While I really like the HDJ-2000, comparing it with other DJ style cans you can notice a bass rolloff that starts off a little sooner than the others. When playing heavy bass sounds, I could feel vibrations emanating from the cup and into the first arm segment. Going by the age old audio mantra of "vibrations are bad", I decided to try some damping.
Without damping, the rolloff is noticeable around 70Hz or so, then sloping down and dropping out around 40Hz. Adding a little bit of damping inside alleviates this remarkably well, pulling the rolloff point down slightly to maybe 60Hz but maintaining a much flatter slope down to about 30Hz after which it drops very quickly. Overall, the bass feels *much* more powerful; maybe even verging on too much for my tastes (but I'm only a moderate basshead). I was also pleasantly surprised to discover that the headphones did not become any less sensitive (contrary to my other damping experiments). If anything, they actually feel louder because the bass presence is improved.
poster putty, or plumber's putty will do ($1 from dollar store, or $3 from hardware store)
some felt and scissors
foam or gauze optional (from your mom or gf's craft/sewing closet)
micropore/medical tape optional (I got some from a Walmart pharmacy near the bandages; you can get gauze here too)
This took me about 30 minutes in total, and negligible materials cost. (like $1 worth of materials, if that)
1. Remove pads - just pull gently on one side and it'll slide off
Hard to see in the pic, but there are three screws there. Take them out and very gently open up the cup; be mindful not to yank the wires since they're rather short here.
2. Next, stuff some putty into the two crevices around the hinge. I figured this was the problem area generating resonance/vibration. In the ortho thread you see guys that also slather putty all across the surface to mass damp, but I want to keep these headphones light. I also stuck some micropore tape over the hinge assembly area, though I doubt it actually makes a difference (fuzzy reasoning is that I don't want a hard reflective surface directly behind the driver); Don't put any thick foam there as it will impede into the driver.
2.1. There's a row of small bass ports (4 of them) between the crevices on the top side of the cup (normally the hinge will obscure them from view). You can experiment with covering them. I covered all 4 with a piece of micropore tape (see step 5 below)
3. Next I cut out a round piece of thin felt (use the earpad as a quick guide and trim later if you don't want to measure). Poked holes into it with the scissors (and widened them with the screwdriver) to match the mounting holes, and also cut a slit to allow for the wire. Note that this is the right earcup. The left earcup has a few more wires and a small board for the mono switch; the only difference for you is you have to cut another slit into the felt to accommodate the board.
edit: 3.1 actually I changed this and replaced the felt with fuzzy light breathable velour, and put the felt in front of the driver under the pad. This levels out the bass hump and makes it more consistent.
4. Put it all back together and you're done. Optionally, I rolled up a piece of gauze and stuck it under the earpads like so (not the prettiest I'll admit):
edit: 4.1 take the felt from 3 and place it under the pad. Easiest way is to slip it under the lip of the pad, then from there secure the pad to the baffle as normal
This does increase bass and reduces isolation a tiny bit, and improves treble clarity (by giving space for the front vents to breathe under the pad), but also blurs the line a bit between bass into midbass. I do it primarily for comfort because I have an unusually wide noggin and the headband actually presses on my temples (I have this problem with all headphones with a headband that curves with the head), so the thicker earpad gives me the clearance I need.
5. Here's a pic with a piece of micropore tape over the vents. I later put this on the inside because it's rather ugly on the outside (though usually hidden behind the arm. It sharpens up the upper mids (around the female vocal range), improves isolation just a tiny tiny smidge, and also reduces wind whistling noises if you wear these outside.
6. I took a piece of blutak (about half a strip) and rolled it into a thin line approx 15cm long, then laid it into the crevice surrounding the driver. This is essentially mass loading the front plate on a very small scale. Covered it with some tape because I didn't want the blutak sticking to the earpads. Hard to say with certainty if there was improvement here, but I think the lower bass extension and distortion improved ever so slightly, and the bass kicks feels stronger when amped. It could entirely be placebo though.
I found some roofing repair material in the garage. I don't know the exact name of the stuff, but it's probably some variant of "peel 'n seal". Anyhow, this kind of stuff has been used as a cheap alternative for vibration damping in cars (the thicker variety of course). I think it's an asphalt based adhesive with a plastic/rubber backing. Just peel the paper off and stick it on. The thin stuff I've got seems just right for headphones. Therefore...
Cutting this stuff was actually rather difficult. The material itself isn't hard to get through, but it sticks to your scissors and makes a mess of things. You have to be careful it doesn't bunch up behind the scissors and pull itself back into the blade as you're cutting.
So anyhow, I cut a ring out and applied it around the edge of the baffle front.
Sound impressions? Bass is cleaner, but yikes I think it got louder too.
If you've got dynamat or other vibration dampener, I'd suggest using that instead.
Added some plumber's putty around the outer edge of the baffle to seal it with the cup (sorry, I forgot to take pics). This improved bass extension and actually just cleaned up bass definition overall
Some pieces of dynamat/fatmat on the rear of the driver (do not cover the holes). Slight improvement to bass detail, treble detail moreso.
Edited by Armaegis - 5/21/12 at 9:41am