Joseph Rael has written several very good books on sound and vibration for healing. He is a Native American also known as Beautiful Painted Arrow. In his latest book, Sound, Native Teachings and Visionary Art, he talks about healing and health using syllables, very similar to Bija Mantras but there is something different about how he sees the world and sound.
In one chapter, he talks about innoncence which he defines as:
"to seek awareness, to surrender completely to infinite vastness and to ask for the self-imposed limitations to be removed so that teachability can happen."
This struck me because when it comes to tools like the Solfeggio tuning forks which focus on the emotional health, people want to know if they will definitely work. The answer to that is really determined by how "innocent" you are willing to be.
Tuning forks or whatever you like to use will not change you. What they will do is create an environment where you can change something. For example, I have been with people who have realizations about who they are and the situation they are in. They cry, they laugh and react in all sorts of ways. But changing the situation, that is up to them and you. How innocent you are willing to be?
If you recognize something you do not like and immediately respond by feeling there is nothing you can do about it, then you have found that self-imposed limitation and that is the real barrier to happiness. That is the realization you are really after.
Once you are aware of that self-imposed limitation and choose to remove it, then healing and happiness take the place of that limitation you had put upon yourself.
Joseph Rael has two books I recommend, Of Being and Vibration and Sound, Native Teachings and Visionary Art. Go buy yourself a gift.