Section 5: Optimizing Your Flying Experience
NOTE: Dr. Jim Yates provided substantial
contributions to this section of ANR 101. Dr. Yates is Professor and chair,
S.P.A. of John A. Burns School of Medicine, University of Hawaii, and
principal of Audiology Associates Hawaii.
Previous sections of this series have discussed active noise cancellation
and the technical issues associated specifically with general aviation
headsets. We've discussed how ANR works, why it's so difficult to get
optimum levels of cancellation, and how to make ANR more effective in the
airplane noise spectrum. We've also talked about the basic physiology of the
human head and the difficulties faced in designing a headset that's really
Naturally, as with any other aspect of flying, safety and occupant
protection should come first, and comfort should follow. Although the
history of powered flight dates back nearly 100 years, concerns about the
effects of aircraft noise on hearing are relatively new. We've all heard the
axiom "there are old pilots; there are bold pilots; but there are no old,
bold pilots." We could add "and precious few with normal hearing." In fact,
in the days of open cockpits and wire struts, pilots flew with ears
unprotected and gradually damaged the hearing they desperately needed to be
safe while flying! It is said that the whisper test, still used in the
flight physical, has its roots in the perceived necessity for pilots to hear
the "singing" of the support wires while in flight.
The effects of "noise"
While it is true that most cockpits today are closed and there have been
advances in sound treatment (i.e. mufflers, soundproofing insulation, etc),
increases in engine power and extended aircraft range have largely negated
any advances in average "quietness." Today's pilots and passengers are
subjected to noise that can have numerous adverse effects, including:
- Permanent hearing loss
- Stress and fatigue
- Masking of "wanted" sounds
- Negative effects on speech perception and recall
Permanent hearing loss
The human auditory system is a bio-electrical marvel. It's capable of
hearing sounds from 20 cycles per second to roughly 20,000! Under ideal
conditions, the human ear is said to be capable of hearing a sound roughly
equivalent to pressure exerted by a gnat's wing, yet able to tolerate sounds
literally millions of times greater. So responsive is the ear that early
researchers adopted a logarithmic scale for hearing measurement. In this
scaling system, a sound of 100 decibels (dB) is 100,000 times greater than a
sound of zero dB, and a 120 dB sound is a million times greater than that
same zero dB sound.
Noise-induced permanent threshold shift can occur from repeated exposure
to damaging noise levels. In Section 2, we presented a chart containing A,
B, and C weighted noise curves. The "A" weighted curve represents a rough
equivalent risk associated with exposure to noise at various frequencies.
1-3Khz noise levels have more damage potential for human hearing than do
those of lower frequencies, though sufficient levels of low-frequency sounds
can produce permanent hearing loss.
One thing is certain: Beyond certain levels (about 85dB, A-weighed),
increased intensity and exposure time will produce increased hearing loss.
The hazard is most pronounced in the region nearer 4 kHz but spreads over a
frequency range as exposure time and dB level increases. In the typical
small aircraft, cabin noises tend to be concentrated in the lower
frequencies. Even so, noise levels in most aircraft are sufficient to cause
threshold shift losses if the exposure is sufficient in duration. Flying
without ear protection for long periods and with repeated exposures places
us at a risk of hearing loss.
Active noise canceling headsets provide relief in two distinct ways:
- They reduce the levels of low frequency noise exposure.
This issue was covered in detail in Section 3. Most GA aircraft have high
levels of low frequency noise and even the best passive protectors are
relatively poor at attenuating this part of the noise spectrum sufficiently.
The best active headsets are exceptional at this specific range.
- They permit the communications audio signals from radios and
intercom to be intelligible at reduced volume levels. Because of
the masking effects low frequency noise has on speech, we have to turn the
volume up to be able to (partially) hear normal voice frequencies. We often
will deliver more than 110db of communications audio directly to our own
ears (through the headset speakers) in an effort to better hear and
understand what's being said! With ANC systems, you will turn down your
audio signal because you can understand ATC much better. (We'll discuss the
audiological reasons for that shortly.)
Stress and fatigue
Noise clearly has the capability of producing stress and fatigue.
However, measuring and quantifying these effects on the pilot has proved
difficult. Stress is colored by previous experiences, conditioning, and the
character of the noise itself. Higher frequency sounds are generally more
disturbing and higher pitched sounds are often associated with danger.
One obvious aspect of stress levels is the perceived loudness of the
sound. Loud sounds are more stressful than ones of similar character but
quieter. Vibration and lower frequency sounds produce fatigue and influence
our ability to focus. The physiological effects of this constant "pounding"
on the nineBlack was studied in depth by the military as a source of mission
errors. The effect on the recreational pilot is less well documented, but no
less a concern in carrying out your flying "mission." Long-term exposure to
aircraft noise not only can produce fatigue but may also lead to mental
Obviously, active noise reduction systems reduce overall noise levels and
that "quieter" environment makes flying less stressful. The effect of
reductions of low frequency noise on a pilot's mental condition hasn't been
well studied, but the anecdotal reports we hear are consistent: pilots
regularly comment on how much better they feel both during and after flights
when they wear ANR headsets.
Masking of "wanted" sounds
While human speech ranges in frequency from slightly below 100 Hz to as
much as 10,000 Hz, the energy of speech is heavily concentrated in the lower
frequencies. 90 to 95 percent of the energy of speech is in frequencies
below 500 Hz. Typically this energy is concentrated in the vowel sounds. The
consonants carry most of the meaning of speech in the 1 Khz to 6 Khz range
but these are very weak (low energy) sounds. Consequently, the weak
consonants are easily "masked" by noise, making it difficult to understand
what's been said. It doesn't take much masking before intelligibility is
impaired, as the following data from one study of adults with "normal"
|Loss of Consonants
|4% or less
|15% or more
The implications for pilots are straightforward: even a 10% loss in
consonant sounds will substantially limit comprehension! Obviously the
danger of missing or mis-hearing verbal instructions is a very real
Given what we've already learned about the low-frequency dB levels
encountered when flying, excessive levels can easily overwhelm the important
consonant sounds. The danger of "masking noise" in an aircraft is that we
may miss important signals either from controllers or other warning signals
that we really need to hear accurately. Masking noises contribute to stress
levels as we "strain" to hear, process, and understand the multitude of
signals and data we manage as we're flying. In a real sense, masking of
"wanted" sounds may be the biggest danger in an aircraft.
Active systems reduce the masking effects of the low frequency spectrum
your ear hears. The most effective systems will substantially enhance your
ability to hear and understand the audio communications. Virtually every
pilot who tries an ANR headset for the first time notices this benefit.
Negative effects on speech perception and recall
Elevated levels of noise substantially impair our ability to recognize
words. When noise levels exceed 85 dB, they begin to have adverse effects on
the speech comprehension. The key to greater word recognition is in getting
the communication audio "signal" significantly above the ambient "noise."
That's a hard task for pilots since we're exposed to cabin noises with a
significant low frequency component. When audiological professionals want to
create speech masking sounds, that's precisely the type of noise they use.
The typical cockpit is an excellent speech masker!
Studies have shown we need at least a 9 dB difference in the audio signal
above the "ambient" noise levels in our headset to achieve 80% word
recognition or better. That difference in dB level is typically expressed as
Signal-to-Noise Ratio (abbreviated S/N or SNR). A S/N ratio of 12-15 dB
allows a 90% recognition rate. We know how loud the noise spectrum is in
most planes...particularly at the lower frequencies. The combination of
masking effects and overall ambient sound levels makes hearing and
understanding communication very difficult. Most of us know what that
"sounds" like...from ATC calls we miss altogether to ones that prompt us to
make repeated "say again" requests. The higher background levels of noise
when flying also changes our hearing "threshold," making previously
understandable words unintelligible. Beyond just the S/N ratio issues
involved in protecting word recognition, our ability to "process" speech and
sounds is adversely effected by higher background noises. For example:
- Accuracy of comprehension declines as does response speed.
- Time sharing of attention among several potential signals becomes more
- Recall (memory) is impaired, as is our ability to handled delayed
In other words, noise affects our understanding, attention sharing,
response time, and short-term recall of what was said. None of these are
good things for a pilot, so anything that can be done to quiet things down
Some final thoughts
The intent of this section is not to frighten, but to serve as a reminder
of all the sound-related issues we deal with every time we fly! Being a
pilot is a complex "job" with many responsibilities. You probably have been
using a basic passive headset and those help you stay on top of your many
tasks. ANR will make doing those tasks both easier and less stressful. An
ANR headset provides additional noise suppression in an area of the noise
spectrum that will make communication clearer and increase
ANR will make you a safer pilot. It'll protect you from long-term hearing
damage. You'll finish the flight more relaxed and enjoy flying more. A
modest investment can enhance the health, comfort and safety of your flying
experience to levels unheard of just a few years ago. So keep your altimeter
up and your dB down!