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Published: Jun-25-2018

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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 HD599


The Sennheiser HD599 is an open over-ear dynamic headphone.
It retails for around between € 150.- and € 200.- and is the top model of the HD5** range.

These are intended to be driven directly from phones and other portable devices.
They are lightweight and comfortable. The colour scheme may be something that needs to be considered as this exact model is not available in black, only in ivory + brown.
When the colour scheme is something one cannot live with the older HD598 is the nearest best thing if you can find one (Not the HD598-CS) or the HD579 with a light grey colour scheme.

It comes with 2 detachable cables. One of which is 1.2m. and is fitted with a 3.5mm TRS plug, the other one is 3m. long and has a 6.3mm plug.
The cable is slightly microphonic so in quiet passages and silences the cable rubbing against clothes is audible in the left cup.
The headband is soft and comfortable and so are the velours pads. The pads do feel a bit ‘prickly’ and firm but reckon that over time they will soften up and feel more comfortable.
There is enough room for most ears. Height adjustment and tilt of the cups is large enough to suit most head sizes well.
The clamping force is ‘medium’ so it won’t move around on the head easily.
It’s very low weight contributes to this as well and ensures one can do longer listening sessions with it.


Type: over ear, open
Isolation: poor
Usage: home
Driver type: dynamic
Pads: replaceable, velours
Foldable: No
Headphone cup connector: 2.5mm TRRS jack, locking.
Cable entry: single sided (left cup)
Cable: 3m cable with 6.3mm TRS Jack + 1.2m cable with 3.5mm TRS Jack plus a 6.3mm adapter.
Inner Pad dimensions: depth = 20mm, Width = 40mm, height = 70mm, oval shaped
Driver size: 38mm
Max. power rating: 0.5W
Max. Input Voltage:  5 V rms
Max. drawn current: 100 mA rms
Max. S.P.L.: 120 dB
Impedance: 50 Ω
Efficiency: 93 dB/1mW  (106dB/1V)
Weight: 250 g.
Clamping force: medium
Accessories: 3m cable with 6.3mm TRS Jack + 1.2m cable with 3.5mm TRS Jack plus a 6.3mm adapter.


Sound description:

It is often said that this headphone is a more ‘portable’ and affordable version of the HD650. I don’t agree. More portable… yes when used directly out of a phone. More affordable.. yes. HD650 alike sound? no.
There are some similarities though. Warmth, lack of subbass and the ‘narrow’ head-stage but there are but also differences.
The overall tonal balance is a ‘warmish’ type of ‘neutral’. This makes the HD599 not super ‘dynamic’ sounding but rather ‘mellow’. Way more ‘mellow’ than the HD650 which merely has a ‘hint’ of warmth.
It lacks a bit in ‘open-ness’ of the sound. The HD599 sounds a bit more leaning to ‘congested’ (does not sound congested) than to ‘open’ is what is meant.
The lack of subbas is audible when one knows there should be more ‘rumble’ in the sound. It is more obvious in the HD599 than in the HD650.
The bass ‘bleeds’ into the mids which is most obvious with male voices which turn a bit ‘bloomy’.
The mids have a pleasant (and slightly warm) character and sound good.
Treble is ‘soft’ and sounds pleasant. It is never harsh nor sibilant but is not as ‘refined’ as that of the HD650. The HD599 is a bit less in showing the finest nuances compared to the HD650.
Overall a pleasant and warm sound signature that does not do much wrong but isn’t exceptional in any aspect either.


Below the frequency response of the HD599 (Left, Right)

FR HD599.png

Channel matching is good.  Subbass is rolled off and bass starts to roll off from 40Hz. Mid bass is elevated by 5dB which gives the bass a bit more ‘punch’. Mids are warm as the response is sloping downwards from 200Hz to 2kHz. From 1kHz to 15kHz the response is quite flat. While having warmth the headphone still has enough clarity and presence.
Treble is of good quality and extends beyond 20kHz.

This headphone is said to be close to a HD650 but easier to drive from portable sources.
Below the HD650 versus the HD599.

HD599 vs HD650

The HD599 is warmer and somewhat bassier and a tad less refined than the HD650. Of course these are in a different price class.
A better comparison (price wise) would be the HD58X Jubilee (only available from Massdrop). Below the HD58X versus the HD599.

HD599 vs HD58X

The HD58X is slightly less bassy/warm and maybe a tiny bit more ‘forward’ sounding (small lift around 1.5kHz) than the HD599 but these may be quite close.


Seal can be an issue with closed-back headphones. Breaking the seal (improper fit on the head) usually means a substantial loss of bass. For open headphones this is usually much less of an issue. The HD599 is not different than most other open headphones in this aspect. Perfect seal and seal loss by thick armed glasses.

seal loss

This headphone needs a proper seal to have decent bass response. Bass starts to roll off below 100Hz when the seal is broken. As the mid bass is still slightly boosted this loss of sub-bass will only be obvious when deep bass is present in the recording.

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 lower. To compensate for this the amplifier is cranked up to the same level (at 1kHz, 10 dB in this case) as the low impedance amplifier. This way the plots are overlay-ed and it is easier to see how the tonal balance changes.

120 Ohm R


The tonal balance changes considerably when driven from a substantially higher (120 Ω) output resistance. About 4 dB more midd-bass. The bass becomes bloated and muddy from higher output resistance sources.

Below the distortion plot of the HD599: (Left 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 a percentage scale (left channel).

DIST HD599 L Percent

The 2nd harmonic distortion in the bass area reaches audible levels (1%) . The 3rd harmonic distortion (which points to clipping alike behaviour) in the bass area is also reaching 1% right up to 100Hz. These levels are audible.
The measurement rig has a relatively high 2nd harmonic distortion so above 200Hz values will most likely be below 0.2% in reality.
Distortion from 400Hz to 15kHz is good.

Below the CSD of the HD599 (Left and Right channel are superimposed)

The CSD shows a decent response. Around 3.5kHz there are some short lived resonances  but are not very audible at that part of the frequency range. Above 6kHz the response is good.

By lack of oscilloscope shots (not enough time to measure that) below a step response plot of the HD599 (Right channel)

Step HD599 R

The step response shows the subbass response rolls away gently as indicated by the sloping horizontal trace. The plot also shows the driver is well damped as there are almost no resonances visible. The initial rise, however, does not reach the desired level indicating a slight lack of ‘speed’.


Those looking for a different looking open dynamic headphone that can be driven directly from a portable devices and like to have a good sound quality as well could very likely like this headphone.
The HD599 is comfortable and quite good sounding and comfortable headphone which feels quite light.
Those that cannot see past the ivory/brown may as well look for alternatives in the Sennheiser stable such as the older HD598 (black) and the HD579 (gray).
The HD599 doesn’t have any real ‘flaws’. There is a bit too much warmth for hifi aficionados but at the same time it does not excel in anything either.
Just a good overall headphone, certainly for the money, but not an exceptional headphone either.

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