You've managed to create a method of deflecting damage by sound alone.
While you are playing your instrument you may use these effects.

Hard Rock
Non-physical damage is reduced by half your proficiency bonus.

AC / DC
Your base Armor Class equals 10 plus your Dexterity and Charisma modifiers.  Does not stack with armor.

Evasive Echoes.
If you're subjected to an effect that allows you to make a Dexterity saving throw to take only half damage, you can take a Reaction to take no damage if you succeed on the saving throw.

Reflective Resonance.
As a reaction you can roll your instrument's attack against Thunder based damage and effects directed at you and allies within 5ft of you. 
A number higher than the attack roll or effect DC disrupts it, reducing the damage it would have done by your rolled damage. 
A critical hit redirects the effect toward it's caster.
The range of this effect increases to 10ft at lv9, 20ft at lv13 and 30ft at lv17.