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.