The difference might be marginal. But in theory, loose fiber would absorb sound better. This is because in loose fiber each of the filaments have to be agitated individually, therefore more sound energy being spent on “shaking ” each individual fiber. In tightly pressed filler the fibers that are “stuck together” being agitated together as one — so less sound energy being spent and absorption would be less. At the same time it is more difficult to vibrate heavier, larger fibers, than it is the lighter and shorter fibers. This is why the longer and denser fibers would absorb more of the lower frequency sound waves.