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published: Jan-26-2014, updated May-17-2021

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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.
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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AKG K550



Type: Over-ear, Closed
Usage: Home, Studio
Isolation: decent
Driver type: dynamic
Pads: replaceable, pleather
Inner pad dimensions: diameter: 53mm,  25mm
Collapsible: no
Headphone connector: fixed
Cable entry: left sided.
Cable: 3m with 3.5mm TRS plug and screw-on 6.3mm adapter.
Driver size: ø 50mm
Nom. power rating: 200mW
Max. voltage: 2.5V
Max. current: 80mA
Max. S.P.L.: 121dB
Impedance: 32Ω
Efficiency: 99dB/1mW (114dB/1V)
Weight: 305g. (without cable)
Colour: black
Clamping force: medium
Accessories: screw-on 6.3mm adapter, warranty card

The K550 is a comfortable over ear headphone with a darker tonal balance with some elevated treble up top.
Alas there are no spare pads available. This would be handy as the pads start to degrade after a few years. One will have to look for after market pads.


The AKG K550 exists in a few ‘versions’ it seems. The ones that have a sharp edge and some that have a much less sharp edge. This particular one seems to be one of those with a less sharp edge but it is still there as can be seen in the frequency response plot below. left, rightFR K550

Below the phase response of the K550.phase K550
Aside from the phase shifts above 5kHz this seems quite decent. Only sharp phase shifts in a narrow band may become somewhat audible.

Below the Group Delay plot for the K550.GD K550
Nothing strange, only some influence of the pads in the lower frequencies is visible.

Below the distortion plots of the K550.Dist K550 R
And below the same plot but in the more common percentage scale.Dist K550 R percent
Distortion is quite low and above 200Hz most likely lower than the shown values as the measurement limit is around 0.2% Note: only 2nd harmonic distortion is shown.

The CSD below shows some short lived ringing at some frequencies but nothing really alarming.CSD K550

Below the Spectrum plot for the K550.spectrum K550
It shows some lingering at 1.5kHz and short lived resonances. Nothing that is potentially sound degrading.

Below the step response for the K550step K550
This plot shows some ringing and the somewhat darker tonal balance is showing. Bass extension is enormous.


Some modifications can be done which removes the ‘darkish tilt’ and makes the K550 sound more realistic.
(The modifications are the same as for the K551)

When the same modifications are done as described in the K551 article the frequency plot is changed to this: left, right

K550 modified version

The K550 is a rather big but not heavy closed headphone that is easily driven and does not require a lot of power.
It’s tonal balance is towards the warmer side of neutral but can be improved with some modifications.
Down side is that AKG does not have replacement pads for this headphone.

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