Originally Posted by juan1894
Hi, the mod for the hd439 is really simple. To detach the earcups you have to push up, there is a video on YouTube by sennheiser USA and explain this. Then, you will notice a gray foam, the screws are below this foam (4 screws). Then carefully lift the driver enclosure and in the back you will find a "tape" that covers three holes, for more bass remove it, assemble the headphones, and it's done!
I have the Sennheiser HD-428 headphones. I've performed the bass mod, with a slight variation. I removed the tape revealing the 3 holes and my headphones sounded like a pair of Beats on steroids. Seriously, my fillings in my teeth were literally starting to feel pain. I then went down to the my bench where I do my headphone work, and pulled out a role of micropore tape. It is a medical tape, like transpore tape, but it is a paper-based tape and generally used for more sensitive wounds, where the transpore tape would grip on the skin like super glue. I used the micropore tape to completely cover two of the holes. The third hole was covered with tape on only 1/2 of the hole. The results? Outstanding bass, but not the tooth filling shaking, migraine causing level of bass.
One additional change that I also made was that I lined the driver casing (the black oval plastic piece around the back of the driver) with plasticine clay. This was done to dampen the headphones a bit and to take care of any odd sounds and rattles that could result due to the increased bass response.
To the other question about how the other frequencies change. The mids were a bit better and the upper frequencies remained the same. To me, these $40 "gems" are more fun than the HD-580s that I've owned at two different times in my headphones' past. The HD-428 can often be found for about $40, as refurbished headphone on the Web. However, the refurbished model is just like new. In fact, I'm nearly certain that Sennheiser might be packaging new HD-428s as refurbished to get around their strict MSRP guidelines.
Just a thought ...