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Published: Mar-21-2019

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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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AKG K701


The AKG K701 is a an oldie. In days gone by the K701, Beyerdynamic DT880 and Sennheiser HD650 ruled the consumer headphone world and each had/has their own fanbase.

The headphone reviewed and measured has seen many, many, many hours on it already.

The K701 is an open headphone with a dynamic driver. It is only available in white with grey/brown accents. The MSRP is around €350.- but retail price (2019) is around €130.-

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. Some headphones have cable entries on the right. Most single entry headphones have it on the left just like the K701.

The cable isn’t thin but also not ‘audiophile thick’ and 3m in length and just mildly microphonic. The cable terminates in a 3 pin 6.3mm TRS jack.
The fact that it has a long cable suggests it is not intended for portable usage. As the K701 is not a high efficiency headphone this too suggests it is not designed for portable usage. Add to that the K701 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 K701 is very easy to drive though with its 62Ω impedance. It is often mentioned the K701 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)

The pads are large enough in inner diameter (55mm) and have a nice depth (25mm) so most ears will fit. The pads are velour with standard foam inside. This creates a decent seal which slowly conforms to the head over time. 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 loose their elasticity over a few years already. They can be replaced but is expensive and not easy to DIY.


Type: On-ear, open
Usage: Home, Studio
Isolation: low (open headphone)
Driver type: dynamic
Pads: replaceable, foam with velour cloth
Pad dimensions: Ø 55mm , depth: 25mm
Collapsible: no
Headphone connector: fixed entry.
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: 90dB/1mW (102dB/1V)
Weight: 235 g.
Colour: white or black
Clamping force: medium
Accessories: 3.5mm adapter

Sound description:

The AKG K701 has a ‘bright neutral-ish’ tonal balance.
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. It is bordering on 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.


Below the frequency response of the K701 (Left, Right)K701 FRChannel matching is excellent. 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 3kHz 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 6kHz makes the treble a bit ‘coarse’. Above 18kHz the response drops off quickly but still shows response at least up to 30kHz.

Below the K701 vs the K7XX.K701 vs K7XX
The K701 is much more ‘neutral’ but is lacking in the lower bass. Also, because the K701 has less bass/mid-bass/lower-mids the treble/brightness is relatively much more accentuated.

Below the K701 vs the K612.K612 vs K701The K612 (better extended K601) is considered ‘neutral’ with a forward sound and sharpish treble. Compared to the K612 the K701 is quite similar but the K612 is just slightly more extended and has a few dB more lower bass.

Below the tonal balance differences between the old rivals K701, DT880 and HD650DT880, HD650 K701


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.sealA seal breach isn’t really problematic at all. The tonal balance is hardly changed when listening to these headphones with or without glasses.

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 considerably lower. To compensate for this the amplifier is cranked up to the same level (9.4dB at 1kHz) as the low impedance amplifier. This way the plots are overlay-ed and it is easier to show the tonal balance differences.120 Ohm -9.4dBThe headphone does not react much to higher output resistances other than in level (9.4dB). 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 sound.

other measurements

Below the distortion measurements of the K701 (Right channel)THD K701Below the same distortion plot but with the vertical scale in percentages instead of level differences. THD K701 percentThe 3rd harmonic and higher harmonics distortion is below 0.5% in the bass area (40-200Hz) which is decent. The 2nd harmonic distortion remains well below 2% in the bass which is to be expected from a relatively small (40mm ∅ dynamic driver).
Above 100Hz the distortion stays below 1%.
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 K701. (Left and Right are superimposed)The dip around 4kHz is not a resonance in disguise. This small dip is entirely compensated in level by the Concha of the ear. The narrow treble peaks (6kHz, 12kHz and 16kHz) are clearly resonances. This also points toward less refined treble.

Below the spectrum plot of the K701 (Right channel). spectrum K701
This plot looks quite good below 500Hz. The lower frequencies are quite well damped and ‘stop’ fast.
Around 2.5kHz 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)stepThis plot shows the impulse response/clarity is accentuated and peaks out 3dB 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.

Below the square-wave response of the K701. On the left 40Hz, in the middle a 440Hz square wave and on the right a 100μs wide DC impulse.SQR K701.pngThe bass roll-off is easy to see in the 40Hz squarwave. 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 quite a lot of ringing.
The 100μs pulse shows the correct amplitude but the pulse on the top of the signal shows overshoot and quite a lot of ringing.

foam ring

The AKG K701 has a foam ring covering the driver. Of course this is there for a reason. On the left the K701 driver with the foam removed, on the right the stock K701 driver with the foam in front of it. The foam is just lying on the driver and pressed onto the driver using netting integrated in the pads. These pads are really easy to remove. Just rotate the pads a few degrees counter-clockwise and the pads come off.

driver K701

foam disc








Below the frequency response measured with and without the foam ring.foam ring
The foam isn’t doing much here. I also tested the black foam ring used in the K7XX and a foam disc (Superlux netted foam) but these all gave the same results.

Below an experiments with a disc made of soft 3-ply toilet paper where the plies are cut into discs and the 3 plies are pulled apart to form 3 very thin and fragile discs.
stock foam ring, 1 ply toilet paper disc below the foam ring.1ply TPThe single ply toilet paper disc reduces the upper resonances quite effectively but does not lower the 6kHz peak which is the most offending one.
Below the CSD of the K701 but with the toilet paper disc added.CSD 1 ply TP K701
This shows the resonances are effctively damped. Only a very narrow resonance remains. 2 plies reduce the upper treble too much and ‘muffles’ the upper treble/air.

On the left the (very thin) toilet paper single ply and on the right the same but with the foam ring placed on top of it.
TP ring


Below the difference in response on the square-wave and impulse response between the stock version (upper 3 scope shots) and with the Toilet Paper applied (lower 3 shots).SQR TP
The plots above show the ringing is substantially damped by the thin ply of toilet paper.

passive inline filter

Another way of reducing the treble peak is by using a passive in-line filter in the headphone cable. The effect of this filter is described in the K702 page.


Changing pads usually results in a quite different tonal balance.
Below the plot of the K701 with K7XX pads fitted.K7XX pads
Interestingly the K701 becomes more efficient with these pads (about 4dB) in the mids and the treble peaks are somewhat less elevated. The dip at 4kHz deepens which removes even more of the bright character of the K701.
Below the same plot but the mids are overlayed.K7XX pads level matched
What’s obvious here is that these pads won’t improve the bass response but rather slightly (2dB) increase the mids and deepen the 4kHz part which makes the sound less ‘forward’ and less bright. The treble is lowered by 1 dB as well so these pads make the sound of the K701 less ‘bright’ and less ‘forward’. The mids are less accentuated when using these pads and ‘mellow out’. But.. no increase in bass nor bass extension.

Below the K7XX vs the K701 but fitted with K7XX (K712) pads.K701 w K7XX pads vs K7XX
This plot shows the K7XX has a different driver with more bass extension than the K701 fitted with the same pads.

When you find the bass levels O.K. and don’t crave for more ‘body’ to the sound fitting some K712 pads and applying 1 ply of toilet paper may be an easy way to reduce the clarity and brightness of the K701 while not turning it into a bassy or muddy headphone.


A filter for the K701 has been re-designed based on the measurements above.
Below the stock K701 (but with 1 ply of toilet paper) vs driven by the kameleon (also with 1 ply of toilet paper)K701 Kameleon vs stock TP modified

Bass response is extended and lifted in amplitude, the 2kHz peak is now at the same level as the mids and the 6kHz peak has been lowered to normal levels. The treble extension gained 2dB at 20kHz.
Below the Frequency Response of the K701 via the Kameleon (Left, Right)K701 on Kameleon

Below the step response of the stock K701 and via Kameleon (both with toilet paper mod)step K701 KameleonThe bass response is improved a lot, alsso the ringing and peaking is a lot lower in level.
Overall sound is still ‘mids’ oriented but better extended and not ‘peaky’.

Below the CSD of the K701 via Kameleon (Left, Right superimposed)CSD K701 Kameleon
Aside from the narrow 15kHz resonance (Left channel) and 16 kHz (right channel) the waterfall plot looks quite good.


The AKG K701 is a sturdy work horse. The white with grey and brown accents differs from that of most other headphones. 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.
For the going streetprices (around € 130.-) 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 K701 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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