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published: Jul-2-2013

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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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Sennheiser HD215


This is a headphone that isn’t very well known in hi-fi land and frankly it should stay that way indefinitely as well. It is marketed by Sennheiser as a professional headphone for monitoring purposes. You can rotate the right earpiece 90 degrees (the one without the cable). In that case you still have the left earpiece on your ear while the other one rests on your head behind the ear so you can clearly hear on one ear what’s happening around you and monitor with the other ear. Isolation isn’t bad but also not very good.

In stock form the sound is only mid range with a sharp edge and can imagine this isn’t a bad thing when monitoring. Completely not suited  for Hi-Fi, but isn’t supposed to do that anyway.  below the FR plot. The left channel appears to roll off sooner but may have been a seal issue. I didn’t remeasure.

sennheider hd215 (stock)

The CSD below shows a resonance around 800Hz and a few very short ones higher up. Not much to worry about when monitoring anyway.

sennheider hd215 (stock) wf-l

As the owner didn’t like the sound either I promised to modify it so the sharp edge would be removed. Playing with lots of dampening materials in the back and front in different configurations gave very different results and in the end settled for a simple ring made of self-adhesive felt that covers the biggest part of the driver and removes the edgy highs. The modification is shown below. Left ‘stock’, on the right the felt ring covering the biggest part of the driver except for the small center hole.

HD215 mod

Below the difference between stock (blue line) and modified (orange). The peak in the highs is reduced by a very audible 5dB. As a bonus the bass appeared as well. It even reaches down to 10Hz !

hd215 stock versus modified (left)

Below the plot for the modified headphone. There is a difference between L and R in the 10kHz. The overall frequency range is flatter albeit a bit too much in the 100Hz to 200Hz are which makes it sound slightly muddy. Voices went from ‘cold’ to ‘warm’ and is now more suited for hifi reproduction. The sound is a fair bit darker and the sharp edge is completely removed. It sounds very good on vocal stuff (a capella) and for single instrument recording such as a solo guitar it doesn’t sound that bad. For all other music it sounds dull and not very engaging. There are no details to be heard and the soundstage is completely closed in. NOT a hifihead phone at all. But at least that nasty treble peak is gone. It could still be used as a monitor (what it is meant for) and the very distracting sharp edge is not present any more.

sennheider hd215 (modified)

CSD is slightly better below 1kHz otherwise no big differences there.

sennheider hd215 (modified) wf-l

Avoid as a Hi-Fi headphone… seriously.

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