The Equalization Tool (EQ) by Sea to Sky Freediving Co.
 
We constantly say this in our courses: the EQ tool is the practice you have to do in order to advance your freediving comfort, depth and abilities. The exercises you do with this tool are a game changer for Frenzel Equalization and eventually "hands-free equalization" (i.e. Voluntary Tubular Opening or VTO). 
 
This simple training tool originates from the OTOVENT system built by ENT/ORL physicians to deal with chronic middle ear negative pressure and collapse of Eustachian Tubes. Freedivers adopt the same concept, with a few more advanced techniques and exercises to train the flexibity, coordination and control of the auditory and ear cannal muscles. 
 
You can find plenty of free tutorials and exercises online and on YouTube. Molchanovs Education also provides plenty of free educational tutorials. 
 
"The magic you are looking for is in the work you are avoiding."