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.
Edited by wje - 1/14/13 at 8:53pm