Kevin is correct. I have a tape that Bob Lund and Jay Marshall recorded of Dunninger giving his reflections on famous magicians. Bob noted that during their previous conversation, the now ill Dunninger's voice was normal but weak. When Bob turned on the tape player Dunninger's voice magically transformed into that booming authoritative voice that captivated radio audiences in the 1940s.
Also, I never knew Blackstone Sr., but was very friendly with Jr. Once as I awaited outside of the theater in Atlantic City, I heard a voice whisper, "Hey Tom, come here." It was Harry and he wanted to know if I'd do the shirt pulling stunt in The Committee. Of course I said I'd be honored. We went to his dressing room, set the gag and it went off perfectly. Only problem was after it was over I had to sit for the rest of the show in my undershirt and suit jacket. I did it without hesitation.