Last time, we were working our way through the custom IEM “factory” at Ultimate Ears. I put factory in quotes because it’s not that big, and most of the work is done by hand. In the last post, we saw the shells being created, today we’ll see how the electronics are married to the shells. 

This is where we start seeing things coming together. As you can imagine, the inside cavity of the IEMs is pretty small. And so are the components that go inside. As a result, the people working on these have small hands and good eyesight. This is very detailed work.

Below is a picture of the balanced armature driver network that goes into the shells. A balance armature is similar to a regular speaker, but because it operates in a sealed environment, they don’t have to worry about what happens behind the driver. The key to getting great sound out of balanced armature speakers is the tuning. That was the part I couldn’t photograph as it’s proprietary. But know that every driver is tuned and each IEM is checked agains a reference frequency response profile. If it doesn’t meet spec, it’s worked on until it does, or the process begins again.

It takes a lot of skill to fit the above components into that small shell, while maintaining the right sound. Once it’s all in place, tuned and tested, it’s time to fix everything in place. You can’t have driver boxes rattling around in your head, so they are glued in place with a special UV cured glue.

A technician adjusts the final fit of the drivers in the shell.

A technician adjusts the final fit of the drivers in the shell.

A small amount of UV cured glue is injected via a very small syringe. 

A small amount of UV cured glue is injected via a very small syringe. 

A blast of UV light and the glue is cured. Cool!

A blast of UV light and the glue is cured. Cool!

Because every shell is a different shape, there is no automated process to make this go faster. Each and every part has to be hand-fitted. To me, that was the most impressive part of the process—how labor intensive it is. The cost of the IEMs started to make a lot more sense when I saw how long they take to make. These aren’t coming off an assembly line hundreds an hour.

After the components are fitted, glued in and the back plate attached, it’s time for some final polishing. Because they will be inserted and removed from your ears hundreds or thousands of times, a perfectly smooth outer surface is critical. 


Like every other step, it’s all by hand. If they remove too much material here, the whole process needs to start over again, so a light touch is critical. Of course, they check the shells against the mold at each step.


The final step is polishing the back plate and making sure the fit is perfect. This last buffing puts a super-smooth finish on the shell which makes it easy and painless to put in place and remove. 


The final step is another layer of quality control. Each box is signed by the inspector and has a serial number that can be traced all the way back through each step of the process. Should there every be an issue, the problem can be found quickly and corrected. 

So that’s the process. Hopefully this gives you a better idea of how those things are made. One of the things that impresses me about UE is the attention to detail and dedication to customer service. They are working on getting the process tuned up and quicker so if an artist is on the road or a church musician has a problem, it can be corrected in days, not weeks. 

All impressions are kept on file so if you lose your ears, a new set can be made without having to visit an audiologist again. In fact, I’m anxiously awaiting a new set that I’m getting to evaluate. As soon as they arrive and I get some time with them, I’ll let you know how they sound!


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