Ten acts and two stages all on one street-this is what folk music fans can enjoy, all for free, when the fifth annual New England Americana Festival takes to a closed-down Brattle Street in Harvard Square on September 27 from noon-9pm. Book-ending the outdoor festivities are opening and closing gigs at nearby Club Passim, the venerable folk music haven that helped launch the careers of Joan Baez and Bob Dylan. Each show-the kick-off bash on September 26 at 7pm and closing night on September 27 at 8pm-are only $15. Now that’s music to our ears.