Strumming Harmonic Blocks
A harmonic is a bell-like sound created by lightly touching a string at a specific point and picking the string.
For frets 1-12, the strongest harmonics [they exist all along the string plane] are at frets 12, 9, 7, 5, & 4. When we lay a finger over multiple strings, lightly, and strum it, this is what we are calling a harmonic block. Any finger can be used [directly over the fret, not in the fret space], but it can only be a single finger [more than one will create a mute].
When we use the 1 finger, the 2, 3, and 4 are free. These can mute the strings. Or, they can ‘slap’ or ‘beat’ the strings to create a thump. It can beat or mute the strings at any point. And, any finger can be the harmonic block, while the others act as a beater/blocker. Yet, the 1 works best in our view [with 2-3-4 as beater]. Try the pinky too, with 1-2-3 as beater.
Harmonic blocks are also good ‘pre-chord sounds’ which can help us synchronize events to a steady strumming motor.