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The Sennheiser CX 300's construction quality exceeds that of most earbuds, and the soft and flexible Y cable is a good length at 49 inches. The CX 300--available in black or silver finishes--doesn't come with the usual accessories, such as a travel pouch or an airline plug-in adapter that you get with the higher-priced models.
Like all the in-ear phones we've tested, the Sennheiser CX 300 won't produce any bass at all unless its soft silicon ear tips form an airtight seal inside your ear canals. That might require a little experimentation, having to switch between the CX 300's three sizes of ear tips. We settled on the largest ones, but the fit was never as secure as we've achieved with other in-ear phones, and a slight tug on the CX 300's cables would dislodge the earpiece from the ear. To evaluate the CX 300's noise isolation, we took a trip on the 4 train on New York City's subway, where the CX 300 proved itself to be an effective noise blocker, almost on a par with the higher-priced in-ear models. The isolation won't make them a safe choice for joggers, plus we heard a significant amount of rustling from the CX 300's wires rubbing against our clothing whenever we moved about.
We directly compared the Sennheiser CX 300 to Etymotic's ER-6i ($150) in-ear headphones and came away impressed with the little Sennheisers. First thing, the CX 300's bass went as deep as the ER-6i's, but the vocals and guitars on Ryan Adams's mostly acoustic new CD, 29, were noticeably less "canned" and hollow-sounding on the ER-6i. The CX 300 rocked out with a live version of the Rolling Stones's "Start Me Up," and the band's power and grit were all there; the headphones definitely played loud enough when paired with our iPod.
Sennheiser's off to a good start, but the CX 300's sound is nowhere as clear and open as that of our favorite Shure and Etymotic models.