[Politburo]

Hi all, i'm new to headphones, having used cheap earpods all my life.
I've recently purchased a sennheiser hd 518 and found out they can be modded to have a more open-back sound.
I have searched endlessly for guides but the few which exists aren't very beginner friendly.
I have managed to take apart the headphones to expose the driver and its connections. Supposedly I have to remove the hot glue around all 11 tabs of the headphone and push it out. I have removed some bits of hot glue but have no idea as to how to push it out or even proceed from here on out.
Any input to help out a newbie would be greatly appreciated
Also do the scratches around those tabs affect sound quality?

 

[Mad Max]

I recommend removing excess flux residues from the little green circuit board.  A good precaution in the long run for the functionality of the headphone.
 
Instead of messing with the grill, stick some polyester fiberfill in the cups like so:
 

 
It will be a process of trial and error to get the right amount.  It is not a lot.  If you  get a muffled sound to an extent, you put in too much.  Eliminating cup reverb in this manner will leave the headphone sounding more open, more detailed, less colored/opaque, and with better separation.  Tweak one cup at a time so you can compare to the unmodified sound.
I also added Dynamat Xtreme to tighten up the sound a bit, but the improvement isn't that much anyway compared to what the fiberfill does.
Studio speakers use fiberfill inside of their cabinets; makes sense that it helps headphones as well since headphones are mini-speakers, basically.

 

[Politburo]

Hi, many thanks for your input.
I know it's a dumb question but how do i place it into my cans the way you did? Im also worried that I may spoil my headphones in the process.
Any links I could use 

 

[Mad Max]

You simply open up the headphone as usual like in your photo.  You just place it there, no glue or anything.
You can't hurt your headphone that way unless you are careless and break the internal wiring or damage the drivers themselves, which you don't need to touch anyway.
If you add dynamat as shown, don't let it face the white screen on the back of each driver.  Don't let it go into the hole in the center either.

 

[Politburo]

Ok, thanks.
So just to clarify i simply press it down on the sides of the cans and just ensure it doesnt touch the white screen or the whole? May I ask why? 
Also how do I gauge the sound, sorry these are my very first actual headphones haha

 

[Mad Max]

Touch or face the white screen or hole; it will affect the sound negatively if it does.
 
Trial and error.  Since you're inexperienced, it will take a while.  You'll know when you put in too much fiberfill.