Sennheiser HD 620S Headphone Review

[Kervel]

Thanks @amirm, do like the new test! 500 hertz is where distortion products matter much more. The THD-freq plot visually overemphasizes distortion in deep bass, which tends to hide distortion where the hearing is most sensitive.

 

[BrooklynNick]

Open vs. closed, different construction, different seal sensitivity, different comfort.

Thank you. I somehow missed that the HD-620S is a closed back. Sennheiser's naming conventions are a bit, um, opaque.

 

[somebodyelse]

Exactly. I have been wondering what are the equivavalents of “free field” and “typical room” when headphones are measured.

https://www.headphonesty.com/2020/04/harman-target-curves-part-1/ along with parts 2 & 3 cover it fairly well.

Also, I was not precise enough. Headphones are very subjective not only because of how they sound on our ears, but also because of how uncomfortable they are (ergonomically speaking), how they look and how they feel to the touch (because unlike speakers, we touch them a lot).

Agreed. It doesn't matter how good they sound if you can't stand wearing them.

 

[Rja4000]

I have a draft of a new distortion measurement. It is a level sweep at 500 Hz showing just THD (distortion) but no noise.

That new graph is interesting.

 

[ducnsh]

I got mine Aune SR7000 today. I was looking for some good closed HP and this HD620S were on my list, but on the end I decide for Aune. From built quality & comfort standpoint Aune SR7000 are exceptional(compare to Hifimans I have). Out of the box sound is neutral, less punch in bass and not that harsh as Aryas Organic. To my surprise sounds more spacious than Sundaras. There is no too much arround them so far ,thus Im waiting on some meassurments. In tzhe meantime I will play with EQ.

Does SR7000 have good noise attenuation?

 

[Alice of Old Vincennes]

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.

598 and 599 are most comfortable headphones available. My son is requesting his third pair.

 

[Klonatans]

I tried these headphones at CanJam London and I couldn't get them wrap properly around my ears, there was an opening at the bottom of earcups that precluded hearing lower frequencies. I didn't expect that and a Sennheiser representative was surprised too, saying I was the only one with this kind of issue.

 

[Doodski]

598 and 599 are most comfortable headphones available. My son is requesting his third pair.

I too have found the 598 to be the most comfortable headphone I have ever tested or used for a extended time period.

 

[Kotrmelec]

Does SR7000 have good noise attenuation?

Yes, absolutely

 

[Spkrdctr]

Great review. I don't really care for headphones but I need them for when I watch movies and the wife has not gone to bed yet. After she goes to be I can fire up the theater system which is much more fun. Amir's tests are a huge help for people using headphones with NO EQ. Just plug and play with Amir's advice and you can get a very decent set. I always look for elevated bass on them. It seems to cover a lot of headphone sins when watching movies with all the good explosions etc. ASR is so user friendly and convenient. Anyone not using ASR to buy equipment is really groping in the dark.

 

[oratory1990]

HD620S measurement results​

I also got these in for measurements. Similar measurement setup to @amirm (GRAS anthropometric pinna and 711 coupler, forming an ITU P57 Type 3.3-compliant ear simulator)

Positional variation​

Frequency Response​

The results below show an average across multiple positions of the headphone on the measurement setup.
Also shown are 90% quantiles - meaning 90% of positions fall inside the shaded area. I measured a total of 27 positions.
You can see how for a large range of frequencies, the exact position of the headphone does not significantly affect the result, but especially for higher frequencies there is some variation. The amount of variation is within the expected range for a closed-back, over-ear headphone.

Frequency response compared to the Harman Curve. Low deviation from this curve is generally desirable


Frequency response compared to the appropriate diffuse-field curve. Low deviation from this curve is generally not required. Good-sounding headphones typically exhibit somewhat of a downwards tilt in their diffuse-field compensated frequency response.
(This diffuse field curve was measured on our actual KEMAR dummy head, it deviates slightly from the one published by GRAS)

Group Delay​

This may not be fully clear for everyone: If the magnitude frequency response changes with position of the headphone on the dummy head, then so does the phase angle frequency response, and hence by definition so does the group delay:

Nonlinearity / Sensitivity​

To test the headphone's nonlinearity, I measured at multiple different signal levels (3 dB steps across a range of 27 dB)

​

some nonlinearity can be seen here. To make it more easily visible, I divided the obtained sound pressure by the input voltage. This gives us the voltage sensitivity ("decibel per volt") of the headphone.
In a perfectly linear system, the frequency response would not change with input levels, so dividing the obtained sound pressure by the input voltage would result in perfectly overlapping graphs.
Using the same color coding as above, we can see how for high input levels the sound pressure deviates slightly from the expected value:

Roughly speaking, this headphone has about 110 dB/V voltage sensitivity.
If we plot only the deviations from perfectly linear behaviour, we get the graph below (same color coding as above):

And zoomed in on just frequencies below 1 kHz, and zooming in on the Y-scale, looking just at +/- 2 dB:

So we see that for frequencies below ~100 Hz, the sensitivity decreases (the sound pressure increases by a lesser amount than the input voltage), while at around 200 Hz the sensitivity actually increases somewhat for higher input levels. This is typical for a vented closed back headphone of this design, and not too worrisome.

If we look at just the values at 60 Hz (where the nonlinearity is highest), we can plot the SPL as a function of input level (this is called the "characteristic curve"):


This lets us observe the deviation from linear behaviour.
For comparison, the sensitivity at 1 kHz is almost perfectly linear:

An even more direct observation of the nonlinearity can be visualized by dividing the sound pressure by the input voltage (looking at the voltage sensitivity), where we can very clearly see how for high input levels the sensitivity drops for 60 Hz, but remains unchanged at 1 kHz:

Distortion​

The above observed nonlinearities in SPL must come hand in hand with an increase in distortion (the nonlinear characteristic curve is the mechanism that creates THD), and to no surprise, we do see high THD at high input levels (same color coding as above):

The apparent peaks at 4 and 7 kHz are correlated with narrowband dips in the magnitude frequency response, they don't show an actual increase in absolute distortion values.

And again, looking at the distortion just at 60 Hz tells us "how much" distortion this headphone has.


We can go to about 102 dB before crossing 3% distortion at 60 Hz (which is a very low estimate for the audibility threshold of THD at such a low frequency).
Listening at 85 dB average level would give us a headroom of at least 17 dB. That's not bad.

For comparison, the same graph for 1 kHz. No issues there.

Unit Variation​

measured 6 units so far, variation in between units is not too bad:

EQ recommendation​

HD620S - EQ to Harman 2018

Overall these are quite well done I'd say. The distortion is not too high to be an issue.

 

[Tircuit]

Why isn’t the magnitude of that 4kHz dip a concern?

 

[ObjectiveSubjectivist]

High Q, so probably not very audible?

 

[solderdude]

Indeed too narrow, position dependent and is not level dependent (which would indicate a driver issue at that frequency)

 

[oratory1990]

Why isn’t the magnitude of that 4kHz dip a concern?

It's very narrowband, like 1/6 of an octave. Not pretty, but not the biggest of concerns.

 

[Joachim Herbert]

I was really interested in these. Not so anymore because the high level of distortion.

 

[oratory1990]

I was really interested in these. Not so anymore because the high level of distortion.

How loud are you listening?

 

[Mauro]

HD620S measurement results​

I also got these in for measurements. Similar measurement setup to Amir (GRAS anthropometric pinna and 711 coupler, forming an ITU P57 Type 3.3-compliant ear simulator)

Positional variation​

Frequency Response​

The results below show an average across multiple positions of the headphone on the measurement setup.
Also shown are 90% quantiles - meaning 90% of positions fall inside the shaded area. I measured a total of 27 positions.
You can see how for a large range of frequencies, the exact position of the headphone does not significantly affect the result, but especially for higher frequencies there is some variation. The amount of variation is within the expected range for a closed-back, over-ear headphone.
View attachment 401632
Frequency response compared to the Harman Curve. Low deviation from this curve is generally desirable
View attachment 401633

Frequency response compared to the appropriate diffuse-field curve. Low deviation from this curve is generally not required. Good-sounding headphones typically exhibit somewhat of a downwards tilt in their diffuse-field compensated frequency response.
(This diffuse field curve was measured on our actual KEMAR dummy head, it deviates slightly from the one published by GRAS)

Group Delay​

This may not be fully clear for everyone: If the magnitude frequency response changes with position of the headphone on the dummy head, then so does the phase angle frequency response, and hence by definition so does the group delay:
View attachment 401619

Nonlinearity / Sensitivity​

To test the headphone's nonlinearity, I measured at multiple different signal levels (3 dB steps across a range of 27 dB)

View attachment 401629​

some nonlinearity can be seen here. To make it more easily visible, I divided the obtained sound pressure by the input voltage. This gives us the voltage sensitivity ("decibel per volt") of the headphone.
In a perfectly linear system, the frequency response would not change with input levels, so dividing the obtained sound pressure by the input voltage would result in perfectly overlapping graphs.
Using the same color coding as above, we can see how for high input levels the sound pressure deviates slightly from the expected value:
View attachment 401628
Roughly speaking, this headphone has about 110 dB/V voltage sensitivity.
If we plot only the deviations from perfectly linear behaviour, we get the graph below (same color coding as above):
View attachment 401627
And zoomed in on just frequencies below 1 kHz, and zooming in on the Y-scale, looking just at +/- 2 dB:
View attachment 401626
So we see that for frequencies below ~100 Hz, the sensitivity decreases (the sound pressure increases by a lesser amount than the input voltage), while at around 200 Hz the sensitivity actually increases somewhat for higher input levels. This is typical for a vented closed back headphone of this design, and not too worrisome.

If we look at just the values at 60 Hz (where the nonlinearity is highest), we can plot the SPL as a function of input level (this is called the "characteristic curve"):

View attachment 401624
This lets us observe the deviation from linear behaviour.
For comparison, the sensitivity at 1 kHz is almost perfectly linear:
View attachment 401622
An even more direct observation of the nonlinearity can be visualized by dividing the sound pressure by the input voltage (looking at the voltage sensitivity), where we can very clearly see how for high input levels the sensitivity drops for 60 Hz, but remains unchanged at 1 kHz:
View attachment 401625View attachment 401621

Distortion​

The above observed nonlinearities in SPL must come hand in hand with an increase in distortion (the nonlinear characteristic curve is the mechanism that creates THD), and to no surprise, we do see high THD at high input levels (same color coding as above):
View attachment 401630
The apparent peaks at 4 and 7 kHz are correlated with narrowband dips in the magnitude frequency response, they don't show an actual increase in absolute distortion values.

And again, looking at the distortion just at 60 Hz tells us "how much" distortion this headphone has.

View attachment 401623
We can go to about 102 dB before crossing 3% distortion at 60 Hz (which is a very low estimate for the audibility threshold of THD at such a low frequency).
Listening at 85 dB average level would give us a headroom of at least 17 dB. That's not bad.

For comparison, the same graph for 1 kHz. No issues there.
View attachment 401620

Unit Variation​

measured 6 units so far, variation in between units is not too bad:
View attachment 401728

EQ recommendation​

HD620S - EQ to Harman 2018

Overall these are quite well done I'd say. The distortion is not too high to be an issue.

Hey Oratory. Do you usually post contents like this somewhere? I would be pretty interested following your articles..

 

[oratory1990]

Hey Oratory. Do you usually post contents like this somewhere? I would be pretty interested following your articles..

Not really. My main job is that of an acoustic engineer, I'm not actually a reviewer

 

[Mauro]

Not really. My main job is that of an acoustic engineer, I'm not actually a reviewer

I guessed. Thanks for your time preparing these little nuggets of reviews for us!