My ears were my measuring device.
I put a fair amount of faith in my ears, but my mind and memory kind of suck for audio!
As an example, more than once I have listened to a new speaker with low expectations, but, when I listened, I was thoroughly impressed by the speakers. I spent the day running errands and thinking about some good songs to listen to when I got home. That evening I queued up the music and was a bit disappointed. They weren't bad speakers, but they weren't the great speakers I remembered.
I think a lot of the reason my opinion can vary like this has to do with expectations. Initially I am expecting mediocre sound and anything better than that is impressive, but after this first session my expectations are for impressive sound, and simply being better than mediocre leaves me disappointed.
This is why I always listen to speakers for a few days before passing judgement and set up an A-B switching to level match and compare to speakers which I know to be of a certain level of performance.
I trust my ears to do a very good job for relative evaluations (level matched with instant switching A-B situations),but feel very outside my capabilities if I try to compare a speaker at home with one at a friends with a 10 minute drive between (unless one actually does something which stands out as bad).
I don't know if everyone is the same on this abilitiy. Probably not. As an analogy, I have an excellent ear for pitch as long as I can hear the correct pitch (a relative evaluation),but I am NFG at evaluating a pitch on an absolute basis; yet there are people with perfect pitch who do this without without even thinking about it (perfect pitch)!
However, I think for most of us, listening without something to compare to (as a reference) is not a very fine gauge for judging sound quality. It is useful, but I would not give it the power of "final word"!
