I don't know if anyone else has mentioned it, but there was a recording
of Jack Johnson issued in the UK in about 1914 on Edison Bell Winner
2685 of a monologue on 'Physical Culture'.  I have no idea of the
matrices or the source of the recording, because the record is extremely
rare and I have heard of only 1 copy - which is supposedly in Scotland! 
I have been told that his voice is rather indistinct on the recording.

Ken Jobling