The Denon AH-C551 is the little brother of Denon’s sweet-sounding AH-C700 (reviewed in our first “Killer Earbud” survey). Like the AH-C700s (which have now been updated to become the AH-C751s), the AH-C551s feature machined aluminum housings that incorporate what Denon terms an “Acoustic Optimizer” port said to improve sound quality by “adjusting the sound pressure balance in front of and behind the diaphragm.”
The AH-C700 won our favor by being a well-rounded performer that offered tons of sonic refinement per dollar, and in many ways the AH-C551 follows that same pattern. Here as in the more expensive model you’ll find effortless midrange clarity, plenty of sonic nuance, and clean, clear delicate highs. Two dif-ferences we noted, however, are that the AH-C551s are—relative to AH-C700s and to other earbuds in their class—ever so slightly bass-shy and also relatively low in sensitivity (meaning you’ll need to feed them more power to achieve equivalent volume levels).
The AH-C551s are at their best when reproducing well-recorded material that is full of midrange nuance and textural details. A great example would be Holly Cole’s rendition of Tom Wait’s “Take Me Home” from Temptation [Metro Blue]. The song is propelled by richly textured acoustic bass, expressive and yet restrained piano lines, and especially by the subtle inflections in Cole’s voice, which the Denons handle beautifully. The AH-C551s let you hear the emotion that develops as Cole delivers this line: “Take me home you silly boy/I’m still in love … with you.” The way Cole’s voice trails off between “in love” and “with you” brings the whole song to life; it’s the sort of small but crucial detail on which the Denon thrives.
The AH-C551s are very light and compact, and I was able to achieve a good seal using the standard eartips without too much difficulty. For the AH-C551s, Denon has introduced a softer rubber material for its eartips, which generally improves comfort but also makes the eartips somewhat more prone to “collapsing” when the earbud cables get jiggled. For this reason, I sometimes had to re-insert or re-seat the Denons in my ears in to ensure a good seal.