after a week with this with a mix of gaming and music listening, I'd like to provide my impressions vs the HD 598, which I think is what most people are looking for in terms of comparison.
Mic: The mic is quite good. My voice comes through clearly in a recording and the noise isolation works very well, much more than some other headsets I've tried. I sit right below a ceiling fan that is permanently spinning at max and with some headset mic, it would pick up the sound of the fan spinning and annoy the crap out of people I'm talking to. I couldn't hear the fan at all in the recording, so I'm quite happy with the mic.
Sound: Decent, but not quite as good as the HD 598 (*see comfort section). I'm testing the sound of these out of an ODAC+O2 setup playing my FLAC collection out of Foobar2000 on the desktop, so source isn't a concern here. These have a pretty nice bass impact, which is quite surprising since the HD 598 is much leaner in the low end and if I recall correctly, distorts faster at higher volume. That's the only point where the PC37X has the advantage though. The mids sound a bit veiled; I believe this is because the whole spectrum overall feels quite congested, which is kinda strange for an open design. The treble is fine for the most part, but there are definitely spikes in certain spectrum. I believe this is intentionally tuned this way for that extra clarity in "competitive gaming", but for music listening, it can pierce at times. Overall, it doesn't sound bad by any means, but the peak in certain areas combined with the congested sound that muffles some details especially in the mids make the overall sound inferior to the HD 598.
Comfort: The HD 598 wins here by a pretty big margin. The PC37X clamps much much harder (much harder than it really ever needs to as an open back). It's not the tightest clamp I've ever felt, but it's pretty tight. The fact that the entire headband is plastic gives me no confidence that these will loosen much, but we'll see. In my opinion though, a headband should always be made of a thinner metal that can be bent to loosen/tighten clamp as needed. The PC37X gets a nod for having a much, much better headband padding vs the HD 598's air padded headband, which I felt put too much pressure on the top of the head and is the biggest negative I have with that pair. This was never a problem for me, but I do notice that the jutting out triangle thing that is on the top left side of the driver cover on the HD 598 has been moved to the bottom left. I know some people have a problem on the HD 598 where the top of their ear was touching this triangle thingy. Should no longer be a problem with them being on the bottom left now. Unfortunately, the biggest disappointment comes next, and this is the biggest disappointment I have with this headphone. For whatever reason (seems to be a sound tuning decision), the inner hole of the pads are much, much smaller vs the HD 595/598, such that I have to position the headphone in an exact specific spot or else it would be unbearable for my giant ears. For reference:
PC37X vs HD 595
should be quite obvious what I'm talking about. The PC37X pads are also slightly thinner in terms of height (not a problem), wider on the surface, but feels very slightly more plush. The PC37X pads feel more "cloth-y" whereas the HD 595 pads feel slightly more "fur-y". I believe the thinner, wider surface was done to help spread the pressure from the clamp better, but I personally found the HD 595 pads more comfortable with my bigger ear. The back of the HD 595 pads are some sort of pleather material, whereas the PC37X is still velour. I believe the smaller inner hole and the velour in the back of the pads contributed to the congested and veiled sound.
HD 595 pads on top of PC37X pads, to better illustrate inner hole size difference.
I tried to line up the inner hole on the top and left side to show the difference on the bottom and right side, but didn't do a very good job lol
595 pads are quite surprising actually. They do reduce the bass impact quite a bit but also reduce the peakiness in the treble and make the sound much less congested, giving the impression of a wider soundstage and more detail in tracks. (umm, wait a minute...)
Build Impressions: Hmm...I have more confidence in the build of the HD 598. They're both mostly/entirely plastic, but the HD 598 feels more...indestructible? That said, the build of the PC 37X isn't bad by any means...they don't creak in any way, and I certainly don't feel like they'd break. The weak points to watch for are probably the swiveling mic/mute mechanism and the volume wheel. They feel like they'd give out before anything else. Moving the mic up and down is kinda weird, it moves up and down with the right amount of tension, but enough that it kinda moves the left cup with it. Not a big deal, but worth mentioning.
Mic: The mic is quite good. My voice comes through clearly in a recording and the noise isolation works very well, much more than some other headsets I've tried. I sit right below a ceiling fan that is permanently spinning at max and with some headset mic, it would pick up the sound of the fan spinning and annoy the crap out of people I'm talking to. I couldn't hear the fan at all in the recording, so I'm quite happy with the mic.
Sound: Decent, but not quite as good as the HD 598 (*see comfort section). I'm testing the sound of these out of an ODAC+O2 setup playing my FLAC collection out of Foobar2000 on the desktop, so source isn't a concern here. These have a pretty nice bass impact, which is quite surprising since the HD 598 is much leaner in the low end and if I recall correctly, distorts faster at higher volume. That's the only point where the PC37X has the advantage though. The mids sound a bit veiled; I believe this is because the whole spectrum overall feels quite congested, which is kinda strange for an open design. The treble is fine for the most part, but there are definitely spikes in certain spectrum. I believe this is intentionally tuned this way for that extra clarity in "competitive gaming", but for music listening, it can pierce at times. Overall, it doesn't sound bad by any means, but the peak in certain areas combined with the congested sound that muffles some details especially in the mids make the overall sound inferior to the HD 598.
Comfort: The HD 598 wins here by a pretty big margin. The PC37X clamps much much harder (much harder than it really ever needs to as an open back). It's not the tightest clamp I've ever felt, but it's pretty tight. The fact that the entire headband is plastic gives me no confidence that these will loosen much, but we'll see. In my opinion though, a headband should always be made of a thinner metal that can be bent to loosen/tighten clamp as needed. The PC37X gets a nod for having a much, much better headband padding vs the HD 598's air padded headband, which I felt put too much pressure on the top of the head and is the biggest negative I have with that pair. This was never a problem for me, but I do notice that the jutting out triangle thing that is on the top left side of the driver cover on the HD 598 has been moved to the bottom left. I know some people have a problem on the HD 598 where the top of their ear was touching this triangle thingy. Should no longer be a problem with them being on the bottom left now. Unfortunately, the biggest disappointment comes next, and this is the biggest disappointment I have with this headphone. For whatever reason (seems to be a sound tuning decision), the inner hole of the pads are much, much smaller vs the HD 595/598, such that I have to position the headphone in an exact specific spot or else it would be unbearable for my giant ears. For reference:
PC37X vs HD 595
HD 595 pads on top of PC37X pads, to better illustrate inner hole size difference.
595 pads are quite surprising actually. They do reduce the bass impact quite a bit but also reduce the peakiness in the treble and make the sound much less congested, giving the impression of a wider soundstage and more detail in tracks. (umm, wait a minute...)
Build Impressions: Hmm...I have more confidence in the build of the HD 598. They're both mostly/entirely plastic, but the HD 598 feels more...indestructible? That said, the build of the PC 37X isn't bad by any means...they don't creak in any way, and I certainly don't feel like they'd break. The weak points to watch for are probably the swiveling mic/mute mechanism and the volume wheel. They feel like they'd give out before anything else. Moving the mic up and down is kinda weird, it moves up and down with the right amount of tension, but enough that it kinda moves the left cup with it. Not a big deal, but worth mentioning.