The comparisons made are subjective to myself and my ears and may not be the same for you.
You have been warned
A couple of years or so back i was on the hunt for some can's and ended up buying a pair of Doc's (Goldring DR150), when i got them i was really happy with them, I however enevitably came across the mod threads on Head-Fi and immediately decided on a recable with good results tighter bass and slightly more forward mids. This sucess caused me to carry on modding (Holes in the back of the driver, deadining the cups, blue tak, etc...), however on the Doc's there is a sort black paper covering most of the driver so i decided to rip it out and the foam infront of it with it, after all of this came out i plugged them in and shock horror they were terrible reduced bass, the mids had done a runner and the treble was ear splitting.
For a couple of months i EQ'd the sound to a listenable level i however was still kicking myself for ruining my can's.
Yesterday however one of the cables split causing intermittent sound, so out came the soldering iron and as i soldered away i noticed that the material that covers the holes at the back of the driver was the same material that i ripped out the front ruining my headphones.
I then had an epiphany the material had a remarkable resemblence to coffee filters so off to the shop i went and bought a pack of 40.
I got home and remade the filter that i had ripped out prior stuck them infront of the driver.
Close but no cigar
Bass- is back but boomy
Mids- are back
So i started pondering and i remembered reading a post (cant remember the thread) where someone wrote that on a dynamic driver the treble originates from the edges, mids further in and bass from the center so i made a new set of filters with holes in the center around 50% bigger than before, reglued them then plugged them in.
Bass Tighter and slightly less pronounced
Mids More pronounced and detailed
Treble is back and now had a great sparkle to it
It seems the fellow headfier was right the larger the hole in the center of the filter (further out on the driver) the more treble there is and going smaller results more bass.
Theoretically then this mod could be used to tune your drivers to produce the sound you desire. also its cheap and easy to remove if you want, and different shapes and sizes can be used if your feeling curious
I would be very interested if this has been done before and other peoples thoughts on this mod.
Any additional info or pictures can be added upon request