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Old 05-10-2008, 01:35 AM
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Default Denon AH-C351 IEM Review


The Denon AH-C351 In-Ear Monitors (IEMs) are Denon's budget-level entry in their IEM product line, which include the AH-C551 and AH-C751, and supersedes the older AH-C350s.

The AH-C351 comes in either black or white, and are appointed with stylish chromed backs. It uses a “J”-style cord (right side is longer than the left side) that is approximately 18 inches long, and attaches to an included 2.5-foot extender that terminates at a 3.5-mm “L”-connector, combining to become a four-foot cable. Included with the earphones are a velvet carrying pouch and one pair each of small, medium, and large silicone earpieces. The AH-C351 has an MSRP of US$49.99, but careful shoppers can find them for around $40-43.

The AH-C351 features what Denon dubs as an Acoustic Optimizer – a slit-sized port behind the diaphragm purported to improve its acoustic characteristics by maintaining a balance of air pressure on both sides of the diaphragm.

These phones were tested on a Creative Zen Vision:M, a laptop computer containing a Realtek HD Audio chip, and a Panasonic personal CD player. No sonic enhancement modes were used, and equalization was used only to balance the phones' frequency range.


Driver size: 9mm
Impedance: 17 ohms
Sensitivity: 110dB/mW
Maximum Input Power: 20mW
Frequency Response: 20Hz – 21kHz


The AH-C351's small profile make wearing them comfortable, even when sleeping. The only annoyance with its physical attributes is the “J”-style cord, particularly irksome since the uneven length means that the left ear bears the weight of not only the entire cable, but also the weight of the interconnection between the cable and the extender. This makes accidental dislodging of the left driver from the ear during heavy activity an occasional occurrence. Despite this annoyance, these earphones are very comfortable to wear for extended periods of time. This headphone seems well-built, and achieving a good seal is fairly easy. However, I found the loud crackling noises by the diaphragms during insertion a bit disconcerting.

Despite its position as an entry-level member of Denon's IEM line, the AH-C351 sounds very good. Its sound is well-balanced for the most part; however, it rolls off considerably at the high end. The highs are still there, but they need a little tweaking of an equalizer to bring them to the level of the rest of the response range. “Burning in” the drivers for about 30-40 hours made the highs less muted and evened out the mids, which started off a little over-emphasized right out of the box.

On the other end of the sonic spectrum, the bass produced by these earphones is tight and well-controlled. These are, however, not geared toward bass-heads, as there is no “bass-boost” or any other gimmicks aimed artificially inflating the low end. Despite that, it is still possible to “feel” the presence of drums, bass guitars, and so on.

Though it cannot be expected to be equal to a decent set of cans, soundstage with the AH-C351's is better than one would expect from a set of IEMs in the sub-$50 range, and were on par with V-Moda Vibes costing twice as much. The sound expands well beyond the confines of the listener's head. I could easily distinguish different instruments from one another, and their relative position within the sound stage. Sound appears to come from in front of, around, and just above me. It is roughly equivalent to sitting in the middle of a small living room with speakers just forward of the front corners. The instruments were assembled around me, and the lead vocal was a few feet in front of me. In one Pink Floyd track, I could hear an airplane flying high above me, and children playing off to the sides behind me.

Isolation is fairly decent. Without any music playing, I can still clearly hear what's going on around me; however, when playing music at a comfortable volume level, outside noises are almost imperceptible. Even while vacuuming, I was only dimly aware of the noise being made by the vacuum cleaner (a Kirby – not exactly known for being quiet). However, a significant amount of the music does leak out through the “Acoustic Optimizer” port, which made for a very red-faced me as I was auditioning an Ultrasone test track consisting of chirping crickets in a room full of people, and noticed everyone was looking at me! When I stopped the track, took my phones out, and asked why everyone was looking at me, my youngest son looked at me and said, “chirp, chirp, chirp, chirp, chirp!” 'Nuff said!

Microphonics, the scourge of every IEM because they are inserted directly into the ear, were not too noticeable. The soft, supple material that makes up the cord's insulation does a good job of minimizing the problem, though it does not eliminate it entirely. Walking around wearing these things, the only microphonics I could clearly hear were the thumping from the cord interconnect bouncing against me. Wearing the cable underneath my shirt tamed the unwanted noises; the sound of the cable moving beneath my shirt while I'm moving around is only barely perceptible. However, if I wear the right-side cord behind my head, the sound of the cord rubbing against the back of my neck is noticeable during quiet musical passages. Overall, microphonics on the AH-C351 is far less of a problem than with the V-Moda Vibes and the Sony Fontonias.

I have one major concern about the build quality of the AH-C351. At the point where the cables enter the driver housings, Denon has chosen to a hard plastic entry point rather than a rubber or soft plastic strain relief. This may prove to be the AH-C351's Achilles Heel if the cables are routinely stressed. Using a soft material may also have greatly reduced what microphonics there were in these phones.

In Conclusion

If you are looking for a no-holds-barred set of studio-quality IEMs, then keep looking. If you're a bass-head who enjoys the muddy thumping delivered by a set of Skullcandies, then these are not for you. If, however, you're on a budget, yet don't want to give up a good, solid rendition of your favorite rock, country, jazz, instrumental, or classical recordings, then the Denon AH-C351 will not disappoint. The AH-C351s are both comfortable and pleasing to the ear. Their high sensitivity makes them plenty loud with most personal audio devices; however, their low impedance may stress cheap MP3 players. Be aware: These headphones will expose poorly-encoded or low-bitrate (less than 192kbps) MP3 files. I have re-ripped a significant amount of my library because of this.


Borrowing from dfkt's IEM spreadsheet:

Bass (Quantity): Medium
Bass (Quality): Good
Mids: Good
Treble: Medium
Soundstage: Good
Clarity: Good
Isolation: Medium
Comfort: Good
Ease of Insert: Good
Microphonics: Medium
Build Quality: Medium
Price/Value: Good

ZenChick - The one them iPod-owners warned you about!
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Last edited by ZenChick; 05-12-2008 at 11:24 PM. Reason: Pictures added
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