From ANR to dB

One thing is for certain in the long wars over whose top-line headset is the best: customers have better choices than ever.

At Sun 'n Fun, I spent some time with three of the premier headset makers, and was able to make time to receive two presentations. In a future edition of ANN, you'll see a side-by-side-by-side test of several of today's best ANR (active noise reduction) headsets; for now, I'll tell you what I learned at the show.

First, there's no free lunch. These sets all cost from several hundred, to nearly a thousand dollars. They're all better than the bgest-available sets of just a few years ago, and, considering I paid over $900 for my Telex ANR set twelve years ago, they're (relative to inflation) becoming more affordable.

'The myth' is dying, as well it should.

Active Noise Reduction is still somewhat misunderstood. The principle is that each ear cup has within it, in addition to the traditional speaker, a microphone, and additional circuitry. The mic hears noise from the environment and relays that info to the circuitry; and the speaker then manufactures an identical sound inside the ear cup -- but exactly out of phase, or "backwards." That additional sound, the theory goes, exactly cancels the outside noise. The misunderstanding is that ANR sets cancel ALL the outside noise -- not just the fatiguing engine drone, but also the "noise" of passengers, stall horns, gear horns... It's not the way it's designed; and it's not the way it works in practice.

Engines and props hum. People chatter.

Modern noise-cancelling sets attack primarily the engine and propeller noise, which are typically lower-frequency sounds. 90 Hz (90 cycles per second) is the de facto standard frequency that is most-attenuated by the circuitry. The higher frequencies, where gear horns and your passengers' speech predominate, receive very little, if any, attention from the noise-canceling circuits. The human voice generally occupies the 200~2000Hz range.

Your mother-in-law will still sound quieter in most cabins when you wear your headset, because the set itself blocks some sound (plain old "passive attenuation"); but she may be more-understandable, because your ears won't have to block that low-frequency sound the engine and prop are making.

Factors:

All the manufacturers agreed, that "any headset is better than no headset," but they also stressed that it's important to use the best set you can afford, right from the start. Although it's tempting as a student to buy a low-cost passive set, your ears will last longer if you start with a great set, right away. Why wait until after your hearing is damaged, to start wearing a set that helps you hear, and protects your diminishing asset? Hearing damage is continuous and cumulative.

Several things go into determining 'the right headset' for you. Perhaps the most-important is individual comfort. Different peoples' heads are different shapes; some headbands and ear cups are more-comfortable for some people. A lot of us wear glasses -- how well does the ear cup seal around the temples? Is the clamping force sufficient, or excessive? Are we flying in a Falconjet, or an open biplane? In other words, will we wear the set, and will it be comfortable in our regular use?  Heavy clamping forces may be necessary in the Stearman -- can we lighten the clamping load in the Extra 400? Most pilots' heads aren't symmetrical; many pilots' ears aren't both put on at the same "altitude;" everybody's ears are different, too -- angle, size, and shape... and don't forget the glasses. Some prefer the plastic, gel-filled earpieces; others like soft leather and foam. Each has relative advantages and drawbacks.

To publish, or not to publish: that's one question.

The Bose people said they don't 'engage in the dB wars,' meaning that they don't publish numbers about how many decibels' reduction in outside noise their sets produce. Telex, on the other hand, has numbers for all their sets. Why the difference?

The Telex demonstration was a case in point, demonstrating to me why each company would have its own tactic. The test, well-constructed for a field demonstration, used an enclosure with anechoic foam and a large speaker inside, producing calibrated noise for an aluminum billet "head," on which various headsets were placed.

First up was the new Bose 'tri-port' set, with perhaps the lowest clamping force in the industry. Bose, which believes its new technology allows the mechanical forces to be reduced, also uses leather-covered foam cups. The result on a block of aluminum is that the Bose set doesn't "grab" very tightly (and if your head is smooth aluminum, it won't grab you, either). The Bose set was tested, and a digital oscilloscope showed noise attenuation on the adjacent screen. That attenuation curve was preserved, as another headset was auditioned. Finally, the Telex Spectra 50D (top photo) was placed on the aluminum 'pilot,' and the test was run again. Strangely (since this was a Telex demonstration), the Telex attenuation curve was indistinguishable from a low-cost competitor's! Our demonstrator opened the test box, saw that he had placed the Telex set a little off-square on the test head, and repositioned the headset. Voilà! the Telex headset outperformed all comers. Then, before I tried on the Telex set, my demonstrator loosened the clamping force on the headband.

That little demonstration points out that any laboratory test results, in order to generate comparable data, need to be carefully controlled; it's also important to note that dB reduction is highly frequency-sensitive -- and that's a deliberate function of the circuit's design. Consider also that any lab test, no matter how fairly-designed and administered, will, by virtue of the fact that sets are designed to do different things, 'favor' certain designs. Your own head, though, cares only about what it needs -- not what the results would be on someone else's head, or in a lab. The tests are important -- they'll narrow your choices; but don't rely only on the tests, before you send your stack of hundreds to the nearest pilot shop.

The Bose demonstration was opposite in approach. I was invited into the big Bose truck/studio, and subjected to the noise from a Bradley Fighting Vehicle. [Actually, the noise inside a real Bradley is in excess of 100 dB at certain frequencies; our room was limited to 90~92 dB, in the interest of not rendering deaf any poor soul who pulled his headset off early.] Bose explained that their design goal was to provide ultimate comfort, with "enough" noise cancellation. Its magnesium headband, light clamping force, and protien leather-over-foam earpieces, along with other features, certainly meet the "comfort" criterion. The 11.5 ounce set also makes "riding in the Bradley" a tolerable experience. How many dB of attenuation? I don't know. Was it 'enough?' Sure -- but would a different set have 'felt' better? I don't know -- I didn't bring a different set. Would I be happy with the Bose performance? You bet... but I don't know how convinced I'd be, unless I tried a lot of sets. Side-by-side -- you gotta do it.

Why you need to use your own head:

Do you want a TSO'd headset, so you don't need auxiliary power? Are you worried about 'special' battery needs? Do you want stereo? Do you need a dynamic mic, or do you prefer an electret condenser design? Left-hand hookup, or right -- or is your headset adaptable, either way? Do you need adjustable clamping force? Do you wear glasses, or a hat? How long do you fly, at a stretch -- is weight, by itself, a major concern? Are you typically rough on equipment -- is cord or plug design a factor?

In other words, although you'll get some idea of which headsets you want to consider from reading the manufacturers' literature, it's important to actually try them yourself. If you're lucky enough to do it in your own airplane, that's even better. Several manufacturers will sell a set on a 30-day return. If your credit card will stand it, consider 'buying' all of your top choices, and flying with them, under as-typical conditions as possible. Then, keep the one you love the best. I've kept that old Telex set for a dozen years...

FMI: www.bose.com/anrheadset; www.telex.com/aircraft