All,
 
Over the past 8 months, I've owned a pair of Sennheiser HD-428s, which I purchased off of Craigslist for $40.00.  It was a refurbished model that the seller was selling and was sealed in plastic bag, with a Sennheiser cardboard top which covered the opening of the bag and was marked "refurbished."  However, when I opened the headphones, they were just like brand new.  I've also witnessed many HD-428s headphones available as a refurbished model, which brings forth a suspicion of mine.  I wonder if Sennheiser is actually taking a new product, placing it into packaging marked "refurbished" so they can sell it for less than the somewhat-fixed "MAP" -- or Minimum Advertised Price that they've been enforcing upon their vendors.  I may be wrong with my suspicion, but I can't find really any faults with the headphone, other than the somewhat cheap and flimsy headband which can tend to be a bit too loose and not grip enough unless your head happens to be big enough.
 
The HD-428s which has the "S" in the model number refers to the headphone as having the short version of the cable.  It is a bit less than 4 feet long and the standard HD-428 has a cable that's quite a bit longer, which many have complained about at times.  However, it's quite common to find the HD-428s nowadays and I'm quite sure your chances of coming across the headphones without the shorter cable might be rare.  As to pricing, there is a deal posted in the thread for deals on headphones and associated gear where this headphone can be currently purchased though an Ebay vendor for approximately $30.00, shipped.  If you have the ability to tinker a bit with these, the deal is insanely good.
 
With this modding guide, I will focus on the following areas to greatly improve the sound, fit and comfort of the headphones.
 
1) To begin, one as to tug on the ear pads to get them off.  They are held in place by about 12 small tabs on the outer section of the ear cup.  Tugging on the pads will not damage the clips - or, at least that has been my experience.
 
When the ear pad is removed, you will see an oval section of grey foam around the driver.  I have marked the screw locations for the (4) screws with blue arrows in the picture provided below.  The screws are Phillips head screws, so you'll need a somewhat-small Philips head screwdriver to open up the cups.  Initially, the screws will be covered in the grey foam, so you have to carefully feel the surface of the foam for the screw locations and when located, notch the foam a bit to access the screws.  Remove all (4) screws and carefully set them aside.  You should then be able to gently tug on the driver housing to get the driver removed from the cup.  Please ensure you don't pull the driver assembly too far away from the cup itself, as Sennheiser used cable on the internals of these headphones that is literally the thickness of a piece of thread.
 
 

 
 
2) With the driver carefully removed, then flipped over so the ear side is facing down, you can now proceed with the modification steps.  In the area that I've marked with the red arrow, there is a rectangular piece of black "mesh" tape.  This tape is covering all (3) of the bass holes on the back of the driver assembly.  Using a small flat-head screwdriver, or a craft knife, you can easily get the mesh tape removed.  With the factory tape removed, you will clearly see the (3) bass holes in the back of the housing.  This is where you can "tune" the bass level that you'd like to achieve.  It is best not to leave all (3) of the bass holes open.  The sound will be like the Beats headphones on crack.  Yes, the bass will be that silly and thick.  I don't think anyone craves bass to the level that they could literally get a migraine from it, but I could be wrong there.
 
Using Micropore tape, which is a medical tape which you can purchase at a local pharmacy, using two small pieces, cover the two outer bass holes, each one with a single piece of tape.  The tape positions are marked with the two purple arrows in the picture.  Keep the middle bass hole open as this will provide you with a greatly improved bass response from these headphones.  The hole to keep open is marked with a red arrow in the picture. Then, using some plasticine (non-hardening clay), carefully apply a somewhat-thin layer of the compound around the outside of the driver housing as indicated by the blue arrows in the picture.  You will have to work a bit at getting the plasticine to stick to the surface, as it is a bit glossy.  However, work with it a bit, and the clay will then form into place.  If it gets a bit thick in areas, those areas will squeeze out a bit of the clay when you put the driver assemblies back into the cups and this is noticed in some of the areas where I have plasticine on my driver housings.  
 
The wires you see in the picture are 22 gauge wires that I ended up installing on my headphones to extend the space in which I can move the driver assembly away from the cup.  You don't have to do this.  This was just a personal preference of mine.
 
 
 

 
 
3) With the modifications completed on the back side of the driver housings, carefully flip the drivers over and set them back into the cups.  Carefully, take one screw at a time and using your small Phillips head screwdriver, secure them back into place.  Don't over-tighten the screws as you don't want to strip the threads.  This will prevent the speaker housing from adequately fitting securely into the ear cup on the headphones.
 
Continuation begins here ...
 
There is a weak spot with the HD-428s headphones.  The headband is made out of plastic and the plastic isn't the best at "gripping" when wearing these headphones.  The plastic has a lot of "give" in it, and for me, it was one of the weakest links for these headphones.  In order to get a great bass response, and minimize leaking by a significant amount, this next section is almost critical to ensure you have a solid, great-fitting pair of Sennheiser headphones.
 
4) I purchased a 3' section of solid steel rod from a local home improvement center.  The rod is slightly less than 1/4" in diameter.  However, getting material any smaller than this might mean a bit more flexibility in being able to bend the rod, or make adjustments to the width of the opening of the headphones every now and then.  For myself, I opted for the slightly larger diameter of rod as I figured once I had mine adjusted properly and set into place, I didn't expect to make any size changes other than possibly a few slight adjustments to fine-tune the fit.
 
Using a cloth tape measure, I measured the distance of of the inside of the headband.  I then cut the rod so that it was about 1/2" shorter on each end, so it would not protrude too far down on the insides of the headband towards the cup area.  I had a somewhat large block of wood, with a 5/8" diameter hole in the block.  I used the hole in the block to slowly make adjustments to the rod so that it was the perfect arc for fitting within the inside of the plastic headband.  Holding the rod against the inside of the plastic headband, I then tried on the headphones, so I could get an idea of the type of grip that I'd be experiencing.  I performed a few slight movements to the rod to allow the head-band to fit my head properly.  I then removed the somewhat small foam and pleather head pad from the inside of the headband as that was where the rod was going to be mounted and that pad happened to be in the way.  It is just held in place with some adhesive and if you start at one of the corners, you can get it to lift up a bit an then you can remove the whole pad.
 
 

 
 
 
5) Here is a picture of the plastic headband with the head cushion removed.  Also in the picture is the metal rod, so you can see how the arc on the rod appears before mounting it.
 
 
 

 
 
 
 
6)  To secure the rod into place, I used black electrical tape.  I positioned it in several areas along the headband and with each application, I wrapped the area with three to four thicknesses of tape.  Also, smaller pieces of duct / duck tape would work for this process, too.
 
 
 

 
 
 
7) With the metal rod secured into place, I was able to then cut some 1/2" thick high density foam.  The foam was cut to size to cover the rod and the headband of the Sennheiser HD-428s headphones.   To secure the foam into place, I used more black electrical tape, but did not pull down hard on the tape, as I didn't want to compress the foam.  Keeping the whole foam area at 1/2" thickness was key as the outer pleather covering that I was in the process of sewing would not appear as good when the product was finished and the thickness of the foam under the covering wasn't consistent.
 
 

 
 
8) With my modification, I've had plenty of recent experience sewing leather and pleather.  I ended up using a nice piece of pleather, which I purchased from a fabric shop.  The pleather has a nice grain to it - which is close to the grain of real leather.  Plus, the finish on it was basically satin, so it didn't shine in a way to make it appear too fake.  The backing of the pleather was flannel material and this flannel worked towards getting the pleather to lay down correctly as I hand sewn the pleather cover into place.   Plus, the flannel backing provides for some additional cushion, too.
 
This is the final picture of the completed product with the pleather cover on the headband fully sewn and in place.
 
 

 
 
Granted, not everyone will be able to pick up some needles and pleather and go to town on sewing a good cover.  However, I do feel that it's worth a shot.  If you mess up, you can always cut off what you've sewn, and star over with a new piece.  If sewing the pleather isn't your thing, you could use black electrical tape and wrap the foam covering of the headband.  If doing this, don't over-tighten the black electrical tape, as you'd want to have a slight bit of flexibility when done so the headband will provide you with some cushion for a more comfortable fit.
 
That's it!!  This is all that's required to take a $30.00 pair of headphones and make them have a superior level of comfort with a sound that is upgraded several notches which will allow the HD-428s to compete with headphones that are in a much higher price league.  Plus, you can give yourself a pat on the back for the great accomplishment that you've finished on your own.
 
Finally, I can't take the credit for process of re-working the bass vends on the backs of the driver cups.  I learned of the process after reading more than a few threads on the process that were scattered hear and there within the forum here.  However, it was my desire to try and create a "soup to nuts"  documented process, with pictures, to make the modification process easier for others to follow.
 
Enjoy !!

* Reserved *

Interesting,
I have a couple of questions,

1. Instead of removing the mesh tape on all three and applying back micropore tape on two, why not just remove the tape on the center hole to begin with, I'm guessing micropore has a purpose here ?
2. what is the purpose of applying plasticine in this process ?

 
step one you elaborated above covers bass, is it ?
 
thanks
 
p.s. Never tinkered with headphones for that matter never seen whats inside a headphone, so pardon me if my doubts seem rudimentary..

Quote:

bob439 said:

Interesting,
I have a couple of questions,

1. Instead of removing the mesh tape on all three and applying back micropore tape on two, why not just remove the tape on the center hole to begin with, I'm guessing micropore has a purpose here ?
2. what is the purpose of applying plasticine in this process ?

 
step one you elaborated above covers bass, is it ?
 
thanks
 
p.s. Never tinkered with headphones for that matter never seen whats inside a headphone, so pardon me if my doubts seem rudimentary..

Click to expand...

 
The process of removing the original black felt / tape is because it can be quite restrictive.  I never tried just removing the center section because when I worked at removing the tape, the whole section came off.   However, I do believe one could try just opening up the middle section through the factory tape removal.  Or, you could take a ball-point pend and poke a hole in the middle hole.  The driver is pretty far away from the driver housing, so taking a ball-point pen and only allowing it to enter into the driver shell for approximately 1/4" should be OK.  That's a great idea that you've suggested.  I only used the micropore tape as I've used it quite a bit with various mods, here and there and I happened to have it with my modding supplies.
 
The use of the plasticine to coat the backs and sides if the driver housing works to dampen any vibrations that could result from the solid plastic driver protectors.  It's a small modification, but one can buy the plasticince for about $4.00 at a hobby or craft store.  I never tried some pieces of Dynamat, but think it would probably serve a similar function by providing a dampening factor on the plastic cups.  Plus, it is thin enough that it might be able to adhere to the plastic surface, and leave room to get the drivers back into the cups.  But, if this method is used, try to test fit a few pieces before going crazy with the Dynamat, then realizing you have to remove a large portion of your handi-work.
 
As to your last question on "covers bass?" - I didn't understand the question.

I mean mod done so far improves the bass alone or over all sound quality ?

Quote:

bob439 said:

I mean mod done so far improves the bass alone or over all sound quality ?

Click to expand...

 
The tweaking of the three ports on the back of the driver enclosure is a bass mod.  However, using the plasticine around the rear driver casing, works to absorb excessive vibrations and reflections that could occur as a result of the bass mods.  One would think that the use of the plasticine would kill off the bass, but it doesn't.  With the bass modification, there is an abundance of bass which is why two of the ports remain covered with the micropore tape and the middle one is open.  But, this still doesn't mean that some "tuning" can still occur with the bass itself.  One could even cover 1/2 of the middle bass port with micropore tape and potentially still have great bass, but just a slight bit less of it.
 
With the HD-428s, the mid frequencies and upper frequencies are actually pretty good as-is.  This mod really doesn't affect those in any way, with the exception being the mids.  Opening the bass port, could have a small benefit with the mids, by making them have a bit more presence.
 
I do have a microphone measuring kit, but could not get it working to use the REW software to capture a frequency response reading before and after the modifications.  Then again, we're talking about a $30.00 pair of headphones and creating a sound signature that has an improvement to make listening to these fun, which is what it's all about.
 
On Innerfidelity.com there should be some measurement graphs for the stock HD-428s headphones.  I believe I've seen such a graph before.  Looking at the stock frequency response, I believe one can see where the bass mod would make the bass bloom and make the headphone a great performer.

Quote:

wje said:

 
The tweaking of the three ports on the back of the driver enclosure is a bass mod.  However, using the plasticine around the rear driver casing, works to absorb excessive vibrations and reflections that could occur as a result of the bass mods.  One would think that the use of the plasticine would kill off the bass, but it doesn't.  With the bass modification, there is an abundance of bass which is why two of the ports remain covered with the micropore tape and the middle one is open.  But, this still doesn't mean that some "tuning" can still occur with the bass itself.  One could even cover 1/2 of the middle bass port with micropore tape and potentially still have great bass, but just a slight bit less of it.
 
With the HD-428s, the mid frequencies and upper frequencies are actually pretty good as-is.  This mod really doesn't affect those in any way, with the exception being the mids.  Opening the bass port, could have a small benefit with the mids, by making them have a bit more presence.
 
I do have a microphone measuring kit, but could not get it working to use the REW software to capture a frequency response reading before and after the modifications.  Then again, we're talking about a $30.00 pair of headphones and creating a sound signature that has an improvement to make listening to these fun, which is what it's all about.
 
On Innerfidelity.com there should be some measurement graphs for the stock HD-428s headphones.  I believe I've seen such a graph before.  Looking at the stock frequency response, I believe one can see where the bass mod would make the bass bloom and make the headphone a great performer.

Click to expand...

 
Thanks wje for the writeup!  I will be performing these mods and let you know how it turns out.  Can't wait for the phones to get here.  

Nice write up and thanks for taking time to do it. It definitely saves lot of time and effort for many of us.
Will try to mod my pair soon.
Instructions with pictures are easy to understand just like building IKEA furniture

I hate to do a bit of self-promotion, but I've been using my modified HD-428s being pushed by my Magni and Modi off of my computer with FooBar.  I'm not applying any EQ at the moment in any way.  I pushed through a variety of music as I listened on.  However, I'm wrapping up the evening listening to Gov't Mule - The Presence of the Lord, which was originally a song from the group Blind Faith with Eric Clapton.  However, their cover of it is pretty good - some good kick drum beats which makes the modified HD-428s really come alive.  It's all about quality of the bass, and not just quantity - or, muddy bass.  This song really shows off the capabilities of a modified pair of HD-428s.  The version I listened to was also a recording and I'm not sure if the YouTube version linked below will be able to demonstrate quite the full bass capabilities, but we'll see.
 
Also, I've had so many pair of modified Fostex T50RPs and modded them night and day to perfect the sound to a high degree.  I will state without a doubt that the bass on the modified HD-428s can really pound hard well above and beyond what the Fostex is capable of.  Also, I'm the owner of a pair of HifiMAN HE-400s, which are known for excellent bass performers.  The bass from these Sennheisers is creeping within the shadows of the lower end of the HE-400s, and the HD-428s are a closed can, so one can have plenty of privacy when listening to their jams with these on.
 
Enjoy!
 

Wje,
I must say....your mods make these phones sounds amazing!!!  I am very surprised there are not more people out there that have not found these gems.
 
It took about 15 minutes of time, and it was well worth it!  I did not do the headband metal rod mod yet.  They squeeze fairly tight for me right now (they are still new).
 
Bass is tight and crisp, mids and highs are clear and defined.  I am also running the Schiit Modi/Magni stack.
 
Some quick photos of what you already posted.
 
 

 

 
Thanks again!
 
Dustin

This is good, I did the driver cover up but it was too forward for my likings.  I also recommend opening the 2 Outer Holes if you are going to use Velours. 

Quote:

dustinsterk said:

I must say....your mods make these phones sounds amazing!!!  I am very surprised there are not more people out there that have not found these gems.
 

Click to expand...

 
Thanks.  Keep in mind, I just created a post based upon information that I've read in the forum here, and took it a few steps further.  As to why others are not doing the mod, that's a good question.  I see that eBay has a vendor selling refurbished HD-428 headphones for $27.00 and the shipping is free.   It looks like nearly 2,000 have sold already.  Then again, if we let too many people know, Sennheiser might jack up the price of their headphones, or cease to make the model so easy to modify into such a dream.
 
I like your putty work.  Much neater than my work.  I have some other clay that arrived a few weeks back and I need to probably remove the plasticine, and reapply some new material.  
 
Anywho ... enjoy the music and have fun.  That's what it's all about.

This mod has drastically made my already nice sounding Sennheiser HD 439 head phones into something a lot more fun and well-rounded. I have a few notes I would like to add to anyone with a Sennheiser HD 4XX set that wants to do the mods from this guide (started by and credits to WJE but really has been around for a while now--I did a search):
 
-- do not open up the two front holes and tape the third one as suggested by an old old post that I read. I tried this and while I got a lot more bass, the highs were so colorful and forward that it was quite painful to listen to cymbals in music. 
-- for my second attempt, I only opened up the middle hole as how WJE suggested and left the two outer holes covered by the original mesh tape. This provided slightly less bass from my first bass mod attempt but the bass will still rock your pants. Seriously, I've never appreciated Far East Movement's "Like A G6" track before. If you want a percentage of how much bass you'll get, I'd say this mod gives about 40-50% more bass and that's not saying much. It improves the boom and does so to a good portion of the lower spectrum.
-- you must do the putty mod if you plan on opening the bass hole(s). As already stated by those who have done it, I will repeat them by saying that doing the putty mod really does tighten up the bass gained. Without this putty mod, the bass becomes really fuzzy and will leak into your mids. Your bassy music will sound really bad. I went to Walmart and picked up a pack of Loctite Adhesive tack in the office supplies section. It comes in a thin, palm-size pack that has 5 strips of the blue stuff. It sticks pretty well but only time will tell how long it will remain clinged to the surface of the driver. I used about 40% of one strip for each side as there's not enough room to apply a thick layer and I only applied as much as I felt was necessary. You probably won't want it thick anyways as it will make it very difficult to open it back up to make adjustments to your mod. The adhesive strength will hurt your fingernails. It did mine.  Still, I find it unbelievable how well this mod does to tighten up the bass from the bass mod.
 
I'm listening to music almost every where I go now where as before my purchase of these Sennheisers, I only listed to tunes once in a while and only with cheap $5 IEMs. So I suppose I'm a noob to the art of "listening to music". So far the experience has been very rewarding. I hope to stick around head fi as there are a lot of helpful members with mountains of information.
 
Edit: here's a picture of the Loctite putty.
http://www.loctiteproducts.com/img/products/big/cntct_putty.png

I was totally on the fence about the HD428/HD439/SR80i/AKG240.. Demo'd the 428s at BB and was horribly turned away by the lack of punch.. came close to purchasing the AKG 240s.. but something kept holding me back from pulling that trigger.

Figure I would try the HD428s after reading so many threads about how the mod really rejuvenates this set (I just bought the refurbs $27 on eBay from VM like 3 seconds ago)

Estimated date to receive is this upcoming Monday the 28th... spending $27 and expecting some good things after mods (based on reviews) is way better than throwin out $100-200 dollars while failing expectations.
 
*fingers crossed with excitement* .. I don't even have a decent pair of cans.. so this will be my first entry level attempt as a newborn Audiophile and modder.

@ RochRx7
 
I'm sure youd be pleasantly surprised, I was in your shoes couple of months back, My first decent cans were HD 428 and I really liked them out of the box.
But the mods done as instructed in this thread just blew my mind off.
 
have fun and i know the wait sucks.
 
cheers