In order to get ride of sound nodes, which are basically sound frequencies that are louder than all the rest. You need to build sound traps to reduce the amount of effect that frequency is having in your room.
The lower the frequency the larger and denser the sound trap will be to have an effect. The higher the frequency the smaller and less dense the sound trap will be.
This is why it is always good to build a larger studio as the lower frequency sound nodes are less common and the high frequency sound nodes can be easily managers and the sound traps can be hidden.