SETUP
Purchasing a pair of custom in-ear monitors from UE or anyone else involves a visit to a local audiologist (i.e., a hearing aid specialist) to have inserts made of your ears. It's a painless process (at least it was for me) in which some goo gets injected and left in for a few minutes until it hardens into a soft spongy plug that is then sent off to the manufacturer. The visit usually adds about $100 to the cost of the earphones.

UE still had the molds from my UE 11 Pro from which to build my UE 18s, so I skipped the audiologist this time. My new 'phones fit as perfectly as the old ones. Once inserted, they made a tight seal and provided a superb block against outside noise. UE says they deliver 26 dB of sound isolation. The UE 11s are very efficient phones that mate well with portable players and can be easily driven to high volumes. Ditto for the UE 18, though these are rated about 4 dB less efficient with the same input signal - a difference that was noticeable in direct comparison and verifiable with a pink noise track and an SPL meter held carefully to the left earpiece of each earphone (an admittedly unscientific test). I accounted for this difference when switching between earphones. But suffice it to say, these things are so efficient you won't likely miss those dBs with any playback device, and both 'phones are extraordinary in their ability to go from very soft to very loud without strain.

I like to evaluate earphones these days with lossless music tracks ripped to my iPod Classic, with the thought that most people buy these for use with portable music players. While I did check the UE 18's dynamic range and efficiency with my iPod, I chose this time to do most of my serious listening from the headphone jack on my high-end preamp and CD player so I might better catch the subtle improvements made vs. the UE 11.