Apparently the tuning vents on the outside of my cups were close to the edge of within specification (the cutout where you can see the tuning screw). Dan drilled them out a bit and was able to fix the channel imbalances that way for me. I know the T50RP drivers, at least in mods like this, can be pretty picky about venting.

While this was no biggie in my mind (sent it in, free fix, pretty easy), this does create further variables due to slight variances in 3D printing and/or application of finish and paint.

In most cases, I don't think these small variances will lead to much in terms of audible differences from AD to AD, especially for less discerning listeners. But, with all that and the T50RP drivers themselves, it does open the possibility for some pairs sounding a bit better overall than others. If someone really wanted to improve the sound, though, it would probably be more productive to focus on actual damping configurations and such. From just an enclosure/housing design perspective, I think the AD has a lot going for it.

To be fair, I do think performance variations are probably pretty minimal, but my pair is proof they can exist even at very minor degrees due to the many variables discussed. Those channel imbalances I mentioned were actually rather slight in the grand scheme of things (hard to measure, though I think this was in the realm of things that measurements couldn't capture well due to other T50RP mod + venting measurements I've tried), it sounded pretty much like the tour unit I tried with tweaks, and I've seen worse in reputable brands. I noticed it, but I'm not sure the general public would. Plus, Tyll's AD measurements make me think the products are relatively consistent within Dan's set specs, so I don't want to make it sound like it's a crapshoot when you buy an AD. I'm assuming they all sound pretty much the same if using the same configuration...just a tiny bit of wiggle room for some pairs to be better or worse overall, but we're probably the only people that would care much! (I wish I had taken better/more measurements of the AD when I first got it in to do a hard comparison of how something like drilling out the vent might affect the sound.)

When I tried the AD for the first time we had a pretty good conversation with Dan about consistency of ribbon-planar drivers. It's a well known fact that this type of driver is the most difficult to manufacture with consistent characteristics due to the inevitable variations in their magnetic properties. Knowing all of this well I wasn't surprised Dan wanted me to listen to a particular one of his sets stating it was fairly close to the reference one he keeps in the office.
   Overall I don't have a problem with this, everyone wants to demo their best but the thing is variations between these drivers can be quite dramatic especially affecting upper high and lower frequency ranges to the point of one set sounding grainy up top and the other overblown  on the bottom.
   In the end this becomes a major problem when general public start reading opinions of Purr1n or Hans on aforementioned Alpha Dogs or what LFF and Tyll think of PM1s. I think with these drivers reviewers should get couple of sets anonymously and this would be the only right way to determine the truth. Otherwise everyone will just think Purr1n, LFF, Hans, Tyll  etc all have ear problems which only becomes apparent when they evaluate planars.
   This is something I realized after dealing with six different sets of OPPOs I listened and measured but I will continue my thoughts in one of the OPPO threads.

Same types of pads from different sets all measure the same on one driver, so the variation in pad quality is out. Though all the different pads measure different on one driver (four different types that I have).