I did a single blind test (3 out of 4 testers knew what we were testing) but the 4th tester did not know, did not ask and did not care what we were testing
For the 4th tester, it was a double biind test. When our resident statistics guy, ran the numbers--all four testers returned statistically the same results. All three amps were level matched, they all ran within their operating range with four ohm speakers. Luckily, we had two pairs of the same speakers which really helped!
Once we were finished, the stats tabulated and we sat down with a cold one to ponder our findings. The first obvious question was did we somehow screw it up so bad that it made the results without winners? Did the room acoustics swamp any differences we would of heard....was it a room issue? Was the pre-amp a total POS? Blame the switch box? Actual switching of cables because of three amps slowed things down--time a factor? We then looked at the results of the CD player testing, no cable switching was involved like the amp testing and we had the same results. One guy brought up maybe we needed insanely expensive speakers to tell the difference between amplifiers. This was solved quickly, who would ever purchase speakers more expensive than we wre using--realistically that would not happen so it was dropped. We were testing equipment that we owned and planned on owning for many years.
Then the question with speaker cables, maybe some uber cable would sound better than the cables we were using? Well, if we could not tell the difference between 3 meters of 16 AWG zip, 12 AWG zip and whatever brand "audiophile" cable that was tested--most likely that would be a waste of time. After all, 16 AWG was the minimum we would use.
You would think that the owner of the most expensive amplifier (me) would of been butt hurt because my amp did not "win". No, I did not purchase the amplifier to have the "best sound", I purchased it because it had a ton of power output, ran very cool and I always liked power level meters (and still do) Oddly enough, the guy with the lowest cost amp also had the most expensive CD player so it was a mixed bag. The biggest difference between a bunch of 20 somethings doing testing and the audio jihad you guys prattle on about was we just wanted to know. We got our answer! A few hours later we were having a BBQ and enjoying the weather. Still friends, no hard feelings and we pressed on.
This was before the internet so had to go old school and actually test our gear. These days many audio people have done more testing with equipment far more expensive than what we used and would use more than four testers--they used dozens of testers in better acoustically treated rooms and so on. They returned the same results we did, this does point towards us doing it correctly VS really screwing it up--that stitistics guy was to be commended.
So if you want to find out, do it correctly. We lucked out in that we were able to adjust the gains even across all the amplifiers by using the gain knobs on the amps and use the volume knob on the tested receiver. One of the CD players had adjustable outputs to simplify level matching. Our goal was to mainly test CD players and amplifiers but we threw in speaker wire because--why not? The CD players were tested using the most expensive amplifier with te thick 12 AWG cables. We also tested speakers, that was very simple as it only takes a few seconds to really tell what we were dealing with. 3 out of 4 of use picked the same winners in order, the odd man out switched his 2nd and 3rd choice.
To get the most accurate readings, don't use your own equipment--try using speakers, amps, CD players or whatever you use that are not your own. If you own a pair of speakers that have a "tell" say the narrow dispersion of ESLs or narrow dispersion waveguides in some speakers and your MLP is very close--you can pick that out by moving your head and such. We did not have that option, all our speakers tested were wide dispersion so even if somebody tried to "cheat"... that would not have worked.
That was the first and last time I tested audio equipment blind--I have my results and my ears have not improved over time. The much, much more entertaining DBT is taste testing different alcohols--or foods and so on. A good idea before you ever do a DBT on audio gear is to test alcohols be it wine, vodka or your favorite hooch. This will show you quickly how accurate people's perceptions are, very easy to do with drinks and sure livens up the party. Be aware some people get all drama momma on you so best to use testers that have thicker skins. If you don't use alcohol, water is OK also...
I've done one blind test with three different pieces of equipment and it was fun but not my idea of how to blow a weekend. Been there, done that and pressed forward. The only testing I do now that would be considered blind is speaker testing when I help people pick out what they like. Oddly enough, the speaker I preferred was also the most accurate of the bunch so I tend to go with speakers that are accurate. No "warm, bright, cold or holographic" speakers for me--I prefer accurate speakers which is good to know! Since I knew the specifications on those amplifiers tested, I now know what specifications an amplifier needs to be and I go by those specs. Sure, my ears are not as good now as they were in my early 20's but it is a habit of pick X distortion or better and XXX S/N ratio or higher.
Generally speaking, I don't pick audio gear for people--not a specific brand or anything. I go for reliability, customer support, cool operation, electrical efficiency and so on if they want to know such things. When it comes to speakers, I offer a bit of advice and training about what speaker efficiency/sensitivity means, how to change watts to dB/W and why you would so such things and how to get a rough calculation of maximum SPL before you purchase things. I also give them a brief overview of speaker impedance, why it matters and to use the proper amplifier for the speaker desired. When it comes down to processors, features and all that--I will explain to them what things do and help them determine if they need it...I'll do that. I don't pick brands of AVRs, CD players, DACs, DVD players, speaker wire, interconnects and let them roll with whatever they want. The only guidance I tend to give has to do with how much power output they require for their room and SPL requirements, do searches on the wed to see if their choice has recalls or a lot of user problem be it failures or software glitches.
In reality, I'm not a specific brand fanboy of any audio company. Nobody is perfect and eventually they will all throw out a dud. It's just a goofy little hobby that the world at large does not care about. Heck, if all the high end audio companies vanished tomorrow I'd bet Kim Kardashians butt would still beat audo on the news reels. So relax, hobbies are supposed to be relaxing, educational and fun.