K518

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published: Dec-28-2014, updated 17-5-2021

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.

AKG K518-DJ

The K518DJ is a cheap AKG headphone that is wisely sold. It has swivelling 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.

specifications:

Type: On-ear, Closed
Usage: Home, Studio, portable
Isolation: decent
Driver type: dynamic
Pads: replaceable, pleather
Pad dimensions: outer diameter: 75m, inner diameter: 35mm
Collapsible: yes, can also fold flat.
Headphone connector: fixed
Cable entry: both sides.
Cable: 2.5m with 3.5mm TRS plug
Driver size: ø 50mm
Nom. power rating: 2W
Max. voltage: 8V
Max. current: 250mA
Max. S.P.L.: 133dB
Impedance: 32Ω
Efficiency: 100dB @ 1mW
Sensitivity: 115dB @ 1V
Weight: 150g. (without cable)
Colour: black
Clamping force: medium
Accessories:  6.3mm adapter, pouch

measurements

Frequency Response of the AKG-K518 with original pads and foam insert removed.  left, right

Good bass extension. Alas the elevated area up to 300Hz also makes the sound muddy.  Mids and treble are decent.

Below the phase plot of the K518
The sharp area around 10kHz can be audible. Pad bounce at 90Hz is visible. The sharp rise around 400-500Hz also is not desirable. This is a very cheap on-ear headphone though.

Below the distortion plot for the K518.
The same plot below but in the more common percentage scale
Distortion isn’t high which is good to know that in this price class low distortion can be had.

Below the step response of the K518. The bass extension is excellent as the signal at 5ms has hardly dropped opposite the initial rise. The wide ‘hump’ between 0.5μs and 3ms shows the ‘muddy lows’ are quite audible.

The CSD of the stock K518 with no inserts
The lingering in the mids is visible. Also at 5.5kHz a rather large resonance is visible.

Another time domain plot is the spectrum plot.
It shows some issues just above 1kHz, at 4kHz and 6kHz.

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.

The original pads are somewhat uncomfortable 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.

The bassy character of the stock K518DJ is lowered and it sounds more ‘balanced’ but still having an extended 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.

conclusion

The K518DJ is a cheap on-ear headphone with elevated lows. Bass sounds a bit muddy. Mids are decent and no sharp or dull treble. Can be driven directly from a phone or small DAP/tablet or laptop.

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