Acoustic systems that turn traditional speaker design on its head are enabling everyone from retailers to the military to put sound exactly where it’s needed. Jon Excell reports
From stereos that place your favourite artists in your living room to entertainment systems that turn your home into the Sydney Opera House, today’s audio technology is unrecognisable from the scratchy old gramophones of yesteryear.
However, with no one but the most diehard audiophiles now able to discern the tiny improvements in sound quality offered by the latest hi-fi systems, it seems conventional loudspeaker technology has developed about as far as it can.
With this in mind, researchers around the world are turning the science of sound on its head and developing a range of approaches to transmitting and amplifying sound that are attracting the interest of everyone from advertisers to military strategists.
In a striking development, Californian firm American Technology Corporation (ATC) has created a system that enables focused beams of high-quality sound to be precisely targeted at individuals in a crowd.
While labs such as Sony and Bell dabbled with directed audio technology in the 1960s Woody Norris, ATC’s founder and chairman, believes he has now refined the technology to the point where it is sufficiently cheap and of high enough quality to be used in a variety of exciting new applications.
Norris’ so-called HyperSonic Sound (HSS) represents a departure from traditional technology. While regular loudspeakers propagate sound using a cone that pumps back and forth and bumps against the air, HSS uses an ultrasound emitter.
Moving between 50,000 and 70,000 times a second, this emitter generates a tightly focused beam of sound audible only to those standing directly in its path. ‘Sound is made at every point along the column,’ said Norris. ‘Its directionality is unbelievable — the beam only spreads to about two degrees. You can hear it if I aim it towards you, but if I tip it slightly up in the air you will hear nothing whatsoever. I can target an individual or one or two people in a group very easily.’
As well as this directionality, one of the big attractions of the technology is its range. ‘With an ordinary loudspeaker, every time you double the distance you lose more than half the power,’ explained Norris. ‘With HSS, because the sound is being regenerated all the way along the column, it goes about 20 times further than a regular speaker before there’s any drop-off.’
He said this makes the system ideal for public address systems at large events: ‘Imagine it being used in a rock concert — people in the front and back rows would get the same level without inflicting pain on the poor guy in the front.’
Now, however, the most promising market for HSS is its use alongside digital signage in shops, where it can be used to emit sounds that can only be heard by customers standing directly in front of the relevant display.
Norris claimed the market is being driven by significant changes in the way products are advertised: ‘There’s a trend away from advertisers spending their dollars on television because there are so many channels that when a commercial comes on, a lot of people will surf. There’s a move to bring commercials closer to the audience and a resistance to making stores sound like a penny arcade.’
Norris, who numbers Wal-Mart, McDonald’s and Gap among his customers, estimates he has about 50,000 of his HSS units in operation.
In the UK, the technology has been in use at Heathrow Airport’s baggage check-in desks since late last year, where it beams information to people queuing, while sparing staff the irritation of listening to announcements all day.
Andy Phillips, an audio and acoustic engineer with Audio Nation, the Somerset-based UK distributor of HSS, said he is investigating a number of other possible UK applications, including the installation of HSS systems alongside monitors in betting shops.
Speaking up: LRAD technology, above, is being used by forces in Iraq, Turkey and Afghanistan
Away from the commercial world, HSS has also attracted the attention of the military. Norris said it is being tested by the US Army as part of a decoy system that could be used to project false information during a battle. He explained that if the emitter is, for instance, pointed at a distant hillside, the noise will appear to come from the hillside rather than the emitter.
He claimed an HSS system is also under trial by the US Navy, which is interested in using the technology as a communication system between ships. He said vessels moored up to half a mile apart from each other could use the technology to communicate with each other in place of easy-to-intercept radio waves.
ATC is well placed in the military world thanks to its Long Range Acoustic Device (LRAD) technology, an extremely powerful loudhailer system that is now widely used by the US forces operating in Iraq, Turkey and Afghanistan.
LRAD is designed to be mounted on high mobility multipurpose wheeled vehicles, runs off batteries and can generate 151 decibels. Based on traditional loudspeaker technology, it lacks the pin-point accuracy of HSS, spreading by 25-30º rather than 2º. Nevertheless, claimed Norris, thanks to some clever signal processing, the system is sufficiently directional for operators standing behind it to carry on a normal conversation.
While mainly intended for use as a warning and communication device, LRAD is increasingly being used as a form of sonic cannon. Perhaps the most high-profile example of this came in November 2005, when the Seabourn Spirit, an ocean liner cruising off the cost of Somalia, used the system to repel an attack by pirates.
‘They tried fire hoses, they tried outrunning them. It didn’t work. They squirted them with the LRAD, and they [the pirates] threw down their weapons, held their ears and the boat was able to get away,’ recalled Norris.
But Norris is not alone in the world of directed acoustics and a strikingly similar technology to HSS, known as the Audio Spotlight, has been developed by a small Massachusetts-based technology firm called Holosonics.
The brains behind this development is audio engineer and MIT graduate Dr Joseph Pompei. Hired by Bose when he was just 16, Pompei said he was driven to develop his technology by the perceived shortcomings of conventional loudspeaker technology: ‘They didn’t give you any control over where the sound was or where it went and there really isn’t a whole lot of scientific innovation left in traditional loudspeakers. Anyone can make speakers, it’s more of a marketing challenge than a technical challenge and that’s not a business I wanted to be in.’
Pompei said his technology exploits the same principles as HSS to produce ‘a nice, tight, directional beam of sound that you can control in the same way we’re used to controlling lighting’.
Like Norris, Pompei believes the big market for his technology is in digital signage. In the UK, Audio Spotlights are in use at a number of T-Mobile stores, where shoppers can use them to listen to ringtones without irritating everyone else in the shop.
The technology also shows promise in museum displays; systems are in place at London’s Tate Gallery and the Natural History Museum. Devices have even been used on the European PGA golf tour, to beam sound to the crowd while maintaining a respectful silence for the golfers.
Pompei believes there is a potentially enormous market for consumer products based on directional sound technology. ‘In the future we’re looking towards the consumer markets being a really interesting possibility — I use one at home to watch television while my girlfriend sits quietly and reads a book.’
He added that while consumers can already buy a bolt-on package, Holosonics is in discussions with a number of electronics manufacturers that are interested in incorporating the technology into a fully integrated package. Pompei has also been involved in studies carried out by GM and Chrysler on the potential use of the system in car stereos, where Audio Spotlight-based speakers could be used to beam music only to those that want to listen. This work culminated in the system being installed on Chrysler’s Maxxcab concept pick-up truck.
On a slightly smaller scale than ATC, Holosonics is also looking to exploit the military potential of its technology. The US department of defence recently bought a number of units for an overhead communications system to be used in military control rooms. Pompei said it will obviate the requirement for headphones and reduce the amount of background noise in what is often a cacophonous environment.
But while ATC and Holosonics are investigating carefully directing sound, another group of audio pioneers is developing equally sophisticated technology that does the opposite; turning your surroundings into a giant loudspeaker.
Leading this audio revolution is Hull-based technology firm Feonic, which has developed a series of products that exploit the eccentric behaviour of the metal Terfenol-D to turn your desk, window or any other flat surface into a loudspeaker.
The material, a compound of iron and two rare earth elements, has magnetostrictive properties. This means that when exposed to a magnetic field it will change shape; or, if deformed, it will generate an electrical charge. Thus it can be used as a very sensitive sensor or as an actuator.
Feonic produces miniature distributed mode solid state devices based on this material that can be coupled with an audio frequency signal source and will cause any material that can vibrate at audio frequencies to radiate sound.
In 2002, the company announced itself with the launch of the Soundbug, an innovative little device aimed at teenagers that promised to turn everything from the classroom window to the desktop into a loudspeaker. Unfortunately for Feonic — and fortunately for hundreds of teachers — the product, while popular with gadget lovers, failed to catch on with kids: a fact that Feonic’s managing director Brian Smith puts down to the device’s relatively poor sound quality.
Since then the company has revised the core technology and, according to Smith, ‘turned the science on its head’. Wary of the Chinese imitators that have bedevilled previous Feonic products, Smith was reluctant to give much detail but said the company’s larger, more powerful, devices improvements have chiefly involved carrying out more signal processing.
Conversely, on its smaller devices, such as the next generation of Soundbug, improvements have focused on enhancing the mechanical performance of the core materials. These approaches, said Smith, have enabled Feonic to ‘use less smart material and produce better-quality noise at a louder volume’.
Smith is effusive about the advantages of Feonic’s technology: ‘If you want to drive 1in-thick glass over a 5x4m area then there’s only one way to do it.’
He said one of the biggest advantages of the technology is that it performs well in environments where acoustics are traditionally difficult to handle: ‘The main advantage of the technology from an acoustic point of view is that there is no directionality associated with it so you don’t get bounce or resonance. If you take a polar co-ordinate of our performance it’s a remarkably round shape you end up seeing from the emitter centre.’ He said this makes the technology particularly attractive for applications in public spaces, where bounce or echo is a problem.
The technology is also applicable to steel and aluminium building structures. The company recently signed an agreement with a leading shipbuilder to supply Feonic’s audio technology for five years. ‘We’re finding that we can permeate massive areas of the ship with very few drives and it’s the resonance that allows us to do that,’ said Smith.
Feonic, which has a number of demonstration systems driving wall panelling and flooring in interior design showroom, is preparing its next generation of devices for production before a summer launch. Smith believes he and his team have conquered some of the problems that affected the success of the Soundbug and is excited about the future for his technology. ‘We’re making really quite nice sounds — good bandwidth, good volume (95 decibels plus). Joe Public would more or less accept it without a subwoofer. An audiophile would want a subwoofer in there as well.’
As well as being used to generate sound, Smith said the technology has enormous potential in the area of active noise attenuation and could be used, for instance, to neuter or reduce the background noise everywhere from restaurants to meeting areas.
‘You can’t do much with noise management using traditional speakers because they’re so directional. If you’re sitting at a table with half a dozen people everyone’s ears are the same distance from the centre of the table so you can affect what you hear by driving the table.’
It is here, perhaps, that Feonic’s technology and the directed sound systems developed by ATC and Holosonics find some common ground. For rather than contribute to the ever-increasing cacophony of the modern world, both technologies could ultimately help reduce the high levels of noise that accompany everything from a trip to the supermarket to a “quiet” meal in a restaurant.
In the words of ATC’s Woody Norris: ‘We’re the guys who put sound where it’s supposed to be. We make it quiet where it’s supposed to be quiet.’