I'm not completely sure if this will work for all eph 100 with volume issue, but seems like pushing in the driver? seems to fix the low volume problem
I too was disappointed when the left side had problems, mainly with volume being so low that I had to tinker with balance option in my mp3 player. This whole time I thought it was a condensation problem, because usually after wearing for more than 30minutes - 2 hours, the left side's volume would get very low. Since then I always tried to 'ventilate' the driver after a certain period of time, but the problem always came back and bothered me. This problem first started after having owned these earphones for about a year.
Today I was using the earphones for extended period time while studying, and after about 3 hours, the symptoms started to happen again. I took out the ear tip, and granted there were some moisture on the inner side of the ear tips, so I wiped them, and blew some air into the driver, but volume was still low.
I did notice that volume would come back if I cleaned the driver edges, but didnt think much of it till today. I noticed that the driver was kind of 'sticking out' more than the right side. So I applied some pressure to the driver, and volume CAME BACK. The driver is still sticking out, maybe by .01 mm, or like 1/64th of an inch ish, but the volume is completely back.
So my hypothesis is that after a bit of use especially with bass heavy music, may or may not be related to the condensation problem, volume diminishing problem may be due to the driver being 'displaced' inside the aluminum? tube. If you have the volume problem, please see if the driver seems to be displaced and try pushing it in with a little bit of force and see if that fixes it.