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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.

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 Sennheiser HD600

HD600 klSennheiser‘s former flagship, the HD600 (sent in by Nicola for measurements), is an excellent headphone today and worth owning. Certainly when you are looking for a true reference sound which shows the recording how it was actually made. When you find the HD650 a bit too ‘dark’ the HD600 is a more logical choice.  The plots below are of the the latest type, white internals and fresh new earpads. The HD600 has very smooth FR with no alarming peaks or dips. The ‘warmth’ hump’ between 30Hz and 500Hz that the HD650 shows is flat in the HD600 version. Because of this it sounds relatively ‘brighter’. It is exceptionally ‘flat’ from 30Hz to (at least) 20kHz +/- 3dB.
When you compare this plot with other measurements on this website you can see how well behave this headphone really is. The 1-2dB ‘lift’ between 3kHz-7kHz gives it a very slight extra ‘edge’ in presence compared to the (older) HD650. I don’t find it objectionable but do think the older pads make it sound slightly more pleasant.
When the pads soften up over the years and become more compliant that ‘slight hump’ will be gone as well and it will become slightly warmer as well (not HD650 level). If you press your HD650 somewhat on the head you can hear waht I mean.
This effect can easily be viewed as ‘very long term break-in‘ where the sound mellowed out somewhat over the years.

Below the frequency response of the HD600 above Left, Right


There is a slight difference between L and R in the lowest part of the frequency response. This isn’t caused by seal or a measurement artefact but is really there. Otherwise the L-R matching is exemplary.  I do not hear any difference in bass between L and R channel though.

Below the CSD of the HD600 Left and Right are superimposed in this plot. Looks excellent. Nice and clean.


Below the distortion plot of the left channel. Also quite good and aside from some 2nd harmonics below 100Hz there is little to complain about and the distortion between 100Hz and 20kHz remains below 0.2% (cannot measure accurately below 35dB SPL). The 3rd harmonics are also well below my audible limit. Excellent headphone measurement wise.

distortion L

The frequency plot below is of the right channel only and shows how the HD600 measures from a 0.1 Ω output R amplifier and from a 120 Ω output R amplifier. The traces are level matched at 1kHz as there is a noticeable reduction in SPL at 120 Ω out.

HD600 120 Ohm

The comparison between the HD600 and HD650 is often made. Below the frequency plot of the HD600 (white driver, new pads) and the HD650 (black driver, original pads). They are level matched in the plot at 1kHz.

HD600 vs HD650 (black)
It is obvious the HD650 has about 2dB more (mid) bass but does not extend a bit further down below. Another intersting thing is the treble part around 3kHz-5kHz is slightly higher. This makes the HD650 (the old one) somewhat less bright. The HD600 and HD650 are closely the same but the 2dB lift in the bottom and -2dB around the 4kHz point make the HD650 somewhat warmer sounding. One could also say that the HD600 has a more neutral tonal balance. It basically only lacks bass extension. One would say 40Hz -3dB should not be a problem but once you heard what’s down there when it is reproduced flat makes a lot of difference in the overall evaluation of this headphone.

Now for the more interesting part of this excercise. Most websites often state that the small ‘lift’ in the 4kHz region is caused by the HD600 driver. The HD650 driver (as shown above) would be ‘veiled’ because of this.
Below the (old black) HD650 driver BUT with new pads versus the HD600.

HD600 vs HD650 new pads

Turns out that the slight lift around 4kHz is NOT caused by the driver but seems to be caused by the pad. More precisely the difference in compliance between the pads as the old  pad is more squishy (see HD650 section below). The only obvious difference between the HD600 and HD650 is just a slight ‘boost’ in the bass area. Even though this is just 1.5 to 2dB it is still audible as some extra ‘warmth’.

So… if you are looking for a really accurate set of headphones the HD600 may be the best choice around when it comes to accuracy.

Of course… you can always connect it to the Kameleon and improve this great headphone even more.
When you wish for slight reduction in the ‘presence’ (between 3kHz and 6kHz) and like some really deep subwoofer type lows the Kameleon filter is the way to go.

below the frequency plot measured when connected to the Kameleon. Left, Right


The differences between the stock HD600 and from the Kameleon are shown below

HD600 Kameleon compare

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