Disclosure: The practice described below is NOT an authentic method taken from any ancient teachings. This exercise came to me intuitively and after extensive period of practice I noticed the effective results.
For this exercise you will need a singing bowl that has at least two noticeable overtones (in addition to the fundamental tone) and a mallet with medium firmness to strike the bowl (choose the mallet that will bring the lowest tone of the bowl along with at least two higher pitched tones).
Bring the rim of the instrument to the level of your forehead (the area of third eye) approximately three to four inches away from your forehead. You can hold the bowl on your fingertips or on an open palm. Also you could sit in front of the bowl that is rested on a surface aligned with your forehead.
Strike the bowl and listen to the polyphonic accord of all sounding tones simultaneously.
Highlight one tone. It could be any tone you want. Now become fully aware of this tone, insulate it from other sounds. Focus on the tone you choose until it dissipates.
Repeat the exercise 10 - 15 times. After practicing this routine, choose another tone from the same bowl. Repeat the second routine also 10 - 15 times. Finally, practice the same exercise 10 - 15 times with the third tone. Please note: the more sustained is the sound, the better chance you will have to concentrate without redirecting your focus on striking the bowl. The bowl could have more than two overtones. After you get familiar with this exercise, you may want to expand your practice by choosing additional tones of your instrument.
After practicing this technique for 12 -14 days, expand your focus by holding in your attention all sounding tones simultaneously. Do this for another 12 - 14 days.
This exercise helped me to enhance attention, and also to separate the energies within myself and to be able to choose which are suiting me the best. This exercise helped me to understand the meaning of the words "Happiness is a choice".We are the vessels that transfer all kinds of energies through ourselves every day. If you make an analogy between these energies and a singing bowl's tones, you'll see that with your focus, you can choose which tone to follow within yourself in order to be well. You also have the fundamental and many overtones. Which tone will be the one you focus on?