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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.

sound descriptions mine

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audio-technica ATH-M40X

ATH-M40XThe ATH-40X 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’. left, right


The CSD (Waterfall plot) below shows some short lived resonances around 4kHz, 8kHz and 16kHz. No idea if it is a coincidence but theses frequencies are harmonics. No deal breaking long lived resonances but also no remarkable performance. left, right

csd m40x

with a few easy modifications the FR below can be achieved. left, right

940 pads + 2mm felt

How to do these modifications and see the results of many other tests done to the ATH-M40X you can DOWNLOAD the article .

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