Section 4: Ergonomic and Interface Issues
In this section, we'll be looking at the comfort and human-factors issues
associated with ANR headsets. The ergonomics of the human head demand a wide
range of adjustments to deliver comfort over hours of use.
Optimizing the physical headset for pilot use
Active pilots have been searching for ways to improve the physical
aspects of the flying experience, but it's not easy to design a comfortable
headset, as you'll see. While active cancellation certainly helps you feel
more relaxed during your hours aloft, you're still constrained by the
physics of pressure, weight, and temperature.
In many ways these comfort and fit issues apply to all headsets...not
just active ones. But the human factors relating to user convenience are
certainly more complicated for ANR headsets. ANR places additional
constraints on the cavity and ear seal design. Furthermore, the electronics
for cancellation require power, and most are supported by some form of
portable power pack. The size and weight of such packs can be a pilot
convenience factor, as can various other features available in the newer
A comfortable headset... the search for the Holy Grail!
Comfort is a relatively recent addition to the pilot's want-list. Early
on, hearing protection and hands-free communication were the principal
reasons for using a headset. The original and most popular headset design
was developed for optimal passive attenuation. The focus was on military
needs, and thus for noise environments often much harsher than those we
encounter in General Aviation.
As needs and materials evolved, some changes were introduced to reduce
weight and improve comfort. But unfortunately, these evolutionary changes
have done little to add comfort in this "classic" headset design.
Why is it so hard to design a headset that fits well and wears
It turns out there's substantial variation in the size and shapes of
human heads. The chart below is data gathered from military ergonomic
standards for head sizes. It compares the dimensional differences for men
and women covering the 5th to 95th percentile of people...basically almost
the whole population!
The challenge for fit: the 5-95% dimensions for head width, height, and
|| 11.6 cm
|| 14.4 cm
|| >1" (each side)
||Head Breadth (width)
|| 13.5 cm
|| 16.5 cm
|| 31.3 cm
|| 37.8 cm
|| 1.3 cm
|| 2.8 cm
Source: Human Engineering Design Criteria for Military Systems,
As you can see, the challenge to get both adjustability and a comfortable
fit is a difficult one. The classic design relied on side pressure to
compensate for the width variations. The metal overhead band has some
adjustment for circumference but no accommodation was provided for ear
protrusion. In analyzing how to make a more versatile headset design, the
issues boil down to size and side pressure!
Obviously the headset needs to adjust big enough (or small enough for
ladies) to properly fit at the start of your flight.
Look at some of the variability in things like head width (over 1 inch!)
or the position of ears on the side of an "average" head! Overhead
circumference means the headband needs to have ample "length" adjustment to
extend the needed 2.5 inches. That's a lot. Ladies and children need it to
compress to fit their smaller heads. Yet many pilots are men with size 7 3/4
hats!! While all this is certainly possible, you'd be surprised how many
existing designs cannot cover that range of heads.
Comfort over time
But for most of you, your "comfort problem" isn't that your headset can't
fit you when you first put it on, but rather that it starts to hurt after a
short time. If you have flown much at all, you also know your comfort needs
change some over the 1 or 2 or 4 hours you might be flying.
Without getting too medical, let's try to understand why. There is very
little "subcutaneous fat" (flesh, padding, etc!) under the skin covering
your skull. The head is also extremely vascular (there is lots of blood
flowing around under this thin layer). The area around the ears is
particularly dense in blood vessels. Head surfaces get tender or "fatigued"
by constant pressure and typically develop sore spots from wearing a
headset. These "hot spots" are actually places where the blood flow has been
constricted (from pressure) and become sources of pain! The combination of
little fat and high blood flow makes this region hypersensitive to
With that understood, then, a premium is placed on "uniform" distribution
of the weight...both over the top of the head and the compression exerted by
the earseals around your ears. Making a headset lighter in total weight is
good, but actually the distribution of that weight is the more important
variable to comfort. Heavier headsets with pads that distribute weight
evenly over a broad area will feel much more comfortable than one that is
lighter but has limited contour distribution over the top of your head.
That's accomplished by proper radial design of the headband system and
effective padding. In summary, the comfort of your headset will have a lot
to do with the overall design and the "head interface"...the way it fits and
conforms to your head shape and ears.
Those all-important ear seals
The ear seal design is probably the most important aspect of overall
flying comfort. Size, shape, and material choice all affect the comfort of
the headset, as well as its noise attenuation in both passive and active
modes. It should be noted there are several "special" aspects to consider in
designing a comfortable earcup cavity. Ideally, the ear would be floating
free in the cavity...not touching any aspect of the seal or speaker system.
That has a direct bearing on the size, shape, and construction of the
optimal ear seal:
- Cavity opening orientation: As noted in Section
1 of this series, proper orientation and shape will also help isolate
the ear from the seal. Many pilots actually tilt their 'oval' shaped domes
backward to better align them with their ear.
- Cavity depth: Notice the >1/2" variation in "ear
protrusion" on the above chart. This must be accommodated either in the
depth of the ear seal or in the dome cavity opening.
- Cavity volume and ventilation: Greater depth also helps
in keeping the ear cooler...more air space that heats up slower. The
material used to surround the seal would also ideally be
breathable...minimizing humidity (and sweat buildup) around the ear. Within
reason, larger is better when designing for ear comfort.
Obviously we'd like the ear seal to create a cavity space that is both
comfortable and quiet. It turns out there are tradeoffs between optimal
comfort and getting the maximum passive attenuation. Let's take a look at
different materials used in ear seals to learn more about the strengths and
weaknesses of each.
Ear Seal Material Characteristics
- The ability to cross-sectionally block out noise.
- How easily the material will flow to cover an uneven surface.
- The amount of pressure needed to seal against a vertical uneven surface.
- The weight of a "normal" aviation earseal for various ANR headset.
- Compared to a silicone seal, how large is the cavity volume created by
the ear seal.
You'll notice that the best materials for blocking out sound are liquid
and silicone. Liquid certainly conforms the best to uneven surfaces (like
the side of your head!) but requires reasonable pressure because of the
vertical orientation...the liquid will stay at the "bottom" of the seal
unless the side pressure is adequate to "squeeze" it up around your ears. In
a headset application, the silicone is actually better since it will stay in
place. Foam/liquid and Thermal-conforming foams don't have as much
cross-sectional density to provide the best attenuation passively.
From a comfort standpoint, silicone gel seals may not be the best choice.
It is a dense material ...does not easily conform to the many variations
around the back of your ears. It only conforms under relatively high
pressure (compared to the other choices). It provides adequate relative
volume but is quite heavy...twice the weight of the other ear seals! Liquid
seals provide very little cavity volume and require medium side pressure for
a good seal. Temperature-sensitive foam materials are clear winners for
conformability, minimum side pressure, and ear cavity volume. It's
particularly effective when wearing glasses. The conformability helps
minimize the localized pressure of the stems pushing on your temples! All of
those characteristics will translate into a more comfortable headset.
As we have pointed out earlier, the best and only sure way to
decide about comfort in a headset is to fly it.
What does this have to do with ANR performance?
Comfort and fit, by themselves, have little to do with active
cancellation but ear seal conformability does. Remember back to Section
1, the discussion about needing a stable acoustic cavity for maximum
cancellation. Even more than in a passive headset, an ANR headset needs to
provide an "acoustically tight" fit. Tight doesn't have to be vise-like, but
a good seal to the head is required to get proper cancellation If you doubt
this, lift off the ear seal of an active headset while flying. You'll hear
the system become unstable and start to oscillate.
Particularly when the amounts of active cancellation are high, a stable
acoustic cavity with no "leaks" is important. That seal comes from either a
dense material under high pressure or something of lower density with lower
What about lightweight ANR headsets... Do they work?
For many pilots, the "superaural" headsets might be more comfortable.
These are the type that sit "on" the outer surface of the ear. They are
light in weight and provide good ventilation for the ear. Their obvious
disadvantages include limited noise isolation, limited passive protection,
and a lack of basic headset features like volume controls.
Because of the sensitivity of the ear surfaces, sometimes these actually
are less comfortable than a typical over-the-ear headset. For some
cabin-class planes, they may be a nice solution. If you have a really quiet
plane, give them a try and compare them to a circumaural (muff-type) for the
tradeoffs between comfort and peaceful flying.
Powered headsets...what a hassle!
The one issue that is most noticeable about active systems is their need
for an external power. With passive headsets the sidetone audio (what you
hear) and the voltage to drive your microphone preamp (for what you say) are
supplied by amplifiers in your avionics. The result is you have no need for
external power for that headset to work. In active headsets, additional
power is required to support the active electronics in the headset itself.
1, we discussed the efficiency of various speakers and electronics and
how they would effect cancellation performance and battery life. All that
ties into this discussion of power and portability.
The majority of ANR headset users require portable power. For most
pilots, a portable ANR system conjures up images of large, bulky battery
packs with a rat's nest of extra cables. That was the norm up until just two
years ago. As a result in improved efficiency, the "typical" ANR headset
battery box went from 6 AA's and a separate cable to just 2 AA's placed
inline with your normal headset cord. All that while battery life stayed in
the 50 to 60 hour range...months of flying for many of us! Most pilots favor
portable ANR headsets that use AA batteries rather than 9-volt batteries,
since most pilots already carry a stash of AA's for their handheld GPS, mini
Maglight flashlight, etc.
Then there's the problem of leaving the headset on at the conclusion of a
flight, something that doesn't do much for battery life! Certainly the best
solution for this dilemma is some "Auto-Off" feature built into the headset.
This feature is now available in several forms. One method senses when you
have it off your head, and automatically shuts off. Clearly the most
convenient method. Others sense the presence of power (commonly from the
radio or intercom) and will shut down in 10-20 minutes after THOSE devices
are shut off. Some form of Auto Shut off should become a standard feature of
all ANR headsets in the future..
People have asked about using rechargeable batteries with ANR headsets.
You can use rechargeable AA batteries in most battery-powered units, though
the life expectancy drops about in half (compared to alkalines), and making
sure that they are always recharged before flight can be a hassle. Some ANR
headets have built-in rechargable batteries, offering the benefit of no
extra "box." The built-in battery can be convenient as long as you remember
to take the headset out of the plane after each flight and charge it fully
for the next use. As with all rechargeables, battery life is substantially
less than with alkalines, but more than adequate for normal flying...if you
remember to charge them before flight.
While battery life is important, the truth is that more batteries are
lost to forgetfulness (forgetting to turn the headset electronics off) than
to sheer hours aloft. That's really the "Achilles heel" of a rechargeable
headset...if you forgot to turn it off yesterday, you are out of luck with
active cancellation today! The rechargeables can't be charged in-flight
while you're using the headset, and you can't change the batteries before or
during flight if the built-in ones run low.
ANR headsets powered from aircraft power can solve these problems and
completely eliminate the issues of batteries, battery boxes, etc. Most
aircraft-powered ANR headsets have integrated panel jacks that allow for a
clean, single connection for all audio and power connections. Others provide
a separate power connection (via the cigarette lighter or a separate power
jack), but this means you have to plug in three separate connectors (mic,
The convenience of the panel-wired single connection is great, but
installation is something that should be done by an avionics shop, so plan
on additional $150-200 installation expense for each headset position.
Unless you fly an awful lot, this could be equivalent to a lifetime supply
of AA batteries! That's one reason that for many pilots, a portable model
makes more sense.
Most of the latest generation of active headsets come with a full set of
standard features for easy use. These would include dual volume controls,
stereo/mono capability, some form of battery gauge, and a padded bag for
carrying and protecting your investment. Different suppliers provide these
features and functions in slightly different ways, so make sure you pay
attention to them when you test-fly different headset models.
Now you know more than you probably thought possible concerning what
headset design factors contribute to a comfortable flight. In the final
section of this series, we'll tie together all that we've learned about
hearing protection, improved communications, and comfort...when we look at
the physiological issues that affect the pilot. We'll explore how
low-frequency noise affects fatigue -- both mental and physical -- and how
that can affect pilot reaction times and decision-making capabilties. A
fellow pilot who is an audiologist will be contributing to this discussion,
drawing from his professional knowledge and experience to help address these
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