Then they can decide from themselves whether a poorly performing /distortion effect box system is preferable to their subjective taste or not
I think it's also important to note that there is another option: if the cheaper option that adheres to the target FR (e.g. Harman) is also tunable without distortion, then you could add EQ to match your preferred target* and save money.
I'm guessing based on reading through these replies that the susvara has some other differences (e.g. phase) that you can't get with an EQ but you can get elsewhere. In general, the phase of a signal means nothing to our ears. However, phase
differences between left and right are very noticeable. One trick to add spatial width in the audio production world is to use a low pass filter to roll off the highs but with different slopes on the left channel and the right channel, but at the same frequency (e.g. 12 dB/oct on L and 24 db/oct on R). The different slopes affect the phase at the target frequency differently, causing not only different phases but this difference also changes. This adds to the sense of space, and could increase what people describe as 'soundstage' or 'etherealness' (you can do this to the lows on each track as well but it's not always desirable - e.g. kick or bass guitar you generally want mostly mono and in the center or it can more easily sound muddy and messy).
Of course, doing this will affect amplitude. However, there is a way to affect phase without affecting amplitude: all pass filters - these reverse phase at the target frequency (so 180 degrees) and roll off the phase change nearby without affecting amplitude. There's probably other math-y filter stuff you can do, as e.g. MFreeformPhase (
https://www.meldaproduction.com/MFreeformPhase) lets you change phases as-desired per-frequency. So if you were persistent enough, you could probably set up an EQ plugin and a phase response plugin into Peace/Equalizer APO and get a response much closer to susvara than just EQ.
I wonder what it would sound like to capture an impulse response of the susvara using a dirac spike, then plug that into a reverb plugin that takes an IR, and play back music on a headphone that aligns really closely to harman (e.g. the stealth) - how close to the susvara would it sound? The IR should capture the phase per-frequency as well right? Would be interesting but I don't know if it's possible.
This all means you could find a (possibly cheap) headphone and create your own tailored soundstage by messing with phase differences at different frequencies on the left and right channels (the more 'objectively better' headphone, the more accurately you can tailor your soundstage to your subjective liking). Maybe you find something you like better than the susvara? But I definitely get the sense that some people/reviewers find these things in headphones and like them, and because of that they attribute it to "must be what the artist intended" or "this was always here in the music but I couldn't hear it until I put these headphones on" when that isn't the case. Non-linearities, distortion, and phase differences can sound pleasing - it's why tape saturation is extremely popular for audio producers (people pay big bucks for sought-after analog tape machines to mix their songs on and why there are so many saturation plug ins) and why people like tube amps. There's nothing wrong with liking it, but there's also nothing wrong with buying a good quality cheaper headphone and adding saturation, distortion, phase changes, EQ, etc yourself.
*This implies you are able to, e.g. you are on a computer, or your DAC supports EQ with enough resolution, etc. You may also just happen to like the response of the susvara and don't want to fiddle with stuff and just plug them in and listen - nothing wrong with that either.
But maybe that is due to lack of lower treble response.
