Out of the three, the YH2 is the airiest and cleanest sounding from bottom to top, while also having the least low midrange presence. Aside from mids, transients are also clearly defined, natural, sharp, and clear; there is a certain transient ‘snap’ to the sound that you don’t get from the average headphones at this price range. Definitely if you like clear and airy tone but still maintaining Yamaha ortho’s fairly laid-back and smooth presentation, the YH2 should be in your sub-$100 list. One edge that they have over the HD668B and AD700 is that they have a more linear mid-treble presentation and certainly sweeter in its coloration (HD668B is a bit cold in the lower midrange, and the AD700 has a slightly awkward mid to treble transition). Bass is relatively light in impact and punch with the YH2. In general, this particular YH2 benefits from an amp with good bass presence and slight touch of low-mid warmth, while being clear enough to let the YH2’s transparency shine through. YH2 is the least efficient to drive in this comparison, and my Ipod Nano has trouble driving it to good volume.
YH3 is the least clear-sounding of the three (still very much clear sounding for this price range) and not the last word in fidelity, but I am always partial to a warm and bodied sounding headphone, and the redamped YH3 fits this criteria. Besides being quite comfortable, the warm tone is nicely done for relaxed listening without being dull because the upper mids still sounds quite lively and forward, maintaining the presentation of the Yamaha orthos. Still, although they have a nice tonal balance, I feel that this YH3 has a lower resolution driver when compared to the YH2 and especially the YHD2 as the overall sound is a little grainier and less clear. The YH3 has the biggest bass impact here—actually quite nice in the realm of vintage orthos, but with less resolution and control than the other two. From my experience, a dynamic and clear sounding amp can really give a good boost to the YH3.
The YHD2, besides being redamped, has been fitted with pleather earpads. The stock flat pads that come stock with the headphones was a big question mark as it severely held back the sound quality. The YHD2, in essence, is a middle ground that marries a lot of what is good about the YH2 and what is good about the YH3. It has the clarity of the YH2 combined with a warmer lower midrange and bass presence that is closer to the YH3 but with better control, resolution, and a bit more bass punch. The driver just has a higher resolution and focus than the YH2 and YH3; notes are solid and transients have great control, resulting in better and clearer imaging than the YH2 and the YH3. Soundstage size is surprisingly not that different from the YH2 and YH3. Another important point is that the YHD2 can work as a good open portable headphone as it has a thin cable and a 1/8” jack, and sounds quite fine direct from the Ipod.
I undoubtedly pick the YHD2 as my overall favorite of the three, as it executes the Yamaha ortho’s mid-treble presentation in a more rounded and higher resolution than the other two, though it will be even more perfect if it can be as airy as the YH2 and has more bass impact like the YH3. One thing that kept popping up in my head is that the YHD2 may not have reached its full potential in its stock housing. I suspect that its uncompromisingly open design is unoptimal for sound quality. A local ortho and cable enthusiast has transplanted his Yamaha YHE-50S drivers (a vintage model with a somewhat similar sound to the YHD2) into a Sennheiser HD497 housing, possibly along with few other modifications, and I can say that it sounds wonderful and realizes the YHD2 potential at a higher and more refined level.