K702

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Published: Feb-3-2020, updated: Nov-11-2021

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 K702

The AKG K702 is a modernised K701. It is an open headphone with a detachable cable, slightly slanted pads and a different color scheme.

The reviewed headphone has had quite a few hours on it already and was kindly sent in by the owner. It is not the older ‘Austrian made’ one for those that wonder.

The K702 is an open headphone with a dynamic driver. It is available in black with very dark blue and matte aluminium accents. The MSRP is around €350.- but retail price (2019) is around €140.-

The headband can adjust over a wide range but isn’t padded. It does not push hard on my head but one does feel a small contact point and the cups have a small tendency to drop a little lower in my case.
L and R markings are located on the headband. A give away for the left cup is the cable entry as well.

The cable isn’t thin, but also not ‘audiophile thick’, and 3m in length and just mildly microphonic. The cable has a 3-pin mini XLR on the headphone side and a goldplated 3.5mm TRS with a gold plated screw-on 6.3mm adapter.
The fact that it has a long cable suggests it is not intended for portable usage. Some people will be disappointed this headphone only has a 3-pin mini XLR plug because this headphone cannot be connected to balanced amplifiers. Given its low sensitivity a balanced amplifier could well be beneficial.

As the K702 is not a high efficiency headphone this too suggests it is not designed for portable usage. Add to that the K702 is an open headphone and that it does not play sufficiently loud from phones/tablets and cheap DAPs makes it obvious this headphone is only really suited for home and studio usage. The K702 is not difficult to drive though with its 62Ω impedance. It is often mentioned the K702 is ‘hard to drive’ which is nonsense. It just doesn’t play very loud directly from a  phone and requires quite some volume for the bass to ‘snap’ into the correct level (Fletcher Munson / equal loudness contour curves)
You need to drive it from a amplifier or source that can provide enough voltage into 62Ω.

The pads are large enough in inner diameter (60mm) and have a nice depth (25mm) so most ears will fit. The pads are velour with standard foam inside and have a 5° angle . This creates a decent seal which slowly conforms to the head over the years. The clamping force is medium and pleasant but this particular headphone has already been worn for quite some time. It does make sure the headphone stays put and doesn’t move around when moving around.

This headphone is quite comfortable and can be worn for long periods without getting too ‘hot’ on the ears. The headphone is light in weight.

The headphone feels and is quite sturdy. There is only one big downside (which is still a problem with similar looking AKG models) which is the elastic bands lose their elasticity over a few years already.
They elastic bands be replaced but is expensive and not easy to DIY.

specifications:

Type: On-ear, open
Usage: Home, Studio
Isolation: low (open headphone)
Driver type: dynamic
Pads: replaceable, velour cloth, 5° angle
Inner pad dimensions: Ø 60mm , depth front: 20mm, depth rear: 25mm
Collapsible: no
Headphone connector: 3-pin mini XLR
Cable entry: left sided.
Cable: 3m terminated in 6.3mm TRS + 3.5mm adapter
Driver size: ø 40mm
Nom. power rating: 0.2W (200mW)
Max. voltage: 3.5V
Max. current: 56mA
Max. S.P.L.: 113dB
Impedance: 65Ω
Efficiency: 94dB @ 1mW
Sensitivity: 106dB @ 1V
Weight: 235 g.
Colour: white or black
Clamping force: medium
Accessories: 3.5mm adapter

Sound description:

The AKG K702 has a ‘bright’ tonal balance similar to the K701.
Bass is light but is ‘tight’ and well textured. The overall sound is ‘open’, dynamic and very ‘forward’ as well as ‘detailed’. Drum hits etc. are over-accentuated.
It sounds a bit too bright and can have a shrill ‘edge’ with some music. With some music there is sibilance. The treble is over accentuated and has enough ‘air’ but isn’t really ‘smooth’. It lacks in ‘finesse’ but is above average in quality. The ‘details’ in the music are ‘fake’ due to the 6.5kHz peak.

measurements:

Below the frequency response of the K702 (Left, Right)There is a slight but not audible channel imbalance. Bass extension isn’t great and it starts to audibly roll-off from 100Hz down. This makes the bass sound ‘light’ but ‘tight’.
The mids from 200Hz to 1kHz are pretty flat and make the mids sound ‘neutral’. The small ‘bump’ around 2kHz makes the mids sound a bit too ‘forward’ but not in an annoying way.
The treble response is a bit ‘jagged’ and has a typical ‘AKG signature’. The jagged response above 5kHz makes the treble a bit ‘coarse’. Above 18kHz the response drops off quickly but still shows response at least up to 30kHz.

Below the K702 vs the K701
The K702 is very similar to the K701 with the only real differences being the color scheme, the replaceable cable and the slightly angled pads which the K701 doesn’t have.

Below the K702 vs the K612.The K612 (a better extended K601) is considered ‘neutral’ with a forward sound and sharpish treble. Perhaps the only real difference is color and the fixed cable to justify the price difference.

Below the K702 vs the K7XX.The K702 is much more ‘brighter’ but is lacking in the lower bass. The K7XX is much less bright and sharp sounding and relatively bassier as a result.
Note: the rather large ‘dip’ aroound 3.5kHz in the K7XX (and K712) are a measurement error because there is no pinna. Pinna gain ‘fills-in’ the gap for the largest portion.

Below the K702 vs the K501.The K501 is an oldie. What’s clearly visible is that AKG stuck to the AKG house sound over all the years. bass-light and bright. The K501 rolls-off a lot sooner though and is really bass-shy where the K702 still can reproduce lower bass notes, albeit at a lower than neutral level.

seal

As the seal of a headphone is of importance some experiments are done to see the effect.
(lots of) hair between the headphone and ear or an ear shape that does not allow a proper seal will affect the tonal balance.
Below: Perfect seal, a small seal breach by thin armed (reading) glasses just above the skin, thick armed glasses and a big seal breach.A seal breach isn’t really problematic at all. The tonal balance is hardly changed when listening to these headphones with or without glasses. Only when there is a substantial seal breach one will notice lower bass notes are subdued.

Linearity

A test that I perform now and then (mostly only when I suspect issues) is the linearity test.
This test measures the frequency response at various SPL (70, 80, 90 and 97dB) and then overlay the plots to see if the driver shows non linear behavior due to damping or other problems. Usually I don’t post them unless something is wrong but in this case I will post the plot. It shows no linearity issues at all, they all overlay.

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, 10Ω, 32Ω and 120Ω output resistance  amplifier. Do note the vertical scale in this plot (2dB/div)

On a higher output resistance amplifier the output level will be considerably lower. To compensate for this the amplifier is cranked up to the same level (9.4dB at 1kHz for 120Ω) as the low impedance amplifier. This way the plots are overlaid and it is easier to show the tonal balance differences.The headphone does not react much to higher output resistances other than in level. There is hardly any difference. Upper treble is 1dB higher in level though. Bass hardly reacts.
The output resistance of the used source/amplifier has no practical influence on the tonal balance.

As plenty of myths are going around about the K701 and K702 many of those myths are about break-in requiring 300+ hours. Don’t worry this is a used headphone with well over 300 hours of usage.

Another aspect that is often said is how bass would be slower and would be muddier due to less damping.
Below the CSD taken with 0Ω, 10Ω, 32Ω and 120Ω output R’s. These CSD’s differ from the usual ones as these go all the way down to 10Hz and have a different time scale. As can be seen not much changes in damping effects. The bottom of the plot is 55dB below the 90dB SPL.

Related to this there is also the Group Delay. Below the plot showing that, aside from the wiggle at 25Hz, not much changes. Not even pad bounce effects between 70 and 100Hz. No idea what the blue wiggle is about. A measurement error I assume.
Another aspect of sound is distortion. Below the distortion plots taken with 0Ω, 10Ω, 32Ω and 120Ω output R’s.
Distortion does rise slowly with an increased output resistance but not in a dramatic way.

Below the distortion measurements of the K702 (Right channel)Below the same distortion plot but with the vertical scale in percentages instead of level differences. The distortion is quite low. Even in the bass distortion is below 1% which is good for a dynamic driver. Above 300Hz the distortion remains below 0.5%.
The 2nd harmonic distortion is probably lower than 0.2% around 1kHz as limits of the test rig are around that level.

Below the CSD of the K702. (Left and Right are superimposed) The narrow treble peaks (7kHz, 12kHz and 16kHz) are resonances. This also points toward less refined treble. The resonances shift in frequency when the ear-driver distance changes.

Below the spectrum plot of the K702 (Right channel).
This plot looks quite good below 500Hz. The lower frequencies are quite well damped and ‘stop’ fast.
Around 2kHz there is a little lingering (the small bump in the FR, it seems happy to vibrate at that frequency) but is very low in level. Don’t think this is very detrimental to the sound. Above 10kHz the resonances are visible but are also short.

The step response plot below  (Left, Right)This plot shows the impulse response/clarity is accentuated and peaks out 4dB above the mids. Beyond 1ms the signal drops gradually and shows the bass roll-off. The ringing goes on for quite some time and is seen in the entire plot.

fixing the elevated treble

The elevated upper mids and treble that is responsible for the bright character can be lowered to normal levels using a passive electronic filter.
The schematic for it is shown below. It can also be used for the K701.

The effect of this filter is shown below. Stock K702 vs filtered K702

Below the frequency response of the K702 with the filter.
The vast majority of the brightness is removed. On some recordings there is still some sibilance audible but the excessive brightness is removed.

Below the square-wave response of the K702. On the left from top to bottom 40Hz, 440Hz square wave and on the bottom a 100μs wide DC impulse. On the right side the K702 with the filter.The bass roll-off is easy to see in the 40Hz square-wave. The signal doesn’t follow the stimulus in the horizontal plane and quickly drops down.
The mids look better as the measured signal looks more like the applied square-wave but does show overshoot and a lot of ringing.
The 100μs pulse shows the correct amplitude but the pulse on the top of the signal shows overshoot and a quite high second pulse that should not be there.

The filtered K702 (the right plots) show the overshoot is removed but there still is a second pulse. There still is a resonance which the filter can not remove. The biggest improvement is in the frequency response.

pads

As the foam in pads has a tendency to get softer (more compliant/squishy) over time this will affect the tonal balance. As the pads remain firm for quite a long time the change will go unnoticed I reckon.
Fresh pads vs somewhat compressed pads.
The most interesting part is that the resonances shift a bit because the ear/driver distance changes.

Those that are wondering what happens with the K702 when slapping on a pair of, not angled, memory foam filled K712 pads can see the effect below.

Is the K702 with K712 pads exactly the same as a K712 ?
Close but no cigar. The 5dB ‘dip’ around kHz is audible and makes the K712 sound a bit less ‘edgy’ / ‘forward’. Also the treble is about 2dB lower which makes the K712 a bit more ‘laid-back’ and ‘smoother’ sounding. But at least the bass is more pronounced and the efficiency is about 4dB higher and fuller sounding.

In a lot of forums one sees the ‘bass port mod’ where wonderful sound changes are described that are attributed to this rather simple modification. In most of those articles people wonder why AKG decided to damp the centre-hole of the driver as it decreases the lower bass. That lower bass is the most often heard ‘complaint’ (aside from the treble) and removing that little sticker makes the sound so much better. But does it and why does AKG put those kinds of stickers on all similar AKG drivers ?

First some measurements regarding the small grille behind the driver. What does it do (aside from looking nice) ?
Below the K702 with the back side of the grille removed and the expose area sealed completely, without the metal grille and the stock configuration with the metal grille.

Removing the grille seems to have no remarkable effects. stuffing the area with damping material will change the frequency response between 400Hz and 4kHz towards the red curve which shows what happens when the area behind the driver is sealed completely.

There was some change visible between with and without grille though in the Group Delay plot shown below between 400Hz and 600Hz but these differences are very small and narrow. Hardly an audible thing.

Let’s move on to the ‘bass port’ which basically is a hole in the centre of the driver magnet that allows air to flow (restricted) from the rear of the driver membrane dome. A sticker further restricting airflow, made from a very fine nylon mesh, restricts air flow (and thus damps) the driver.
Covering the whole completely restricts airflow and lowers bass levels, removing the sticker reveals a very narrow hole and lowers damping and increases the lowest octave.
Below the frequency response of the stock K702, with the sticker completely sealed and with the sticker removed (the bass mod).
This looks like removing the sticker is a no-brainer. With little effort bass is extended greatly. Why does AKG put a sticker on that hole as bass is improved without it ?
Of course we can also use some simple EQ and boost the lowest bass. This can make the bass go even lower but of course the ‘bass port mod’ extends bass without having to resort to EQ.
Below the stock K702, with the sticker removed and the stock K702 with some EQ in the 32Hz and 64Hz band using an old analog graphic equalizer. EQ wins, one can even extend it futher if needed but 30Hz -1dB is enough.

Turns out there is a reason after all for the presence of the sticker. It is easily visible in the distortion plot.
When that sticker, purposely placed there by AKG, is removed something else besides the amount of bass also changes. And not for the better. The distortion, especially the more audible 3rd, 4th and 5th harmonic.
At 40Hz the 3rd harmonic increases from 0.5% to 4.5% ! (disregard 50Hz, there is a hum component in the measurements)
This can’t be explained by increased bass amplitude as the plot also shows a distortion plot taken using the old analog equalizer (Realistic) which even extends bass even further. That distortion is hardly higher with EQ.
So those contemplating whether or not to perform the ‘bass port mod’ I would say don’t. AKG engineers aren’t idiots and installed that damping material with good reason.

summary

The AKG K702 is a sturdy work horse. The black/dark-blue and chrome accents give it a different look compared to the white K701. The only real longevity issue is the elastic bands that aren’t easily replaced by owners.
This is a comfortable headphone that can be tweaked in sound by using different AKG pads. These pads aren’t cheap though. Some experiments were done on the K701 and will be the same for the K702.
For the going street prices (around € 140.-) this is a good and comfortable headphone that can take a beating. It is a bit bass light but the bass itself sounds excellent and well textured. The bright ‘neutral’ signature can be improved by EQ or as described above.
The K702 has been around for many years already, just like the DT880 and HD650 and have been surpassed as ‘TOTL’ headphones for these brands but still are good performers.

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