Developer Joe Pompei—an MIT student and occasional musician who was frustrated by the inability to control sound from traditional speakers—shows off the four Audio Spotlights embedded in the MAXXcab's headliner directly above the seating positions.

"The variety of sound sources is only going to increase with the availability of voice-enabled navigation, e-mail, cell phones, video games, and movies in your future vehicle," said Steve Buckley, Electrical Product Innovation Manager at Daimler-Chrysler Corp. "The Dodge MAXXcab is great test bed for this technology because it already includes features such as the back-seat 'edu-tainment' system for the kids and front-seat plug-and-play computer with voice-activated features."

In the MAXXcab, four Audio Spotlights are embedded in the headliner directly above the passengers. Two speakers "shine" on the front-seat passengers while the other speakers are aimed at rear-seat passengers, creating two distinct audio environments. In future applications, each passenger could have a unique sound environment, Buckley said. The technology was developed as an MIT Media Lab project by 27-year-old Joe Pompei, an MIT student and occasional musician who was frustrated by the inability to control sound from traditional speakers.

"The location of sound, and how it is distributed around the listener, greatly defines the listening experience," Pompei explained. "We're used to doing this with light—we already use light bulbs, spotlights, and projectors to control our visual environment. With the Audio Spotlight, we can now have the same control over sound."

The Audio Spotlight consists of a thin, circular transducer array and a specially designed signal processor and amplifier. The lightweight transducer is about 13 mm (0.5 in) thick and nonmagnetic. The signal processor and amplifier are integrated into a system about the same size as a traditional audio amplifier, with similar power requirements. Unlike traditional speakers that transmit nondirected audible sound at wavelengths of several feet, the Audio Spotlight transmits millimeter-sized ultrasonic waves, which form a narrow beam of sound that becomes audible as it travels through the air. The current system produces relatively low-volume sound at typical passenger positions because it has not been optimized for close-range listening, Pompei said. It is currently designed for long-range projection, though further development in transducer design will solve that problem, he added.

"Personalization of the various 'infotainment' features is a key development area for DaimlerChrysler," Buckley added. "This is especially important for the driver, who needs useful information like traffic updates without being distracted by their spouse's music or a child's video game."

Audio Spotlight technology is still in development, and has commercial interest from several MIT Media Lab sponsors representing a variety of industries, Pompei said. None of the technologies in the system is inherently expensive, and many components are actually smaller than today's systems, according to Pompei. If produced in volume, he anticipates it could be competitively priced with conventional audio systems.

Kevin Jost The Dodge MAXXcab concept truck is the first automotive application of Audio Spotlight—an MIT Media Lab technology that directs a narrow beam of sound much like a spotlight projects light.

AEI September 2000