Video displays aren’t the only technology that’s growing thinner. 
Flat loudspeakers have been around a long time — almost as long as loudspeakers themselves. Patents dating back to 1929 granted to E.W. Kellogg described the first “electrostatic” (ESL) designs, and inspired the first commercial ESL in 1957 by Quad. Since then, the ESL concept and its many commercial variations have lived primarily in the domain of esoteric hi-fi enthusiasts. Audiophiles still debate the relative sonic merits and flaws of the

Warwick Audio Technologies CEO Steve Couchman holds the flexible laminate that is the core of their Flat Flexible Loudspeaker (FFL) design.

design, but now, just in time for the final stages of flat video display evolution, Warwick Audio Technologies, a UKbased company, has taken steps toward a variant of ESL design for commercial applications.

Specializing in the development of Flat Flexible Loudspeaker (FFL) technology for original equipment manufacturers (OEMs), Warwick Audio has announced a groundbreaking new loudspeaker — less than 0.25mm thick — that’s flat, flexible, and could be hung on a wall like a picture. The company believes its particular method of sound generation could make public announcements in places like passenger terminals clearer, crisper, and easier to hear.

Warwick Audio Technologies is a spin-off from the University of Warwick, where the concepts were originally engineered. Steve Couchman, CEO of Warwick Audio Technologies, believes its FFL technology could entirely replace the loudspeakers currently used in homes and in cars, as well as in public address systems used in applications like transportation terminals and shopping centers.

“We believe this is a truly innovative technology,” says Couchman. “Its size and flexibility means it can be used in all sorts of areas where space is at a premium. Audiovisual companies are investigating its use as point-of-sale posters [digital signage] for smart audio messaging, and car manufacturers are particularly interested in it for its light weight and thinness, which means it can be incorporated into the headlining of cars, rather than lower down in the interior.”

Making sound means moving air, and, especially for low frequencies, it means moving a lot of it. So a flat design is normally at a disadvantage compared to cone loudspeakers for bass reproduction. While full specifications are not yet available (a technical paper is said to be forthcoming), their current design begins low frequency drop-off below 800 Hz. But for applications where speech intelligibility is critical, this LF performance may be less relevant. And you can always supplement LF with a subwoofer — which, thanks to the way we perceive sound, can be hidden out of sight. On the upper end, current “proof of concept” panels do in excess of 85 dB at 1 kHz, rising linearly to 105 dB at 20 kHz.

All loudspeakers work by converting an electric signal into sound. Usually, the signal is used to generate a varying magnetic field, which in turn vibrates a mechanical cone, which moves air and produces sound. Warwick Audio Technology’s FFL technology is a carefully designed assembly of thin conducting and insulating materials that result in the development of a flexible laminate, which, when excited by an electrical signal, vibrate and produce sound.

Couchman says, “The sound produced by FFLs can be directed straight at its intended audience. The sound volume and quality does not deteriorate as it does in conventional speakers, which means that public announcements in passenger terminals, for example, could be clearer, crisper, and easier to hear.”

The FFL was first developed by Dr. Duncan Billson and professor David Hutchins, both from the University of Warwick, with early trials using just two sheets of tinfoil and an insulating layer of baking paper to produce sound. Since then its design has significantly evolved, and the technology is now ready for commercial exploitation, according to the company.

HOW DOES IT WORK?
The laminate comprises three layers. The sheet materials are bonded in the production process to maintain the active thickness over an area between the A5 and A3 paper sizes. Electrical contacts to the outer layers of the laminate allow a boosted audio signal to drive the laminate, reproducing sound.

All loudspeakers operate on the principle an electrical signal is converted into sound using a mechanical device. A conventional cone speaker has an electrical signal that generates a varying magnetic field, which in turn vibrates a mechanical cone, producing the sound.

FFL technology produces sound by directly applying the electrical signal to the laminate, which vibrates in time with the electrical signal. The laminate is composed of two conducting surfaces (membranes) separated by an insulating layer. An electric field (rather than a magnetic field) forms over the laminate. The FFL loudspeaker is voltage driven and draws very little power. Unlike power-hungry alternatives, very little electrical current is wasted as heat. The directionality of the sound produced by the FFL is controlled by flexing the laminate, allowing sound properties to be modified in a similar way to the image in a curved mirror.