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Published: Aug-17-2018, updated: Aug-7-2021

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NO SMOOTHING is applied to the shown plots. Most measurement sites have some smoothing applied which ‘irons flat’ sharp peaks and ‘wiggles’. I do not use smoothing because some info about sound quality is lost when plots are smoothed.

Aside from a small correction of the microphone itself also some correction in the lowest frequencies is applied to the plots to compensate for the perceived loss of bass when using headphones. This is described HERE in more detail.
A ‘horizontal‘ frequency response curve on the shown frequency response plots on this website thus indicates a perceived ‘flat’ tonal signature.

ALL measurements are made with a good SEAL on a flatbed measurement rig.
The shape of your head, bone structure, pad size, pad ‘softness,  (compliance), hair or no hair and or wearing glasses may (drastically) change the frequency response of some headphones, so… your personal experience may differ substantially from these plots.

Frequency response (tonal balance) is the most sound-determining aspect of headphones. A horizontal line shows audible neutral response in the plots on this website. Deviations in different severities at different frequency bands have an effect on the sound character.
The bigger the deviation the stronger the effect.

Below an aid to help determining the sound character of headphones with relation to the frequency response.


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Sennheiser HD820

HD820The Sennheiser HD820 is a closed over-ear dynamic headphone. It is marketed next to the HD800S and can be considered the closed version of the HD800S.
The price of the HD820 is a lot higher though, around € 2000.- (medio 2021)

Comfort of the HD820 is as good as that of the HD800S, thus very high.
The weight is low which is a good thing when wearing it for longer periods.
Clamping force is very low and because the pads are very large in diameter and have a larger surface contact than that of the HD800(S) it feels slightly different on the head.
The different pads which are thicker (higher) and wider is essential for a very good reason namely: seal.
The pads should not be interchanged between these models.
There is a chance, however, that depending on the shape/ size of the owners head seal may be broken resulting in less (sub)bass.

The connector is a LEMO-type 2-pin connector manufactured by ODU GmbH. This isn’t the cheapest connector around so when looking for a replacement cable be prepared to fork out quite a lot of cash.
There are plenty of (expensive) options when you want to use another cable. The one supplied with it was very low in microphonics and supple. Definitely an improvement over the stiff cable supplied with the HD800.

The HD820 can play quite loud and remains distortion free. The sound does not ‘fall apart’ at high listening levels… provided an amplifier is used that can supply a lot of voltage.


Type: Over ear, closed
Isolation: decent
Usage: Home
Driver type: dynamic, ring driver
Pads: hybrid, pleather outside and microfiber cloth on the inside and skin.
Foldable: No
Headphone cup connector: proprietary ODU GmbH 2 pin connectors.
Cable entry: dual sided
Cable: 3m, 6.3mm TRS +  balanced 4-pin XLR cable + Pentaconn 4mm 5 pin connector.
Driver size: 56mm ring radiator
Max. power rating: 0.5W
Max. cont. input voltage: 12V rms
Max. drawn current: 40mA
Max. S.P.L.: 125 dB
Impedance: 300 Ω
Efficiency: 99dB/1mW  (103dB/1V)
Weight: 360 g.
Clamping force: very low, 3.4N.
Accessories: cable: ¼” (6.35 mm) stereo jack plug, unbalanced 4.4 mm Pentaconn stereo jack plug, balanced XLR-4 connector, balanced.
USB flash drive with instruction manual (as PDF file) and individually diffuse-field frequency response curve, instruction manual, storage box, microfiber cloth

Sound description:

Bass is well extended. Much more so than the open versions HD800(S). Bass is also boosted but not in the ‘Harman’ kind of way. A tout bass was something that I felt was missing with the HD800(S).
Does this mean perfect bass ? Sadly not.  The bass, though in level a lot better than the open versions, can be somewhat muddy and is not as well defined (correct tonality) compared to the open versions.
Bass does not ‘bleed’ into the mids which is a good thing.
Mids are ‘open’ and there is excellent ‘clarity/presence’. Male voices sound slightly ‘off’ in timbre and are a bit less ‘weighty’ than they should be.
The treble reproduction is MUCH improved over the open versions. No more sharpness, sibilance. The treble is still highly detailed and not ‘over etched’ as in the open versions.

The HD820 improves on the ‘weak points’ of the HD800(s) for me. More bass, better sub-bass extension and near perfect highs.
This comes with a price and leaves room for the development of a future HD850 ?
The price one pays here is some muddy-ness in the bass department and not so perfect bass tonality/integration with the mids.

When I would refuse to use EQ and would not look at price tags I could choose the HD820 over the HD800(S) and have decent isolation as well.


Below the frequency response of the HD820 (Left, Right)

Freq response

Channel matching is good, as should be expected in this price range.

While the sub-bass is present and extends to 10Hz the bass around 150Hz is boosted 6dB and followed  by a steep 15 dB drop. The boost around 150Hz makes the bass more punchy but also a bit muddy. The dip at 300Hz makes the bass sound a bit ‘hollow’ and somewhat ‘dis-attached’. On the upside of things the ‘dip’ ensures the bass does not ‘bleed’ into the mids. I suspect the dip is there for this purpose.

From 400Hz to 20kHz the response is excellent. The small ‘drop’ between 2kHz and 7kHz may not be there in reality. This is because the drivers are angled and make use of concha gain. The perceived tonal balance between 400Hz and 20kHz thus is flatter than the measurements (without a Pinna) suggest. Mids indeed sound great with the proper amount of clarity/presence. Not too forward and certainly not laid-back.

Below the differences between the HD820, HD800 and HD800S. (Right channel only)HD800 vs 800S vs 820

The differences between the HD800(S) and HD820 are quite obvious. One could easily conclude the HD820 sound nothing like the HD800(S). There are certain aspects though that are clearly family traits. The open and spacious sound. The distortion free mids and the ability to play very loud yet always sound clean and accurate are traits that are still there.

Fortunately the ‘elevated treble’ is gone in the HD820.
One can see how the ‘resonator’ of the HD800S lowered the 6kHz peak by a fair amount but is still there a bit. The 10kHz peak is still there in both open versions.
When looking at the HD820 we can see a MASSIVE reduction (-15dB) opposite the HD800S and also the 10kHz peak is lowered considerably.
One would perhaps think that this would make the HD820 less ‘detailed’ but this is not the case. It is very detailed and realistic. In comparison the HD800(S) sound ‘hyper detailed’ and ‘sharp’.

Then of course there is the bass and it’s integration with the mids.
Albeit a bit lean in the bass HD800(S) the tonal accuracy of bass instruments and male voices is formidable in these headphones. As the HD800(S) reacts very well to EQ it is quite easy to make the bass response extend well and get rid of the ‘lean’ bass.
The HD820 has a quite different bass. You can hear deep rumbles without any EQ. Bass is present… a tiny bit too much for my taste. Bass quality is not as good though. A raise in the bass is welcome but not in the 150Hz area. That should remain below 100Hz.
The peak there creates a punchy but also ‘muddy’ bass when it is a bit too high. In case of the HD820 it is just a bit too high alas. In some recordings the bass sounds decent and  ‘punchy’ but in other recordings is sounds a bit ‘muddy’.
The dip around 270Hz prevents the bass from bleeding into the mids but also makes the bass a bit ‘dis-attacted’ from the rest of the music.
People that are really focussed on the quality of bass notes will probably not like this headphone.

output resistance / damping-factor

As this is a dynamic headphone the frequency response might be amplifier output resistance dependent when certain higher output resistance amplifiers are used.
To test this the headphone is measured via a low impedance amplifier (0.2Ω) and a high impedance amplifier (120Ω). On a higher output resistance amplifier the output level will be considerably lower. To compensate for this the amplifier is cranked up (2.2dB) to the same level (at 1kHz) as the low impedance amplifier. This way the plots are overlay-ed and it is easier to see how the tonal balance changes.


As can be seen the tonal balance does not change at all when connected to a higher output resistance amplifier. Well.. maybe +0.2dB more lows. It seems like the HD800 driver relies on mechanical damping only so no need to worry about ‘damping factors’ and output resistances of amplifiers.

Below the distortion plot of the HD800S : (only Right channel shown)
Note that this headphone was measured at ears-unlimited-logo where  background noises were present in the demo room. As this is an open headphone distortion levels and spectrum plot performance may thus be better in reality than as shown on the plots.

The distortion products are shown in dB.

Dist HD820 R

Below the same data but shown in a more common percentage scale instead of a dB scale.

Dist HD820 R percent

The distortion profile is impressively low, certainly for a dynamic driver. Distortion levels can be considered below the audible limit.

  • The measurement rig has a relatively high 2nd harmonic distortion so real distortion values above 200Hz will be lower than the measured 0.1%.

Below the CSD of the HD820 (Left and Right channel are superimposed)


The CSD shows an excellent response with no obvious and deal-breaking resonances or lingering above 1.5kHz. A small and short lived resonance can be seen at 10kHz and  but doubt this is detrimental to the excellent treble quality.

Below the HD800 CSD plot as a comparison.


A different plot is the spectrum plot. This basically is a CSD (Waterfall) plot as shown above but viewed from above where the level differences are colour coded instead of being in the vertical axis. Also the frequency range of the spectrum plot is wider (from 100Hz instead of 500Hz). The time span is also bigger in the spectrum plots and expired time is shown from below to top where in the CSD the time is shown from rear to front.

Below the spectrum plot of the HD820 (Right channel)

Spectr HD820 R

This plot shows a more than decent response. Some short lived and low level ‘lingering’ around 1.5kHz is visible but not on a worrying level nor time-frame.
Bass is actually very fast in decay.
No obvious ringing at higher frequencies a very short one at 6.5kHz.

By lack of oscilloscope shots (not enough time to measure that) below a step response plot of the HD820 (Right channel)

step HD820R

The fast impulse response of the HD800S is clearly seen as it reaches the -5dB line.
There is no overshoot and VERY short lived and well damped ringing. The slow rise between 1ms and 2.5ms shows the lows are boosted. The slow drop after 2.5ms shows the great bass extension of this headphone.

Below the HD800 and HD800S compared to the HD820.

step compared
It can be seen that the 6kHz resonance of the HD800 is ringing longer and more severe compared to the HD800S.
The HD820 clearly has superior bass extension and much less ringing in the treble. The bass boost (5dB hump) is less desirable but bass extension is great.


Seal can be an issue with closed-back headphones. Breaking the seal (improper fit on the head) usually means a substantial loss of bass. The HD820 is not different than most other sealed headphones in this aspect.
Perfect seal, with thin armed glasses, with thick armed glasses and with a complete loss of seal (a gap of a few mm).


What can be seen here is that seal is very important for bass reproduction on the HD820.
For this reason it has different pads than the HD800(S). They are thicker so they can comply better to facial contours. This is quite important as the pads are very large in diameter. The pads also are a lot ‘wider’ in the area where they touch the skin. Again for the exact same reasons. These efforts will ensure a good seal which is essential for good bass reduction. Wearing thin armed glasses only reduces the bass levels about by 5dB.
This isn’t necessarily a bad thing as it has a bit too much of it anyway. Also the 270Hz dip is smaller = better bass reproduction.
Wearing thick armed glasses will result in a substantial loss of bass (-10dB which is about half the amount of bass).
A gap of a few millimeters here and there will result in a massive loss of bass.
A suggestion would be to remove at least thick armed glasses and ensure you have a good seal. Easy to check by slightly pressing the cups on the head and listen for a change in the bass response. Little to no change means a good seal.


The HD820 is quite an expensive headphone. Whether one is ready to spend 2400.- Euros or US$ for it is a personal choice. At almost double the price of the HD800S one can ask the question whether or not a closed option is needed.
Aside from the bass response, which is quite different, treble response is greatly improved.

Comfort and looks are very similar to the HD800S. The sound is not.
Without EQ and regardless of price I personally like the HD820 a bit better. More bass of still decent quality and very nice mids and treble.
In comparison the HD800S is leaner and brighter/hyper detailed but is more accurate in bass tonality/accuracy.

When using EQ (bass lift and treble peaks lowered) the scales tip towards the HD800(S) but under the condition that isolation is not needed.

For a closed headphone this is an excellent sounding headphone. It will be difficult to find a closed headphone with better dynamics and detail retrieval.
Bass quality may put some people off and may even lead to listening fatigue.

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