4th July 2024

Closed-backed headphones with an open sound? A contradiction, surely? Paul Rigby checks out this new design and sees how they compare to other Sennheiser designs

The essentials then. To begin at any rate. What we have here is a pair of closed backed, over-the-ear headphones using dynamic drivers that connect to your chosen device using a 1.8m cable terminating in a 3.5mm plug with a 6.35mm converter, if you need that. And that cable hooks into the headphones, not via a Y-shaped cable yoke but into the base of the left cup only. 

Weighing in at 326g (cable inc.), not particularly light but not that heavy either, the price is at that intriguing £299.99. £300 basically. At £300, we are talking about a design that will be noticed by audiophiles as a serious competing option on one side of the fence. And on the other side of the fence the 620S headphones will also be noted by those with lower-cost headphones as a possible upgrade. 


I’m going to address both markets in this review. Comparing the HD620S headphones with the cheaper HD569 model but also with the more expensive 650 and 660S models to see how they sit with the bigger, more expensive designs in the range.

Just to add more meat to the designs themselves, the 620S headphones use a 42mm angled transducer with a 38mm diaphragm held in place by steel-reinforced headband sliders and artificial leather cup pads. 


Impedance is rated at 150 Ohms which is the same, for example, as the more expensive 660S designs but a lot higher than the much cheaper HD569 headphones (23 Ohms) so you’re possibly looking at audiophile-quality kit to drive the 620S ‘phones to get the best from them. That is, something serious in terms of amplification either in terms of desktop or mobile sources. 


Saying that, in terms of driving them, getting them going at all? The sensitivity is rated at 110db, higher than the 660S headphones (96db) or even the Sendy Aiva designs that I reviewed recently (103db) so the 620S designs shouldn’t be too hard to drive. 

So, based purely on figures alone, on a broad, broad level you might say that the 620S headphones are aimed at audiophile desktop users or those who like to run higher-end mobile digital audio players. In addition, again based purely observation and specs, the closed-backed design should produce enhanced bass so I’m guess that rock fans will be served well via the 620S headphones. Supposition right now? Absolutely. Sure. That’s just my rough guess until we get to the sound quality tests. 


Oh and the cable itself is removable. If you can grab a higher-quality cable later on as an upgrade, do so. In my experience, all Sennheiser headphones benefit from cable upgrades. Check out both Atlas and Chord as first stops for those. One thing, if/when removing, don’t just yank this cable. It is locked in with a twisting lock. So twist anti-clocksise and then firmly pull.  


I have a big head – you might have noticed – which means that the strongly sprung headband on the 620S headphones press clamp on my skull with some force. Its not uncomfortable, especially over a long listening session, I got used to it, but I would have preferred less pressure. Saying that, my wife has a small head and she found the fit to be perfectly comfortable. She had no issues or complaints at all because her head didn’t force the headband outwards and never added pressure because of that. 


I have to say the headband never hurt my head while my ears were easily surrounded and covered. The pads never pinch or trapped my ears. There was always lots of room.


So how do they sound then?


To begin I decided to go mobile. Just to see if a good quality DAP can drive these headphones. I connected the HD620S headphones to my iBasso DX260 digital audio player and played one of my favourite review tracks, the Doves’ Universal Want from the album of the same name at 24bit/96kHz, plugging the headphones directly into the 3.5mm socket. 


The grand piano of at the beginning of this track sat in a slightly larger space with more air travelling around it from the 660S headphones (£429). The piano also sounded slightly fuller with greater resoanance. Although the 660S was an improvement over the 620S, that improvement was not by leaps and bounds. The 620S did give a surprisingly good account of itself in this area. Of course, the 660S offered even better performance in balanced mode but in single-ended mode? The 620S was decidedly competitive. It raised my eyebrows, certainly. 


Bass from the 660S was better balanced across the soundstage but the 620S offered more impact, more weight and punch with the bass guitar being a star player on the 620S instead of merging into the mix via the 660S.

VS HD650

The 650s (£320) offer a wider soundstage, a broad, open prairie of a soundstage in fact with air and space the runs off into the distance while the wind blows through your hair but that means the 620S scores in terms of focus and precision instead of the 650’s large sonic canvas.


The mids were upfront, from the 620S, piano was more direct yet the overall delivery remained balanced and broadly neutral. Again, the 620S headphones scored in bass terms with punch and impact.  

VS HD569

Via the cheaper HD569 headphones (£150) music needed a much reduced gain, for a start. The 569s also offered a leaner, thinner midrange and treble, less delicacy, less fragility, stripped and offering a more essential suite of information.


The 620S headphones on the other hand sounded richer, complex, detailed and sonically more interesting. Bass was relatively rolled off via the 569s. The 620S offered a better grip, giving you more guts and emotion in bass terms. 


All of the Sennhesier headphones compared to thus far were open backed but the Meze 99s are not only closed backed but also managed to provide that open-backed sonic trick promised by the HD620S designs. Comparing the two while using my DAP? I’ve always liked the 99s and have given them a good rating on my website but I was pretty shocked how much more open and spacious the 620S designs sounded.


More than that, the bass on the 99s sounded very wool.ly and uncontrolled when compared to the 620S designs. The Sennheiser’s had a great focus, releasing more detail and a midrange insight that was a relief to hear when compared to the 99s. The 99s sounded rather overblown in comparison. 


I wanted to finish the sound tests by pushing lots of power through the 620S headphones with my valve-driven, high-end, home-based headphone amplifier. Just to see if its inherent personality would change in any way. I kept the 99s in place and played a CD via my Leema Elements CD player plus Topping D90LE DAC. The music in question? Get Me to the Church on Time via Rosemary Clooney and the Bluebird release, Rosie Solves the Swingin’ Riddle! 


The 99s sounded much better via the larger headphone amplifier, better balanced, more cohesive midrange, delicacy in the treble and a well rounded bass but the 620S offered a broader, more expansive soundstage, reach in the midrange with an impressive upper midrange performance, fragility around the treble and with a well-behaved, rather civilised bass performance.


Even so, there was just a touch of power behind the drums, the tubular bells that appeared throughout the song and the upright bass. Not enough to lose the music’s own balance but enough to provide a hint of strength, solidity and authority. 


I really wasn’t prepared for this. That the HD620S headphones would perform so well in a mobile and a shelf-based lounge system and over contrasting musical genres. That they would dominate the competition priced at a similar or lesser price point and also worry headphone designs at a higher price point. 

The overall sound quality was just so impressive and yes, Sennhesier is correct, for a closed-backed system they do blend power but also an open midrange and treble. It’s quite a feat, I have to say as is that price point. The HD620s are great all rounders. They offer great sound at a great price. What more do you need?


Price: £299.99

Website: https://www.sennheiser-hearing.com

GOOD: open midrange, focused bass, broad soundstage, balanced output

BAD: Clamping headband fit