This is a meditation focused on listening to the om noise. The om noise is sometimes called the soundless sound, so-called as this noise is seen more as a vibration. This om noise is always there- you can listen to it at any time, although when loud noises are also present (washing machine, airplane flying overhead, blender whirling, etc.) their noise is the sound your ears detect. A quiet environment is best for this sound meditation.
This type of meditation is considered a focus meditation, where sound/vibration is the subject of meditation. It is also a meditation that can be used to work on the void/throat chakra or open the third eye.
Sit with your eyes closed in a quiet environment. Sit there silently for a few moments, then bring your attention to the om noise around you.
It is there, this sound of om.
Do you hear it?
It is similar to the sound of a lamp post or an electrical box on a hot summer's day.
You can focus your attention on your ears, the physical apparatus which hears the sound, or on your throat or third eye chakra. Noise is attributed to the throat chakra, which represents the void, while om done as a mantra has been used to open the third eye. See which one seems to work better right now. It may be different or change if you do this meditation on another day.
Focus on the om sound- is it close to you? Is it close to your ears or close to your head? Does the sound seem right next to your body or farther away? Is the sound closer to one ear yet farther away from the other ear? Does the distance between you and the sound change as you focus on it (it gets closer or farther away)?
Do you feel the sound as a vibration? Is there a soothingness or lulling feeling that comes when you really let go and merge with the sound, like being rocked in the cradle of the universe? Does the sound seem to disappear and be like a vibration felt in everything? Can you hear the vibration in other sentient beings (like your pet, friend, family member), in nature, and in inanimate objects? Is the vibration found inside of your body?
You can listen to the sound for as long as you like i.e., make this your meditation for the day and go for a set amount of time such as 30 or 60 minutes. Do this meditation for a few days or weeks in a row and notice any changes that come.
Do note that if you have thoughts, simply return your focus back to the om noise. If your mind is particularly chatty, use another meditation to evacuate the excess energy, as you will need to have some degree of silence/stillness to do this meditation.
I have done this meditation many times and find it best to do at bedtime, when it is quiet. If my mind is very chatty, I assess the strength by its noise and try another meditation that will help to rid the excess energy first. There are many meditations that can help you to do this, such as some of Osho's meditations like gibberish, doing a mantra (it could be any word, even just repeating a nonsense word like mi mi, la la, na na, etc.), doing deep breathing, focusing your attention on the tongue, and many others. Do some exploring (trial-and-error) and see what works best for your particular mind :)
After 10-15 minutes, if the mind is still noisy, then try this om meditation on another day, as you will not be able to hear the om noise when mind is in the way! If the mind has gotten "bored" and is now quieter, give the om meditation a try and see how it goes. You can always go back to the first meditation of evacuating energy and leave the om meditation for another day.
Indeed, one of the things that comes with meditation is to customize your practice according to your unique mind, and that incudes taking into account what is happening in the present moment. One meditation may work on one day, but not so much on another.
You will see that in some of the Osho meditations, a one hour time period is broken down into different types of meditations. Using this principle, you can therefore tailor your meditation to what works for you--- and avoid the "trap" of the mind feeling "guilty" because you "failed" at your meditation! This comes with time, but this openness also allows you to use any meditation technique (or a number of them) according to what is needed in that moment. From experience, any time I tell myself that I cannot quiet my mind, and frustration is now there, what is really happening is that my mind is fighting with itself, and has a desire to "be quiet." I let go of the desire and accept what is--- chatty or not, "i" am not mind.
Speaking of which, while this is a focus meditation (object: om sound and subject: you), the om is a vibration that permeates all things. Indeed, you may find this "you" dissolving with this meditation, which is really the point of all meditations; that you are the witnessing self.