Klipsch Image X10 Impedance Adaptation

Klipsch Image earphones are unique IEM with remarkable bass frequency response from such small bodies. Besides the volume balance on each frequency range, I feel X10's sound quality itself is quite competitive against the quality of Etymotic Research ER-4S.
Comparing the stock X10 with ER-4S, I prefer ER-4S because of its definite clarity in high frequency, with my 1st-Gen iPod nano. Yes, I love ER-4S, but sometimes it is physically tough for me to screw them.

Below is the page from a popular Japanese site, reviewing headphones and earphones.
http://fuchinove.chillout.jp/canalsokuteikekka.html
You can find data of X10 the at 4th line from the top, and at the right side end column, there is a data of impedance vs frequencies.

This X10's impedance characteristic on this site is really unusual. Under 1kHz range, its impedance is around 30ohm, but at the 10kHz, it rises over 300ohm. This data shows that X10's frequency response characteristic is heavily dependent to the output impedance of a headphones amplifier. Also in this site, the author measured output impedance of several digital audio players and they are less than 10ohm, while, as far as I know, headphones driver's impedances of conventional integrated/power amplifiers or CD players are often something around 50ohm~200ohm.

I thought, because of this unusual impedance characteristic, there might be some room I could improve frequnecy response of X10 by adjusting impedance. If I plug X10 to the headphones amplifier such like with 100ohm output impedance, response to low to mid range becomes 1/4 (=30/(30+100)), and high range becomes 3/4 (=300/(300+100)), means much more high response than my iPod. Ok, let's go.

First, I plugged my X10 to the headphones jack of McIntosh MC2505 power amplifier, which is with 220ohm resisters at headphones driver.

It was great, and I found the impedance curve in above site is reasonably so so reliable, though there are still many unclear conditions which may affect impedance characteristic, such like how he seals output port of the phones. Anyway, Image X10 was no longer a simple king of bassier, with MC2505.

Then, I made a 5min-DIYed impedance adapter with 110ohm resisters.

It worked really great with iPod. It's balance was very close to HD650 with more clarity in high range, and it was my first experience I could fully enjoy Beethoven's #9 Sym by earphones.

Next, I tested an attenuator cable bundled in the Audio-Technica plug/cable kit 'AT3A53LK'.
http://www.audio-technica.co.jp/products/hp/at3a53lk.html
The impedance of this cable is 267ohm, and I found it was too much. X10's sound was so spoiled, and it was like a budget earphones.

Ok, let's go seriously.

Took a mini plug apart from a cheap plastic molded Sony cable.

Cut off the plug of X10's cable.

Installed 100ohm resisters both for L and R.

Placed the end of X10's cable.

Soldered the wires.

Hot glued.

I did.

I selected 100ohm for enjoying some bassier characteristic of original X10, so that I can also enjoy ER-4S for higher definition sounding. If you have no ER-4S, then 120~150ohm may be a good compromise between deep bass and treble resolution.

Easiest way may be to use ER-4P => 4S adapter (75ohm) or to simply buy an impedance adapter from APureSound if you live in the states. They have 75ohm and 120ohm adapters in stock.