A990Z has some flubby bass because of the Double Air Dampening System. What is Double Air Dampening System? Audio Technica surround the driver with a plastic cage. There is a doughnut shaped large piece of foam inside the cup. The cage then rests on top of the doughnut shaped foam, which creates a second chamber. Hence the Double, and the air dampening being made from foam my guess. How does a boutique headphone designer dampen his headphones? I looked up how ZMF dampens his headphones. He uses antislip foam against the cup. And then outside rim of he uses some sort of dampening foam, it's not dynamat. And he uses some sort of fiber filling that I see used in vintage speakers. My plan, will order ballistic acoustic dampener. See pics below to see what I did to just experiment with this idea: My findings: It's a start. I already prefer the sound of this over the DADS bass system. I think will be improved once I get acoustic dampening material for the outer housing rather than foam and some poly fiber filler.