I got myself a pair of Superlux HD668Bs based on a recommendation as a good value hi-fi headphones. I like them, but they sound a bit too harsh to me, so I decided to make their high-end a bit softer. Quick search showed me that doing so is a relatively common procedure, so I went for it.
This is what I did:
1) I took the cushions off (look how thin the original foam is)
2) I cut four circles from a fleece kitchen towel, I used the yellow kind from Lidl
3) … and inserted them between the original foam and the speaker. I used two layers as they are very light and thin
That’s it, it’s really simple and the results are quite impressive, I did not notice any loss of clarity or quality, but headphones are much more pleasant now and I can use them for much longer periods of time, especially at higher volume levels.
With the high-end a bit less prominent, mids and lows shine a bit more now, making the headphones more balanced, so they can be used both for listening music and some home studio mixing, which is what I use them for.
I am pretty sure this can be experimented with - different materials, thicknesses and layers can be used to achieve different results, so happy hacking!