DYNAMICS THROUGH TEXTURE
Music is all about managing moments of unity and contrast, harmony and dissonance. But an often overlooked tool is texture.
Texture in this case refers to how you realize a melodic, rhythmic or harmonic element in your arrangement. For instance, you have written a haunting melody for an art film you are scoring. Now you have to figure out what instruments you will use, what doubling, and what counter melody or harmony you will use, if any.
Let's say you start with an orchestra-wide unison. Then, at a key moment, a single English Horn carries the melody. This will have impact. Even if the unison and solo play at the same volume, the contrast in texture has added a dynamic of sorts. The reverse is also true. Let's say the solo was first and then at a dramatic moment it became a huge unison.
The key is contrast. We are not wired to detect absolutes, we are wired to detect changes from the norm. If it's been 110 degrees then drops to 80 it feels cool. But if it's been 50 degrees then jumps to 80 the same same temperature feels hot.
Set up an expectation and then deviate from it when the time is right. Changing from high pitched instruments to low, from thin orchestrations to thick ones, or from harmonic sections to unisons are just some of the ways you can add dynamics to your piece.