Behold the punctured ear tips!
I very much like the results after I drilled very small holes in the supplied silicone sleeves. You may have to click on the above image to see the holes in the enlarged photo. (The story is continued from here: http://www.head-fi.org/t/594945/6-panasonic-rp-hje120-surprisingly-usable/15#post_8854187. Basically, I played with the cheaper Panasonic RP-HJE120 before deciding how to change the sound of the MH1C.)
I ended up making four tiny holes per tip--still a bit bassy, but I didn't want to overdo it. With this "mod", the bass response now more closely matches what I hear from live music. The timbre of musical notes has been improved since the proportions of the fundamental and the harmonics is in better balance. After some time with a tone generator and matching the volume, I can tell that (for my ears at least) the response above 1 kHz hasn't changed much.
I normally use a parametric EQ like Equalizer or Accudio, but many apps like Pandora, YouTube, and Netflix can't use them. The punctured tips have the potential to match the huge bass reducer filter that I use on the MH1C. They actually sound pretty good now. The time domain characteristics aren't completely independent of the magnitude response, so I would guess that the transient response has been improved also. I'd love to see impulse response and CSD measurements on these things after EQ or after using these tips.
Isolation isn't as good after the change, but I'd rather trade that for better spectral balance. Also, driver flex during insertion has been greatly reduced. The technique also worked for the HJE120, but I can see it working for any bassy IEM, e.g., UE100, Klipsch S4, etc.
If we can find a way to get controlled leakage from foam ear tips, we may be able to neutralize the sound of v-shaped IEMs.
I forgot the size of the drill bit, but I started with the smallest #80 wire gauge bit and went down from there. A #75 is still too small. With the one pictured above, it took many passes of the bit through the hole, and in both directions before I got the opening of the desired size. I had considered other ways of puncturing the sleeve, like using a needle tip with a soldering iron, but I never got to try them because the drill worked well enough.
Edited by yuriv - 11/17/12 at 12:54am