I've recently had a few sets of impressions made and tried different sets of IEMs made from them. Here are my tips for those looking into custom IEMs. I spent a lot of time talking to my audiologist, doing research and have experienced the differences that different jaw positions can have on the end result.
The quickest and easiest way to get a good seal is to recommend use of a bite block during the impression. This recommendation is not always the best one however and can lead to an uncomfortable fit for some (especially if the wrong size is used).
How jaw motion affects the seal:
When you open your jaw, the back of your jaw bone pushes up on your ear canal changing its shape. Because of the way this shape change occurs it is more likely that impressions taken with the jaw closed will cause the seal to break when the jaw opens. This also means if you take the impression with your jaw open, when you close your mouth you'll feel greater pressure from the IEMs in your ears than when you open your jaw. The "perfect comfort" point will be the position your jaw was in when the impressions were taken.
Things that effect your jaw position and thus your ear canal shape:
- Leaning forward (jaw slides forward slightly)
- Leaning backward (jaw slides backward slightly)
- Lying down (jaw slides back a lot)
- Clenching your jaw (never do this on a bite block)
- Relaxing your jaw
Notes on bite blocks:
Bite blocks usually have two positions a horizontal and vertical. Their purpose is to keep the jaw stationary so the mold will be accurate. You do not want to be moving your jaw during an impression at all. That said, you also never want to bite hard on a block. If you use a block, hold it as lightly as you can between your teeth and try to relax as much as possible. The vertical bite block position (larger) is a bit overkill for most people and my audiologist didn't recommend it.
I did not use a bite block to get my "perfect fit" but I did hold my jaw relaxed and very still during the impression. Don't talk to your audiologist or move during the impression if you are not using a block. Focus on keeping the angle of your head at the desired angle and not moving at all. Without a bite block in your mouth, tilting your head will move your jaw position if your jaw is relaxed. If you aren't sure if you can keep your jaw very still for about a minute straight you should probably go with the block.
My first set of impressions were taken with a bite block in the vertical position (large) and resulted in an IEM shape that never really got comfortable.
How to to maximize the comfort of your custom IEMs:
The tips i'm mentioning here relate specifically to comfort only. Comfort does not always equal a solid seal although it can for some people. You have to have a seal for a successful set of IEMs obviously, but there is such a thing as too much seal when it is to the point where the pressure causes discomfort.
Ideally for a comfortable fit you should hold your head and your jaw in the "average" position that you will hold them in when using your IEMs. In my case, I am an audiophile who does not sing. I tend to listen sitting leaning forward slightly while using the computer or when laying down. I don't talk when I listen to music, and I don't eat with IEMs in. This makes my average position sitting up straight with my head just ever so slightly tilted up/back and my jaw relaxed (teeth apart) but not forced open. This position yielded an amazingly comfortable fit for me, i don't even feel my IEMs in my ears after about 5 minutes. Luckily in my case this also produced an excellent seal.
If you are a singer, take note of how wide you open your mouth when you sing. You likely don't need to take the impression with your jaw open at 100% of where you tend to open it at its widest. Again you want that "average" position. This will be the position your jaw is in the most when you use the IEMs.
If you only listen to your IEMs lying down on your back, have your impressions done while you lay on your back. In short, do whatever it is you'll be doing the most when you use your IEMs. If you do multiple things while using your IEMs, find your average position between the two and use that.
Get a complete ear impression in and out:
All ears and jaws are different:
In my case I took my second set of impressions with my jaw relaxed and my lips just barely apart. Even if I open my mouth ultra wide, I still don't break the seal on my IEMs. If I was a singer I would be fine with the impression I am using currently only for audiophile use. In fact, there is nothing I can do with my jaw position to break the seal. Not everyone may have the same experience however.
The amount that the ear canal is affected by jaw movement will vary from person to person. Most IEM companies will instruct you to use a large bite block. It essentially guarantees a good seal, it just may not end up being a comfortable one for all people. In these cases they will often revert to recommending a less open mouth or even a closed mouth impression.
Hopefully this helps some of you trying to attain that "perfect fit."
If you have had a different experience or have your own information to share please do add it to the thread!
Edited by Sproketz - 11/5/11 at 10:02pm