Black Box Basics

The Art of Noise, Revisited

November 1, 1991

Checking on the state of active-noise-canceling headsets

Ah, what a difference a little time makes. When we last checked in on the latest developments in active-noise-canceling (ANC) headsets, two years ago, they were still something of a novelty. Only the Bose Corporation had a set ready for the market, the Bose Aviation Headset, and its near-$1,000 price tag was better than three times the cost of high-line passive headsets of the time. Many pilots wailed at the bulging price tag, but as they started to get an earful of the Bose's capabilities — both through the company's extensive demonstrations and word of mouth from owners — quite a few of them changed their tunes and let the pocketbooks do the singing.

In our last review, we looked at the production Bose headset, a prototype set of Telex's ANR headset, and a very early version of Sennheiser's lightweight ANC unit (see "The Art of Noise," December 1989 Pilot). Now Bose has been joined in the marketplace by the Telex ANR and by the David Clark DCNC. Sennheiser's HMEC-series lightweights have been sold to Lufthansa and are being considered as optional on a number of business jets. A muff- type active set is still on the drawing boards, says the company, probably to use Peltor, Incorporated, domes and ear seals.

For those who missed the original installment on active headsets — and the technology involved — herewith a brief recap. Comfort in traditional headsets — meaning full-ear-cup, muff-type — has largely been a compromise. Very light headsets with little clamping force are quite comfortable but usually cannot provide an appreciable level of noise attenuation. Muff-type headsets are effective at reducing the racket you hear, but as pilots have long lamented, some of the units become almost painful after a few hours' use. With passive sets, you get a simple trade-off: comfort or quiet but not both.

What's more, even the quietest noise-attenuating headsets, while quite good at filtering out high and mid-frequencies, can do little with low- frequency pulses like the thrum of the engine and beat of the propeller. Studies indicate that low-frequency sound can be some of the most fatiguing, too, and it is the predominant frequency of noise in an airplane cockpit.

Electronics help the active sets step in on the frequency spectrum where mere passive headsets fear to tread. Simply put, the electronics sense the noise inside the ear cups from microphones mounted near the wearer's ears, take that signal and invert it, and send this mirror-image of the noise back to the speakers in the ear cups. The result is that the low frequencies are effectively canceled out, and the throbbing of an engine becomes a distant drone. The advantages of this type of noise canceling, though immediately apparent, shine ever more convincingly at the end of a long flight.

Of the three current active offerings, though, there is a clear winner in comfort — the Bose. Combining superior noise canceling (the best of the bunch by a sizable margin), ear seals that are so comfortable as to be sensuous, and a baby's-bottom-soft head pad, the Bose coddles your ears like no other headset, all the while providing an amazingly quiet atmosphere. Bose labored long and hard to bring this level of comfort — by using an unusual frame arrangement that keeps the clamping force constant over varying head sizes and giving the ear seals considerably more surface area than any of the competition's.

Those ear seals also do the best job with eyeglasses of any seals we've used: No matter how thick the bows, the Bose hardly seems to notice, with performance degrading not one whit. You can't say that of the other seals.

Now for the caveats. When the electrons are flowing, the Bose is the quietest of this trio. But should you have an electrical failure, or should your copilot step on the cigarette-lighter cord, you'll be in for a surprise. The very qualities that make the Bose unit so good in the active mode compromise it in the passive mode — contrary to Bose's protestations that the headsets are comparable to passive units when turned off. Simply put, without power, the Bose does not attenuate low-frequency noise as well as a standard passive headset.

And although we suffered just one component failure out of the two Bose headsets in our possession — the new microphone gave up the ghost in the first few hours of use — they still have the quality of being slightly fragile. (The jungle-gym frame doesn't help on this account, allowing as it does the ear cups to entangle themselves in a Twister-like mess if you don't stow them carefully.) In time, those marvelous ear seals begin to look like a jellyfish wrestling match gone wrong — Bose recommends they be replaced periodically. Frankly, if you treat the Bose with the care normally accorded a $1,000 piece of equipment, they should last, and the durability cautions above should be of little concern. But we wouldn't lend our set to the Samsonite gorilla.

David Clark's entry, the DCNC, on the other hand, appears to be built specifically for such a simian's sympathies, or lack thereof. High-quality (and, we think, a tad too heavy) cords abound, and each piece of hardware seems as though it could have come back from Operation Desert Storm looking factory-fresh. The DCNC has a substantial feel and substantial heft of 25 ounces, the chunkiest of the three.

David Clark wanted a true fail-safe package, so in each ear cup lives a circuit board, sensing microphone, and two speakers. One speaker works solely to cancel noise, while the other brings in radio and intercom signals; the circuitry coordinates the signals, so the speakers don't work at cross- purposes. Any part of the active circuitry, from the power source to the active-noise-canceling speaker itself, can fail without impairing communications. (Incidentally, all three headsets here will provide communications without the active noise canceling turned on, but a failure of the speaker will render that side mute.)

Going with two drivers in each ear cup might have diminished the DCNC's ability to cancel out low-frequency noise, though. To work well, an active headset must provide a good enclosure for its speaker to produce the low frequencies needed to offset the noise; making a speaker smaller or putting it in a smaller enclosure tends to compromise this ability. In side- by-side comparisons, the DCNC was noticeably down on noise-canceling power compared to the Bose, although the difference between ambient and perceived noise in the active mode is still impressive. At least, the DCNC is still a match for standard passive sets with the power turned off.

David Clark has addressed the comfort side of the issue with new gel ear seals — a vast improvement over the previous DC-standard liquid-filled seals and even older foam seals. In fact, we'd encourage owners of other models of David Clarks and DC-look-alikes to buy a set of the new seals — they will fit older headsets without modification — and see how they transform your old head-pinchers into something far more comfortable. A new, soft head pad is also part of the deal and another option we'd quickly add to any headset; finally, DC has cured the familiar skull-top hot spot. Even so, the DCNC is only marginally more comfortable than standard Clarks.

Telex's ANR model differs from the David Clark and Bose offerings primarily in its power source, in this case a pair of 9-volt batteries housed in a small, thin box in the middle of the cord. (At press time, there was no way to provide external power to the sets, although the company says it is working on a power cord option.) With two fresh batteries installed, the ANR is almost the equal of the DCNC for sheer noise attenuation, which is to say substantially better than passive sets at low frequencies and as good at the other frequencies. Also, like the DC, the ANR is fine as a passive set, albeit a smidgen louder than the green domes.

Comfort, however, is not the ANR's long suit, at least not in as- delivered form. The single reason: Apparently, the electronics in the smallish ear cups have pushed the speaker/microphone assemblies fairly close to the wearer's ears (not in itself a bad thing). But between that assembly and the ear is a circular foam pad, which makes another thin pad touch the ear. After an hour or so, that pad imparts a most annoying burning sensation in the outer ear; we don't know anyone with ears small enough to evade this pad's press. The solution isn't necessarily to buy something else but to merely remove the circular pad. We tried that, and the comfort level soared, surpassing the DCNC's by a smidgen — largely on the basis of the Telex's lesser weight.

Since we last tried the ANR, Telex has redesigned the ear seals. Before, on the ANR and ProAir 2000E, the seals were unique to Telex, but now the cups have been altered to accept standard seals. Those provided with the ANR appear identical to the previous-generation Clark liquid-filled seal. As with the last time we tried the Telex model, we didn't get the factory's advertised 40 hours' use from the batteries, but it was reasonably close, and the headset gave plenty of warning before it went off line.

A side note on cords and power supplies. Both the Bose and David Clark headsets require outside electricity to work in active mode. This means plugging into a lighter socket and then into the radio or intercom. Combine a portable intercom and two active headsets, and you will soon have an incredible tangle of wires on the floor. Bose offers a panel-mount expansion box, and both the standard Bose article and the DCNC's box can be affixed permanently. We highly recommend to aircraft owners that these options be explored.

An option for the renter-pilot is to go with a new product from intercom maker PS Engineering. At one point, Bose was looking to produce an intercom that would eliminate the cord clutter inherent in its Aviation Headset and hired PS Engineering to perform the initial research and development. Bose ultimately decided it wasn't interested in producing and selling an intercom and has allowed PS Engineering to market the fruits of its R&D labors, an intercom "compatible for use with the Bose Aviation Headset," called the Inter-Muse.

PS Engineering has, in a portable unit barely larger than its Aerocom II intercom, combined a two-place (which is expandable to four or six places) stereo intercom, music interface, and power supply for the Bose headset. The Inter-Muse will accommodate two Bose headsets, as well as a standard headset in the copilot position. (Which means you should own at least one Bose headset.) The Inter-Muse includes a pilot-isolate feature, which also controls the type of music muting. Either the music will drop into the background when someone speaks on the intercom or a radio transmission comes through, or it will remain at full strength, a mode the company calls, somewhat tongue-in- cheek, the sing-along mode.

As with all PS Engineering intercoms, each intercom station has its own squelch circuit, meaning that only the microphone spoken into is heard through the headphones; this dramatically reduces noise, especially with more than just a pair of users on line. In the Inter-Muse, the pilot and copilot have individual volume and squelch controls, as well as a push-on, push-off control for the Bose active noise canceling circuitry.

We used the Inter-Muse extensively with the active headsets here and can report that we're thrilled with the results. First and foremost, the usual bundle-of-snakes wiring is reduced to an acceptable level. The intercom itself is up to PS Engineering's typically high standards, with smooth, unobtrusive voice activation, excellent audio power and quality, and one of the slickest music-mute schemes we've tried. The Inter-Muse's $495 price tag seems reasonable, especially in the context of $1,000 headsets. And to banish some of the cable snakes to the closet would be worth virtually any sum. The Inter-Muse will be available only factory-direct.

Comfort and noise-canceling ability is only part of the headset picture — microphone performance also is important. This year, Bose upgraded its microphone and mounted it on a flexible stalk, which we think offers significant improvement over the original; older Boses will be updated free of charge. Though the new mike is distinctly better than before, it's still no match for the David Clark M7A. For noise-canceling properties and overall sound quality, the DCNC has it knocked, followed closely by the Telex's mike. They are all still so close, though, that you could, as they say in horse racing, throw a blanket over the contestants.

Though we thought it might be difficult to cull a winner from this trio, the slightly different strengths of each headset pretty much suggests an application. If you own your own airplane and want the utmost in comfort and sound insulation, go for the Bose. In those two aspects, the Bose is the clear winner. But if your needs involve some rugged use, or if you never thought David Clarks were particularly uncomfortable in the first place, start writing that check for the DCNC. Finally, if you are, like many of us, a renter-pilot, you should seriously consider the Telex ANRs. The advantages of self-powering are the greatest where you switch from airplane to airplane — we suspect a lot of CFIs have been asking for ANRs for Christmas.

Of course, cost always enters into the purchase decision. At the suggested list price level, all the current active sets are close: $965 for the Bose (which is stereo-compatible), $995 for the DCNC (also in stereo), and $949.95 for the Telex (strictly mono). But the Bose is only available from the factory, so you can't count on any price breaks. (We hear, though, that factory support from Bose has been exemplary, so paying the premium might work out in the long run; David Clark also has a sterling reputation in this area.) The Telex ANR currently is heavily discounted and can be had for about $680 if you shop around; we expect the price of the David Clark offering to come down once it hits the streets.

None of these headsets can compete on price with passive sets, that's true. But when it comes to peace and quiet, as is true in so much of life, you get what you pay for. Time, and customer approval, have proven active- noise-canceling headsets to be anything but a novelty. If you're not sure what could make an otherwise sane pilot pop a cool grand (or nearly so) for headsets, try on an active set — and let your ears decide.


For more information, contact: Bose Corporation, The Mountain, Framingham, Massachusetts 01701-9168; telephone 800/242-9008. David Clark Company, 360 Franklin Street, Post Office Box 15054, Worcester, Massachusetts 01615-0054; telephone 508/756-6216. PS Engineering, 12636 Red Fox Drive, Knoxville, Tennessee 37922; telephone 615/675-2600. Telex Communications, 9600 Aldrich Avenue, South, Minneapolis, Minnesota 55420, telephone 612/887-5510.