Replying to myself here ...It's been a long time since I've even touched a Fostex headphone or seen this thread.
Here is my T40RP mkII mod.
My goal was to make a fun, yet tasteful 'bass monster' headphone. I've got enough reference headphones already.
The biggest obstacle with modding these headphones is the crazy bass around 100hz that SO many mods have.
Also, very often when going for a 'bass mod' the bass rolls off below 100hz.
I feel like I achieved what I set out to accomplish.
• Open the rear ports (remove plastic covering the vents)
• Inside of cups covered with adhesive felt - left just the bottom vent open.
• Aftermarket Ori pads
• Paxmate around driver front (make sure to leave the side vent open)
• All stock driver damping removed (this was causing HUGE bass energy around 100-200hz)
• Replaced stock damping with micropore tape, leaving middle and top vents open
• 'Mad dog'esque adhesive felt on back of driver
• Smaller adhesive felt rectangle on front of driver
• 0.30g of Twaron Angel Hair acoustic filler
• One circle of acoustic filler (arctic cotton/thermolam/whatever you have) inside the ear pad - this does 2 things - treble attenuation and 'spacer' that drastically improves sub-bass response.
• DIY suspension headband - makes the biggest improvement, obviously.
(Dip at 4kHz is a well known artefact when measuring closed-backs with miniDSP EARS.)
I updated the mod to bring down the mid-bass.
Increased quantity of Twaron Angel Hair from 0.30g to 1g
New mod with 1g of angel hair -
Old (white) vs New (purple)
Finally got rid of that last final 'bloat' that plagues SO many of these Fostex mods.