[FYI] Basic Guide to In-Ear-Canalphones (rev.4) - Page 7

Technically speaking, volume is pressure. Volume, by definition, is 'sound pressure level (SPL)' measured in decibel.

When your ear canal is sealed by the IEM, the volume of air remains constant as long as the seal is maintained (unless your eardrum has hole(s) on it, but that is another story). Since the volume of air is constant, the pressure should remains constant as long as there isn't any other external force (such as the vibration from the transducer). What the transducer does, is to create vibration in the air as sound wave. Like any wave, sound wave has its high and low peaks, meaning positive and negative air pressure. Remember, the pressure can not build up because the transducer does not add more air into the ear canal nor change the volume of air in the ear canal. Once the transducer stops vibrating, the air pressure will go back to the original level, which should be around atmospheric pressure if you seal your ear canal correctly in the first place.

What headphones usually damage your hearing, is volume (SPL) and time exposure. Your ear is just like any mechanical device, if you stress it either on workload (volume) or work hour (time exposure), you will damage it (and worst if you stress it on both at the same time). However, you generally can't damage your hearing by headphone because of pressure 'building up' in your ear, unless 1) you already have some very complex medical issue in your ear and not fit to use headphone in any way, 2) your headphone happens to connect to a working air pump when forcefully clamped onto your head, or 3) you are experiencing extremely rapid air pressure change, such as explosive decompression on an airplane or a deep sea submarine, or in close proximity to an explosion - I have my doubt you will be in one of such condition. But if you do, I would think hearing damage from headphone is likely the last thing in your mind.

If you are referring to the IEM companies list, I do have an more current list and I will update the list on rev2. If you don't want to wait, the list is already on my blog (link in my signature), left side.

I just finished update the guide to Rev2 and now you can find the new PDF version here if you wish to keep a copy. You are free to distribute it as long as it is not for commercial use.

The update consists mainly of the omission of out-dated information and two seperated list of IEM brand, for both universal and custom. They will be continuously updated in the future.

Glad to know that the guide is helpful.

I just updated the format and included a list of science journals' articles in the references for the research type among us. Some of them are free with a little google around while the other are paid subscription.