Critical mass approaching among 18-34 year-olds.

The percentage of Americans that regularly listens to Internet radio rose sharply this year to 12% (approximately 30 million listeners) up from 8% last year, according to a new study by Edison Media Research and Arbitron. The online radio audience is closing in on critical mass among 18-34 year-olds, with roughly one in five listening every week.

Presented to a roomful of ad buyers and media planners in New York on Thursday (April 14), the January 2006 study consisted of 1925 interviews of participants in Arbitron’s Fall 2005 radio ratings survey. Intended to illuminate adoption rates for new radio platforms, it also examined satellite radio, podcasting and nascent HD radio technology.

The first such study, in summer 1998, found only 8% of Americans had ever listened to online radio. Now 43% say they have listened to Internet broadcasts at least once, and one in 5 (approximately 52 million) say they have listened in the past month.

Habitual Web radio listeners skew male (58%) and are becoming more evenly distributed across demos, the study found: 12% of teens, 15% of 18-24s, 26% of 25-34s, 21% of 35-44s, and 19% of 45-54s say they have listened in the past week. Percentages were dramatically lower among listeners 55-plus.

Dubbed “The Infinite Dial: Radio’s Digital Platforms,” the study makes a case that radio’s definition is being re-written. "Radio is undergoing a renaissance in distribution platforms,” Arbitron president of sales and marketing Pierre Bouvard said. “All of this seems to be additive to terrestrial radio. It’s not one robbing the other but layering on top.”

Despite seemingly endless new digital entertainment options, 77% of survey participants said they would continue to listen to terrestrial radio as much as they have in the past.