A lip oscillation is a continuous pitched sound produced by squeezing air between your lips. This is often also referred to as the lip bass.
Check out the HUMANBEATBOX.COM's article explaining how Lip Oscillations work.
How it's done
- Make sure your lips are moist
- Blow out a raspberry using your lips as if you were bummed out about something. It's pretty much the first sound that babies make!
- Clench your teeth together for a tighter concentrated flow of air
- Play around with different pressures and air strength
- Add humming or falsetto vocalization to create a synthesizer sound!
Another way people make lip oscillations is to do a dry spit. Imagine you have tea leaves in your mouth and you want to spit them out. You purse your lips together and push air out quickly. Well, that's a short lip oscillation.
The main thing to remember here is that there are 3 components to this sound: Airflow (outward), Point of resistance (usually teeth); and Point of oscillation (Lips). The sound will vibrate from the point of resistance to the point of oscillation, so a point of oscillation that is further back in the mouth will give a deeper sound as when a sound has more space to vibrate in it lowers its frequenc – the same reason that you lower your tongue and/or widen your jaw to lower pitch. You don’t need to use your teeth as the point of resistance, you can move it anywhere you want, personally I like to Roll the back of my tongue as I breathe outwards as my resistance sometimes to produce a fluid and deep sound (I named it ‘mouth lip bass’ as it vibrates in the entire mouth); you can move the point of the resistance to the lips by covering the bottom lip with the top, keeping the jaw open, this with cancel out the vibration limit meaning that it will vibrate inside of your mouth, throat, and lungs – as you can imagine that will be a very deep sound.
That last technique you described, where the vibration limit gets “cancelled out” and the oscillation vibrates inside of your mouth, throat, and lungs, are you describing the outward subwoofer bass that pash and vahtang use? If so, I also believe this is the sound coupled with the outward K rimshot to create the Zekka or Two.H snare