The OM Sound Physiology

The Om Sound and Phonetic Anatomy 

The O or U sound is caused by the tongue body pushing the soft palate against the underside of the skull. The small oval of the lips  allows the vocal cords to generate and vibrate the soft palate and base of skull by acoustically creating over pressure in the sound chamber of the mouth. The sound waves must pass narrowly between back of the thorax and tongue. At some frequencies the whole cortex is vibrated because of this proximity.  If your tongue is adjusted properly and the tone is right for you, you will feel  the vibration at the base of your skull on the back of your neck.

The 'M' sound is caused by vibrating the roof of the mouth without the tongue near the base of the skull.  This sound vibration can be felt in the sinuses and chest cavity.  The level of vibration felt  is controlled by pitch or tone. You have an individual note that will maximize the vibration.  

Women and men experience a different optimum pitch or tone that sets off vibration in the chest and cortex because they are smaller. They have higher pitched vocal cords and smaller cranium and chest cavity. Their optimum pitch or tone is likely to be higher.