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Positive Feedback ISSUE 3
october/november 2002


Sacrť bleu! Once more he strikes! The mysterious Auro D’Oro slips another article under the virtual PFO door, then rides away into the night. Our obviously experienced traveler leaves us with tales of noise-snatching devices in the night…


NC-11 headphones, or some noise canceling doobies
by Auro D’Oro


sony_mdrnc11.jpg (9192 bytes)

A scout reports from the front…

Have you ever thought about how most products don’t live up to their hype? Oh sure you have: most of us have. And that is a raison d’etre for the existence of this ‘zine. To report to the PosFeed community, at large, when we have found such audio products that—and isn’t it a telltale minority in these times?—do live up to their hype.

As your trusted advance scout I have to report back that I, cynical me, have found such a product—well, three of them. They are the (relatively) new noise-canceling headphones designs from Sony. Other manufacturers have been making similar products (Jensen, Panasonic, Bose) for a few years, and if you want to you could price shop until you find your comfort zone. They all operate on the same principle: if we can measure the frequency (or pitch) and amplitude (or loudness) of the environmental noise (say, a jet engine), and match that with an out-of-phase noise of about the same frequency and amplitude, we could get them to null each other out. The principle is clear and, in theory, should work quite well. But betwixt the cup and the pinna… there’s the rub! Can it be done, and for less than a fortune?

Sony has tried, and at least three price points: less (#MDR-NC5, $79.99), more (#MDR-NC11, $149.99), and a little more than that (MDR-NC20, $179.99). So I thought if I covered their products, that would be pretty much like covering the field.

Let me make one thing perfectly clear before I wax eloquent. In my opinion, Sony has made some major mistakes and markets some questionable products, which sometimes makes me wonder who is in charge there. I remember the L-cassette, the ill-fated Beta-Max VCRs, and eight-track cassettes. I’ve owned Sony direct-drive turntables that rumbled from the day I got them on-line, and Sony pre-amps that were so undistinguished as to be an industry joke.

But in noise-cancellation technology, Sony delivers a lot of product for the price. (I’m not sure who holds the basic patents; Bose was first to market noise-canceling headphones. This would be an interesting thing to know.) I paid out-of-pocket cash for my fives and elevens, with no courtesy discount, at Circuit City. J&R gives somewhat better discounts. When I asked Sony to loan me a review pair of NC-20s, they ignored me—just goes to show what being a "high profile reviewer" with PF Online will get you!

Why noise-cancellation in a headphone??

Do you travel much? Long air junkets, or train journeys? Do you live in a noisy part of town, or somewhere that you can get little isolation from family TV shows? Or does the air-conditioning/heating system in your home make it difficult to listen? Especially to music that has quiet passages, like chamber music? Or intimate club jazz? Doesn’t that draw your jockey shorts up in a knot? Well "noise-cancellation" may be just the ticket for you. Iím not an electrical engineer, nor exactly up on the latest comparator circuits and how they work, but the Sony folks say their "Noise-Canceling Circuit actually senses outside noise with built in microphones and sends an equal-but-opposite canceling signal to the headphones [which] cancel noise from 40Hz to 1,500Hz, more than 10dB noise cancellation at 300Hz where the human ear is super-sensitive."

The theory is, instead of making your little Walkman CD player shout down the damn jet engines, making more noise for your nervous system to deal with, making you grouchy and irritable, maybe stressed out (without realizing it) by noise pollution when you get where you’re going, where some important deal may hang in the balance of your mood swings—the iddy biddy noise cancellation circuit card with its own AAA battery power supply will provide you with music against a quieter background and you’ll be all relaxed and charming enough to conduct business, and (as a bonus) all smiley, huggy, and kissy when you get home.

At least, thatís the theory. A few martinis might help. It sounds like the admanís dream: canít you just see the video ads? "Lucy, I’m home."

Well Iím here to tell you these little noise canceling doobies work, and work well. Let me see if I can guess your next question. "How good can they sound?"

Well, nothing is perfect. Even the sun has spots.

Some theory, some speculation

This brings me to Peter Walker, the developer of the early Quad Electrostatic Loudspeaker. When asked why his electrostatics were made of the material he chose (.5 mil Mylar film) and of the shape he specified (about a square yard panel), he answered something like this: the theoretically ideal transducer would be nearly infinitely low in mass, and, as far as was practically possible, nearly infinitely small. The moving diaphragm approached that small a mass if we compare, say, the weight of a square yard of one half one thousandth of an inch thick Mylar film to the cone of a typical 12" loudspeaker. And the square yard size was large enough, moved enough air, to deliver 45 Hz in a standard test. Any smaller and the bass reproduction would have been compromised. So, the early Quad speaker was as close as Peter Walker could get to the ideal: infinitely light and small—well, small enough for his purposes.

Now consider the typical driver in a set of headphones: it is (plus or minus) about an inch in diameter (25.4 mm) and it is designed to play full-range. See what I’m getting at in my sneaky way? The difference between the Sony NC-5 and NC-20 isn’t much. They each use a 30 mm (about 1.2 inch) diameter driver that employs a Neodymium magnet, with its high gauss to weight ratio. If they aren’t identical, they are pretty close. The difference between them is mostly the seal around the ear, which most affects the bass roll-off.

In order to bring the bass performance into control, Sony engineers (I hypothesize) designed the set up that seals the ear to the driver by using a roll of leatherette around the perimeter of the ear cup. What we get is a chamber of air that is larger than the ear, and as deep as from the driver to the eardrum. I’d guess that to be about two tablespoons of air, maybe three. That can be quantified and averaged and the ideal Q of the headphone driver arrived at for either an open or sealed rear compartment set up. For a team of Sony engineers, this would be a trivial problem. They claim the NC20’s can deliver bass to 16 Hz. I guess that means the 3dB down point, or F3, which has become the convention for expressing bass extension. Do I have your attention yet? That’s 16 Hz as measured in a simulated ear, I’d guess. Like I said, I’m no engineer.

The next task, I guess, was to model a set of headphones using open cell foam at the "ear pad" that rests the driver and its cup on the ear. The natural tension of the headband keeps them in place. This set would be modeled as a ducted box. The leakage comes through the open cell foam that allows air to escape around the uneven contours of the ear, but in a controlled way. Open cell foam itself comes in varying densities; that is, the bubbles are of differing sizes, and it can be cut to varying thicknesses. The NC5’s are claimed to deliver bass down to 30Hz, which I interpret to mean its F3, or 3dB down point. So, you might think of paying the extra $100 for the bottom octave of bass, or more aptly, for the labor and material required to make a comfortable pad to surround the driver’s ear cup and seal it to the listener’s head. Or you might think of these NC5 headphones, as I prefer, with their noise-canceling circuit, and F3 at 30 Hz, as a pretty solid value for $70.

The most surprising were the cute little NC-11 doobies. These are of the in-your-ear, or earbud type. The drivers measure 9mm in diameter and form a seal with their soft silicone surrounds well into the ear’s canal. With the earbuds in place the air chamber between the ear drum and the driver must be pretty small, maybe equal in size to one cigarette filter, more or less. When we remember that the area of a circle is pi (3.1416) times the square of the radius (pie are square), with a little pencil and paper we can quickly compute that the moving area of the NC-11’s 9mm driver is about 10% of the NC-20’s 30mm driver. (Pie are round: cornbread are square.) Think of it as the top of a .32 caliber bullet, or just somewhat larger than the eraser on a standard sized pencil, as compared with a standard one inch tweeter. That is to say, it would take about ten .32 caliber bullets bunched in a circle to equal the diameter of the on-your-ear driver. A 9mm diameter driver is really getting near to Peter Walker’s ideal of infinitely small and infinitely light.

Sony claims the nine millimeter driver to have a sensitivity of 102dB/mW (that’s for one milliwatt) when its noise-canceling circuit is on, and its low frequency is claimed to be 3 dB down at 10Hz.

The engineering is pretty complex. The driver is mounted in a closed rear housing enclosure, and the air is vented toward the eardrum through what looks like a sealed front housing that has a circle of perforations and a plastic hypodermic needle pointing out of it. So the rear wave is used as a brake, or shock absorber, for the diaphragm, following the principles put forward by Henry Kloss and made manifest in his AR acoustic suspension speakers of the ‘50s; and the front wave is loaded not unlike the Klipsch horns in their driver housing. If you were an audio historian you might see the whole thing as a miniature Klipsch horn fit inside your ear. I wouldn’t be surprised if the exact diameter of the inside of that needle meets the specifications that Paul Klipsch formulated back then, scaled down proportionately, and allowing for some adjustments for miniaturization and computer modeling.

We can realize how 10 Hz represents considerable know how. One driver, reproducing the entire audio range, with relative flat response, and considerable dynamic range. It is to your ear’s canal what a set of Pipe Dreams is to your dream house’s living room. See what I’m sayin’ here?

The Sound

"How does it sound?" one might ask. ‘Philes always ask that question, y’know?!

It sounds really quite nice, approaching the speed and clarity of electrostatic headphones, and that’s no faint praise. Considering that you can adjust your bass contour on most CD Walkman devices—flat, plus one, and plus two – and you can adjust the seal of the bud by choosing among three different size silicone plugs; small, medium, and large, there is considerable flexibility in this system. You can virtually season to taste. For example; for medium-low-level listening I like to use the plus two digital bass setting, but for realistic levels of acoustic instruments I like to use the plus one setting.

By the way, if you’re obsessive about associated equipment, my CD player is a Sony D-E356. With my levels set, and the earphones firmly in place, I can hear pipe organs chuffing, as in the First Impression Music CD, FIM SACD 050, Antiphone Blues for saxophone and organ. This recording, done in Spanga Church, Sweden, has pretty incredible sound staging, and when I go from flat to plus one the church seems to get larger, and when I go to plus two, it gets larger still. The organist, Gustaf SjŲkvist has masterful control, while the sax playing by Arne Domnťrus is absolutely soulful, as in Duke Ellington’s classic "Come Sunday." As you might expect, all the selections seem to have religious overtones.

Which brings me to another album that every Ellingtonian should have, Great Jazz Vocalists Sing Ellington and Strayhorn, Blue Note 55221. On this album Joe Williams sings "Come Sunday," and when you compare his treatment of the same material to the Swedish temperament, you see that (cultural postures aside) each has a true and profound respect for the music and its sentiment. Acoustically, there are recordings that date back to the ‘40s on this Blue Note CD, and representatives from just about every decade since. Moreover, the lineup of singers is like the roster of an all-star team. Amazingly, through the "less-is-more" NC-11s, one can make out the sonic differences easily. Each of these songs has a recording engineer’s thumbprint on it, and NC-11 catches it and sorts it like the FBI’s NICIC computer sorts and identifies criminals’ fingerprints. Properly set up, the bass definition might be one of the strong suits of these darling doobies.

But they are not for everyone. If you are one of those people who can’t stand the feeling of things inside your ears, well obviously you aren’t going to appreciate these 9mm NC-11 headphones, and they may not be for you. You might want to start with the modestly priced, 30mm, NC-5s.

At first hearing, the 5s sound richer, not as shimmery, with the cymbals not as brilliant or as forward in the mix. The comparison is not unlike sitting closer (NC-11s) or further away (NC-5s) in the room with the performers. Though the vowel sounds are of near equal loudness, the sibilants (or consonant clusters) are less loud, decreasing with the square root of the distance. So, what we hear seems less detailed, though we sit not that much farther back in the hall, certainly nowhere near the rear wall. The best part is, either of these lightweight headphones will travel well and cancel out 75% of plane or train noise—and we get our choice of sound palette options (dry and citrus, or rich and chocolate).

The elevens might strike some as a little thin, or even harsh at first, especially if you try them out in a quiet environment. Ordinarily, on a train or plane with all that racket, the fine details of the treble range might be some of the first things to get lost. Under those conditions, with the constant droning noise, and with the noise canceling circuit on, I was glad to have the elevens as detailed as they are. My hearing isn’t what it once was.

So, if you are no longer young, and if you want to hear all the detail you can in a noisy environment, or if you want to take advantage of the latest technology, go for the elevens. If you have developed any reservations about what I’ve just told you, go for the fives. Neither of the Sony phones are as good as the Grado RS-1’s—what is?—but they do a damn nice job at their price.

And who couldn’t use a bit more noise-cancellation in their life?

For more information, go to, select the "portable audio" tab, then enter "MDR-NC11" as the keyword for the search.