Recently found a simple mod for my PK2 that works surprisingly well. I understand that Yuin buds are slightly falling out of fashion on head-fi, but I'm still curious to see if other users notice the same difference and if this unleashes further potential in the buds.
There are two slot holes behind each ear bud of PK1/2/3. Some have suggested closing them or closing one of them. The mod I found to be very interesting is to close a vertical half of the holes. Specifically, I used masking tapes to cover the left side of slot holes on the right bud and the right side of the left bud. This accomplishes two things:
1. It changes the tuning of the enclosure, similar to altering the shape/position of port in speakers
2. It reduces the amount of backwave reaching our outer ear - notice that the left side of the right bud (and right side of the left bud) tends to be closer to our pinna. The mod directs the backwave away from our ears so that it doesn't interfere with the original signal.
After the mod, I find that there is a significant reduction of reverb, so much so that I tend to turn up the volume by a small notch. Yet it allows me to hear more details in the recordings, and the environmental acoustics that are actually in there as opposed to those generated by the backwave. Everything becomes cleaner and better defined, and surprisingly the sound is also less fatiguing. I don't get any more bass than before, but the better detail makes the bass sound tighter.
Now in some slightly dry or not-too-many-instruments recordings, the opposite mod might sound better - that is, to cover up the right half on the right bud and the left half of the left bud, as it directs the backwave towards your ear more. Interestingly, while you get a lot of reverb this way, the reverb quality is still better than unmodded, which means the tuning change does something. Once in a while I might swap my left and right buds to listen to a reverb-rich version of a track. Ultimately though I think the less-reverb configuration is more natural.
I'd be curious to see if other people have the same observation. I need to add though that my PK2 has had two other changes to it before I did this mod. One is that it has a silver-plated copper DIY cable. The other is that my earbud cover has been set up to expose all the holes in front of the driver. The way I achieve this is to use first use a black foam cover with a hole in the middle. Then I pull the cover back so that the hole is large and the foam almost just covers the edge of the earbud, and I secure this position by adding a rubber ring on top of the foam cover. Exposing the holes in front of the driver allows much more detail to come through, while the cushion around the edge allows a comfortable fit and decent bass sealing.
Edited by ms142 - 2/24/13 at 3:22pm