There are very powerful mantras to develop the magic hearing and acquire clairaudience: AUM CHIVA TUN E.
AUM is vocalized in this way: open the mouth wide to pronounce the A, then round it with the O and close it with the M. And the sound of each vowel must be prolonged.
The mantra CHI is vocalized by a long sustaining sound of the I [the I is pronounced like the letter E in english].
The mantra VA by prolonging the vowel A [the A is pronounced like AH].
The mantra TUN, with force, so that the letter T hits the U [the U is pronounced like OU in the word “you”].
And this U is prolonged for quite a while and then we give the N a bell-like resonance.
Finally, the E, alone, is prolonged for as long as possible, like this: EEEEEEEEEEEEEEEEEE… [the E is pronounced like EH]
In AUM, the tone goes up with the vowel A and goes down with UM. The rest of the mantras in a lower tone than UM.
Perform this marvelous exercise for half an hour daily accompanied with upright conduct and very soon you will begin to feel its effects.
Samael Aun Weor
Logos, Mantra, Theurgy, chapter 9