That doesn't seem quite right to me. I would have thought that if you did a number of different measurements on the same headphone and took an average of them, then I would think you'd be able to resolve differences between headphones of the difference we see between the HE400i 2020 version and the HE4XX.....I'm fairly certain they're not just the same model of headphone underneath, so you'd expect to see differences between them and by extension I think the trend of difference between them would be that which Oratory has pictured & which bobbooo showed in his post:
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For instance, this is a slew of measurements from Oratory on HD600:
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The variation between the different measurements in the above graph is pretty stable up to 4kHz, and the average is gonna be pretty representative over that range. The main differences between the 400i 2020 version and the 4XX as seen in the first graph in the post is happening between 500Hz and 5kHz (most of which is the highest area of accuracy on the graph) so certainly over most of that range I think it's possible to resolve an average 1-2dB "real" difference between these two headphone models with no issue. If you rely on just one measurment, then no you can't resolve the difference with any confidence, but with enough measurements I think there's validity in the difference seen.
Totally correct. There are differences in the frequency response of the original HE400i, HE400i (2020 version) and HE4XX that are greater than measurement variation. Let's take another look at Oratory's measurements of all three in detail:
That's a difference in the sub-bass of 5.7 dB between the 4XX and original 400i (2016), and 2.5 dB between the 4XX and 400i (2020).
Here at 2 kHz (around where our ears are most sensitive), we have a difference of 3.1 dB between the 4XX and 400i (2020).
And we have a difference of 4.5 dB between the 4XX and original 400i around 5.6 kHz.
Now let's take a look at Crinacle's measurements (right channel, 3 reseat measurements, on a similar GRAS rig):
So at 2 kHz that's a measurement deviation around the mean of ±0.5 dB for the original 400i and ±0.2 dB for the 2020 version.
And a measurement deviation at 5.6 kHz of ±0.8 dB for the original 400i and ±0.6 dB for the 2020 version.
Now let's look at Rtings' frequency response consistency measurements of the original 400i:
At 2 kHz we have a measurement deviation around the mean of ±0.3 dB.
And at 5.6 kHz we have a measurement deviation of around ±0.5 dB.
These figures are in general agreement with Crinacle's. Rtings calculate an average deviation of 0.38 dB between 20 Hz and 10 kHz, among the top 10 of all open-back headphones they've tested, and say this about the frequency response consistency:
The HiFiMan HE-400i have a great frequency response consistency...The treble delivery is also very consistent across multiple re-seats, with the maximum deviation below 10KHz being less than 2dB.
All the above measurement deviations are less than the measured differences between the three HE4** versions from Oratory's measurements at the beginning of this post. These differences are indeed real, and not within measurement variance.
Similarly for unit variation, Oratory said this about the HE4XX (this was well over a year ago, so he may have measured even more by now, my emphasis):
I measured 3 specimens by now, including yours and one that Olaf (from OluvsGadgets) brought to the lab.
I built an average from all of them and use this for the EQ PDFs. They are all pretty close together actually, so much so that it doesn't make much sense to create an EQ setting specifically for one specimen only. Unit variation was excellently low on the three specimens I tested. Quite surprised by this!
Let's compare these headphones to a few other Hifiman models:
As the graph shows, at any one frequency up to 10 kHz, none of these headphones have responses that differ from the HE4XX by more than the HE400i (2016 or 2020 version). If the latter three (or just first and last) are the same within measurement variance, does that mean all these headphones are also the same within measurement variance? No, that would be absurd. Hifiman obviously have a 'house sound', but there are definite sonic differences between these headphones. In the bass, the HE400i models are the outliers from the median response with the worst bass extension, and at around 500-600 Hz too where they exhibit significant resonances that the others, including the HE4XX, don't. Between 1 and 2 kHz the HE4XX is the outlier, on average closer to the Harman target than any of the others. Between 2.5 and 5 kHz, the HE400i (2020) is the outlier, furthest from the target. And around 5.6 kHz the HE400i (2016) is the outlier, furthest from the target with a deep notch there. These are all real differences, not within measurement variance. The HE4XX's frequency response not only follows the Harman target the closest on average among these 5 headphones, but of all the Hifiman models Oratory's measured, which is evidenced by it having the highest calculated preference rating among them of 88/100. According to the best objective, scientific model we have, the HE4XX is Hifiman's best-sounding headphone. (It also happens to be one of their cheapest.)
Now let's compare the above frequency response differences to these more familiar headphones to many from Sennheiser:
These measurements are much closer to each other than any of the HE4XX, HE400i (2020), or HE400i (2016) are to each other, with only 1-3 dB difference in the upper mids / treble. Does that tell you that they are the same headphone? No. And that would still be a no even if the differences are within measurement variation. Why? Because this measurement variation is not just random error from the measuring equipment.
The variation is intentional and desired, in order to simulate and account for actual statistical variation in real-world use of the headphones by the consumer, be that unit, positional, or channel variation, which are all averaged to account for this real-world variation. In other words, this measurement variation is a feature not a bug!
It may be the case that one channel of one particular HD600 unit at one particular seating position might measure the same as one channel of one particular HD650 unit at another particular seating position, but statistically, on average, the measurements above for each headphone will be closest to what you will perceive listening to two channels in amalgam, with your particular unit, placed (for most somewhat randomly) on your head, and that's what matters to the listener. If you want more treble, then on average you will get this choosing the HD600 over the HD650, just like on average, you will get a headphone that more closely follows the Harman target if you choose the HE4XX over either of the HE400i models, as shown by industry standard, professionally made measurements.
But wait, we don't have to just stare at graphs to show these headphones are indeed different. There is at least one very obvious physical difference between them - the pads.
HE4XX's Focus A pads on the left, HE400i (2020)'s Focus pads on the right:
And the original HE400i's pads (which at least on the outside look the same as the above Focus pads from the 2020 version):
Here's what Oratory (a professional acoustic engineer of course
who helps design headphones as part of his job) says about pads (my emphasis):
Pads certainly affect the sound a lot more than people would often think. I'd go as far as to say they're as important as the actual driver.
And it's not just visible material differences on the outside that can have a big effect. On pads' acoustic influence, he goes on to say:
That depends on more than just the material itself.
You can make well sealing earpads out of velours, for example - if the core material is closed-cell.
You can also make leaking earpads out of leather (perforated leather being the most obvious example, but also leakage in the stitching and bonding area).
The effect of earpads is rather tricky to predict. Personally I'll say it's even trickier than the effect of drivers.
The perforated leather inner edge of the HE400i models' pads could then possibly be the (partial) cause of their weaker bass extension to the HE4XX, the latter's pads featuring tightly woven material in its place which may provide a better seal. Other differences may explain the weaker still bass of the original HE400i to the 2020 version (e.g. differing internal pad or earcup material/structure, driver differences etc.). Of course as Oratory says though, pad effects are tricky to predict so the obvious physical differences between the Focus and Focus A pads of the HE400i and HE4XX respectively could have any number of acoustic consequences for the headphones.
So what's the lesson here? Don't be fooled into thinking two headphones are sonically the same within measurement error just based on somewhat similar frequency response, a photo of the back of the driver and the same initial number of their model name. It's both unfair to manufacturers and misinformative to consumers to entertain such rumors founded on zero concrete evidence. The default position should be innocent until proven guilty i.e. headphones sold as different models are indeed sonically different, unless strong evidence suggests otherwise. Hopefully this finally puts an end to the persistent baseless conjecture that the HE4XX are the same as the HE400i (either version). There are both physically visible (e.g. pad), and measurable acoustic differences between them, that exceed measurement variation. Oh, and a belated Happy New Year to everyone
This one can't be worse than the last, right? Right??