[Harp-L] Viva La Difference Tone

[Gary Lehmann <gnarlyheman@xxxxxxxxx>]

I recently bought a custom comb for my best short harp (it's a Special 20
in D), and it plays better--so I thought I had better tune it as best I
could, so that the chords sound good.
Then I put it back together and tested it, and was able to come up with the
phenomenon you will hear if you go to Slidemeister and open the sound file
attached to the thread with this same subject line.
I am  blowing holes 4 and 5, so that would be D and F#. Then I am
*bending*--except that you can't bend the blow notes of the bottom holes of
the standard tuned harmonica--
What I hear is the D continuing to sound, the F# bending to F and the
subharmonic D (the note is the same as would be sounded on hole 1, but is a
difference tone) going to Bb.
Can someone explain to me how this is happening?
Gary