Universal to Custom Reshell — Things to Know Beforehand

Editor’s Note: Please give a warm welcome our newest writer, who will be giving us his “Yeoisms” from time to time. He’s fanatical about custom in-ear monitors, and hopes to shepherd more people to the custom realm. Check out his bio, and his articles! His first couple of works take everyone back to basics, and consider the fundamental principles behind going custom for in-ears.

It’s undeniable that the vast majority of us started off in this hobby with a universal-fit in-ear monitor before eventually going for a custom in-ear monitor. But in between, some of us we may opt to reshell our universal in-ear monitor into a reshelled custom version. Many people make the assumption that “I will get better isolation and sound when I customize the earphone for my ears — hence, it is a CIEM! Besides, these CIEM demos don’t sound that much better than my current earphone!

I admit, I used to have this thought too when I was just starting out. But after everything, with the experience I have gained, I can confidently tell you that a re-shelled universal will not be equal to a CIEM (unless you reshelled a pre-existing CIEM with a poor fit or which was someone else’s) for these following main factors:

  • The universal IEM was not tuned to be reshelled. An IEM such as the Westone 4 or Shure SE535 was tuned specifically to fit the form factor it fits in, i.e. it only has one single output port. That kind of design is inherently a sonic compromise, compared to a CIEM designed from the ground up with multiple output bores, even with the same exact frequency response as a known universal IEM.
  • Additionally, when a custom IEM maker reshells an universal IEM, they will usually only reference a generic ear placement for the IEM and measure the frequency response in their ear simulator measurement apparatus, without considering the insertion angles or the distance from their simulated ear drum (also known as the Drum Reference Point, or DRP) to the exit of the IEM itself. Getting a completely accurate sound for a reshell requires a lot of small, minute adjustments that are very time-intensive, including estimating the residual canal volume (the volume from your ear drum to the second bend of your ear canal, which is unmeasurable from a pair of impressions) and then adjusting the tubing length to match the sound profile that was measured via the ear simulator. Keep in mind that the ear simulator also only targets the “average” ear response. Hence getting a “better” sound will become subjective.
  • For IEMs that are well-known and often reshelled, such as an SE535 or UM3X, these CIEM makers usually have a set formula for reshelling these earphones. Remember, the CIEM maker would much rather you purchase their own designs than reshell someone else’s creation for you.
  • CIEMs are tuned to be customized. Hence, their universal demo versions will never sound as good as the fully custom-made version. Regardless of whether the demo model uses silicone tips or Comply tips, ear tips contribute to unpredictable canal resonances that almost always do not flatter the intended sound profile, especially in the treble. Also, since these universal CIEM demos usually cannot be inserted up to your ear canal’s second bend (which is where almost all CIEMs are terminated), the added residual canal volume also skews the treble response in unpredictable ways, contributing to peaks and nulls that adulterate the sound. Thus, I feel that the custom unit almost always sounds better.
  • If you are going to be trying an universal demo for a CIEM, always try to pick an ear tip that hangs least over the edge of the output bore as much as possible. The diameter of the ear tip should always be wider than the outside edges of the output bores. Finally, always insert the demo unit as deeply as you can possibly fit it. Doing so will minimize the adulteration of sound because of added residual canal volume contributing to unintended treble resonance.

Therefore, if you wish to reshell, I believe you should be aware of all the possibilities beforehand. Reshelling does in fact alter the sound; it will not merely give you the same sound, but with more isolation. In fact, added isolation contributes to a change in how you perceive your existing set of earphones! Lastly, all things being equal, a CIEM will alway prove to be a superior acoustic design to an universal IEM because it was designed from the ground up to fit inside a custom shell. Therefore, the acoustic designer has a lot more room to operate. It is up to you to be able to hear the differences in sound quality, however, and to do so, you’ll need to get the best fit out of any CIEM demo. Hopefully, this guide will prove useful to you.

Also see the related article, ‘Going Custom: Yes or No?

About Yeo

I’m an audiophile based in Singapore with a special interest in custom in-ear monitors and their related products. I think I’m one of the youngest here, but that won’t stop me from helping others to the best of my abilities.

4 thoughts on “Universal to Custom Reshell — Things to Know Beforehand”

  1. Hy are possessor of l the product Future Sonics MG6Pro I would like to remodel to my ears,
    I would like to know the cost and time for instruction and Italy thanks


  2. Hey Inna Singaporean too and I would like to ask if a CIEM of 4 drivers, 1 sub, 1 lows, 1 mids and 1 highs will usually cost how much including fitting, except for the choosing of colour and shells.


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