This is the place to discuss all things Fiio FT1 - the closed back. For the open back, head on over to the FT1 Pro thread.
I have DMS’s unit here with me right now and was able to measure it, both on the B&K 5128 and the official GRAS 43AG.
Fiio FT1 HpTF (B&K 5128, GRAS 43AG and B&K 4128c)
B&K 5128 Calibrated
B&K 5128 Raw
B&K 4128c Calibrated
B&K 4128c Raw
GRAS 43AG Calibrated
GRAS 43AG Raw
Interesting to note how the 5khz peak is stronger on the GRAS, but a bit lessened and shifted closer to 6khz on the 5128. This is kind of the point of Blaine’s CanJam presentation on non-HRTF related HpTF variation (rHpTF as he calls it).
Point being, the headphone’s behavior itself changes depending on the head and ears that it’s on, and showing results of the same headphone from these different fixtures, each with their own DFHRTF calibration is a good indication of that.
Less relevant data below 
Harmonic Distortion
95dB @ 1khz
105dB @ 1khz
110dB @ 1khz
Nothing too out of the ordinary for moving coil headphones. It’s all mostly below 2% even at unrealistic volumes. You’ll go deaf before you hear any distortion products whatsoever with your music.
What about ringing and ‘internal resonances’?
This headphone is minimum phase, so there’s no reason to care about time domain information. It is all proportional to frequency response
Impedance curve
So this is definitely nonlinear impedance. Though not particularly high, I haven’t seen exactly that 2khz feature commonly. I’ll keep testing this. Most devices will run this just fine but there may be some odd interactions with ultra high output impedance amps, like certain tube designs.
Notes:
- Sound: Bass quality is exceptional on this one. Some of the best bass you’ll hear at any price point. I cannot stress this enough, it’s the perfect balance between impact and textural qualities, while not drowning anything else out.
- The rest of it is also very good, but my nitpick here is that the treble isn’t quite right. It can sound a bit… dark at times, but then also punctuated excess lower treble harmonics that makes the treble sound a bit compressed overall.
- Build is acceptable, the cups feel cheap but considerably better than its competition around its asking price. Like the K371 feels a lot worse in the hand. The headband creeks a bit but it’s fine.
- Comfort is mostly okay, especially for those with smaller ears. I didn’t have any issues with the headband, but I really struggled with the pads after a while just because they’re a bit too small for me. Like the pad material and compliance is all totally fine, it’s just that the opening was too small for my larger than average ears. Most people will probably have no trouble with this, but if you have large ears, keep this in mind. I ended up swapping to some Yaxi pads and just doing EQ, purely for comfort reasons.
Overall, this is easily the best closed back at its price point. The K371 was good, but its tenure is seemingly now over, with the FT1 taking its spot as the default closed back recommendation under $200. In fact, while I have a few things to nitpick here, this reminds me a lot of my old Denon AH-D2000, which I loved. So I’m likely to buy this one and then see what I can do with pad swaps.
) on his HBK 4128 rig, including comparisons to a couple other closed headphones, like the AKG K371 and Focal Azurys.
