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Hang 'em high: flat-panel speakers bring new dimensions to sound

A British company has developed flat-panel speakers using technology developed to isolate airplane cockpit noise. The sound quality is not quite as good as conventional speakers, but due to their flat nature the speakers can be decorated.

Flat-panel speakers bring new dimensions to sound

This magician wasn't David Copperfield, merely a man in a lab coat. And his magic was no illusion. Without any sleight of hand, he produced a 9 x 12-in. panel made of a superthin composite also used to make airplanes, deftly attached a wire to the back, and turned it into singer Tracy Chapman. Okay, so Tracy Chapman wasn't really there, just a loudspeaker like nothing we'd ever seen before. But it still seemed like alchemy to us.

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If U.K.-based New Transducers Limited (NXT) has its way, we'll be hearing a lot more than Chapman's earthy voice coming from flat-panel speakers in the next few years. Born of a British Defence Research Agency project aimed at finding ways to isolate noise in airplane cockpits, NXT speaker design is the latest venture of British electronics company Verity Group, whose respected loudspeaker brands include Mission, Wharfedale and Quad. Verity Group is licensing the flat-panel technology under the name NXT to companies that include NEC and JBL parent Harman International.

Forget The Norm

To understand how the NXT flat speakers work, it's best to temporarily forget what you know about how your living room speakers operate. The model of an amplifier connected to a loudspeaker doesn't change with NXT technology, but the similarities end once the electrical signal hits the voice coil. No woofer, no tweeter, no crossover. Just a tiny magnet, a voice coil and a panel that could be made of aluminum or paper.

In a conventional speaker, the signal from the amplifier energizes a magnetized voice coil that's connected to a diaphragm. The diaphragm vibrates, causing the surrounding air to vibrate in response to the audio signal and to recreate the original audio wave form in as linear a form as possible.

NXT speakers operate in a world of "psychoacoustics" and, well, utter chaos. The magnet-and-coil assembly moves a microscopic 40 microns, barely nudging the rigid panel to begin a series of bending waves that travel in all directions.

"You end up with these bending waves that are now crossing at every angle and at different speeds," says Jon Vizor, director of marketing for NXT. "And it becomes this chaotic mass of crossing bending waves that form the modes that produce the music."

Although NXT operates in a different sphere, its goal is that of conventional speaker design: to simply reproduce the audio signal as faithfully as possible.

"At one extreme, you're trying to design a transducer that's as nonresonant as possible," says Dr. Floyd Toole, vice president of engineering at Harman International, licensor of NXT technology in the United States. "At the other extreme, you have a system that in its ideal form is nothing but resonance. And there are so many resonances and they're so densely packed together in the frequency domain that no one of them stands out as being discretely audible as a source of unwanted coloration. What you hear is a facsimile of what you should be hearing."

Flat Is Flat

NXT can make panels as slim as 0.3mm deep using plastic, glass fiber, carbon fiber, aluminum or any number of stiff, lightweight substrates. The company boasts working samples of full-range speakers that cover eight octaves but weigh less than 2 ounces. NXT offers no claims for reproducing frequencies below 200Hz in a reasonable-size loudspeaker and expects flat speakers designed for the home to be supplemented by beefy subwoofers. The first NXT-licensed product for the U.S. market--which includes subwoofers from sister company Mission Electronics--was expected to reach stores by mid-August. The $799 system comprises a pair of 12 x 11 x 1-in. flat panels that mount on the wall and a traditional pistonlike 10-in. powered subwoofer to handle the bass.

"Our technology is scalable from credit-card size to 120-sq.-meter cinema screens," Vizor says. "And it has the same acoustic benefits and properties no matter what the size. The difference is bass performance. You need very large screens to get very low bass."

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The multimedia speaker is a prime target for both NXT and Harman. In fact, the first commercial application of NXT technology was in the NEC model PC-9821 laptop PC that sells in Japan. The 0.5mm flat-panel speakers slip behind the PC's screen when they're not in use, and deliver a sound that beats most laptop speakers. Desktop PCs and personal digital assistants (PDAs) are also prime candidates for the technology, as are talking posters and banners, public address systems (because of the diffuse sound pattern there's no feedback) and car audio speaker systems.

While NXT sets its sights on future applications for flat-panel speakers, several companies that have various patent swaps and cross-licensing agreements with NXT--including Sound Advance Systems, Fostex and Noise Cancellation Technologies Inc. (NCT)--are delivering their own versions of flat speakers in the United States.

According to Dave Claybaugh, vice president of NCT Audio Products Inc., his company and NXT are both trying to create the same result but are going about it differently. NCT uses a cool-running piezoelectric driver, rather than a magnet and voice coil, to induce vibrations in its panel. Also, NCT is shooting for a minimum flat-panel stand-alone low-end response of 100Hz, rather than the 200Hz NXT has promoted, Claybaugh says. In order to achieve that level and to come to market first, NCT cobbled together a hybrid design using a flat panel and a traditional cone driver to handle the midbass frequencies. Its Gekko system also includes a separate 10-in., 65-watt subwoofer.

"We ran into a lot of the same challenges that NXT has run into," Claybaugh says. A primary challenge has been to design small drivers that can handle a lot of power-enough to produce highquality, full-bandwidth sound. But he's bullish on the prospect of a true, full-range flat-panel speaker. "An all-flat-panel speaker is absolutely feasible," he says. "But it will probably be a couple of years before we see an all-panel speaker alone."

Panel, Panel On The Wall

We all know that speakers can look pretty gruesome if they re ungainly and placed incorrectly in a room. So, obviously, these speakers are bringing new ideas to home decoration--as well as speaker technology. The question is: After you get a speaker off the floor, what do you do with it on the wall? NXT sees a mirror speaker as one alternative, while NCT turns its speaker into art.

NCT's 11 x 14 x 2.5-in. Gekko speakers ($299 each) come in black or white, but the interesting twist is the replaceable grille ($79), which bears a print that's stamped onto acoustically transparent silk. The company's catalog boasts 450 art prints, including reproductions of paintings by Picasso, Matisse and Van Gogh.

See also: 6.5 car speakers reviews, best 6.5 car speakers

NCT has its sights on speakers for hotels, concert halls and commercial space. Also in the works is a surround-sound speaker system for the car, comprising NCT's piezo patch on a panel in the headliner and a separate subwoofer for bass.

In their quest to develop a new speaker technology, flat-panel designers have been called tricksters who are trying to reinvent the laws of physics, claims Vizor. NXT argues that its design principles have been used for decades in submarine design and bridge building, not just in loudspeaker design. Harman's Toole observes that using one or two transducers to excite a panel has posed a number of considerable problems in physics and engineering that NXT has had to solve. "This is not a hoax," Toole says. "It's a genuine engineering exercise, and to the extent that it works as well as it does, it's been successful."

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