Impact Airfoil 5.2 loudspeaker system Airfoil Bending Wave Driver

Sidebar 1: Paul Paddock on the Airfoil Bending Wave Driver

It's rare to find a truly new speaker technology, so I couldn't help but be intrigued by the Airfoil's Bending Wave Drivers. I asked designer Paul Paddock how they work.

"They fall into the class of devices called 'Traveling Wave' drivers. Basically, you're setting up a shock wave with a linear voice-coil along one edge of the diaphragm, that ripples through the membrane."

"So you're setting up a longitudinal wave in the membrane, and as it propagates along the membrane, transverse waves are given off and create sound?"

"Exactly. Imagine a traditional driver, but here, you want it to break up immediately, but in a controlled fashion—there's no pistonic motion. We set up a wave that moves smoothly, and dissipates as it moves around."

The Airfoil towers' winglike shape was "arrived at experientially. The goal was to achieve an even response curve and a smooth polar response. Actually, the back two-thirds of the diaphragm are an energy dump. They really only serve to dissipate the waves, so that they don't reflect off where the membrane meets the enclosure. There's some midrange given off, but most all the action is in the first third."

Paddock laughed when I asked about the membrane material itself. "It's a cousin of Mylar, and used throughout the speaker industry. In the audio industry, you're pretty much limited to what you can get off the shelf. An enormous buy for us represents sample quantities for the plastics industry. But it has to balance a lot of conflicting demands. It has to perform the way you want it to, it has to look good, it can't cost a fortune, and it has to last a long time—and not deteriorate in sunlight. But I don't want to get too tied up in the particular plastic, because I'm always looking at new things that come along—and five years down the road, I may want to change plastics."

"Speaking of years, how long have you been working on the Airfoil driver?"

"On this particular concept, it's bumping up on two years now. The driver first emerged about two years ago. I was trying to do something else, actually—a bit purer approach—but it kept doing what this one does. So I took a hard look at it, and found that it worked quite well.

"There are a lot of other things that play into it as well: the stuffing behind the membrane, the suspension, the strips attached to the driver to control vibrational modes...there are all the same things that you have in traditional cone drivers, a host of competing requirements."—Brian Damkroger