Introduction
Before starting off, a BIG thank you to Gurubhai for initiating the first orthodynamic headphone loaner program in India. :cheers::signthankspin:
That said I will try to do justice with the three way comparison with his erstwhile Yamaha HP-2s and his current YH-2s.
The HP-2 and YH-2 look like twins separated at birth and only upon looking at the top of the headphones where the model no is printed does one realize that they are different models. That and the different after market cables used. The blue Mogami Quad cable on the HP-2 is very striking to the staid black cables found on both the YH-100s and the YH-2.
Both the HP-2 and YH-2 (along with many other Yamaha orthos) were designed by renowned Italian designer Mario Bellini. However the YH-100 and YH-1000 which were the flagship models at different years were not designed by him.
Both the HP-2 and YH-2s are very lightweight compared to the bulkier and heavier YH-100s. You can have them on your head for hours without any issue. It is not so with the YH-100s as they can feel heavy on your head and neck after an hour or so.
The HP-2/YH-2 have the same 46mm driver in them and both share a similar semi closed housing so theoretically they should sound identical. The YH-100 use a larger 55mm driver and consequently has a larger housing.
Equipment
The hardware chain is like this : Foobar -> Audio-GD Compass DAC/AMP -> headphone.
Music
I have no specific tracks but I listen to a lot of different music from different genres. However most of them were all 320 kbps with a few FLACs and even fewer 192 kbps tracks.
Testing methodology
For the YH-2 I have left the equalizer alone, but for both the YH-100 and HP-2, I have made a compensation of a few -db in the 10 khz and 7 khz band respt to tone down the sibilance that crops up due to the Compass being a bit bright. The compensation is less for the YH-100 compared to the HP-2.
Sound
Ok down to business. Some of would probably skip right to this part.
Yamaha YH-2
When I first got them, I put them on my head and waited to hear the sibilance that I get with the other two headphones. It was then that I realized that this is a very different headphone as its has a rather dark signature.
It has a very smooth sound that reminds me in many ways of my HD650. The bass has enough depth and impact to sound fine with most music but it rolls off pretty quick and has no sub bass. 40 hz is about as low as it can go. The bass has a slight mid bass hump but its fast and the bass never steps out of line with even really fast paced music nor does it intrude into the mid range.
The midrange is where the orthos show their magic. Pianos, trumpets, flutes all sound rich and lush. The vocals are are also very transparent and neutral. Though the vocals are slightly recessed. That said the vocals have good weight/body.
The cans have a rolled off treble that give them their dark signature. Because of the rolled off treble, certain genres of music sound off like Rock and Classical music. However they make poor / sibilant recordings very listenable. Due to the smooth grain free treble you can listen for hours and hours without any fatigue.
These are closed cans (actually semi-closed as they have numerous small vents) and hence cannot match the soundstage of an open can. However the imaging is fantastic on the YH-2. Placing the position of different instruments in your head is very easy and you can easily pick out individual instruments from the mix.
Another plus point of ortho technology is they have a very fast decay and no dynamic I know can keep up. The HD650 is the total opposite with a rather long decay which makes for lovely vocals, but sounds disjointed and defocused with hard rock or metal music.
To sum up, the overall sound is dark (rolled off treble) , warm (slight mid bass hump). fast (quick decay), intimate (small soundstage width but precise imaging), smooth (fatigue free sound) and lush.
Yamaha HP-2
These cans were my first introduction into the ortho world and Gurubhai had filled my poor head with how awesome orthos were and how amazing they sounded. When I finally got them I practically ripped open the box, plugged the headphones into my Compass , cranked up the volume, and..... my face fell. It was VERY sibilant and I could barely listen for a few minutes before keeping them away. After a little research I found out that my Audio-GD compass was the culprit as it was on the Bright level 2 setting. A change to Neutral setting helped a LOT.
That said they still exhibit some sibilance and I had to do an EQ of the 7 khz and 10 khz band and then the sibilance is gone.
Now I earlier mentioned that the HP-2 and YH-2 share the same drivers and pretty much the same housing. So they should sound similar right ?
Err not really. If the YH-2 is Ying then the HP-2 is definitely Yang. The HP-2 is definitely a bright can but if you EQ down the 7 khz and 10 khz band, it is downright awesome. :clapping:
This is especially true with Rock music or any other faced paced genre. I sometimes catch myself smiling whenever I use these headphones on my favourite rock music tracks.
The treble is what you first notice. Its extended, crisp and very detailed. Detailing is maybe a notch over the YH-2 but I believe its more because the treble is accentuated on the HP-2 while it is softer and more polite on the YH-2.
The mid range is almost as good as the YH-2, but for the sibilance that crops its head from time to time. With the EQ on, the midrange is a lot smoother but still not a match for the YH-2.
Bass is very similar to the YH-2. The HP-2 also has a slight mid bass hump but its not very pronounced and sounds quite pleasing. Its still very quick with keeps up with the rest of the audio spectrum.
The soundstage is again more or less the same as that of the YH-2 - Small but with decent depth and good imaging. Classical music especially sounds amazing with these headphones as the flutes, trumpets, violins, etc sound lush (An ortho characteristic no doubt). And since the HP-2s have both precise imaging and crisp treble, listening to classical music is a real treat ! I actually started collecting more classical music purely after I got this headphone.
So to sum up, the sound is bright (accentuated treble), warm (slight mid bass weight), fast (quick decay), intimate (small soundstage width but precise imaging) and lush.
Yamaha YH-100
My second ortho after I got smitten by the HP-2s. These are modded by a dbel84 from head-fi.
If I had to use only three words to describe the sound, it would be
ruler flat neutral. 
I have no idea how long dbel84 took to tune these headphones but I simply cannot imagine a flatter response. Everything seems to be just in the right place with nothing forward or recessed. Bass extends down to 20 hz easily without any noticeable rolloff.
However my Compass causes sibilance in the YH-100s as well and I again have to compensate for that via the EQ in Foobar.
That small negative aside, these are easily the best headphones I have heard till date even on my mediocre Compass. The bass is soo tight, deep, controlled, textured (add all the nice audiophile terms here to describe it) etc. It just doesn't seem to get boomy no mater what you throw at it.
The treble is also noticeably better than the HP-2. It doesn't seem accentuated like with the HP-2 but its still very crisp, extended, grain-free, detailed, smooth and for sure there are no annoying peaks in the treble coz I am sensitive to treble and I don't experience fatigue when listening to these cans for a prolonged duration.
Mids are again spot on. Its neither forward nor recessed, it just feels just where you would expect it to be. The mids are VERY transparent, detailed and smooth. (After using the EQ to tone down the sibilance)
Detail retrieval is amazing and even with my less than stellar Compass its a notch or two above the HP-2 and YH-2. Its definitely a notch above my Sennheiser HD-650s which is saying a lot considering these cans are at least 30 years old !
The soundstage is the only place where it cannot improve on its other siblings the HP-2 and YH-2 as it is still a semi closed design (Closed but with several small vents). So it has all the strengths and weaknesses of the HP-2/YH-2 like small soundstage but good imaging. However instrument separation is definitely better than the HP-2/YH-2. No headphone/IEM/Earphone I have heard can match the YH-100 for instrument separation. Notes are well separated and dont blend into each other. The same is true (to a slightly lesser degree) with the HP-2 and YH-2 cans.
The true test of neutrality for these phones is that it sounds great no matter which genre or track you throw at it.
If I lived in England and wore a nice top hat like they did in the old days I would tip my hat to dbel84 for taking so much time and trouble to mod these cans to sound so good. :cheers:
However the downside now is that my rig is definitely holding back the YH-100. I need a new DAC and amp now. :sad:
So to sum up, the sound can be described as Neutral (Bass, mids, treble all in place), fast (quick decay), intimate (small soundstage width but precise imaging), detailed (top notch detail retrieval) and lush.
The YH-2 will now be packed in the same box I got it with and will be on its way to iaudio next. Enjoy.
.man,am so looking forward to some 'propah' education 
.cheers
hyeah:
.glad to know you have rid urself on one,bad gremlin there 
