Hallo Martin,
try reading efattah tutorial (the bible) downloadable from:
Liquivision F1 and Fluid Goggles Home where you'll find:
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Hands-Free (Voluntary Opening of Eustachian Tubes)
Description: During the descent, “open” your Eustachian tubes by flexing the muscles surrounding them. The Eustachian tubes don’t actually open, but rather muscles prevent them from contracting with the increasing water pressure. This encourages the movement of air from the lungs to the Eustachian tubes, thus maintain equal air pressure.
Advantages: Ideal for streamlining and energy conservation. Safer than other techniques when performed correctly.
Disadvantages: Requires training of muscles around Eustachian tubes. This technique is difficult or impossible for some divers to master due to the small size of their Eustachian tubes. Slower descent speed may be necessary for effective equalization. Not usually effective at depths that are well below a diver’s residual lung volume.
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Or amazingly even better go to:
The Frenzel Technique :: FDTF :: Freediving Team of Finland
where included in the frenzel technique, they spend the whole section 7 in describing how to train the eustachian tube.. I had actually no time to test the method, but I probably will in few days. Hope it helps.
