Ahh, Equalizing
The mouth-fill technique that I invented in 1999 is not easy to master. Currently, only Peter Scott and Herbert Nitsch can do it well (other than myself), and even they can still improve their efficiency.
The mouth fill can be used with various sister techniques, but it really needs the power of the frenzel to get the air in the mouth into the ears.
If done properly, it gives the illusion of full lungs all the way to depth, with maximum possible equalizing speed.
In my case, doing only inverted dives, I would fill my mouth at 30m, close my throat, and then use only the air in my mouth to equalize. It is important to understand that after 30m, I don't equalize 'on demand', I equalize continuously. My tongue applies constant pressure. There is a constant squealing noise as the ears equalize continously. Because of that, I don't even think about equalizing after 30m, once the muscles are doing their job, I can think about relaxing, streamlining, etc.. Even at 88m there was still air left in my mouth to equalize at that depth and further. With a mask I once went to 76.5m and still had air left in my mouth to equalize my mask and ears. As the mouth becomes empty, you must touch your chin to your chest to collapse the dead space in the back of your throat.
Herbert fills his mouth at 45m, which I think is a bit too deep. He would run out of air in his mouth at 75m, and then squeeze the ears after that.
Once the air in the mouth is used up (at 120m+ if done properly), then you can switch to a water equalizing technique, which is too dangerous to describe here.
Above all, I must insist that these techniques can be done by anyone. I strongly dislike it when I hear people complaining that a technique 'doesn't work for them.' It simply means they need more practice.
The mouth-fill is best practiced with a buddy in 15m of water. One mouthful at the surface should get you to 15m when using a mask. Whatever depth you get to, you can then compute your max depth based on your mouth-fill depth. For example, if you can fill your mouth at the surface (1 atm) and make it to 15m (2.5atm) with a mask, then you can reach two and a half times your fill pressure.
Now, filling your mouth at 30m (4atm), you should be able to reach (4atm x 2.5 = 10atm) = 90m, with a mask.
Suppose that you have a very stretchy rib cage and a powerful diaphragm. Then, it is possible with great effort to fill the mouth at 45m. Suppose also that you are using goggles, so you can reach 20m using one fill at the surface. Then, your limit depth is (5.5atm x 3 = 16.5atm) = 155m.
Then, at 155m, you transition to a water equalizing technique, which typically allows you to reach 1.5 times your water-fill pressure, putting you at 16.5atm x 1.5 = 24.75atm = 237.5m.
Experts will argue that you must transition to the water equalizing technique before complete collapse of the mouth/throat, and they are right, but the calculations remain the same.
Eric Fattah
BC, Canada