ÆON Open

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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.

sound descriptions mine

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MrSpeakers ÆON Flow Open

AEON open

The MrSpeakers ÆON Flow Open is an open orthodynamic over-ear headphone intended to be driven directly from portable and desktop equipment.
It retails for around € 800.- which is not really cheap but also still under the magical € 1000.- barrier.
For this you do get a modern looking lightweight and comfortable headphone.
The earpads are large enough to fit most ears comfortably.
Pad rolling is not an option here as thepleather pads are glued.
When the pads need to be replaced MrSpeakers can provide new pads which can be stuck on the headphone once the old pads have been removed.
The isolation from outside noises is decent for an open design. Others can hear what you are playing and you can hear outside noises but slightly attenuated.
The low impedance also suggests it is designed with portable usage in mind. The impedance being 13Ω  may be a bit on the low side for some sources / amplifiers.
The supplied DUMMER cable is somewhat on the stiff side and a bit microphonic.
When ordering one can choose between 3.5mm TRS (+ 6.3mm converter) or a balanced 4-pin XLR connector.


Type: Over ear, open
Usage: Home and portable at home
Driver type: orthodynamic
Pads: pleather, glued
Collapsible: No
Headphone connector: Hirose connector
Cable entry: double sided
Cable: replaceable,  2m with gold plated 3.5 mm TRS plug or 4-pin XLR
Driver size: 35mm x 50mm
Nom. power rating: unknown (assumed 2W)
Max. voltage: 5.1V (assumed 2W)
Max. current: 400mA (0.4A) (assumed 2W)
Max. S.P.L.  126dB (assumed 2W)
Impedance: 13 Ω
Efficiency: 95 dB/1mW  (114dB/1V)
Weight: 321 g.
Clamping force: low/medium
Accessories: DUMMER cable,  clamshell travel case, screw on 6.3mm TRS converter

Sound description:

Sound evaluation is done in ‘stock’ configuration meaning the ‘1-notch’ white felt insert is used.
The sound has a slight muddy / hollow character. Strangely enough the sound character that one would associate with closed headphones. The ÆON closed on the other hand sounds ‘open’.
The ÆON open is not as ‘dynamic’ as the closed version. Bass is not very well defined as in slightly muddy and not ‘tight’ or ‘punchy’. The mids are ‘warm’ sounding. A bit too ‘laid back’ for me in the sense that it is overdone and is lacking clarity.
Treble is present and ‘soft’ in character but somewhat ‘subdued’. Treble extension is good. Whetther one prefers the sound with any of the 3 inserts is a personal question.
It is a very good thing that these inserts are available.


Below the frequency response of the ÆON open (Left, Right)FR AFO

The frequency response shows a ‘coloured’ response till 1kHz.
Bass sounds a bit muddy / hollow and is not as well defined/tight as the closed version.
Bass extension is there but not in the same quality/level as the open version.
The mids are ‘warm’ due to the downwards sloping frequency response from 300Hz to 3kHz. A 10dB difference is a bit too much though which makes the ‘warmth’ verge on / turn into muddyness and being ‘overly laid back’. The ÆON open lacks clarity/presence’ as a result.
On the right channel a sharp dip is visible which the left channel doesn’t show.
In the CSD further below it can be seen that this dip is a measurement artifact.
It also varied considerable in depth depending on positioning on the test-rig but the left channel never showed any dip.
The treble does sound ‘smooth’ and is not lacking ‘air’ but does sound a bit subdued. Treble extension is only up to 18kHz and drops of quickly above 20kHz. Pointless to play files with ultrasonic content on this headphone which can save you quite some space on your portable player. Don’t worry too much about this though… hires will still sound hires.
The channel balance is excellent.

There is also a closed version of this headphone. It has a quite different sound (sonic character) though but some similarities are also observed.
Below the ÆON closed versus the ÆON open (1-notch insert)open vs closed


The ÆON open comes with 2 inserts with which one can play with the mount of treble somewhat.
Note: When replacing the foam the headphone will be on a slightly different position when put back on the measurement rig which results in slightly different measurements.
To show tonal balance differences a bit more clearly some ‘smoothing’ is applied which ‘irons out’ small wiggles and is a closer representation to perceived treble levels.

One of these inserts is made of black foam. The type that is often found in front of a driver and is ‘acoustically transparant’.
This foam insert has no ‘notch’ in it. Below the frequency response plot of the ÆON open without an insert and with the foam insert.
no filter vs foam
No tonal changes here. This will give the most treble and provide extra protection for the driver against hairs and dust.

Below the effect of the ‘1-notch’ insert versus ‘no insert‘ is shown.
The 1-notch insert (synthetic felt) lowers the 8kHz and 16kHz peak slightly and makes the treble smoother and a bit more subdued.

1 notch vs open

Below the effect of the ‘2-notch’ insert versus ‘no insert’ is shown.
The 2-notch insert (synthetic felt) lowers the 8kHz and 16kHz peak by about 5dB and makes the treble smoother and a even more subdued.2 notch vs open

Below the 3 inserts in one plot. No-notch (foam) insert, 1-notch insert and 2-notch insert.foam vs 1 vs 2 notch

The differences are quite noticeable. Which insert one prefers is a personal matter.
In any case it is a great idea to supply these inserts with this headphone.
The 1-notch insert could well bring some improvements with the closed version as well.

References aout this headphone being a worthy HD650 replacement are found on the interwebs stating it sounds like a HD650 with subbass.
Below a comparison between the current HD650 and the ÆON open (1-notch).HD650 vs AFO
More subbass… check, more bass and warmth … check.
This makes the HD650 sound more realsitic and more ‘forward’ and ‘clear’ as in more presence as the (2kHz to 6kHz) on the ÆON open is a lot lower in amplitude.
Bass and mids are also higher in level making the ÆON open even warmer than the HD650 which some already find a bit ‘too warm’ and ‘too muddy’.
Treble extension and quality of the HD650 is clearly superior.
To me (personal opinion not a fact) the HD650, as well as the HD660S and ÆON closed, are the ‘better’ sounding ones.

Below the distortion measurements of the ÆON open (Left channel).

Note that this headphone was measured at ears-unlimited-logo where background noises were present in the demo room. As this is an open headphone the distortion levels and spectrum plot performance may thus be better in reality than as shown on the plots due to ambient sounds being measured along with the headphone.DIST AFO L

Below the distortion plot but displayed in percentages.DIST AFO L percent

Ignore the spikes at 50Hz, this is mains hum present in the portable measurement set-up. These spikes are NOT there in reality.
The distortion levels are very low.
Below 0.3% in the lows is really excellent.

The peaks in the higher harmonics are caused by background noises in the room it was measured in. There was a lot of activity going on during the measurements. 
The 2nd harmonic distortion is most likely lower than the 0.2 to 0.1% shown in the plots. This is due to the limit of the measurement rig which is being reached

Below the CSD of the ÆON open. (Left and Right are superimposed)CSD AFO

At 2.5kHz there is a small resonance. This short lived ringing isn’t problematic at all.  For an orthodynamic headphone this CSD looks pretty good.

output resistance / damping-factor

As this is an orthodynamic headphone its impedance is as good as ruler flat so a higher output resistance amplifier will have no consequences for the frequency response/tonal balance/damping.
Driven from 0.2Ω and 120Ω (level corrected so tonal balance differences are more easily spotted)120 Ohm
The level difference is substantial (20dB) but the tonal balance does not change at all.
The green trace is ‘buried’ behind the red trace

Below the spectrum plot of the ÆON open (right channel).SPECT AFO L

This looks pretty good. There are no obvious resonances or lingering that can affect the sound in a negative way. The bass area does show some lingering but at a low level.
The amplitude ‘problem’ is more audible than ‘time’ issues here.

The step response of the ÆON open (Left channel) belowSTEP AFO L

It shows the sub-bass extension is decent. The downwards slope after the initial rise is gentle. The higher frequency resonances directly after the initial rise are short lived and low in amplitude.  Quite well damped. Another thing that becomes clear is that the initial rise does not reach the 0dB line. The higher frequencies thus are subdued by quite a few dB compared to the lower mids/bass. More evidence of the subdued higher frequencies.
Compare the plot from the open version (above) to the step response of the closed version (shown below).
step Aeon L
There is only a small emphasis in the 200μs to 300μs region (3kHz to 5kHz) which gives the closed version a clearer character than one might assume based on FR only.


Fit and finish, comfort, weight (for an ortho) are excellent. The sound quality, however, is not of the same class. It isn’t a poor sounding headphone though. It just has a sound signature that does not agree with my preferences.
I find it too warm, bass is a bit wooly.
The mids lack clarity and have a ‘hollowish’ character to it.
Treble is present but a bit subdued but of high quality without sibilance or sharpness to it.
For € 800.- there are lots of other headphones around that sound better to my ears.
The ÆON closed for instance is the much better sounding to me which has a very ‘neutral’ and more realsitic sound.
Some people, however,  prefer a warmer/bassier sound with less clarity and soft treble.
For them the ÆON open may be a better option.

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