LATEST HEADPHONES DRAW ON TECHNOLOGY TO STIFLE NOISE.

Byline: Rich Warren Chicago Tribune 

Quiet! Noise assaults you everywhere you go, even when you've got headphones on.

Most living rooms shut out the irritating din common to on-the-go headphone listening. Ambient noises - such as engines, wind and tires - pose a threat to your listening pleasure. Without thinking, you may raise the volume of the music or speech in your headphones to overcome the surrounding noise.

Don't do it! You may be blasting your hearing to deaf! And turning up the volume above the noise increases sound leakage from the phones that may annoy people around you.

In the last couple of decades, researchers have learned how to manipulate, if not annihilate, ambient noise. Circuits can invert any sound and fold it back on itself, greatly attenuating, if not silencing, the original sound. It wasn't long until this technology benefited headphone listening.

In noise-canceling headphones, a miniature microphone - like the kind used in a hearing aid - picks up ambient noise. The mike feeds the noise to a circuit that inverts the phase of the noise, creating anti-noise. The circuit then amplifies the anti-noise to the same level as the ambient noise, and presto - most of the noise disappears. No circuit perfectly duplicates the noise, nor its frequency extremes, so some noise always sneaks through.

Several companies offer noise-canceling stereo headphones. Some fail miserably, while others noticeably enhance listening pleasure. Here are two to consider:

High-quality Bose:

Bose sets the standard by which to judge all other noise-canceling headphones. Bose designed the phones, however, to protect the hearing of pilots, and markets them to the aviation and space industry.

Now in its second generation, the Bose Series II Acoustic Noise Canceling headset passively seals out noise, as well as actively canceling it. The substantial phones are about the same size as the full-size phones of yore, but far more comfortable. The silicone gel/soft-foam earpads not only seal out noise, but distribute pressure so evenly and softly that you can forget that you're wearing them.

Two pieces compose the Bose phones, the headset and the control/battery box that provides the noise-canceling power. You can use six "AA" alkaline batteries that provide power for 40 hours, or a quick recharge nickel-cadmium pack for 16 hours between 90-minute charges.

Although designed for pilots, they provide pure bliss for frequent fliers, as well as travelers on other modes of transport. Having used them extensively, I maintain they reduce jet lag on long overseas flights. The catch is that they cost $1,075. To try them out for 30 days, or for more information, call [phone].

Budget-minded Koss:

While most noise-phobes can't afford the ultimate, deluxe Bose earmuffs, they just might be able to consider the $200 Koss Quiet Zone 2000.

These use an improved version of Koss' comfortable, collapsible, lightweight PortaPro headphones. They provide great sound quality, but without sealing the ear, meaning there's no passive noise cancellation.

A small black box contains the electronics and the pair of "AA" batteries that power the unit for about 200 hours. That seems to be a realistic figure, as I've been using the QZ/2000 for more than three months and the batteries keep going. A green LED indicates power on, and a red LED warns when the batteries have 30 hours left.

I've tried several of the small, Koss-style phones from other companies, with minimal success. Either they barely cancel noise, generate more internal noise than they cancel or eat batteries for breakfast.

The Koss QZ/2000 really work. These phones not only improve the sound of your personal stereo when flying, but also plug into any electronic aircraft sound system (Koss provides an adapter for the weird two-prong kind). You can finally understand the movie dialogue, although you'll still have to pay if you're flying coach.

The QZ/2000 can lessen the pain of vacuuming, and even the annoyance of the fan in your computer. By canceling ambient noise, both the Koss and Bose phones improve the intelligibility of external voices, such as pilot announcements on the public address system.

The Koss phones and box fit into a supplied leatherette pouch, with a hook for hanging on belt, purse or shoulder bag. The whole package weighs less than 10 ounces. Koss phones are widely available at electronics stores.