Last weekend, I traveled to Klipsch's headquarters in Indianapolis to check out several new speaker systems. The visit followed a two-day trip to the Rock and Roll Hall of Fame in Cleveland, where Klipsch sponsored a weekend celebrating Smokey Robinson's career. It was serendipitous timing; the company was about to roll out its newest X Series in-ear headphones. As a result, I was able to hear all four models in the X Series during my visit.

The four new X Series in-ear headphones, from left to right: X6i, XR8i, X12i, and X20i.

Before I listened to music through the new in-ears, Vlad Grodzinskiy—the senior manager of product development for headphones at Klipsch—showed me a chart comparing the measured frequency response of each model, so I could understand what each one offers the listener. In addition to the charts, I was able to demo the X Series using my own USB DAC/amp—an Emotiva Big Ego —and my own music. I chose to replay Massive Attack's "Karmacoma" as I swapped between the four new models, and I correlated the differences I heard to the response curves I saw, which proved to be an informative experience.

At $180, the X6i is the least-expensive model in the X Series. It uses a single full-range armature to create a clean, clear sound that measures very flat. The bass response was a bit lighter than what I typically find ideal, but it had good low-frequency extension, and the bass was tight.

The step-up $280 XR8i "hybrid" model combines the full-range armature found in the X6i with a dynamic driver. Essentially, it adds a micro-subwoofer to the mix. The result is a boost of several dB in measured—and audible—bass response versus the X6i. I found the XR8i's mix of deep, punchy bass with clear midrange and highs to be very agreeable. Klipsch says the XR8i is well suited for watching movies as well as listening to music, thanks to how well it handles bass.

The X12i ($350) uses a smaller but higher-quality "audiophile" armature than the two models below it, which ups the performance ante in the midrange while producing deep, tight, satisfying bass in a truly tiny package. The sound quality of the X12i was even more refined than the XR8i, but it did run into some trouble when I turned up the volume—it can't play quite as loudly as the XR8i or X6i. However, if you value your hearing, you'll likely never need more output than the X12i offers.

At the top of the new X Series is the X20i ($550), which adds a supertweeter armature to the full-range balanced armature of the X12i to create a 2-way in-ear headphone with exceptional sound quality. What makes the X20i special is its dual balanced-armature design that requires no internal damping to achieve a very pleasing—and accurate-sounding—frequency-response curve. Klipsch claims that the twin armature drivers offer lower distortion and better clarity than competing in-ears with three or four balanced-armature drivers.

The X20i measured better than the models beneath it, and it sounded better to boot. Although the X20i is tiny and super-light, it even includes an interchangeable cable. In addition to its reference status, Klipsch says the X20i is its most durable in-ear headphone.

While great sound quality is crucial for any headphones, comfort can make or break the user experience. Klipsch touts its exclusive oval eartips as a solution to the fatigue many people feel when wearing in-ear headphones. I did not get to test the new X Series models for long enough to form an opinion about how comfortable each one is for long-term listening, but I do own a pair of Klipsch X4i in-ears that also feature oval eartips, and they are very comfortable. I also appreciated the 40 dB (or so) of passive ambient noise attenuation that results from a tight seal with the ear canal.

I liked what I heard from all the new X Series models, but the X20i stood out—I was amazed at how great it sounded, especially considering its small size. I also loved the powerful sound of the hybrid XR8i, with its subwoofer-worthy bass that the other three models could not match—especially at higher output levels. All of the new Klipsch X Series headphones are available now from Klipsch's website , as well as from numerous authorized retailers. From what I heard when I demoed them, they are all worthy of your serious consideration.