Denon AH-C551 in-ear monitor headphone review

Denon is one of the most prestigious hi-fi brand. Their range of full-size headphones has often received plenty of accolades from audiophiles. The Denon AH-C551 is one of their first forays into the world of in-ear monitor portable headphones. At around £50 per pair, the C551 is designed to compete with the headphones like the Sennheiser's CX 95 (now discontinued and replaced by the CX 550) and Klipsch Custom 2.

Frequency response: 15–25,000 Hz
Sensitivity: 104 dB SPL/mW (1mW)
Nominal impedance: 16 ohms
Attenuation: up to 26 dB (95%)
Transducer: Dynamic driver

The C551 is similar to their high-end IEM, the AH-C751. While not as big, the C551 retains a similar bullet shape profile. Despite its look I was surprised by how light the headphones are. Like the CX 95, the Denon comes with an extension cable that terminates at a gold plated 3.5mm L-plug. The cords are well made and isn't as sensitive to microphonics as the one found on the CX 95, and is also less prone to getting itself tangled. Despite the good impression I found the Y-split and stress relief to be disappointingly fragile looking.



The C551's housing is made of machined aluminium, a nice change and premium compared to the sea of plastics favoured by Shure, Ultimate Ears and Sony. They are wonderfully engineered and looks prettier than the CX 95. In each of the earpiece lies a 11mm neodymium dynamic transducer. The large driver size meant that the canal body is a bit larger than the CX 95. This results in less isolation as I was unable to push the drive unit into my small ear canals. Despite that I had no problem getting a good fit and seal with the supplied silicone tips (which are interchangeable with Sony and Sennheiser headphones).

At the back of each earpiece are these holes that Denon calls Acoustic Optimizer, more commonly known by simple people as bass ports or air vents. These ports are said to provide the sound characteristic of the headphone by "adjusting the sound pressure balance in the front of and behind the diaphragm", whatever that means. Ergonomically they can be worn with the cords hanging down or over the ear style (for less microphonics). The Denons are not the most comfortable in-ear headphones I have worn, but they are also not the worse. Unfortunately they also leak plenty of sound, no thanks to the large Acoustic Optimizer vents.



Enough chatter, what about sound quality? Well they have a nice warm sound signature. Compared to my CX 95, I have to admit I much prefer the CX 95 (to be fair the CX 95 does have hundred of hours of burn-in/listening time to it compared to about 60 hours on the C551). The bass on the C551 for example hasn't got the same impact, though I did find the bass performance to be tighter. Regardless the bass performance is more than adequate for bass heads and fans of electronic genre.

The soundstage isn't as airy or wide as the CX 95, though that isn't saying much as all IEMs suffer from the same problem when it comes to imaging (except perhaps the IE 8). The sound quality overall is good but is a little harsh on the treble and the mids are a bit grainy. Details and definitions are also comparatively weaker to the CX 95. Overall the sound signature is dark with good mids but recessed highs.

Despite the C551 being only second IEM, Denon appears to have delivered a quality product. The problem here is that while the C551 is a perfectly fine quality product, there are better products out there (at least in my opinion) within the same price range. Sennheiser's CX 95 does seem to better them at almost every level, at least when it comes to sound quality and bass impact and mid-range. The Klipsch Custom 2 on the other hand offers delightfully lush mids with good highs and adequate bass response for a reasonable price.

The C551 is available for around £50 from Amazon UK.