Drop has these for $109.00 now, down from $129.00.
https://drop.com/buy/drop-hifiman-he-x4-planar-magnetic-headphones
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I got a set a couple months ago just to replace my 4-XX's which had an unfix-able low-freq buzzing in the right channel. For the money they're a no-brainer and even more so now. Not the most resolving cans and a little spicy in the sibilance zone but if you want a basic planar with double sided magnets (rather brittle ferrite, not neodymium like 4-XX as far as I can tell) and want the basic smooth syrupy planar sound these are pretty darn good. Sound is pretty close to the 4-XXs.
Just a short review:
Build quality is very good, mine is solid in all aspects build-wise.
My first impressions were:
sliders good and easier to move than my 4-XX and stay in place;
pads are like soft marshmallows (in a good way--these aren't the Focus A's of the 4-XX but a newer, much softer pad);
clamp is
very gentle (they must have used 5-XX frames for these as the 4-XX has a much firmer clamp).
Headband padding is the same as 4-XX and with this can being around 400g, it can get weighty after a bit but nothing too bad.
Sound-wise, it's a pleasing planar signature with the caveats as above. They are pretty hard to drive and do much better with some real current. My Shanling M6 Pro 21 with 760mW at 32Ohms does a very good job out of the 4.4mm balanced connection but I get more bang out of my Schiit M2U. I can imagine with even higher wattage (and some EQ) into these you might have a bit of a giant slayer (for $109!!!) on your hands. Bass-wise, if something calls for it these will deliver although a bit rolled off right at the bottom. Mid-range is good but micro-details, while there, may be lower in the mix than other aspects. Vocals are good but not HD-6XX. Again, higher current is going to somewhat remedy these shortcomings. Highs are good, nothing to really note other than there can be some sibilance at times but nothing too bad.. Sound-stage is pretty nice.
I've done some minor mods that have helped: I attached a Sennheiser OEM headband pad to the headband using some small velcro strips. With the Senn pad installed I have to push the sliders all the way open but it works pretty well and the clamp is still fine. This mod makes for a more comfortable, somewhat disappearing set as it distributes the weight across the top of the head a bit better and pretty much eliminates the head top hot-spot. It can easily removed if so desired. I also swapped over my oval Brainwavz Hybrid Memory pads. They fit my ears better and are still very comfortable softness-wise and may clean up the sound signature slightly. I've also taken the thin film dust covers off the screens and I think it might add a bit more openness, while maybe taking away slightly from the coherency of the sound stage. Also installed a KK Cable II-SO balanced 4.4mm cable for use with the Shanling's 4.4mm PO.
Anyway, I'm really not shlepping for Drop here, just noticed the price decrease and wanted to report that these are pretty good headphones. My set was very well made (just avoid poking around in the Magnet area) and are a nice replacement/addition for the 4-XX with a fairly similar sound.