double node harmonics

If you're referring to artificial harmonics, then by definition there aren't any set positions for them. The overtone series is the same as it is for natural harmonics, though, so if you want the octave, stop the node with your right hand thumb or index finger 12 fret positions above where you're fretting with your left hand and pluck with any of the free fingers on your right hand.

If you want the fifth, stop the node 7 fret positions above; the second octave, 5 fret positions above, etc. etc.

 

Artificial harmonics still only have one node. The fretting hand is not a node point.

He's talking about something else.

 

When you place a fretting finger lightly over the 7th fret, it causes the string to vibrate in 3 equal segments. When that happens the vibrating string has 2 nodes, equidistant from each other and from the nut and bridge respectively. These nodes are spots on the string that seem to be standing still while the rest of the string is vibrating. Is this what you mean by a "double node" harmonic?

That note incidentally, is the same as the note obtained playing the harmonic at the 5th fret on the next lower string. (Or should be, if your instrument is in tune.) Playing the 5th fret lightly causes the string to vibrate in 4 equal segments leaving 3 nodes. This note is two octaves above the note the string sounds when plucked normally.

I sometimes have difficulty getting this harmonic to resonate well, especially on higher strings, usually when I try to pluck the string anywhere near the 3rd node. Plucking lower, nearer the bridge pickup usually corrects this. Technically, I guess, plucking the string at 1/8 th the distance from the bridge to the nut should give that harmonic ("tri-nodal") the optimal sound.

So on the 7th fret harmonic when the string has two nodes, and you're plucking up near the 19th fret (where the 2nd node is) you're trying to make the string vibrate at the node, where it should be sitting still, essentially wiping out the harmonic sound. To get a feel for this, try lightly fingering the 7th and then the 19th frets, and you'll find the notes are the same. Then try holding the harmonic at the 7th fret and plucking at the 19th. Dud, right?? Ideally then, plucking the string halfway between the 19th fret and the bridge (or the 1/6 th point on the string) should give you the best sound on a "bi-nodal harmonic".