In case you are not aware, each bowl has a specific frequency that corresponds to a musical note A-G. My understanding is that the bowl's "note" is unknown when the bowl is made and is only revealed at completion. I am not a musician or very musical but it doesn't surprise me that music is in sync with our energy system. The point that I'm getting to is that using a bowl of note A (third-eye chakra) won't necessarily be effective at clearing a blocked heart chakra (note F). Here is a link listing the pairs:
http://www.omcrystalsingingbowls.com/notes-and-colors-of-chakras/

Now, with that said, these bowls are just a tool. Our thought/will is the force that really causes and solidifies change within our energy system, and therefore within us.

Peace and Love to you my friend.