PRX, a Cambridge-based public media company, is announcing Thursday that it's spinning off a new company, RadioPublic, to develop a mobile, on-demand listening platform. So far, RadioPublic has put together more than $1.5 million in a first round of funding from non-profits, for-profit media companies and venture capital.

Investors include Project 11, The New York Times, Knight Foundation Enterprise Fund, American Public Media, Graham Holdings Company, UP2398, Matter Ventures, Homebrew and McClatchy.

Unlike PRX, a non-profit, RadioPublic will be a public benefit corporation. Jake Shapiro,...