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(Pocket-lint) - Denon is on a mission with its new C-series of headphones, a mission to bring exceptional sound quality to the masses at affordable prices. We've seen the company's flagship C821R in-ear headphones, which use a Dual Air Compression driver to deliver a big and powerful sound.

On test here is the next pair down, the C621R, which have their own tricks and features to give you a sound that's a huge step up from the headphones you get bundled with your phone or portable music player.

At £79 they're a lot more affordable than their flagship sibling, but has the drop in price sacrificed sound quality?

Denon AH-C621R review: Design

  • Weigh just 5g
  • 11.5mm drivers

The first thing that struck us when we opened the C621s was just how premium they look and feel. We expected it from the £169 C821s, but to be given a similar luxurious build quality and packaging for £90 less is great.

Denon supplies the in-ears with a pair of Comply TX-400 foam ear tips, four pairs of silicone ear tips, and a silicone carry case that requires you to wind the cable around it.

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The aluminium housings are incredibly light, and they weigh a grand total of just five grams. We wore our pair for nearly seven hours straight and didn't once feel as they were getting uncomfortable. Quite the contrary, for most of our listening time we didn't even feel they were in our ears.

The ear tips are angled inward, towards the ear canal, to ensure you get to hear every single soundwave coming out of them. The addition of the foam ear tips makes sure they stay put, as well as providing a tight seal to help block out the majority of outside noises.

Inside the earpieces are custom 11.5mm drivers and there are Acoustic Optimiser ports to the front and rear which are there to normalise the air pressure around the drivers and the leave the sound going to your ears distortion-free.

Denon AH-C621R review: Features

  • Companion app available for iOS and Android
  • Three-button in-line mic with quick access to Siri

As with the C821 in-ears, the C621s can be used with the Denon Audio companion app for iOS and Android, at the cost of £1.99. You can use the app as a music player for any stored files you have on your phone, but not for any music downloaded from streaming services such as Apple Music or Spotify. This is strange, because the app asks to access your Apple Music collection on startup, leading you to believe it can play back songs from the cloud.

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The app does let you adjust equaliser settings for each track. You can choose from a range of preset options set by Denon, or adjust the curve however you want it and then save your custom settings.

We said it with the C821s and we'll say it again here: we feel having to pay an additional fee for the app is a bit annoying. Sure, it's not a huge amount of money, but if you're investing a considerable amount of money in Denon's headphones, the company should reward you with a free app.

The C621s also have a three-button in-line mic on the cable. The centre button sits in a trough compared to the up and down volume buttons, which makes it easier to distinguish.

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A long press of the centre button will also activate Siri. The same can't be said of Android voice assistants such as Google Assistant. This pair of Denon in-ears is clearly aimed at the iPhone and iPad users out there.

Denon AH-C621R review: Sound quality

Given they haven't got the same drivers as their bigger brother, we knew we weren't going to get as powerful a sound from the C621s. This was confirmed on our very first listen. However, that's not to say we didn't like what we heard, as the C621s retain the company's balanced and detailed sound signature - they just lack that real oomph.

But then that isn't what this pair of in-ears is designed to do. There's still plenty of bass power on offer, and in some instances we actually appreciated not having such an in-your-face sound profile.

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The C621s exhibit impeccable timing and fantastic energy. We listened to some upbeat dance tracks and they bounced along with excitement, making the whole listening experience fun.

Best USB-C headphones for Android phones 2021

Feed these in-ears some laid back acoustic Clapton and once again they present well, with great timing and superb placement. Vocals are at the front where they belong, guitars in the middle, with the drums heading up the rear in support.


The Denon AH-C621Rs are a seriously impressive pair of in-ear headphones for the price.

They offer a significant upgrade over the headphones you're likely to get with your smartphone, not only in terms of sound quality, but build quality too. Their secure fit and comfort levels are some of the best we've come across, thanks to their lightweight design.

Apple users will also love the instant access to Siri, and while Android users can't take advantage of voice-assistants, it's still possible to take advantage of the in-line microphone for hands-free calls and controlling music playback.

Our only real gripe is a tiny one: having to pay two quid for the companion app to open adjustable EQ settings. Still, add that to the £79 price point and the C621R are a bargain, all things considered.

With heaps of in-ear headphones costing £100 or far more, the Denon AH-C621R prove you can get terrific sound on a budget. Sure, they're not wireless and don't have any super fancy features - but for listeners happy to accept the wires, these are an exceptional upgrade over the in-ears included in your phone's box.

Alternatives to consider

Pocket-lintDenon C621r alternatives image 2

Denon AH-C821

If you can afford the extra money, the AH-C821 in-ears will give you a bigger, more powerful sound. They're just as comfortable as the C621s, although are a little heavier, so you may notice them in your ears a bit more. It's a small trade off for what is an exceptional sound. 

Read the full article: Denon AH-C821 review

Pocket-lintDenon C621r Alternatives image 1

Rockjaw Resonate

The Rockjaw Resonate offer something slightly different to most pairs of in-ear headphones: customisable tuning filters. You get three different filters in the box, each offering a different sound profile, so you can switch them out to suit your personal tastes. They cost a little more than the Denons on review here, but the filters work well enough to make them a consideration.

Read the full article: Rockjaw Resonate review

Writing by Max Langridge. Originally published on 17 June 2017.