I knew from Amir's measurements about all the classic resonance issues their headphones have, and QC reputation, but the reviews were great and price was right. Given the price discounts on the Christmas sale, splurged a bit and got it. But immediately i noticed some grittyness, later when i actually measured it you could even plainly hear the distortion when its a sine wave and not masked by complex music.
So here is the left and right channels (GIF form showing one then the other channel). Both are an average of 7 measurements in slightly different positions, averaged to negate position variances. Notice how the drivers are actually quite well matched in FR, everything considered. Except in low end slope, but i'll get to that. The midrange is totally cooked. Something is going on with the 5K region, and it corresponds to a dip in the frequency response. I would not EQ that dip, you're just feeding energy into the resonance.
Something is wrong with the low end, and its not a matter of just measurement seal. I provide this graph to show what the seal grouping between measurements is, and between drivers. As you see variation in measurement is much smaller than variation between drivers. The rolloff slope is completely different, and if you notice the above gif, the distortion is as well.
I debated whether i should RMA it or live with it. But i knew that now that i noticed it and characterised it, i will always know, and it will bug me.
I ended up returning them, Hifiman were very polite and professional, and so i send out my headphones to their Poland center.
The first thing that surprised me a bit was that it was just a residential house in a small village (you can easily find the adress online if you google it, check it out on google maps). Apparently same case in America, with their Poland being New Jersey.
But hey it works, if its cheaper for them and cost probably gets passed to customer, no problem.
So 30 days later i get another unit back and now its time for round two of measurements.
This one was already opened and resealed with "Hifiman Tested" seal, so it's representative of known good working and checked unit from Hifiman.
Its in spotless condition so i suspect it's a new pair, they just checked it to make sure same customer doesn't receive bad lottery twice in a row.
Again pretty decent driver matching between L and R. Distortion in mid-band is basically gone, now there is just some quirk at 5.7kHz to contend with.
When i played a sine at that exact frequency just to hear how it sounds, i got some tone from hell, it has very high 3rd and 4th harmonic content. Its saving grace is that its very narrow Q and im contemplating just making a very narrow cut so the headphone doesnt even play those frequencies, i'll see with time if its necessary.
Whatever it is, it's present in the group delay as well.
Here's a distortion comparison to an 6xx. Not bad everywhere below 3k, and probably acceptable above. Though, thats where hearing is very sensitive.
But ok, lets call this overall a win. Consclusion is, it might as well be true that every XS owner has a completely unique set of headphones, depending on how the machine making diaphragms was setup that week, how it tensioned them and so on.
Another unrelated tidbit for the redditors amongst us, XS is 18 ohms and 6xx is 300 ohms, but they end up being about the same loudness at the same volume setting.
For 110dB volume you need 1.07 V(rms) on XS, and 1.15 V(rms) on 6xx. So you need about the same voltage gain.
How could that be, one is "18" and the other "300", reddit taught me i need a super amp when the number is big!
It's due to sensitivity difference (92 vs 103 db/mw).
In fact electrically XS is a much harder load, for the same 110db it will be drawing 64mW, compared to only 4 mW (!) for the 6xx. It requires about 15x times the current to drive to the same volume.
I point this out because i see on r/headphones people are always saying with low impedance headphones "oh yeah mate, its fine from your phone", but then recommending they need a super amp for a 6xx or whatever. Of course it might sound better if you get a decent amp depending on what you're coming from, but parroted advice dished out purely based on headphone impedance is very misleading.
So here is the left and right channels (GIF form showing one then the other channel). Both are an average of 7 measurements in slightly different positions, averaged to negate position variances. Notice how the drivers are actually quite well matched in FR, everything considered. Except in low end slope, but i'll get to that. The midrange is totally cooked. Something is going on with the 5K region, and it corresponds to a dip in the frequency response. I would not EQ that dip, you're just feeding energy into the resonance.
Something is wrong with the low end, and its not a matter of just measurement seal. I provide this graph to show what the seal grouping between measurements is, and between drivers. As you see variation in measurement is much smaller than variation between drivers. The rolloff slope is completely different, and if you notice the above gif, the distortion is as well.
I debated whether i should RMA it or live with it. But i knew that now that i noticed it and characterised it, i will always know, and it will bug me.
I ended up returning them, Hifiman were very polite and professional, and so i send out my headphones to their Poland center.
The first thing that surprised me a bit was that it was just a residential house in a small village (you can easily find the adress online if you google it, check it out on google maps). Apparently same case in America, with their Poland being New Jersey.
But hey it works, if its cheaper for them and cost probably gets passed to customer, no problem.
So 30 days later i get another unit back and now its time for round two of measurements.
This one was already opened and resealed with "Hifiman Tested" seal, so it's representative of known good working and checked unit from Hifiman.
Its in spotless condition so i suspect it's a new pair, they just checked it to make sure same customer doesn't receive bad lottery twice in a row.
Again pretty decent driver matching between L and R. Distortion in mid-band is basically gone, now there is just some quirk at 5.7kHz to contend with.
When i played a sine at that exact frequency just to hear how it sounds, i got some tone from hell, it has very high 3rd and 4th harmonic content. Its saving grace is that its very narrow Q and im contemplating just making a very narrow cut so the headphone doesnt even play those frequencies, i'll see with time if its necessary.
Whatever it is, it's present in the group delay as well.
Here's a distortion comparison to an 6xx. Not bad everywhere below 3k, and probably acceptable above. Though, thats where hearing is very sensitive.
But ok, lets call this overall a win. Consclusion is, it might as well be true that every XS owner has a completely unique set of headphones, depending on how the machine making diaphragms was setup that week, how it tensioned them and so on.
Another unrelated tidbit for the redditors amongst us, XS is 18 ohms and 6xx is 300 ohms, but they end up being about the same loudness at the same volume setting.
For 110dB volume you need 1.07 V(rms) on XS, and 1.15 V(rms) on 6xx. So you need about the same voltage gain.
How could that be, one is "18" and the other "300", reddit taught me i need a super amp when the number is big!
It's due to sensitivity difference (92 vs 103 db/mw).
In fact electrically XS is a much harder load, for the same 110db it will be drawing 64mW, compared to only 4 mW (!) for the 6xx. It requires about 15x times the current to drive to the same volume.
I point this out because i see on r/headphones people are always saying with low impedance headphones "oh yeah mate, its fine from your phone", but then recommending they need a super amp for a 6xx or whatever. Of course it might sound better if you get a decent amp depending on what you're coming from, but parroted advice dished out purely based on headphone impedance is very misleading.
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