1879 Jan., "A Night with Burglars" in Gleason's Monthly Companion, vol. 8, no. 1, p. 281 (Google preview):
The two who sat at a table in an obscure corner of the room were the noted burglars "Whispering Jack" and "Jim the Cracksman," as they were nick-named by their associates.
[T]he microphone enabled a Whispering Jack Smith to make a rhythmic mumble pass for singing and gave Bing Crosby a means of taking advantage of his casual, intimate style.
2002, J. John Loughran, Developing Reflective Practice, ISBN 9781135717230, p. 136 (Google preview):
Case 3 Whispering Jack: Jack was a quiet and perceptive young man who was well respected by his peers.
Under the lone operating streetlight, Whispering Jack comes into full view. . . . In his usual low tone, . . . Jack speaks in the manner that earned him his nickname.
Some referred to him as "Whispering Jack" for his booming voice while many others called him Pappy.
c.2009, B. J. Sears, "Reddington's Phonelescope," Professor Sears' Technological Rarities (retrieved 27 July 2014):
Whispering Jack Reddington graduated from the Colorado School of Mines in 1899 and began his career as a mining engineer. His real passion however, was the transmission and amplification of sound waves.