I inherited these from my Dad so they are special to me beyond their unique sound.
I like the old school look and that they are made in Brooklyn.
The soundstage sounds average to me for an open back, I feel the imaging may be better but that could be just that they are especially adept at pulling out detail in mids and highs. A cymbal splash is not just a "ting" but focused impact followed by the tone of the ringing. Ditto guitar strings.
Bass is there, impact of mid bass is great just not forward. Weak sub bass.
Everything it does is really good, it just does it its own way. The polar opposite of typical consumer headphones. Zero muddiness.
Yeah, the fit is not great. They just sort of hang off your head, resting against your ears but it's not uncomfortable particularly for me.
They are easily driven by anything but are best matched to a tube amp.
My LA Figaro 339 make these sing with detail expanding the soundstage increase the bass, making for a sound that rivals more expensive headphones.
Not perfect but very good for the money and different enough to make for a worthy addition to any music lover.

I had the original hp100 and now these, essentially the same but with some minor structural and aesthetic improvements.
I would say the most impressive is it soundstage and imaging, its really quite good especially for the price and that it's closed. This also improves its detail as everything has room.
The bass is powerful. Sub bass is better than most and it's quite accurate, the bass is a bit less forward when compared to the sub bass but not weak at all. Due to the light sealed build it gives a visceral bass experiance that it really fun. If you are a bass head, I would recommend these, just eq the bass to taste. Electronica is bliss with these headphones. In fact I would argue these are the best combination of fun and detailed edm headphones out there. Super immersive.
Mids are its weakness but not bad by any means, just that some guitar and vocals can sound distant when compared to the rest. It's hard for me to put my finger on exactly but it's almost like if you had right left and center channels, the center seems a bit further away than the right and left. This is kinda the effect but don't let this turn you away because, for the money, these really are great.
The treble is sweet. It's sparkle full yet never simbilant. Dunno how but you get all the shimmer without pain, it's quite the feit.
Just listened to Hans Zimmer Batman and it's a treat. These headphones do bombastic like no ones business.
I find these quite comfortable, some find the cups shallow. They are light weight.
The biggest negative is the plastic Y section to the cups. I had this crack in earlier models and the design still looks the same but I inserted gorilla glue inside the hollowed seam that runs along it to add strength. Just in case.
I own Focal Elex, Grado 325e, Massdrop plus iem, far more expensive yet I still come back to these cheap Chinese for some fun pounding bass and honestly am not completely wanting for detail. That says a lot considering I paid just $140 Canadian.
Incredible bargain.

Read a ton of reviews before purchasing. However, I will be honest and say that I was a bit let down by the bass. Don't get me wrong, its very detailed and balanced and perhaps there lies my issue, I was under the impression that these were more bassy. I am a bit of a basshead, in that, I like to feel it. Obviously, to many these have plenty of bass and the upper bass is there but it diminishes as it gets deeper to my ears which surprised me, again due to reviews. For the vast majority of what I listen to the bass is fine but for electronic stuff there is near zero rumble where there should have been. This could be due to the fact that I cannot insert them but rather rest them inside using the largest tip for a seal which itself is very vague(fit), perhaps due to the thin silicon used. My theory based on other reviews and my findings is that there is simply too much air volume between the driver and my ear drum to get deep bass. Really this is the only thing I have an issue with.
UPDATE: I finally figured out what I needed to do fit wise. For some reason the smaller tip would not seal despite being a very tight fit and realized the L tip was required but still needed to be inserted which takes a bit of actual force. The comfort could be worse but could be better. But inserted with the large tip does deliver that elusive bass response. Sealed, it really hits hard. Matter of fact I just got the PannyHJE900 known for its Monster like bass and the Yams are very similar. It is just that the Panny just sits there and it seals.
 
Mids are very engaging. Not recessed at all, nor are they affected by bass bleed. They are not warm or particularly thin but really detailed. I hear things I never noticed before and they kill my old Klipsch X5 BA IEM. This is the earphones strength IMO.
UPDATE: Just got the Panasonic HJE900 and they are both really quite similar in that both are very quick, clear and both use a micro driver.Neither would I describe as thick or warm but not cold either. This gave me further insight to the Yamahas mids which decimate the Panasonic. Not that the 900s are bad, they are recessed and not even that badly. I guess what I am saying is that it is true, most of the music is in the mids. I am listening to psytrance and both deliver on the beat but all that cool sound effects flowing about in stereo is much more clear on the Yams. This only helps to draw me further into the soundscape. More immersive and enjoyable. The Pannys make that all sound a bit distant. This is really what sets the Yams apart because it is extremely common to have the V shape sound with the exception of flat, analytical but boring IEMs. The Yams have that dynamic fun sound while still able to deliver all that musical info often overwhelmed by other fun IEM.
 
Treble is also really good but not up to the mids level. I am hearing cymbals that I never heard before and they have there own realestate like all the instruments through these things which only helps with detail and complex metal music where everything is loud. To be nit picky they could have some more splash or just a bit more forward after hearing my Panasonic HJE900(which is too bright).
 
Finally, I am still surprised what a tiny dynamic can do. There is mucho detail but these are on the fun side rather than the analytical side without being too soft or warm. An IEM that makes you want to listen to every album again to see what you missed before. I came from Klipsch X5 and have the SoundMagic HP 100 and they don't approach the Yams for insight and resolution. However, the fit and weak sub bass makes listening to electronic stuff a bit conflicting because they really draw you into the sound with their detail then the sub bass comes and I am left hearing it buried by everything else with zero rumble. I must keep reminding myself that bass is perhaps the most conflicted aspect of sound as everyone has what they think is too much or not enough. That for some audiophiles, apparently being able to actually hear the bass drum is fine and forward bass. Also, many never listen to electronic music where sub bass is a must and therefore don't notice it as much.
UPDATE: The bass is no longer a real issue as I have finally figured out the correct fit. I still could use more deep sub bass but then that is hard to find on any IEM. I am accustomed to the Soundmagic HP100 which is blessed with incredible sub bass. It is literally as loud at 40Hz as it is at 100-150HZ.

I've recently got into a bit of the budget audio bug, buying a small list of head/earphones over the past 2 years including Shure SE110, Klipsch S4, Klipsch X5, V Moda M80 and finally my awesome Soundmagic HP100. I'm still learning allot about audio and what sound signature I like most but its an interesting hobby that doesn't require a ton of money if you don't have it and that brought me to the HRT Headstreamer. I've read allot on these new usb DACs that supposedly sound as good as ones many times more pricey and that sounded good to me as I like the idea of improving sound on top of the headphones I already have. Still not sure exactly how  something converting a bunch of 1 and 0 can improve sound but it works.
Its like when your ears pop and everything sounds clearer and bigger. the sound stage opened up and everything is much easier to decipher. I can listen to Gorguts (death metal) and clearly hear every instrument which says allot because death metal is a very condenced music with evreything being played fast and equally loud, often becoming a wall of sound that makes it very difficult to distinguish various instruments. I'm getting the impression that this is a real "audiophile" type of sound coming from this DAC as nothing is coloured at all, it simply reproduces a very clean sound.
For the price I paid its an incredible deal and still is at asking price. It is made in the US of high quality components using an aluminum tube with durable plastic face plates. The design is great being very minimalist which means less noise and things to go wrong which also appealed to me. I have read some complaints on the lack of a volume knob but having this attached to a computer, the computer's volume is very convenient. I don't have to worry about a volume knob busting off when traveling.
This is a great portable product that vastly improves the sound of any computer for very little money. I'm a happy customer.

Read all the reviews here on headfi and you'll get a very accurate idea of what you'll hear.
I have been buying portable earphones since the early 90s, mostly Sony and their $100 models.In the past several years I've gathered Klipsch S4(great budget gear) then the V moda M80 for my first headphone and its great in a warm smooth way with plenty of great bass for my taste, and because it was on sale the Klipsch X5 which opened my eyes with the astonishing detail it relayed, and this made me want an over ear that was somewhere between the M80 and the X5. I wanted detail but also deep bass and something neither had, soundstage!
Like many, I was looking around the $200 level and the real contenders were the AKG K550, Beyer 770LE and Quart 8.35D oh and these of course. There just wasn't much written about the 8.35 and there were issues with comfort and soundstage so that was scratched. the Beyer was sounding appealing but it has scooped mids and harsher highs scratch. The AKGs have got real good reviews but that would depend if your head was huge because they are big and the bass, which isn't strong in the first place , disappaers without a good seal. I chose the Soundmagic after reading almost no negative feedback except one guy in Portugal that says they have a upper bass suck out, so I went for it.
These are much more neutral than warm like my M80s which was what I wanted because while warmth is smooth and all I wanted to hear more fine detail and these deliver without being harsh at all. They are actually quite smooth considering their sound. The soundstage is huge compared to anything I've owned. Having everything seperated only aids in being able to detect finer sounds and layers. I read allot about how the M80s have "polite" treble and I can understand that description but frankly they need more sparkle and with the HP100 you get that. I can clearly hear the splash and crash of cymbals whereas before they were buried behind the warmth. The mids are neither forward or recessed and are crisp and sharp and not at all interfered with bass. The bass is awesome. Listenig to a song that isn't bassy and you get the impression they wouldnt be bassy because these are a bit on the clinical side, but the moment bass enters it is there in great proportion and again in a very detailed manner. You can here exactly how the bass sounds rather than just a oomph. Somehow these manage to deliver very deep bass that makes electronic music fun, literally vibrating the cups on your head!
Bottom line is I am very happy. I think its difficult to pull off cans that have this kind of detail yet still can have incredible rumble. This is what I wanted and I am very pleased. Oh and the build seems solid with plenty of comfort and adjustments. They feel solid and the pivots aren't wimpy. The looks are neither here nor there for me as I buy them for sound, besides my M80s will be my portables. I'd put these against any headphone of this class.