Sennheiser HD 620S Headphone Review

[amirm]

This is a review, detailed measurements, listening tests and Equalization of Sennheiser HD 620S closed back headphone. It was kindly drop shipped by a member and costs US $300.

The headphone feels robust and "tight." It clamps rather heavily on my head causing mild discomfort. So be sure to have return privileges if you buy it in case it causes the same issue for you. Maybe it breaks in over time.

Despite the large cups, I was surprised at the level of variation I was getting in attempting to measure it on my GRAS 45CA fixture. I eventually optimized it but there could be some variations left in there. I was happy to see company release measurements using the same fixture, albeit, very smoothed:

As you see, the bass is substantially lifted from HD600 series which is very welcome. There is some loss of smoothness in response though. Let's see if our testing shows the same.

Sennheiser HD620S Measurements
As usual we start with our frequency response measurement:

Looks like we have very good correlation with company measurements. Our higher resolution graph though shows a deep cancellation at 4000 Hz. We will see signs of this appearing in other tests. As is though, overall compliance is very good -- something we have not experienced in this price range.

Relative graph as a result, doesn't show much work to be done with equalization:

Distortion was high in bass which is something we have seen in Sennheiser headphones before:

I have a draft of a new distortion measurement. It is a level sweep at 500 Hz showing just THD (distortion) but no noise. Why 500 Hz? Research shows that harmonic distortions of 500 Hz have the highest chances of reaching the most sensitive part of our hearing and hence being above threshold of hearing. Here is how the HD 620S performs relative to Dan Clark E3:

We see that additional non-linearity factors enters the scene around 95 dBSPL which then scales all the up to massive clipping either by the headphone, the amp, or both. That limit is quite high though at 127 dBSPL. In contrast, the E3 maintains a lower distortion throughout but due to its lower sensitivity, runs into a wall at 123 dBSPL.

Group delay shows same issue at 4000 Hz:

And 10 kHz.

Impedance is nominally 159 Ohm but shoots up higher at lower frequencies:

So don't go taking chances with headphone amps that have non-zero output impedance.

Sensitivity is slightly below average:

Sennheiser HD 620S Listening Tests
The immediate reaction was that of neutrality although not all the way there. Spatial aspects were muted. Despite that, every reference track I threw at the headphone sounded very good to excellent. Seeing how I have curated this track list on a reference speaker and headphone, this bodes very well for accuracy of the headphone sound. Still, I wanted to examine the effect of correcting the upper bass issues with EQ:

I had to reduce the amount of attenuation at 118 Hz as a sound got a bit too bright. Where I have the filters provided a sound with a bit more clarity in upper registers (due to lower distortion?) with the bass sounding lighter and less "wooly." I can't guarantee that everyone would prefer it though. It is a subtle change trading more clarity against more bass.

I was surprised that sub-bass impact was not there until I really cranked up levels -- something I do with HD600 series but didn't think I needed to do here.

Conclusions
I think the "big news" is that we have a reasonably priced headphone that comes close to delivering neutral sound. Until now, we had no options in this price range. Some flaws do exist though in the form of a few kinks in frequency response. All but the trough at 4 kHz can be fixed with EQ. The 4 kHz issue may be responsible for not so great spatial qualities. The build is not for me with that tight clamping and firm pads.

I am going to put the Sennheiser HD 620S on my recommended list even though I would not buy it myself due to fitment issues.

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As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

 

[amirm]

Manufacturer Specifications:

 

[markanini]

I appreciate the effort to make a well-tuned closed back that doesn't cost an arm and a leg. I'd give HD620S a demo based on Amirs review. Still AKG K371 exists for less money with pretty good spatial qualities for a closed back, in my subjective opinion.

 

[restorer-john]

How about describing the specifics of the 500Hz (draft) test you are using? Particularly sweep duration (heat) as that will be a major factor. Will the test be consistent for every headphone?

And why use a driver amplifier that potentially clips before the limits of the headphone are reached? Just use a high performance medium power amplifier with THD at least x10 better than the headphones.

But, do you intend to push the drivers to destruction and if not, what is the limit you are going for? Will it be power based or voltage based? At what point will you stop?

 

[phoenixdogfan]

Great review, Amir. The thing happening at 4000 hz almost looks like some kind of deliberate notch filter. Have to wonder if there is some sort of distortion or frame resonance that would be elicited if that particular frequency were not so attenuated.

 

[WalterW]

For sure not stellar measurements, but considering the price and lack of decent competitors for closed-backs below $500 a quite decent offering.

 

[amirm]

How about describing the specifics of the 500Hz (draft) test you are using? Particularly sweep duration (heat) as that will be a major factor. Will the test be consistent for every headphone?

This is not a thermal stress test. It is simply a level sweep and recording pure THD. Heat is not a factor at all.

 

[amirm]

And why use a driver amplifier that potentially clips before the limits of the headphone are reached? Just use a high performance medium power amplifier with THD at least x10 better than the headphones.

Topping A90 is a very powerful headphone amplifier with vanishingly low distortion and noise (likely 100+ times less distortion than headphone). Most people have amps that are less powerful. As such, what it produces is far more than good enough for this assessment. Using more powerful amp may indeed damage the headphone under test.

 

[amirm]

But, do you intend to push the drivers to destruction and if not, what is the limit you are going for? Will it be power based or voltage based? At what point will you stop?

Not at all. The interest here was to show the knee in the curve where distortion starts to climb faster (no longer flat line). What it shows as the limit is there as a bonus.

 

[zepplock]

I appreciate the effort to make a well-tuned closed back that doesn't cost an arm and a leg. I'd give HD620S a demo based on Amirs review. Still AKG K371 exists for less money with pretty good spatial qualities for a closed back, in my subjective opinion.

AKG K371 have very small ear cups. Majority of people I know who tried them did not find them to be a good fit. It's nice to have alternatives.

 

[Soria Moria]

From a regular consumer standpoint I'd definitely pick the equally priced Audeze Maxwell over this but this is still a good product!

 

[totti1965]

I think, that for headphone reviews it would be increadible helpful to ALSO check the items with known parametric correction curves (5 to 10 band).
Implementation would be easy: https://community.roonlabs.com/t/headphone-settings-for-parametric-and-convolution-equalizer/63730.

The other possibility would be using the rooextend item of Dr. Charly Oehlrich (forum member, co-inventor of the audiovolver), which has for additional 50 dollars (livetime purchase) or so correction curves for 5.000 Headphones included, with just one click.

rooHead - Incredible Headphone Sound

Dear Ronners, It’s my pleasure to finally complete rooHead after a long period of announcing it. rooHead provides FIR equalizers for your headphones, bringing the headphone sound to the level of a calibrated system with speakers in a reference listening room. For more information please also...

community.roonlabs.com

rooExtend - Home

This rooExtend DIY page offers useful plug and play extensions for the music server Roon based on a Raspberry PI. They complement Roon in the areas of audio input, control and playback.

rooextend.com

I can just speak for myself: I am using a Massdrop Sennheiser HD 58x jubilee, which is very, very good for $150.
But: with correction to the Harman target (in the Bass region I just add 7dB instead of 10 dB) it was a completely Jawdropping Experience. The sound is now a real $ 5,000 Killer!!!

So I think headphone listening without parametric equalizing is pretty much useless: To much potential is lost / wasted.

 

[Ron Texas]

Thank you @amirm for another great review. I'm surprised at how close these cans are to the ideal curve. Most open back headphones need significant bass boost. It's said that it is difficult to design closed back headphones due to having to manage the back wave. However, closed back headphones work better in noisy environments or in bed when you don't want to annoy your wife/partner.

 

[Adamant11746]

As someone who has owned these for about 2/3 of a month, I can confirm that the clamp does indeed decrease significantly with break-in. When I first got them it was very tight, and it gradually loosened until they're now pretty comfortable. The distortion is disappointing, but at the levels I listen at (quiet compared to nearly everyone else I know) it won't be a problem. The big draw for me is that they're a decent set of closed headphones that is A) relatively affordable, and B) has spacious pads (I need at least 70mm of height, somewhere between 45-50mm of width, and a lot of depth as well). Common recommendations like the AKG K371 and Fiio FT1 just don't fit my fairly large and very sensitive ears.

 

[Bob from Florida]

The pair under review is the second pair I have ordered. I have been listening to the first pair since the middle of August. Liked them enough to order the second pair during Amazon Prime Days early October which were drop shipped for the review. I have a second listening station set up for them. I also noticed the initial tight fit, but extending the sides a bit more than needed plus use seems to have made them comfortable.
I am using them with no EQ and am completely satisfied.

Thanks @amirm for testing them!

 

[Maiky76]

Here are some thoughts about the EQ.
Please report your findings, positive or negative!

Notes about the EQ design:

• The average L/R is used to calculate the score.
• The resolution is 12 points per octave interpolated from the raw data (provided by @amirm)
• A Genetic Algorithm is used to optimize the EQ.
• The EQ Score is designed to MAXIMIZE the Score WHILE fitting the Harman target curve (and other constrains) with a fixed complexity.
  This will avoid weird results if one only optimizes for the Score, start your journey here or there.
  There is a presentation by S. Olive here.
  It will probably flatten the Error regression doing so, the tonal balance should be therefore more neutral.
• The EQs are starting point and may require tuning (certainly at LF and maybe at HF).
• The range around and above 10kHz is usually not EQed unless smooth enough to do so.
• I am using PEQ (PK) as from my experience the definition is more consistent across different DSP/platform implementations than shelves.
• With some HP/amp combo, the boosts and preamp gain (loss of Dynamic range) need to be carefully considered to avoid issues with, amongst other things, too low a Max SPL or damaging your device. You have beed warned.
• Not all units of the same product are made equal. The EQ is based on the measurements of a single unit. YMMV with regard to the very unit you are trying this EQ on.
• I sometimes use variations of the Harman curve for some reasons. See rational here and here
• NOTE: the score then calculated is not comparable to the scores derived from the default Harman target curve if not otherwise noted.

OK L/R match.

I have generated one EQ, the APO config file is attached.
Probably over the top...

Score no EQ: 72.3
Score Amirm: 75.1
Score with EQ: 92.5

Sennheiser HD620S APO EQ Flat@HF 96000Hz
October242024-112452

Preamp: -3.10 dB

Filter 1: ON PK Fc 120.4 Hz Gain -5.62 dB Q 1.88
Filter 2: ON PK Fc 224.1 Hz Gain 2.61 dB Q 3.37
Filter 3: ON PK Fc 743.8 Hz Gain -4.69 dB Q 1.32
Filter 4: ON PK Fc 816.7 Hz Gain 5.10 dB Q 3.41
Filter 5: ON PK Fc 2541.4 Hz Gain -1.89 dB Q 2.94
Filter 6: ON PK Fc 7665.1 Hz Gain -6.13 dB Q 5.00
Filter 7: ON PK Fc 5295.1 Hz Gain -5.15 dB Q 4.66
Filter 8: ON PK Fc 8221.3 Hz Gain 8.43 dB Q 1.30
Filter 9: ON PK Fc 14661.1 Hz Gain -6.70 dB Q 0.98

 

[NoteMakoti]

If these are anything like the 598s I had in college, the tightness of the fit eases up with time. I put mine around some textbooks before bed to break the fit in and it works wonders.

 

[restorer-john]

@amirm

You replied (thanks) three times to my questions and answered none of them. I'll ask them again, hopefully more clearly so you can answer them?

1) Specifics of the test? How long does the test run for and is it consistent in length every time?

2) Why would you use an amplifier that clips before the headphones are driven to their limits, to test distortion at high levels of the actual headphones? That makes no sense does it? As you said, you don't know what clipped and what didn't. The topping amplifier appears to be the culprit here with both pairs of headphones. So what have we learned? Not a lot other than you need a more powerful source if the limits of the drive amplifier are reached first.

3) What is the limit you are going for? At what point will you terminate the test?

I get it. It's a "draft" test, but it's half baked.

 

[WOLFAGRAM]

Hello Folks.

I am going to put the Sennheiser HD 620S on my recommended list even though I would not buy it myself due to fitment issues.

Headphones are indeed one of the most subjective (if not the most subjective) pieces of audio gear.

I would never buy an uncomfortable headphones, no matter how amazing the rest is.

I am also not a fan of, what seems to me, a „plasticky“, and somewhat „90s hi-fi“ look and feel of most Senheisers.


Cheers.

 

[solderdude]

I am going to put the Sennheiser HD 620S on my recommended list even though I would not buy it myself due to fitment issues.

Yep, the fitment is indeed a bit problematic and I reduced the clamping force on mine with some careful bending of the extenders.
The higher clamping force does ensure better seal which is essential for good bass.

[from dark to lighter color red]
Perfect seal (lightly pressed onto the fixture to remove the wrinkles in the pads)
pads not having a perfect seal due to wrinkles in the pads (corresponds with Amir's measurements)
seal broken with a thick arm pair of glasses resting against the skin
seal broken with thin armed glasses not resting against the skin
seal broken with thick armed glasses not resting against the skin.

The driver is rated at 0.2W (continuous without any damage), the 127dB SPL required 0.5W (8.7V). It seems the driver can handle this just fine.

Here's the effect of output resistance to the frequency response:

0.2Ω
10Ω
32Ω
120Ω

resonances in time:

The 900Hz and 4kHz are the most obvious ones and as such also visible in your GD plot.