Dr. Mead C. Killion, the founder of Etymotic Research, used to say: "Adding custom earmoulds to high-fidelity earphones could compromise fidelity." But recently he seems to have changed his mind on custom moulds: "but we found a partner in ACS that allows us to maintain the Etymotic sound signature while providing an extra level of customisation."
I trust Dr. Killion, so I've gotten my self a pair of CUSTOM•FIT ear sleeves, exclusively made for my ER-4B. ACS Ltd. (Or more precisely, DST Swiss) took care of the entire process. The cost was $100, which was quite affordable, but 2.5 months of waiting period was just little too long, IMO.
This is the result, and I AM VERY DISAPPOINTED with the quality of this CUSTOM•FIT ear sleeves. Yes, I am. Here's why:
As you can see, the insertion depth of CUSTOM•FIT is extremely shallow, causing a linear distortion mentioned previously.(insertion up to the reference plane, 13mm away from the eardrum, is a must) Due to the distortion caused by the insertion depth, ER-4B sounds like a hollow tin-can and does not work along with binaural recordings or any other HRTF synthesis.
Furthermore, the lengths of an acoustic tube on both channels are not matched, resulting in λ/4 resonance of the tubes at different frequencies. This skews the frequency response of ER-4B even further.
If someone is willing to pay $100 only for the sake of comfort of ER-4, CUSTOM•FIT is the way to go for. However, if you're serious about the fidelity of what you hear, stay away from it.
Of course, I've requested a re-make of my ear sleeves to the DST SWISS with detailed instruction,
Update on 11/09/2010:
Update on 12/21/2010: On Dec. 9th, 2010, DST SWISS sent me another pair, by charging me $85 without my authorization. And the result was more or less the same to the first pair! So I contacted Dr. Kasper again on the same day to address the issue. On his email, he said DST SWISS is not affiliated with ACS USA anymore, and I can get the refund of $85 charge. (which I got on Dec. 15th) Dr. Kasper promised to send me another pair, this time made by the lab which is now 100% owned by ACS. THANK GOD I don't have to deal with those DST SWISS anymore..!
Update on 01/17/2011: Dr. Kasper forwarded my inqueries to Mr. Matthew Sinisi, Customer & Provider Relations Representative of the new ACS USA. Mr. Sinisi told me the UK lab got my ear canal scans, and they'll make the sleeves ASAP. After initial 2.5 months + later 3 months, I will finally be able to get the sleeves with quality that I originally expected from ACS.
Update on 02/18/2011: I finally got new sleeves, and they fit perfectly. Their physical built quality is top-notch; Yet, acoustically, they are more or less the same to the ones made by DST SWISS. Below is the analysis.
Update on 02/19/2011: Dr. Kasper informed me that new sleeves are in production now with above issues taken care of. Hopefully ACS get it right this time, so that ACS and I do not have to go through this kind of ordeal ever again.
Update on 03/14/2011: The 4th pair is here. Below is the analysis.