A new-style ultra-thin, lightweight loudspeaker that is flexible and inexpensive to manufacture has been developed by Warwick University spin-out Warwick Audio Technologies (WAT).
At less than 0.5mm deep, the developer claims it is thinner than any other flat panel speaker currently available, and can be made in any shape or size — from a few millimetres to several metres.
The speaker works on electrostatic principles, which operate by interacting with charges of static electricity to create the movement necessary to produce soundwaves.
WAT’s speaker differs from other ‘flat panels’ currently available because it does not rely on a conventional moving coil device or piezoelectric element.
Mark Thompson, WAT’s marketing director, said the only external excitation device used by the speaker is its amplifier, which is used to adapt audio signals to make them suitable for broadcast.
Electrostatic speakers are not a new technology, but Thompson said they have always been expensive and heavy.
‘What we have is an adaptation of that technology, which reduces drastically the size, weight and thickness of the speaker but doesn’t entirely compromise the performance,’ he said.
To enable WAT to reduce the speaker’s size it had to rely on new thin film materials and a different kind of design.
Conventional electrostatic speakers are made with a thin flat diaphragm, usually consisting of a plastic sheet impregnated with a conductive material such as graphite sandwiched between two electrically conductive stators.
‘We just use a single stator,’ said Thompson. ‘That’s how the idea for electrostatic loudspeakers started in the 1930s, but then someone had the bright idea that if you use two stators you only need half the voltage.’
Throughout the years the major downside of electrostatic speakers has been the excessive amount of voltage they require. Most require 3,000V, said Thompson, when their speaker only needs less than a tenth of that voltage amplitude. Thin materials and a new design allowed them to reduce speaker size by a factor of ten.
‘The electric field is just the voltage divided by the distance,’ he said. ‘So if we reduce the distance by a factor of 10 we can reduce the voltage by a factor of 10 and keep the same electric field.’
The designers of the speaker say the technology demonstrates several key and unique advantages for the future design of sound systems.
The actual speakers are so thin and lightweight that the physical space needed is minimal, which makes them ideal where space is at a premium, such as in-car entertainment systems. The speakers are also extremely flexible, so they can be easily contoured to fit complex shapes.
Their flatness also makes them ideal in situations where precise sound direction is required.
‘I’m sure you’ve heard UK rail system announcements where everyone is very confused because the noise from one speaker is interfering with the noise from another,’ said Thompson. ‘Well that doesn’t happen with this system. You can put loudspeakers together or have them in an array. You avoid those situations and direct the sound to the audience.’
The developers said the speakers could also be used as a potential advertising tool. Posters could incorporate them in a way that would bring them to life.
WAT estimates there are approximately three billion loudspeakers sold every year, and claims that flexible technology is suitable in nearly all these applications. additional sales and price premiums could be generated with innovative applications previously restricted by old technology.
WAT has received £500,000 from Synergis Technologies and the Mercia Technology Seed Fund (MTSF) to develop the technology further for commercialisation.
‘This funding will help us kick off the next stage of development,’ said Thompson. ‘We expect in a year from now to have another wave of funding to launch the product.’
Researchers claim to have reduced the size, weight and thickness of flat panel speakers without compromising performance. Siobhan Wagner reports