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published: May-27-2014, updated: June-6-2021

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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.


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audio-technica ATH-M40X

ATH-M40XThe ATH-M40X is the cheaper (€ 100.-)  brother of the M50(X).
It differs VERY much from the ATH-M40fs in looks, comfort, size and above all sound.

Below the frequency plot of the ATH-M40X. There seems to be a little quality control / matching issue going on here. I measured it several times and in several positions and even reversed it on the test rig and the (substantial) difference between L and R is really present. 4 dB difference in the 100Hz-400Hz region is a bit strange. According to some reviews, and audio-technica, this headphone is ‘flatter’ than the M50X and indeed it sounds ‘flatter’ than the M50X but still has ‘big’ bass. Personally I like a bit of bass so don’t mind it IF there weren’t that much difference between L and R.
Product variance or issue ?
The headphone sounds better than it measures and has a (somewhat fatty and elevated) bass but no ‘warm’ sound. This is caused by the ‘dip’ between 200Hz and 1kHz. This gives voices a ‘clear’ sound and because the FR drops off above 2kHz there is no ‘shrill’ sound. The highs are ‘clear’ and soft but the ‘details’ (the part above 10kHz) is elevated too much but not annoyingly high. The overall sound is ‘good’ albeit a bit on the bassy side and the treble is smooth but a bit ‘artificial’.


Type: Over ear, closed
Usage: Home, studio, portable
Driver type: dynamic
Pads: replaceable, pleather
Collapsible: yes and can be folded flat
Headphone cup connector: 2.5mm locking TRS
Cable entry: single sided (left).
Cable: 1.2m with 3.5mm TRS jack, 3mwith 3.5mm TRS jack + 6.3 screw on, and 3m coiled cable.
Inner Pad dimensions: depth = 18mm, Width = 35mm, height = 52mm, oval shaped
Driver size: 40mm (angled 9 °)
Max. power rating: 1.6W
Max. voltage: 7.8Vrms (22Vpp)
Max. current: 200mA
Max. S.P.L.: 133 dB
Impedance: 38 Ω (measured)
Efficiency: 101dB @ 1mW
Sensitivity: 116dB @ 1V
Weight: 240 g.
Clamping force: medium
Accessories: 3 cables, 6.3mm screw on adapter, soft pouch.


ATH-M40X frequency response (Left and Right channel are overlaid)


The CSD (Waterfall plot) below shows some short lived resonances around 4kHz, 8kHz and 16kHz. No deal breaking long lived resonances but also no remarkable performance. There is quite some lingering below 500Hz. (Left and Right channel are overlaid)


Below the distortion plot for the M40X. (Right channel only)dist M40X R
Below the same measurement but the vertical scale is in percent. dist M40X R percentThe distortion is pleasantly low and remains below 1% in the bass area.

Below the step response of the M40X. (Left and Right channel are overlaid)step M40X

Suggestions for some modifications can be downloaded here.


The audio-technica ATH-M40X is a headphone that is decent for monitoring duties. It is lacking a bit in tonal accuracy when used for music enjoyment.
The ATH-M50X is a bit warmer/fuller sounding and has somewhat better treble. The build quality seems good but the pads are a bit sweaty and may are not the most comfortable ones.

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