HOW TO? Feathered blur using Compound blur effect

I’m trying to make an effect of a sound wave. There’s a guy in the center of the screen and when he yells, there are air-distorting waves coming out of his mouth at a high frequency. 

Something like this:

To create this effect I’m using a combination of animated stroked circles (graphics layer) of a black color and a compound blur targeted on this graphics layer. The problem I need to fix is make the strokes feathered. I tried the compound blur settings (there’s a feather), 2 rounded crops on a black solid (one - inverted, both feathered, blur to blur the stroke. Nothing makes the circles have soft edges. Any ideas? Maybe a different technique?

No AE. NO AE.