TL; DR: the SDR modded HD800 is basically the HD800S, but still not entirely the same frequency response-wise. As such the HD800 IMO is great value especially nowadays you can find them used in the market for about US$700-900. Their bright tonality in stock form is already great for classical/accoustic music, and you also have the option of converting them to basically the 800S with the SDR mod.
Enough said. You get very close to the 800S with the SDR mod, so close that it’s well within unit variation range. Given their similarity I’ll talk about them together, with the HD800 original as the frame of reference.
Tonality:
HD800 is defintely on the bright side of things. Mainly it’s just the mid-treble at around 6khz though. Upper treble is somewhat boosted, but within reasonable range so it’s not that overbearing. Instruments have decent sparkle to them, and it’s sharper than the SDR/S version. Treble is significantly more tamed with the SDR mod or 800S although it might still be a tad bright for some.
Mids on all three is almost the same, with the SDR version having slightly more upper mids than the rest, making vocals slightly more prominent. The difference is still very small though (within 2db). Bass – very difficult to tell these apart. Several measurements have found higher second-order harmonics on the 800S, which is said to give them a bit more warmth (‘wooly bass’). Personally I feel this may have to do more with the tamed treble peak so that tonality is more balanced. Of note the mid-range timbre, as can be seen from the FR between 200-2000hz, actually has its peak around the lower-mids upper-bass range (200-300hz). Some call this ‘Sennheiser veil’, but it is only obvious when you compare to good planars with linear mids.
Technicality:
Many have praised these as the world’s most capable dynamic drivers and I can see why. Very resolving mids albeit a bit withdrawn. Bass is lightening fast and deep especially for open-back dynamic cans. Maybe not as authoritative as closed-backs or planars, but the sense of attack is really impressive. Soundstage – do I really have to talk about this? Easily the widest headphone out there, at least out of all those I’ve put on my head. Depth is not as good as width, but no slouch either. Some may complain the HD800 series makes everything sound ‘grand’ and ‘big’. True, but it’s more of a matter of taste I suppose.
Pads:
Unfortunately I haven’t come across third-party pads that I think makes for improvements to the sound. If you know one, please let me know.
UPDATE 17/Apr/2023:
Nope, these are no good…
the unheard of headphone lab 