Regarding filters for the er4s, that's nothing like vent modding. You are using a makeshift vent to release pressure. The effects of this could vary drastically between users, materials, tips, etc. simply put, the earphones weren't designed to do this mod. But if it works, by all means do it. The er4s "was" designed to use filters and those filters are permanent replaceable parts that are consistent and even sold by the company. So i would say you can't compare those things really. Not to say the er4s isn't flawed in some areas, or that people don't mod them. My point was just that i think it's fine to do these mods, and i'm not discouraging anyone from trying them. I was just implying that it isn't an especially good product if an unsupported mod is required to make the sound good. Not just sound better, but from what we can tell... Sound good. Usually the mod reduces bass. If the bass variances didn't exist, most people wouldn't need a mod. That's the fault of quality control. I liken it to something like a new computer with a broken cd drive. If you can tape the cd-drive shut to get it to work then who cares?... Well, realistically i don't know many people that wouldn't return a computer with a messed cd drive. So why should the tenore be any different? In the real world it is probably because not many othet affordable iems sound so good. So people are willing to "tape the cd drive shut" to get it working, since the cds rip so incredibly fast or something... Anyway, point being, they sound great. Mod them if you need to. But it doesn't excuse the need for a mod like that. :-o that was all i meant. I love modding things to improve them. But it's one thing to shape the sound with a mode. It's another to mod something to fix a problem that shouldn't be there. But i guess you could argue whether it would be necessary for someone to do even if they had a neutral set. At that point i'd say do what you need to if you like them. I was just speaking from the viewpoint that people were bringing the bass back down in bass heavy sets.