If we go by the ‘Meditation is a state of focused awareness’ approach, we can choose an object during our meditation.
For spiritual enlightenment purposes, I have focused on one of 3 objects at different times during my meditation practices. They are the breath, the feeling of Love, and the formless awareness itself. These two articles will explain this approach and give detailed info about the meditations focusing on these objects:
What we keep focusing on, we create more an experience of in our reality. So, whatever frequency you keep focusing on, you will have more an experience of.
What is a frequency? It is the number of vibrations of sound per second. So, basically, if you are focusing on a frequency of audible sound for your meditation, you will be able to focus on between roughly 20 Hz. and 20 KHz. This approach will keep your awareness between these frequencies. Any frequency will have different effects on the human system. For further information on this, research brain wave entrainment and brain wave frequencies. Notice that for meditations focusing on audible frequencies, these frequencies correspond to somewhere starting from Beta brain waves, to covering Gamma brain waves.
For spiritual enlightenment, our awareness must transcend all forms and become aware of itself as the formless Awareness. Also, awareness must become aware of Divine Love energy that is one with everything. With regards to the idea of the ‘best frequency’ of meditation, if we limit ourselves focusing to a certain sound frequency, logically it follows that our awareness will not expand to other frequencies. However, unconditional love energy is one with every form, not limited to a certain vibration of form. The point of meditation is to experience our oneness with life in every moment. So, whatever comes into our experience, we must be in complete acceptance, we must experience it as it is, we must stay as the formless awareness that we are. It is OK to explore frequencies to understand what they are, what focusing on them actually creates within us, but the idea of ‘best frequency’ is not inclusive, yet we must be totally inclusive for complete spiritual enlightenment. Ensure that this idea of ‘best’ does not keep you from becoming aware of the formless awareness that contains everything, or the divine love energy that is one with everything.
I feel, just like the idea behind using drugs to create our happiness, the idea of using frequencies to create our happiness can be harmful. This is using our mind and dependency to objects to create our happiness, but the source of happiness is not the mind, it is who we actually are, and it is not the mind. If you are exploring frequencies, I suggest doing it with awareness, seeing the experience as it is, and moving on when you feel you are done. Don’t buy in anybody’s idea of ‘best’, do you see the similarity between this and the approach of religious fundamentalists? They never experience truth themselves, they just get trapped in a story and it traps their life energy. Those who seek truth must go beyond ideas and experience truth for themselves. This is how spiritually enlightened beings are created.