You don't... The participants don't know what each headphone feels like. That is obviously controlled for.
I would, however question the ears you used to do this test. The average person will like the bassier, intimate headphones more than headphones like the HE-90 and HD800, which focus on detail and presentation. The HD800 and HE90 also lack impact, which is a major part of getting you involved in the music and is a deal breaker for some people when a headphone is lacking in that department.
This is why I used Classical musicians. A lot of the music that was played were complex orchestral music, and I requested they pick their preference based on which headphone is the most realistic in reproduction and true to the recording. Other pieces included solo cello, solo violin etc and I requested that they pick based on timbre reproduction. Especially for solo violin pieces (Bach Chaconne droool), the bassier and wow element tends to get removed from the judgement process.

I have compared my Senn HE60 and Stax SR007 MK1 at different times.
If I do a comparison hwere I swap the headphones back and forth, I find the HE60 far more appealing.
If I pack the HE60 away it takes about 3 songs for the Stax to reveal it's timbre and detail to it's fullest extent.
I have no doubt that the Stax is the better headphone, it's just that I find the Senn HE60 more addictive to listen to.
I truly believe this phenomenon is a trap to watch out for when comparing different headphones.

You should take a picture of your setup with the Orpheus and these other phones. I want some visual stimuli.

The comparisons are not for a short duration. Of course, there is the addictive quality of the Orpheus but I am using seasoned musicians to tell me which headphone sounds truest to the recording followed by what signature do you prefer.

Again we are going to need a picture of the setup. What amps were used for the LCD-3/HD800s? Were all these driven by the same source (how did you manage to accomplish that???) How was the test conducted? How is it a blind test if they can feel the difference between the headphones?

The amp section of the Orpheus, Goldmund Telos 5000 and the
Onkyo PA-MC5500 Power Amp. Both, among the best amps out there specifications wise. In one of my past display pictures will be the basement studio room where I did the tests and that is the source I used. The one in the centre, I don't remember what it is called.

I currently have exams and am going back to Seoul in a few weeks time I will upload the pictures then. I am in London atm.
Again, the blind test has its limitations, but the participants didn't know what feels like what and swapping the order of headphones around will make it even more difficult to know. But Yes I did this on an ad-hoc basis and of course there are limitations to the variables I can control. The amp/source I used belong to my father. With regards to the source, I will need to ask my father. Sorry about the lack of pictures at present, I don't have a nice camera and the only things I take photos of tend to be big large speakers.

You drove the LCD-3 and HD800 from power amps? Anyways since you can't take some pictures can you share your method of blind testing with us?

You see I bought two 009's some time ago to do a blind test on a selection of electrostatic amps. I would love to hear how you performed your test and learn from your methods.

This is why I used Classical musicians. A lot of the music that was played were complex orchestral music, and I requested they pick their preference based on which headphone is the most realistic in reproduction and true to the recording. Other pieces included solo cello, solo violin etc and I requested that they pick based on timbre reproduction. Especially for solo violin pieces (Bach Chaconne droool), the bassier and wow element tends to get removed from the judgement process.
Well then, that makes much more sense. Though it's impossible to have a completely unbiased test, I feel this is the closest you're going to get to it. Well done.

You drove the LCD-3 and HD800 from power amps? Anyways since you can't take some pictures can you share your method of blind testing with us?

No I used the Beredynamic A1 (sorry I forgot to mention) and the Orpheus headphone amp for all the headphones. But to satiate my need for pointless tinkering, I paired the headphones with the power amps ESP P100 just to see how it would turn out (and it was fine). More of a pointless electronics tinkering exercise.

Sounds like the whole thing is BS.

Sounds like you forgot to mention a lot of things. Like how you connected the 009 to the Orpheus amp, or how it's hardly optimal for driving an 009. A Beredynamic A1 huh. Let me know where I can buy this amp it sounds very interesting! There's a bunch more hurdles I was faced with when doing these blind tests but you should definitely answer these questions first.

I hooked up the headphones to the power amps using the ESP P100. It's specifically designed by the guru Elliott to act as an adaptor and lower the voltage using resistors so that one can connect headphones to power amps (very DIY design but extremely efficient and effective! As I said, a completely pointless tinkering exercise). Regarding the Beyerdynamic A1 (misspelt earlier) you can purchase it on pretty much any decent online store. The Orpheus Amp, you can specifically request an adaptor to be made for use with other headphones.
But, yes the power amps served the purpose fine, as the ESP P100 did its job perfectly.

Sennheiser provides adaptors for using the Orpheus amp. The ESP P100 is Elliott's design for a power amp to a headphone adaptor. Very DIY but gets the job done excellently. Beyerdynamic A1 (sorry for the misspelling), can be purchased anywhere. With regards to the blind test, it was relatively ad-hoc and a lot of it was done using my father's gear.
Maxvla, no need to be so rude. You can think it's BS all you want, I have an engineering degree and partake in these experiments on a ad-hoc basis. You can discredit my attempt as a joke or laugh at it. I am not saying it's good or very reliable, but these were my experiences.

So, you are telling me that you managed to organise a listening session involving a few musicians, none with as much as a camera phone or even a point and shoot to take pictures of all that equipment? Also even if the artiste did not go by visual stimuli, they can and may well react to touch stimuli. Another point is that I know some musicians and while they may know how and what makes an instrument sound good, their preferences to what is 'neutral' or 'lifelike' may be skewed.
On equipment, what is this ESP P100? and how did you couple it to the amplifier just like En_R asked? Another would be nitpicking, the A1 and the Goldmund are hardly the 'best in class' I'm pretty damn sure. Especially the "beredynamic" LOL.
I have a bunch of other stuff to pick on like your sonic impressions but I will leave it at that.

@Maxvla I feel your input is unnecessary, un-constructive, and unwanted.
Put simply, shut up.

That setup is always going to be problematical.

Credits to uchihaitachi for this excellent write up. I'm pleasantly surprised that even the HD 650 outperforms its much more expensive counterparts like the orpheus and HD 800 when expectation bias has been taken out of the equation. Would love to see more blind tests like these done with different headphones/amps/dacs in the future.

There's no real risk in using a heaqdphone connjected straight to a high powered amplifier if you take care with the volume control.
The resistors in series with the headphones can affect the performance of the headphones.
If using a high impedance headphone like the HD800, T1, etc, it's probably a good idea to have an 8 to 10 ohm resistor (High Wattage) in parallel with the headphone so the amp can see a normal load while still driving the headphones.

Just out of curiosity, which set up do you think is the best of the headphones you tested? As in all around, price to performance, which do you prefer in the headphone world? Thanks.