In my previous 'Ible I explained how to make your own in ear monitors (IEMs). I'm not going to cover all the background information here that I did there, so if you want some more background should check that one out before proceeding. But Following the methods outlined there, the result is a solid, filled earpiece, which, if you do it right, comes out perfectly fine. However, professionally manufactured IEMs have earpieces that are hollow shells into which all of the components are installed. The advantage of hollow shells is primarily that the components are not encapsulated in plastic, which makes them easier to service or remove (though that they aren't made to be taken apart). But it's also cleaner and neater to retrofit the internal components in a premade shell then to try and make the shell around the components. Also, pouring plastic over the components leaves room for error (like plastic filling the sound outlet of the drivers, filling the acoustic tubing, filling the female connectors, etc, all of which happened to me in the process of figure things out) that can be very difficult to try and correct. Additionally, there are open port drivers (much like closed vs. open port sub-woofer cabinets) that obviously couldn't be used in the filled earpiece. There are people over at Head-Fi that have come up with ways of making hollow shells. The first method is to use a fast curing compound, fill the earmolds, dump out the excess, and then slowly keep the earmolds turning until the material sets. The second way is to start off the same, fill, dump out excess, but then to wrap up the earmolds and throw them in a clothes dryer, so that they are constantly tumbling, which keeps the material more or less evenly distributed. Either can work with the right materials and some trial an error. However, the way it's done for reals is to use UV curing (light polimerizing) acrylic, and that is what I'm going to describe here.

Step 1: Tools and Materials

Let me just preface this by saying that UV curable acrylic can be expensive and hard to get, at least the stuff that's actually made specifically for this use. I've found other UV curable materials that are much cheaper, and perhaps worth playing with, like UV curable nail polish (see Nailite). It's probably unclear why you need a UV curable material at this point, but it will become evident later on.

The material used in professional manufacturing of hearing aids and IEMs, called otoplastik, is made primary by two companies (from what I can tell), Egger and Dreve, both of which are German. This stuff is on the expensive side, partly because they don't sell small quantities, but the pro-rated price (price of material per set of shells made) is actually only a few dollars, if that's any consolation. Dreve makes an acrylic lacquer, that is supposed to be used to "build up" a finished shell, but it's the smallest quantity available, 20mL for ~$30. You could probably make 3-5 sets of shells from that, depending on thickness. The material that is actually made for shell making is significantly cheaper in terms of $/mL but the smallest quantity sold is 91mL and that costs ~$60.

In terms of the materials needed, again, I've discussed/referenced a lot of this in my other 'Ible, so I'm not going to go into too much detail.

Also, while I will be focusing on showing you how to make hollow shells with the UV acrylic, I did make some shells using urethane epoxy, just as proof of concept (anticipating that most people aren't going to want to go through the hassel and expense of the UV acrylic route). So keep that in mind when reviewing the materials listed below.


-Impression making kit
-Nailpolish (or lacquer paint)
-Plastic resin
-Rubber resin
-UV curable acrylic (available from Lightning Enterprises)
     Balanced armature drivers (Mouser or Colsan)
     Caps and resistors (if you want/need crossovers)
-Acoustic tubing
-Acoustic dampers
-Connecting wire (from IEMs to source)
-Hydrocolloid material (like gelatin)
-2oz disposable wax lined paper cups


-UV light
-Dremel (with lots of bits!)
-Soldering iron
-A helping hands
-Some long wood screws


<p>Struggling to get a decent wall thickness, going down the epoxy route right now as I'm just making them for myself. am turning the mould's on an old glass lathe (its huge!) but I'm guessing they need to be tilted back whilst turning on the lathe? hence why I cant get them to be very thick?</p>
I tried using a rotator to make a hollow shell with a two part acrylic, but couldn't get good results. Yeah, because you need to tilt it back a little to keep the material from pouring out you get thicker walls in the canal and thinner walls in the body. Another option to think about... I recently made a pair of earphones using Shure SE shells (linked to an ebay listing below). They actually came out really well (unfortunately I didn't document the process otherwise I would have made a new Instructable). You don't get the same isolation as a true IEM, but the process to make them is significantly faster and easier.<br><br>http://www.ebay.com/itm/C0-Repair-DIY-Unit-Housing-Shell-for-SE535-se425-se315-se215-W40-Earphone-/131499238359
Even better news! I talked to 1964 Ears and the colloid they use (krydtaloid) is the same stuff I just for from lightning enterprises. You won't find the smaller portions on their site so call and talk to chris. Let's show him some love for breaking it down... Marozie, can you help me get the wire I need to connect the posts to the twfk driver?
Doesn't have to be anything special. Really small gauge magnet wire works well. Also, too me a while to find the IEM connectors, but you can get them all over the place, they're called TF10 connectors. I think I picked some up on eBay.
<p>For me the hardest part of this was locating the materials.. Good news for you,</p><p><a href="http://www.lightningenterprises.com/" rel="nofollow">http://www.lightningenterprises.com/ </a> has decided to sell the hydrocolloid in smaller batches for us DIY guys.. It's around $27 Shipped for a pound. I highly recommend it because it's reusable and will make a great impression of your ear!</p>
You nailed it. Most of these supplies are intended for audiologists, and therefore not sold retail. Many of the suppliers even require you to set up a professional account just ot view their catalogues. On top of that, even when you can buy supplies they're mostly in bulk which kills your cost margin and makes these projects untenable for lots of people to even attempt. Great new about that hydrocolloid - using gelatin to cast the investment can be pretty hit or miss due to the fact that it's so flexible and can easily result in a deformed shell.
Man you've got some serious patience, I'd love to do this as I love gadgets etc. but I know that I'd lose it working with tiny part's not to mention the time it'd take I'm not the most patient person! LOL Great job though they look awesome, I've always wanted to make a wet of those ear pieces & have it so I could listen to my ipod/phone etc. bluetooth device with literally NO WIRES.
Use a small dab of melted wax in the bottom of your cup to stick your impression to, this will keep it from wondering around when you poor your mold material in. It will also prevent it from getting under the bottom edge.
I found, instead of trying to build the cast up later in the process, I melt bee's wax to a water consistency and give the impressions a quick dip. This does two things, 1) it gives your impression an even smooth surface over the entire piece and 2) it builds it up slightly to give you a good tight fit without being uncomfortable. It takes a little practice, but works very well.
Hey, how did you manage to get the Sonion drivers. I really want to use the 2091i as a woofer, and I've contacted Sonion, who say they only sell trays of 100, and Colsan who have not responded.
Don't know what to tell you. I got them from Colsan.

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