Citing Sources -- Chicago -- Author-date style

Reference list for an online audio recording

Sections 14.274, 14.276, and 15.33 of the Manual offer information on citing an online sound recording, but their guidance is minimal.  The following example is taken from section 15.33, but there isn't a lot of explanation regarding why it is formulated the way it is:

Coolidge, Calvin. [1920?] "Equal Rights" (speech). Copy of 78 rpm disc in RealAudio and WAV formats from the Library of Congress, "American
     Leaders Speak: Recordings from World War I and the 1920 Election, 1918-1920."

Meriam Library | CSU, Chico