Diffusion tweak

Is there such a thing as speaker grills designed specifically to diffuse higher frequencies at the source? I think that's what happened anyway. My Zu Omen Defs needed some sort of cover to keep the dust and dander off (3 large dogs and gravel road out front!). So I cover them with  fluffy blankets made of several layers of cotton muslin to capture the aforementioned figuring they were thick enough and anti static.The fabric is thin and light but very fluffy.

Last night I left them on after firing up the system instead of removing them first and damn! The bass and lower mids were richer but there were no details lost.Totally not expected. I'm in the process of breaking in a new Linlia tube which is incredibly detailed and quiet but also emphasizes the leading edges of notes rather than tone as it runs in.Other members say it gets better in time so I wait impatiently:-) So right now the music is warm and beautiful again,but retains the refinement of the new tube and nothing sounds muffled.