[leeperry]

adding foam in the cd1k was spot-on! 5mm gave muddy bass and wonky mids...6.5 is spot-on, everything's perfect so far

and I haven't covered the whole cups inner surface, to still keep some resonances

so dampening = yes! but not entirely!

 

[Logistics]

I would imagine that tricks they use on full-size drivers may be applicable. For instance, some pro's use felt over the pole-piece to keep harshness out of the high-frequencies, and apply things like 3M SJ2040X to speaker baskets to keep them from resonating so I imagine applying it to the inside of headphone cups could be good to avoid the cups' resonant frequencies. I haven't seen any articles about perhaps, changing the cups or at least modifying them to be more ideal chambers. For example: a spherical speaker chamber is considered ideal by some due to the lack of standing waves and reflections back at the driver. It should be MUCH easier to apply in this situation. Plus, it may give you an opportunity to add custom termination/cabling.

 

[bigshot]

Wouldn't a headphone cup's resonant frequency be so high, it wouldn't matter?