I bought these headphones a few days ago (for only £69 new! ), and since then I've had a chance to measure them on miniDSP EARS rig as well as experiment with EQ on them. The overall take is that I'm really quite impressed with them, they measure well in terms of pretty good channel balance, and also low distortion that I measured, and I've managed to arrive at a good EQ for them too.
Measurements on my miniDSP EARS rig:
I'll keep the important overview graphs big & then I'll keep the nice to know extra detail graphs as thumbnails so as not to overwhelm the page & people's patience! All these measurements are based on an initial process of reseating the headphone roughly centrally 10 seperate times & measuring both earcups for frequency response at each reseat - so there's been 20 measurements in total (10 per channel), after which each channel is averaged. Don't worry that the graphs look strange in comparison to Amir's, it's because it's not the same type of measuring rig.
Channel Balance:
Channel Balance is good, with the help of REW I worked out that the right channel was on average 0.6dB elevated vs the left.
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following a thumbnail showing all 20 measurements (just some extra detail)
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Distortion Measurements:
Distortion was very low all the way up to 100dB, but unfortunately my rig won't really let me measure any higher than that, but 100dB should cover pretty much everyone's use case including bass EQ. There was a distortion spike at 2kHz in the Left Channel that was obviously most noticeable in the measurements at 100dB, but I don't really see that as a problem because you won't be running 2kHz at 94dB nor 100dB when listening to music. I'll show the most applicable 94dB distortion measurement as a large graph and the others as thumbnails. Distortion was below 0.5% pretty much everywhere at all levels up to 100dB, especially in the bass which is where you need to functionally use the extra SPL.
94dB:
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84dB:
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100dB:
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EQ Experimentation & Development:
So obviously this section is going to contain my own subjective experiences of the headphone after EQ and also my personal taste for EQ, but I generally like Harman and from my own previous experience I know I need enough energy above 8kHz otherwise the headphone can sound dull & lifeless. I started off with Oratory's EQ, and it was good, but it lacked sparkle & bite for me, and given that I knew I need enough energy above 8kHz then I tried increasing his 10000Hz High Shelf Filter - it sounded best with his High Shelf Filter at 4dB for me, but it still wasn't quite right. I thought about this and concluded that it's possible there's still not enough energy at 8kHz because the High Shelf Filter by definition will only gradually increase energy above that point (gentle slope) so I concluded it wasn't possible to save the Oratory EQ just by tweaking the High Shelf - instead I realised I would need to develop my own EQ from the ground up using Oratory's measurement data and positioning the Target Curve (Harman) lower down on the measurement so that the naturally occurring treble that is in the headphone can be retained, but at a higher level than the rest of the frequency response (hard to visualise if you've not done a fair bit of EQ experimentation with REW, so don't worry). Basically, I took the Oratory data from Jaako's AutoEQ website for the HE400SE and used REW to develop my EQ, and I ended up with the following:
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If you were to compare that graph of the finished EQ vs Oratory's you would see that the area around 10kHz and above sits higher on the graph on my EQ. There are some other differences as well, and the best way of seeing that is by comparing the Total EQ Curve of my EQ vs the Total EQ Curve of Oratory's EQ (and my EQ is the blue line in following graph):
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You can see that there's definitely more energy in my EQ above 8kHz, and there's also a couple of other smaller energy increases around 4kHz & 6.5kHz. The extra energy increases around 4kHz and 6kHz are due to the fact the measurement has been EQ'd exactly to the Harman Curve, whereas Oratory didn't EQ those two little areas completely up to the Harman Curve. I've found the extra energy in those 3 different treble areas have given the headphone the extra bite & sparkle that it needed. Essentially everywhere else the EQ is the same as Oratory's though, albeit you can see some tiny differences here & there. Following are the filters for my EQ if you want to try it (all Peak Filters):
Negative Preamp Required: -6dB
PK Fc 20.00 Hz Gain 5.70 dB Q 0.500
PK Fc 148.0 Hz Gain -0.40 dB Q 1.000
PK Fc 245.0 Hz Gain -3.10 dB Q 1.000
PK Fc 956.0 Hz Gain -6.10 dB Q 1.000
PK Fc 1488 Hz Gain -3.20 dB Q 3.229
PK Fc 1662 Hz Gain 7.70 dB Q 1.000
PK Fc 3001 Hz Gain -3.40 dB Q 2.263
PK Fc 5076 Hz Gain -2.40 dB Q 3.539
PK Fc 7997 Hz Gain -3.80 dB Q 4.885
Pleased with the headphone, very good buy & especially for the money, good measurements even in the sample I received, and a good EQ result, very good headphone.
Small Addition just for interest: I find that the frequency response of the HE400SE measures better than the HE4XX I own, following are the two measured & compared on my miniDSP EARS rig, you can see the HE400SE is a bit smoother in some areas and has better bass extension:
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EDIT: one last parting tip, when I first received the headphone there was no sound coming out of the right earcup - I immediately found that by wiggling the jack that the sound came back - I narrowed it down to a faulty 6.35mm jack adapter that Hifiman included with the headphone - I swapped it with a 6.35mm jack adapter that I already owned and it was fine.