Introduction: Sennheiser HD201 + Cheap Earmuffs = Perfectly Noise Proof Flat Natural Headphones & CHEAP Too!

Well I had old sennheiser HD201 headphones, I started hating it soon after buying since its sound was flat, low on bass. I was searching for new headphones when I came across this idea of combining earmuffs and headphones. I just googled it out and found out that quite a few guys have already tried it, so I was sure it will work in my case too.
The result is too good, since sennheiser hd201 are decent enough on its own. Now I can hear the complete range of frequencies, bass is good enough since it's completely soundproof. In fact I am playing a loooooong playlist right now with these on!

Materials used:
Sennheiser HD201
3M earmuffs
Soldering iron
Solder wire & flux
Scissors, cutters etc

Step 1: Removing the Headphone Driver Unit From Sennheiser Housing

Removing the spongy pads (from sennheiser) is easy, just pull out abruptly from one side, as it is there is no use for it later.

Remove the four screws and open the headphone unit. Now you will find that the speaker driver is sealed inside a rectangular cover which is closed with screws and some adhesive. I used a lot of brute force to pry it open using a screwdriver.
The 2nd and 3rd pics show the speaker part after removing the rectangular cover.

Step 2: Pull, Break, Burn and Drill!

Pull off the sponge pads from earmuffs carefully and keep it aside with the glue part upside. Remove the foam from inside the earmuffs using your fingers.

Simply break-off the panel around the rectangular speaker plate using pliers, soldering gun or whatever tool you can find. I was impatient, so I put a few holes with soldering iron and broke it off with pliers. Look at the seam of the rectangular cover and where it goes around the speaker, don't break/burn the seam (those twin lines on the border of the white paper), You will need it to fix the cover properly later on.

Then use the soldering iron to make a hole at the base of the earmuffs unit. Don't make it too wide. I widened it gradually till I got its diameter exactly the size of rubber sleeve.

Step 3: Trial and Error

I tried to fit the cover through the earmuffs hole, and it passed through perfectly. If your earmuffs are different sized then you may need to cut/melt the earmuffs to widen the hole accordingly.

Pass the wire through the hole in the earmuffs, then put the rubber sleeve in place on top of the wire. Now pass the wire through that rectangular cover and solder it on the speaker driver.

Fix that cover back in place using as little superglue as possible. Plug in the headphone jack in your device for testing.

Step 4: Fitting the Entire Speaker Unit Inside the Earmuffs

First put the foam back inside the earmuffs. Then push the speaker unit through the hole, use force if needed.

It will be firmly in place for a long time because of the foam packing behind it. You can move it a little as per requirement.

Now tear up the black fabric from the sennheiser earpads and slip it inside the earmuffs on top of the speaker unit. I don't know its exact purpose, but this fabric feels better against ear lobes instead of the solid plastic. It also looks better.

Repeat the same steps for the other side and enjoy!