I've noticed a couple of people wanting to buy the HD418/428/438/448 these past few weeks, and after digging through several threads I've come to the conclusion that a lot of HD448 buyers were disappointed with the depressing (lol) amount of bass in their headphones.
So why did I create this thread? I recently mustered the guts to open up my HD438s to do some modifying, so yes I'm fairly new to modifying. I suppose this guide could help other newbies too. The methods in this thread have been covered in several other threads, but there was no thread dedicated to the modding of Sennheiser HD4*8 models so I thought I'd share.
The internals of the HD418, HD428, HD438 and HD448 are very similar, so I believe these mods will apply to all four headphones. Be extra careful with the wires and the drivers. You do not want to damage anything since opening your headphones up will void the warranty.
First off we have the,
Tape Mod ♞
This is what it looks like. [Disregard the 4 holes, that's for later]
Step 1: Detach the ear pads from your headphones. This requires quite a bit of force.
Step 2: Get some double-sided tape and tape the sides of the circle ring as shown in the picture.
Step 3: Attach the ear pads back on, all you have to do is clip them to the tiny hooks on the edge of the oval.
Step 4: Press the gauze of the ear pads inwards towards the drivers to ensure the gauze sticks on to the tape.
What this modification does is it reduces the vibrations caused by the gauze of your ear pads when playing music at a high volume. Personally I don't think this mod is that important (I did it anyway) but if the gauze vibrations bother you, try it.
♞ There should be no noticeable differences in sound quality.
The next modification requires you to open up your headphones even further. What it does is increase/decrease/tighten the bass on your headphones, depending on your preference. By default, there is a black mesh that covers three holes (iirc). This image below shows the backside of your HD4x8 headphones' driver enclosure.
Bass Mod ♞
Step 1: Use your fingers to locate the 4 screws hidden under the grey foam.
Step 2: Get a Phillips screw driver and twist the screw out from above the foam.
Step 3: Once all the 4 screws are out, pull the driver enclosure out by pivoting from one end of the ear pad hooks.
Step 4: Remove the black mesh.
There are a couple of configurations.
Leaving all the holes (which were initially covered by the black mesh) uncovered will give you a full-blown bass. There will be lots of bass but the quality of the bass will not be as refined as it was. I suggest you experiment with the covering the holes with tape (this involves repeating steps 2-4 a couple of times) to get the best results.
Edit 1: I covered one of the holes and the bass sounds a little tighter.
You can also try adding some deadening material in the chamber that surrounds the driver enclosure to tighten the bass, dynamat would be good for this.
Edit 2: Apparently the space in the chamber behind the driver enclosure is too small to attach dynamat or any other sound deadening material, or am I not doing it right?
♞ There is a huge difference in sound before and after this mod.
♞ Left and right cups have different internal wirings.
☛ Place all the screws in a cup.
☛ Preferably do it on a table with a large surface area with ample lighting.
☛ Careful with wires, you might accidentally rip them loose.
I used my phone's camera to take the pics.
Edited by koolkat - 8/11/11 at 12:47pm