Disclaimer: This pair is owned by Inks.
After losing two units of 8320 & three units of 9927, now the modification technique has been fully finalized. The IEM shown above is the ultimate Monoprice 99RC, with enlarged & elongated nozzles and a pair of cyanoacrylate-coated drivers.
By default, Monoprice 9927 has several fundamental issues:
1. An annoying peak @ 5 kHz range
2. Short bandwidth
3. Bad fitting
Thus, a cyanoacrylate adhesive has been coated on the diaphragm to solve #1. Also, nozzles on both channels have been replaced with a pair of drill-carved 5/16" long pvc pipes (3/16" ID) to correct #2 & #3. With the enlarged bore size, the entire acoustic output has been widened to 3/16" as well.
The ultimate goal is to knock off the problematic peak, while keeping all the original acoustic properties intact. In addition, with careful calibration, the balance of both channels is now equalized.
Although the result is still quite far from true hi-fidelity, the tonality is now much more neutral, easily overwhelming any budget-priced IEMs, such as Vsonic VC02 or HiFiMAN RE400. Currently omitted, adding a small amount of acoustic resistance at the output of the IEM will definitely help tame any remaining harshness.
A special thanx goes to my mentor, Soonja, as well as Inks, who provided me with a bunch of disposable spare pairs.