Does hands-free equalization involve any type of pressurization such as is done with Frenzel? Or is it that the eustacian tubes are simply opened and the dead space in the ear canal equalizes in pressure with the throat?
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I don't know how to perform hands free equalisation, but basic physics dictates that a positive pressure must be applied for it to work. The air spaces of the mouth and throat will compress at the same rate as the inner ear, so the pressure will be the same in all areas and there will be no pressure differential, thus no air will flow through the eustachian tubes. Hence a pressure differential must be applied across the eustachian to cause the air to flow in to the ear, though, as you're not forcing the eustachian tubes open with the pressure then the pressure can be relatively low. So, I'm guessing a slight mouthfill or gentle Frenzel will suffice.
As I said, I don't actually know, so someone will probably come and prove me wrong.
No, quite the opposite, the lungs and all airspaces compress, that's a given. The inner ear will be at exactly the same pressure as the lungs, throat, mouth etc - why wouldn't it be, there's only a thin membrane separating it from the outside world? Equalisation is the action of maintaining the size of the airspaces that are not flexible enough to not implode, rupture or whatever under the compression, usually by taking air from more flexible areas.
To the original question:
Hands free is general term meaning any way you can equalize without holding your nose. A multitude of techniques can be used. BTV is specific, although you can get there multiple ways. BTV means using the muscles around the eustaction tube opening to open the valve. Some divers have conscious control of those muscles. They can move them like most folks move their fingers. Others can activate the muscles indirectly by moving their throat/scalp/ears around. Some of the later eventually learn how to be the former. Same practical result, very different process to get there. Of course, for BTV to work, you have to have a slightly higher air pressure in the throat than in the tubes.
Many divers use a combination of BTV and a soft Frenzel (working against the pressure in their mask). this can be done hands free. Some can just Frenzel or just BTV as desired.
I use both, can use them separately. With increasing depth, first I can do pure BTV, then need to add mild Frenzel, eventually, near my equalization limit, I have to grab my nose and Frenzel hard. Others will be quite different.
Connor
ahh ive been trying to find answers on this everywhere. i hope i can still get a reply. i use btv but i dont know much about it. i usually only dive to about 40 feet, a little over 10m. when i use btv i dont ever push air, all i do is open the tubes and then they equalize. so ive been trying to figure out if im letting air in through my throat or if water is flowing into my ears( i almost always come up with both ears full of water when i btv)., does anyone know?