This is about how to build a single Balanced Armature earphone using Klipsch X10 shell and Knowles BA driver (used in ER4PS Hi-end IEMs). All materials are available at earphonediylabs.com.
Step 1: Wiring
Pull the wire through the back cover like this.
Step 2: Soldering
Before soldering, make sure you fix it's position on the vice clamp - hi-end drivers with strong magnet and may stick to your soldering iron!
Be very careful when you soldering the wire to it. Over heating in a few seconds may kill this tiny BA driver. And the soldering panel is extremely small and very easily get short-cut. Also notice the polarity of the driver and don't make mistake.
Step 3: Gluing the BA Driver Into Housing
Apply around the BA driver and carefully position it to the housing. NEVER get glue into the opening of the BA driver - once you did there is no way back...
Step 4: Verify and Gluing Shell
Your build is working now, you can connect it to your cell phone and verify if it sounds properly before you glue the shell up. And glue the front housing (gold or silver) and the back end cover (hard rubber) together, and you finally get this.
Step 5: How Does This Klipsch X12 Kit Sound?
Ultra-high resolution! It outperforms original Klipsch X12 because of the upgraded BA driver - Knowles ED 29689. And literally you can refer to most ER4P/S impressions, because they're built with exactly same BA driver! (background knowledge: unlike dynamic drivers, balanced armature drivers is fully sealed. So the sound quality is solely determined by the BA driver, the acoustic design has minor impact). Here is a reference from Head-Fi:
It is analytical and bright, fairly neutral while slightly on the thinner and colder side, tight and impactful bass that isn’t quantitatively large, resolving and fast which are very typical of BA based IEM. ... The overall sound signature is analytical, a little on the bright side but not harsh, resolving and fast with slightly upper mid ~ lower treble focus; fairly neutral while still retains a tiny sense of warm. Bass is very tight, impactful but lacks a good body, while instruments separation is good, air and depth reproduction isn’t – thus soundstage is mediocre.