelengths and the physical barriers are much less effective.

While the ANR provides comparable protection in the middle and upper frequencies, it really earns its salt in the low/low mid frequency ranges, providing much more noise protection than any of the other models. If you’ve worn ANR in a cockpit before, this probably makes sense to you. Once you turn on the noise reduction, the engine and exhaust noise are decreased significantly. Although humans are most susceptible to hearing damage in the mid/high frequency ranges, hearing damage can occur in lower frequency sounds as well, and for long-term exposure in the cockpit, ANR can help mitigate those risks.

Another noteworthy comparison is the active headset with ANR turned off versus the passive headset. This is another common point in the FBO debate—My active headset with ANR turned off works just as well as a passive headset—but the data doesn’t support this argument. We see much more attenuation in the passive headset because of its design. The passive headset features rigid sound cups, tighter sealing rings, and more clamp against the head, which, as we’ve already discussed, form a physical barrier between your ears and the noise. The active design, by comparison, compromises some of the structural integrity used for passive noise reduction in favor of weight reduction and user comfort. While an active headset with ANR disengaged is better than nothing, it’s certainly not favorable in the long term.

The data, while interesting to people like me, confirms what most pilots who’ve flown with active headsets can already tell you. ANR is a night and day difference over the protection benefits of a passive headset, and you really want to carry spare batteries, because if your ANR dies in flight, it’s going to get a lot louder fast. The sticker price of a good ANR headset can cause jaws to drop, but when you consider the risks of long-term noise-induced hearing loss on your ability to fly, the investment more than pays for itself.

Joshua Boatman is a private pilot and live sound engineer living in Tulsa, Oklahoma.