During my work on a Jaap Sahib dictionary and sound-spirit elaboration, I collected some inspirations about the mystic sound “Ong” (like, for example, in “Ek Ong Kar” or in “Ong Namo Guru Dev Namo”).
Ong & Aum
ਓਅੰ (pronounced Oaŋ or Ong) is a sacred and mystic sound and syllable, possibly first introduced and extensively used by Guru Nānak (1469-1539). Due to its similarity in sound and usage in sacred texts and mantras, it seems to be a variation of the more ancient ॐ (pronounced as Om or Aum).
Some claim that Ong signifies the creative or active – or, also, tantric – aspect of Om. Since it is most prominently used in ੴ (pronounced Ek Ongkār or Ikk Oṅkār) between “ek” (“one”), as the sign for transcendent, ultimate Oneness, and “kār” (“creation”), as an expression for the immanent temporary form of creation, it could be argued that Ong symbolises the process of creation and destruction between these two aspects of existence, implying a Divine seed-force that evolves into the universe. Since this process is universally described as effected through sound, word or music, Ong could be understood as symbolising the sound (naad) or word (shabad) of creation and destruction, transferring and transforming between spirit and matter, soul and body, purusha and prakriti, nirgun and sargun, nagual and tonal, respectively. Since the bridge, connector and transporter between these two fundamental aspects is also part of the definition of word Guru, Ong could also be understood as symbolising Shabad Guru.
Different Vibrations
By chanting the syllables Om and Ong, one can experience the difference in vibrations they produce in the body (mostly the head). It could be argued that the stimulation of the brain (most importantly thalamus, hypothalamus, pituitary and pineal gland) is different, whereby the former, ending on “m” with mouth closed, sounds and feels more closed, contained and peaceful, whereby the latter, ending with a palatal-nasal sound with mouth open, brings the vibration closer to the centre of the skull, therefore closer to the brain, and sounds more active, revolving and forceful.
The Sole Imperishable Thing
ॐ (pronounced Om or Aum) is a sacred and mystic sound, syllable and symbol in Indian religions, also referred to as praṇava or akṣara (“letter of the alphabet, imperishable, immutable”) or ekākṣara (“one letter of the alphabet, the sole imperishable thing”), and only in later times oṃkāra (“the syllable or sound or maniestation of Om”). It signifies the essence of totality, ultimate reality, supreme divinity, consciousness, soul, creation, truth of Atman and Brahman. The syllable is often found as an incantation at the beginning and the end of chapters in Vedic texts, but is also chanted before or during meditative and spiritual activities such as prayers, ceremonies of rites of passage, or Yoga. It first appears in the Upaniṣads as a mystic monosyllable, and is regarded as the object of the most profound religious meditation and spiritual efficacy.
In the Maṇḍūkya Upaniṣad it is said that this syllable is all what has been, that which is, and is to be, that all is Om, only Om (cf. doxology, “ād sach jugād sach” etc.). Literally analysed, Aum is taken to be made up of three letters or quarters: the letter अ (a) is Vaiśvānara, the spirit of waking souls in the waking world, उ (u) is Taijasa, the spirit of dreaming souls in the world of dreams, and म (m) is Prajñā, the spirit of sleeping and undreaming souls. In later times it came to be used as a mystic name for the Hindu triad, representing the union of the three gods अ (a) Viṣṇu, उ (u) Śiva, and म (m) Brahmā. Buddhists place it at the beginning of their vidyā ṣaḍakṣarī or mystical formulary in six syllables (“oṃ maṇi padme hūṃ”). Om also is a word of solemn affirmation and respectful assent, sometimes translated by “yes, verily, so be it” (cf. “Amen”); it is also regarded as an auspicious salutation (e.g. as “Hari Om”). However, the whole Om is said to be ultimately unknowable and unspeakable (cf. Tetragrammaton, YHWH, HaShem), into which the whole world passes away, blessed above duality.
The Divine as the Protector
Bhai Kahan Singh Nabha claims in Mahaan Kosh that Om and Ong are derived from the Sanskrit root अव् av, which means (among many other things in different contexts): to protect, save, guard, defend, govern, rule; and therefore Om and Ong refer to the Divine as the protector.

The following quotes from Yogi Bhajan (all taken from the manual Praana Praanee Praanayam) would support an understanding that there is no fundamental difference between Om and Ong, but that Ong is a particular way to reproduce the otherwise transcendental sound of Om with the human voice:
“Ong Shabad is the creative sound of the word Om. Om cannot be chanted, cannot be heard, cannot be sung, but you can create it. It is a creative word. That is why Guru Nanak used Ong. It is the right pronunciation of the word Om. Ong means creative force of God.”
“There is no word Om or Aum. Actually the sound Om is the sound of the conch, which can only be created. It cannot be written and it cannot be expressed. It is the sound of Infinity in formlessness. When it starts working it frees man of all possessions.”
“Ong is never chanted through the mouth, it comes through the central nerve channel, the Shushmana, which corresponds to the tip of the nose. […] It is created in the conch of the human brain, not with the mouth.”
“The sound comes from the back of the nose, but you have to keep your mouth open. It can go to any pitch. It requires practice, but the practitioner enjoys it. It is very fruitful. It is bliss… Therefore it is very important, if you want to be in love with your self, to practice this sound. That will give you a great essence and joy of life.”
“With the back of the tongue, just create the sound by the vibratory effect. It will vibrate the pineal and pituitary and when the pituitary starts vibrating, the pineal has to come to help. The moment they start playing this game with each other, you go into the altered state.”
“Ong is the sound of the Ajna chakra, the sixth centre of consciousness. [my insert: The symbol or mandala of the Ajna chakra includes the Om sign as the seed mantra in its centre, accompanied by the seed mantras for Shiva and Shakti on the two petals, symbolising pingala and ida nadi, respectively.] Vibrating the thalamus is a privilege. That’s why there is no such thing as Om. There is, however, the sound of the Infinite which comes through the central channel, the Shushmana, and touches the central nervous system”
“When you correctly utter the word Ong, you harness the entire energy of the soul. The entire electro-magnetic field of the universe becomes yours.”
“It may make you cough or sneeze or there may be pressure in the ears, but it will give you bright eyes, better ears, and good nose – your eyes, nose and throat will be perfect. It will affect your thyroid. It will vibrate you whole brain and do a lot of good things.”