Fostex T50RP Incremental Mods and Measurements
May 26, 2021 at 8:26 AM Post #2,761 of 2,762


Headphoneus Supremus
Oct 11, 2009
Frankfurt am Main
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.

1621158413960.png 1621158426930.png 1621158452040.png 1621158399463.png
1621159684334.png 1621159709522.png

(Dip at 4kHz is a well known artefact when measuring closed-backs with miniDSP EARS.)

Fostex T40RP mkII mod.jpg
Replying to myself here ...

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 -
Fostex T40RP mkII mod 1g Angel Hair.jpg

Old (white) vs New (purple)
Angel Hair mods compared.jpg

Finally got rid of that last final 'bloat' that plagues SO many of these Fostex mods.
Jun 11, 2021 at 7:56 AM Post #2,762 of 2,762


Jan 21, 2009
Just bought another T50RPMK3. I used to own one early produced and then sold them. The 1st difference is gold-plated connectors on the new cable, old were white-plated. The 2nd possible one is soft cushions like MK2 leather, I guess previous were significantly harder. 2015 vs 2020. Am I right?

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