If you're handy, and with a bit of practice, you can actually take impressions that are as good as or better than an audiologist.
I would never have attempted this, but one of my best friends is an audiologist. I had her take impressions for me for my Ety mods. She had stacks of the impression medium and materials lying around, so I had a chance to try it out.
You may think it's unadvisable to do this, and I would agree, to an extent. By nature I am a very cautious person; I’m ten-parts planning to every one-part action. But I’m confident in my dexterity and fine-motor skills, and would not take a risk with something so important to me (my ears and my wallet!) without first making a full assessment and consulting an expert.
I have now been researching this for well over a year, and have been repeatedly surprised by what I’ve found.
First, many audiologists are very casual about the ear-mold procedure. The material used for impressions is very forgiving- it has a long curing time and is stable even if poorly mixed. The problems that arise are due to other issues. The ear canal is very flexible and changes size and shape when you chew and speak, and even when you lose and gain weight. Hearing professionals recommend that impressions be taken as often as every two years for hearing-aide users in order to ensure a good fit and therefore seal required for optimum performance.
For me, as soon as the material was expressed into my canals, the sound attenuation was so profound that I felt compelled to talk to try to listen to how much I couldn’t hear (?!?). If you talk with the material in your ears, it's going to have a negative affect on the “quality of fit.” Also, when your mouth and face are at rest, your jaw is in a different position than when “at attention.” Your tongue actually rests on the top of your mouth when relaxed. The tiniest bit of activity will result in a change of jaw positioning. The important lesson from this is to be conscious of about how much or how little your jaw is open when relaxed, hopefully like you’ll be when listening to music. When you go to have impressions taken, leave your mouth open just about 1cm more than it opens when at rest. To be certain you don’t move, it’s best to find something to bite down on that will keep your jaw stable for the entire time it takes the material to set. An “open-mouth” impression is inadvisable, as the canal is not only considerably larger in this situation, but it’s a completely different shape. The resulting IEM will be very uncomfortable, even after being shaped.
Good impressions are not hard to take and will fit exactly if taken properly. The skin of the ear canal is flexible. There is quite a bit of room for error when taking impressions. To improve the chances even more, get custom molds made out of a hard material that has an outer layer composed of a different, softer, material, like silicone. This has a better chance of providing a comfortable fit and tight seal as it can provide flexibility in addition to the flexibility of the canal itself. Also, read up on curing times and environmental variables associated with faster/slower setting rates. Temperature and humidity can have a big affect the time it takes for the impression to become stable. Audiologists can be eager to complete the impressions procedure and want to “stick a fork in it” to see if it’s done. The way they often check is by pushing on the material or by pulling the ear lightly toward the back of the head to see if the ear separates from the impressions. Either of these procedures will reduce the likelihood of a proper fit.
