I decided to get the Thieaudio Legacy 3 and I've been testing it for about a week. My unit is the clockworks version from Amazon and has the serial number 902. The switches don't protrude from the back and the QDC connectors are tight with the stock cable and my 2.5mm cable with TFZ/NX7 connectors. Driver flex is present but not nearly as bad as the BLON BL03.
On
@antdroid's test tones, 3 and 4khz sound equally loud, and both are significantly louder than 4.5khz, but I don't think it's twice as loud. Based on this I believe this unit has the new/better/correct tuning.
Isolation
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In my ears the isolation is moderate, as is the insertion depth. A bit more isolation than the Moondrop Kanas, and less than KZ ZS3, both of which fit deeper. Significantly less isolation than Mee Pinnacle PX, which also fit deeper. The L3 has less isolation than I hoped, but it's enough for many situations at home. Comfort is good with Spinfit CP360 S or Azla Xelastec MS.
Sound
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I didn't spend much time comparing the switch configurations because I couldn't tell if there was any difference, which seems to be normal judging by Crinacle's graph. I mostly used 00 and 10.
The L3 seems to me to have some elevation somewhere in the upper mids and treble. Electric guitars seem a bit harsh, and some vocals seemed a bit unnatural. EQ seemed to alleviate this somewhat. Treble extension seems good to me, audible until 16khz.
The sub bass seems to have good but not great extension, and I find the sense of impact/slam/rumble/etc lacking, and I wasn't able to improve that noticeably with EQ. It's clearly better than the balanced armature models I've heard; it's just not as good as some other (cheaper) dynamic models I have. I tested extension by checking for the lowest frequency I could hear using an Android app called Frequency Sound Generator.
L3: 27hz
PX(+EQ): 30hz
BL03: 22hz
Kanas: 17hz
Planamic: 22hz
It seems very unlikely that the dynamic driver on mine is defective like I read someone experienced with theirs. I have experienced a defective on arrival dynamic driver in a similar resin filled hybrid model, the Hisenior H6, and the complete lack of any bass in the defective H6 side was extremely noticeable. (Unfortunately I no longer have the H6 to compare, since when I paid ~15$ to send it back to China for repair via USPS it never arrived, and I was only able to get a refund of 44$ of the original 139$. I won't be ordering something that expensive from AliExpress again.)
The overall level of detail sounds about as good as my two favorite earphones, the Mee Planamic with EQ intended to mimic the BL03 frequency response, and the BL03 with the nozzle filters replaced with rolled pieces of hiegi earbud foams. However, to my ears both of these have better sub bass extension and impact as well as more natural mids and treble. I wonder if this preference is due to some property of balanced armature drivers, but I don't have much evidence for that beyond not liking the balanced armature models I've heard as much as dynamics or planars.
Overall, the Legacy 3 is mostly good but it doesn't exceed my current favorites in any particular aspect or as a whole.
Notes
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All testing done on Radsone Earstidio ES100 over LDAC, except for the BL03 which was connected to BQEYZ Z3 Bluetooth cable over aptx-hd. I used single flange tips on every earphone.
Primary test tracks:
• Radiohead - Electioneering
• Radiohead - The Tourist
• Hundred Waters - Currency
• LVL UP - The Closing Door
• Japandroids - Lucifer's Symphony
• Men I Trust - Porcelain
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I'm probably going to return these because I prefer the sound of other models and the level of isolation isn't much higher than those, or even close to the PX.
I think I must have a lucky match between my ears and the shape of the PX. I wish Mee had reused that shell for the Planamic. Maybe I'll try covering the PX in tegaderm film to reduce the skin irritation from the metal. It's unfortunate that there isn't any way to test isolation and fit before buying. I'm also considering the ER2XR, now that they're 100$...