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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.


post separation


The K518DJ is a cheap AKG headphone that is wisely sold. It has swiveling cups and can be transported flat.
The headband is not very comfortable for bald headed people and the rubber surrounding it may catch some hears as well.
I solved this by sticking an HD25 padding strip under the headband (not pictured).
The stock sound is rather bass oriented, Not bad sounding but also not an great sounding headphone with decent isolation.
It is a closed on-ear with a decent clamping force for an on-ear.
Frequency Response of the AKG-K518 with original pads and foam insert removedleft, right


The CSD of the stock K518 with no inserts BUT with some felt stuck inside the cups to lower ‘echos’ from the cup walls.

csd stock K518DJ no insert

A resonance at around 5kHz. Aside from the uneven frequency response and the resonance around 5.5khz there is not much to worry about.

Below the difference between a stock K518 with and without the (easily removable) foam inserts.
As can be seen the difference is quite subtle, just a few dB less mids and treble.

K518DJ foam insert

The original pads are somewhat uncomforatble to me, they are a bit too stiff for me.
To improve this I tried Sennheiser HD25 pads and ‘Aldi’ headphone pads that came of the Silverscrest KH-2347.
Below the differences between the K518DJ + foam insert versus the K518DJ with the soft pleather KH-2347 pads + inserts.

stock + insert vs kh2347 + insert

The bassy character of the stock K518DJ is lowered and it sounds more ‘balanced’ but still having an extendedt bass response and better clarity.
To my ears it is an improvement but if you like big bass I would recommend using the stock pads.

Below the difference between a stock K518DJ + inserts versus HD25 padded K518DJ+2 mm felt disc in front of the driver.
Without the felt disc the 2kHz peak is much higher and unpleasant sounding.
If you like midrange oriented headphones this may be an option.

stock + insert vs hd25 + felt

post separation

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