Imagine the whole dashboard panel being a speaker. Or the cover of the door side pocket making good quality sound. Or the interior light panels doubling as speakers.
All seem pretty damn far-fetched... even crazy if you want good quality sound? It's not. With NXT's patented SurfaceSound flat-panel loudspeaker technology, a good quality speaker can be ultra thin and light. Already being used in some commercial, computer and residential applications, the technology is set to break into cars in the big way.
The major companies that have taken out licenses on the technology make that clear - try General Motors, Fiat and DaimlerChrysler! And in the general field of consumer goods, the list is as startling: Acer Computers, Ericsson, LG Electronics, Matsushita Communications, NEC, Philips, Siemens and TDK.
NXT SurfaceSound technology has made it possible for high-fidelity loudspeakers to be fabricated in virtually any size and shape, including curved and contoured configurations. With a minimum thickness requirement of just 0.3mm, SurfaceSound speakers can be incorporated into interior components such as door panels, trim panels, ceilings or even moulded into the dashboard.
Because they produce sound in an entirely different manner to conventional loudspeakers, SurfaceSound loudspeakers offer unique acoustical benefits, and are said to create a smooth, full-range sound quality throughout the vehicle without the beaming and discontinuity of standard car audio speakers.
So what makes this new technology so exciting? And what is its potential in automotive applications?
Let's start off with the last first. Already, General Motors has demonstrated several concept cars incorporating the SurfaceSound technology, giving a clue to how that company sees its use.
The Buick Bengal
General Motors' Buick Bengal concept vehicle is a front-wheel drive roadster with a convertible top, featuring a supercharged 3.4-litre V6 engine and six-speed automatic transmission. It has voice-activated controls - the 'Quiet Servant' system of the Visteon Corporation, which can recognise up to six languages and regional accents - and a reconfigurable head-up display that shows gauges on demand.
The head-up display and a four-position joystick on the steering wheel eliminate the need for gauges and knobs, enabling the entire instrument panel to become a large NXT flat-panel speaker. Four additional NXT speakers round out the Bengal's audio system.
Pontiac REV
The Pontiac REV is a radical, all-wheel-drive sports coupe with an on-the-fly adjustable suspension and five-speed automatic/manual transmission with on- and off-road capabilities. Much of the REV's body is constructed from ultra-tough composite exterior panels, and the vehicle features rear doors that slide open out and backwards, and which can be operated independently of the standard front doors.
The REV's sound system features NXT SurfaceSound speakers in the door panels and rear hatch area. The speakers blend invisibly into the interior, while providing rich, powerful and dynamic high-fidelity sound.
The Technology
Conventional speakers use a cone-shaped diaphragm that moves back and forth like a piston. The mass of the cone and the air load impose a resistance on its movement, called the Radiation Resistance. This coupling of the cone with air (it has to move air to make sound) is very good up until about 1000Hz. However, beyond that frequency - where the wavelengths of the sound become comparable with the dimensions of the cone - a major change occurs, with the diaphragm's acoustic output beginning to fall as the frequency rises.
As a result, high frequencies become more and more directional, with the sound energy progressively narrowed into a beam.
Of course, conventional speaker technologies overcome this by matching the size of the speaker with the sound frequencies needing to be produced: woofers are larger than tweeters. Large speakers provide the volume displacement needed for low frequency reproduction, while small speakers take care of the high frequencies. However, electronic crossovers are then needed to split the sound up into the correct frequency bands for each speaker. According to NXT, this brings with it a whole host of negative side effects - phase distortion, off-axis disruption of output, and others.
So a full range speaker with a constant dispersion of all sound waves would both allow one speaker to be used instead of a tweeter, mid and bass unit, and get rid of the requirement for a crossover.
And here's the crux of the NTX system - instead of a diaphragm moving back and forth like a piston, the NTX SurfaceSound system uses a panel that is excited to vibrate randomly across its surface. Each small area of the panel vibrates largely independently of its neighbours - NTX suggests that it can be envisaged "as an array of very small drive units, each radiating a different, uncorrelated signal but summing to produce the desired output".
Taking such an approach has advantages because "such a randomly vibrating diaphragm behaves quite differently because power is delivered to the mechanical resistance of the panel, which is constant with frequency."
"The radiation resistance is now insignificant because the air close to the panel also moves in a random fashion, reducing the effective air load. This means that diaphragm dimensions no longer control directivity: you can make the radiating area as large as you want without high frequency output becoming confined to a narrow solid angle about the forward axis.
"Such diaphragm behaviour clearly opens up the possibility of a full-range driver freed from the familiar restraints and compromises."
And if you're thinking, "Well, that will never work!" you're apparently wrong.
The panel that forms each speaker is constructed of advanced composite materials, and is excited by small voice-coil style electric actuators. Taking this approach to excitation allows the new speakers to be used with conventional amplifiers.
But hold on - won't the panels need to be mounted within a traditional enclosure? (A normal speaker pushes out sound waves from both its front and back surfaces. If you let the waves directly meet one another they cancel out, giving a lack of sound energy, especially at low frequencies. A ported enclosure changes the phase of the rear sound waves, allowing the waves from the back of the speaker to strengthen the front waves.)
Nope, the NTX system doesn't apparently need a speaker enclosure!
"Another major benefit is that the panel's acoustic output from both sides of the NXT panel are useful. In applications where the panel is not required to be baffled, as in high-end free-space loudspeakers, the power radiated from the back face sums up constructively with radiated power from the front face of the panel. This is due to the complexity of distributed-mode radiation and the uncorrelated phase of the individual radiating elements as seen from the far-field point of view."
So there, now you know! But surely to get any decent treble response you'd have to make the panel very small? And what happen then to the bass response? The company goes on:
"The technology is truly scaleable: you can make the panel large without directivity or treble response suffering. In fact it actually improves in performance as it is increased in size because the frequency of the fundamental bending resonance is lowered, which not only extends the bass response, but also increases modal density in the mid and high frequencies."
Well, I guess you can see the thing working at high frequencies - all those panel sections radiating sound like a collection of tweeters - but where does the air displacement come from to get gutsy bass? Well, here your suspicions are right - the NTX panels will not reproduce the deepest bass.
"Small NXT panels still have to be combined with a conventional woofer to cover the lowest two or three octaves in high quality applications, but the necessary crossover is far removed from the ear's most sensitive region around 3kHz - precisely where most conventional loudspeakers are forced to hand over to the tweeter, " says the company.
Conclusion
The flexibility of size, shape and depth - together with the claimed improvements in the quality and directionality of the sound - of this new design of speaker makes their use in a car very attractive. Not only can manufacturers have better packaging of the interior, but they can also distribute the sound sources around the cabin more easily. With the bass being produced by a single conventional subwoofer, it's likely that these speakers will see automotive production in the very near future. In the aftermarket, the advantages of having a wide-range driver so thin that it can be attached to flat surfaces around the cabin are obvious....
http://www.nxt.co.uk/
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NXT
The potential for complexly vibrating panels to act as loudspeakers emerged serendipitously in the course of research conducted by Dr Ken Heron of Britain's Defence Evaluation & Research Agency (DERA) into using lightweight composites in military aircraft. Once they saw how composite panels acted as efficient sound radiators, after some research the DERA filed the first patent application for a panel form loudspeaker. That was in 1991. DERA itself wasn't best equipped to realize the concept's full potential, but NXT plc - one of the UK's largest hi-fi companies, owning the Mission, Quad, Wharfedale and Roksan brands - learnt of the discovery, recognised its potential and took out a licence with DERA to develop the technology for commercial use. Fundamental research at NXT plc identified the key operating principle for loudspeaker use. This led to the creation of a new class of sound radiator operating under this distributed-mode principle. On 27 September 1996 NXT plc publicly announced the establishment of a new arm - New Transducers Ltd, a technology company, now known simply as NXT - to develop and licence the product as the intellectual property holder. In the interim NXT has fully explored the technology, developed new applications and know-how, investigated a broad range of suitable panel materials, related technologies and the manufacturing base, and put in place comprehensive world-wide patent protection, on which $4m has been spent already. More recently it began licensing the technology to companies operating in various market areas where NXT's unique attributes promise significant advantages over conventional alternatives.
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