Om || (AUM) is a practical tool that can be used for emancipation, merger in brahman (brahma sayujya). As a sacred letter it is full of potency- potent enough create the universe; so also dissolve it! The three syllables of a  u and  m are located at the three plexus of consciousness-manipura (at the navel), the anahata (heart level), and the ajnya (between the eye-brows) level. These are the srushti, sthiti and the laya levels. The spiritual seeker should concentrate on the sound of these three syllables and use it to enhance his energy level. Once he/she gets complete command over the plexus (chakra) the sadhaka can break open the nadi granthis (valves?) and activate flow of energy to higher levels- from a (brahma granthi) to u, the Vishnu granthi and then the m which is rudra granthi. By breaking through the three knots, one can enter the highest level of sahasrar prajnya- the ultimate brahman.

   This facility is available to all those who are desirous of  enjoying supreme bliss. This will ensue a complete merger brahman and there will be no rebirth. 

   But, before taking to contemplation, meditation, focused attention on Om, the sadhaka should be aware of the Kundalini vidya. The activation of the dormant serpent power, kundalini, is necessary in order to open up the sushumna nadi and enter it. Normally, the vital airs (the air we breathe) move up and down the ida (left/moon/cool) and pingala (right/sun/warm) without entering the central sushumna nadi. Thus, the plexus/chakras remain unaffected and we are denied the higher powers/super human powers. This is the crux of the problem. 

   Thus, Om is closely linked to kundalini shakti. We are denied the benefit of this power in this life, or even in the future lives, unless a guru comes our way and helps by divine intervention. So, should we bother about this facility (kundalini shakti) or not? The answer lies in the earnestness of the spiritual seeker, sadhaka, and his concerted effort to attain to sayujya. Spiritual attainment is not an easy job.

   The potent syllable 'Om' (aum) is the energizer as a mantra; it is also a great benefactor; this mantra is so powerful that all evil forces are driven away by the very utterance of this mantra. Once the suras / devatas went and complained to Brahman to save them from the repeated onslaughts of the demons/asuras, The saattvic suras and rishis could not defeat the rajasic asuri shakti, The Lord asked them to use the sacred letter / mantra Om and throw a kusha grass/ darbhe (meaning any trivial thing!) at the evil forces and they will disappear. This is the power of the mantra.

   The suras and the Rishis (pious ones who want to meditate) were thus saved from the asuras (evil forces/evil thoughts/ powerful forces that obstruct meditation).

  The suras thus came victorious. The Lord asked them: "What would they give Him in return for this great favour?" The asuras said they do not know and in turn asked what would He like to have? The Lord said, "It is enough if the sacred syllable is used as an affix and a prefix before every mantra. It would strengthen the mantra without which the power would be wasted". Thus we use 'Om' before and after every mantra.

   The source of the power of "Aaum" is Parabrahman (A); and, the manifest form of Brahman is the creator chaturmukha brahma (at the navel), the great benefactor, protector vishnu (at anahata/heart level), and the dissolution power of maheshvara at throat level; (also enlightenment and removing ajnyan at rudra granthi). 'A' is para, 'a' is pashyanti, 'u' is madhyama, and 'm' is vaikhari when pronounced. If it is not pronounced loudly, and just meditated upon, it will go straight to ajnya level instead of going out of mouth. Thus it is more effective chanting the mantra 'Om' within one's breath than loudly pronouncing it!

  Om /Aum/aummmmm and many other types of sounds are produced while chanting Om. None of these is correct. Morecver, there are different types of sound and decible levels of this mantra. Some utter this mantra is a shrill voice, some like a humming bee, some shout loudly like a thunder, and some make noise of a conch blown or striking a temple gong, or a metallic sound. The loudest shouted on the top of a hill in a solitary place is the best and the most effective. All others are not very effective.  

  Another important point to be remembered here is that 'this sacred letter Om should be breathed in (inhaled) and not breathed out (exhaled), 

  Whoso meditates on Om as brahman becomes brahman! 

(See Bhavanopanishad)